Transition metal oxide sorbents and transition metal hydroxide sorbents for carbon dioxide capture

Abstract

This invention relates to materials, methods, and systems for carbon dioxide (CO2) capture. More specifically, this invention relates to materials, methods, and systems for removing, capturing, separating, and / or adsorbing carbon dioxide (CO2) from a gas mixture. Additionally, this invention relates to materials, methods, and systems for direct air capture (DAC) of CO2 from ambient air. This invention also relates to materials, methods, and systems for direct air capture (DAC) and methanation of CO2 from ambient air.

Description

TRANSITION METAL OXIDE SORBENTS AND TRANSITION METAL HYDROXIDE SORBENTS FOR CARBON DIOXIDE CAPTURE CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No.63 / 543,649 filed October 11, 2023, and U.S. Provisional Patent Application No. 63 / 651,795 filed May 24, 2024, both of which are incorporated herein by reference in their entirety. FIELD OF THE INVENTION

[0002] This invention relates to materials, methods, and systems for carbon dioxide (CO2) capture. More specifically, this invention relates to materials, methods, and systems for removing, capturing, separating, and / or adsorbing carbon dioxide (CO2) from a gas mixture. Additionally, this invention relates to materials, methods, and systems for direct air capture (DAC) of CO2from ambient air. This invention also relates to materials, methods, and systems for direct air capture (DAC) and methanation of CO2from ambient air. BACKGROUND

[0003] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0004] The rapid rise of atmospheric carbon dioxide (CO2) concentration starting from the 1900s has become one of the most urgent environmental concerns. Advanced development of negative emissions technologies is crucial for carbon dioxide removal to reverse the trend. Direct air capture (DAC) is a novel CO2capture technology and considered as one of the major negative emission technologies. Direct air capture (DAC) can be achieved from two main pathways, either from an aqueous-based absorption process or from a solid-based adsorption process. Adsorption process using solid sorbents has the greater potential to be applied in large scale from benefits such 4886-5761-4062.1 Page 1 of 164094876-000018WOPTas lower heat requirement for regeneration. The most essential part of adsorption-based DAC is the choice of solid sorbents. Estimated DAC sorbent costs have been found to span a wide range between 20% to 90% of DAC total cost. The DAC total cost is highly dependent on the sorbent performance and manufacturing costs. Therefore, cost reduction based on development of advanced DAC sorbents is vital to push adsorption-based DAC closer towards the next stage in practical and commercial applications.

[0005] Existing direct air capture (DAC) solid sorbents include supported amines, zeolites, metal-organic frameworks (MOFs) and alkali earth-metal oxides (e.g., magnesium / calcium oxides). Each of these existing adsorbent materials suffers from numerous specific limitations such as a propensity for oxidative degradation, intolerance to the presence of water or water vapor (e.g., humidity), need for pre-dehumidification processes, high manufacturing costs, high regeneration temperatures, high operational temperatures, and high operational costs. These limitations of existing solid sorbents significantly hinders and / or limits their use in commercial / large-scale DAC processes. Therefore, there is an ongoing need for new direct air capture (DAC) solid sorbents, and for improvements in direct air capture (DAC) solid sorbents. The embodiments of the present invention address these needs. SUMMARY OF THE INVENTION

[0006] In various embodiments, the present invention provides a solid sorbent for removing carbon dioxide (CO2) from a gas mixture, the solid sorbent comprising: at least one transition metal hydroxide. In some embodiments, the gas mixture comprises ambient air, flue gas, natural gas, exhaust gas, or biogas, or any combination thereof. In some embodiments, the at least one transition metal hydroxide comprises at least one transition metal selected from the group consisting of nickel (Ni), cerium (Ce), iron (Fe), and any combination thereof. In some embodiments, the at least one transition metal hydroxide is porous, or non-porous, or combination thereof. In some embodiments, the at least one transition metal hydroxide is selected from Ni(OH)2. In some embodiments, the solid sorbent further comprises at least one dopant. In some embodiments, the at least one dopant comprises cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo), manganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), or vanadium (V), or any combination thereof. In some embodiments, the solid sorbent further comprises water or water vapor.4886-5761-4062.1Page 2 of 164094876-000018WOPT

[0007] In various embodiments, the present invention provides a system for removing carbon dioxide (CO2) from a gas mixture, the system comprising: a reaction chamber, wherein the reaction chamber comprises an inlet port, and an outlet port; and the solid sorbent of the present invention positioned in the reaction chamber. In some embodiments, the system further comprises a mechanism, device, or equipment for introducing water or water vapor into the reaction chamber; and optionally further comprises a mechanism, device, or equipment configured to contact the gas mixture with the solid sorbent positioned in the reaction chamber; and optionally further comprises a mechanism, device, or equipment for desorbing or removing the adsorbed carbon dioxide from the solid sorbent. In some embodiments, the gas mixture comprises ambient air, flue gas, natural gas, exhaust gas, or biogas, or any combination thereof. In some embodiments, the system further comprises a mechanism, device, or equipment for performing pressure swing adsorption, vacuum swing adsorption, temperature swing adsorption, or moisture swing adsorption, or any combination thereof.

[0008] In various embodiments, the present invention provides a method for removing carbon dioxide (CO2) from a gas mixture, the method comprising: providing a solid sorbent of the present invention; and contacting the solid sorbent with a gas mixture. In some embodiments, the method further comprises contacting the solid sorbent with water or water vapor before contacting the solid sorbent with the gas mixture. In some embodiments, the gas mixture comprises ambient air, flue gas, natural gas, exhaust gas, or biogas, or any combination thereof. In some embodiments, the method further comprises desorbing or removing the carbon dioxide from the solid sorbent. In some embodiments, the desorbing or removing the carbon dioxide from the solid sorbent is performed by contacting the solid sorbent with an inert gas, wherein the inert gas comprises water or water vapor. In some embodiments, the desorbing or removing the carbon dioxide from the solid sorbent comprises adjusting or changing pressure applied to the solid sorbent, adjusting or changing temperature of the solid sorbent, adjusting or changing vacuum applied to the solid sorbent, or adjusting or changing moisture level (e.g., adjusting or changing water or water vapor level or content) of the solid sorbent, or any combination thereof.4886-5761-4062.1Page 3 of 164094876-000018WOPTBRIEF DESCRIPTION OF THE DRAWINGS

[0009] Exemplary embodiments are illustrated in referenced figures. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.

[0010] FIG.1 depicts in accordance with various embodiments of the invention, radar plot comparison of solid sorbents for adsorption-based DAC.

[0011] FIG. 2A – FIG. 2C depicts in accordance with various embodiments of the invention, N2adsorption-desorption isotherm (FIG. 2A), pore size distribution from BJH- desorption branch (FIG.2B) and XRD patterns (FIG.2C) of PNMHs.

[0012] FIG. 3A – FIG. 3B depicts in accordance with various embodiments of the invention, DAC capacity with different humidity level in the feed CO2stream (FIG.3A), and CO2(400 ppm) / N2breakthrough curves for α-Ni(OH)2under dry and humid conditions (67% RH) (FIG.3B).

[0013] FIG.4 depicts in accordance with various embodiments of the invention, general structure of α-Ni(OH)2and proposed CO2chemisorption pathways involving metal hydroxide layers or anion interlayer as active sites on PNMHs.

[0014] FIG. 5A – FIG. 5D depicts in accordance with various embodiments of the invention, XRD pattern (FIG.5A) S 2p XPS spectra (FIG.5C) FTIR spectra (FIG.5B) and humid DAC capacity (67% RH) (FIG.5D) of α-Ni(OH)2and α-Ni(OH)2-SO42-.

[0015] FIG. 6A – FIG. 6B depicts in accordance with various embodiments of the invention, effect of adsorption temperature on DAC capacity of α-NiCe0.1(OH)xunder dry and humid conditions (FIG. 6A) Water vapor adsorption isotherm of α-NiCe0.1(OH)xat different temperatures (FIG.6B).

[0016] FIG. 7 depicts in accordance with various embodiments of the invention, Correlation between humid DAC capacity (67% RH) and BET surface area for PNMHs.

[0017] FIG. 8A – FIG. 8B depicts in accordance with various embodiments of the invention, (FIG.8A) FTIR spectra of α-Ni(OH)2after exposure to dry CO2, humid CO2(H2O) and humid 400 ppm CO2(D2O). (FIG.8B) FTIR spectra of α-Ni(OH)2using dry CO2purge on humid CO2(D2O) saturated sample. Humidity level is at 67% RH. CO2concentration is 400 ppm. Background spectra under Ar before exposure to CO2was subtracted.4886-5761-4062.1Page 4 of 164094876-000018WOPT

[0018] FIG. 9 depicts in accordance with various embodiments of the invention, DAC Cycle stability of α-NiCe0.1(OH)x. Adsorption condition: 25 °C, 400 ppm CO2 / balance N2. Regeneration condition: at 150 °C He purge for 2 hours.

[0019] FIG. 10 depicts in accordance with various embodiments of the invention, XRD pattern of α-NiCe0.1(OH)xand α-NiCe0.1(OH)x-no AMOST.

[0020] FIG.11 depicts in accordance with various embodiments of the invention, FT-IR spectra of α-Ni(OH)2, α-NiCe0.1(OH)x, α-Ni(OH)2-SO42-.

[0021] FIG. 12 depicts in accordance with various embodiments of the invention, N2adsorption-desorption isotherm of α-Ni(OH)2-SO42-and α-Ni(OH)2.

[0022] FIG. 13 depicts in accordance with various embodiments of the invention, XRD patterns of β-Ni(OH)2-T, β-NiCe0.1(OH)x-T, non-porous Ni(OH)2.

[0023] FIG.14 depicts in accordance with various embodiments of the invention, Water vapor adsorption isotherm at different temperature of α-Ni(OH)2and α-NiCe0.1(OH)x.

[0024] FIG. 15 depicts in accordance with various embodiments of the invention, XPS spectra of Ni 2p region of α-Ni(OH)2and α-NiCe0.1(OH)x.

[0025] FIG. 16 depicts in accordance with various embodiments of the invention, N2adsorption-desorption isotherm of PTMOs.

[0026] FIG. 17 depicts in accordance with various embodiments of the invention, XRD pattern of Ce10NiOH and Ce10NiO.

[0027] FIG. 18 depicts in accordance with various embodiments of the invention, CO2adsorption isotherm of Ce10NiO at different adsorption temperature.

[0028] FIG.19 depicts in accordance with various embodiments of the invention, dry and humid DAC capacity of Ce10NiO powder.

[0029] FIG.20 depicts in accordance with various embodiments of the invention, humid DAC capacity of pelletized Ce-doped NiO at different Ni to Ce molar ratio.

[0030] FIG. 21 depicts in accordance with various embodiments of the invention, cyclic stability of Ce10NiO powder. Regeneration condition is under 250oC He purge for 2 hours.

[0031] FIG. 22 depicts in accordance with various embodiments of the invention, FTIR difference spectra of Ce10NiO before and after 400 ppm CO2sorption.

[0032] FIG. 23A – FIG. 23B depicts in accordance with various embodiments of the invention, humid DAC capacity of pelletized Ce-doped NiO at different Ni to Ce molar ratio, M14886-5761-4062.1Page 5 of 164094876-000018WOPT= NiO, M2 = CeO2, (FIG. 23A); and dry and humid DAC capacity of Ce10NiO powder (FIG. 23B).

[0033] FIG. 24A – FIG. 24B depicts in accordance with various embodiments of the invention, DAC capacity with different humidity level in the feed CO2stream (FIG.24A), M1 = Ni(OH)2, M2 = Ce dopant; and DAC Cycle stability of α-NiCe0.1(OH)x. Adsorption condition: 25 °C, 400 ppm CO2 / balanced N2. Regeneration condition: at 150 °C He purge for 2 hours (FIG. 24B).

[0034] FIG. 25A – FIG. 25C depicts various embodiments of the invention, DAC over porous transition metal oxides (PTMOs). Effect of Humidity & Metal Doping (FIG.25A), Surface Species (FIG.25B), and Cycle Stability (FIG.25C).

[0035] FIG.26A – FIG.26B depicts various embodiments of the invention, Feasibility of integrating DAC and Methanation over PTMOs. Methanation of CO2from DAC (FIG.26A), and Steady-State Methanation using Simulated Air (FIG.26B).

[0036] FIG.27A – FIG. 27D depicts various embodiments of the invention, Non-porous transition metal hydroxides.

[0037] FIG. 28A – FIG. 28D depicts various embodiments of the invention, Template- assisted porous transition metal hydroxides (T-PTMHs).

[0038] FIG.29 depicts various embodiments of the invention, Carbonate-assisted PTMHs.

[0039] FIG. 30A – FIG. 30C depicts various embodiments of the invention, Carbonate- assisted PTMHs.

[0040] FIG. 31A – FIG. 31D depicts various embodiments of the invention, Carbonate- assisted PTMHs.

[0041] FIG. 32A – FIG. 32B depicts various embodiments of the invention, Carbonate- assisted PTMHs.

[0042] FIG.33 depicts various embodiments of the invention, carbonate-assisted PTMHs.

[0043] FIG. 34A – FIG. 34B depicts various embodiments of the invention, potential mechanisms for CO2binding.

[0044] FIG. 35 depicts various embodiments of the invention, potential mechanisms for CO2binding.

[0045] FIG. 36 depicts various embodiments of the invention, interlayer CO32-as active sites.4886-5761-4062.1Page 6 of 164094876-000018WOPT

[0046] FIG. 37A – FIG. 37C depicts various embodiments of the invention, interlayer CO32-as active sites.

[0047] FIG. 38A – FIG. 38C depicts various embodiments of the invention, interlayer CO32-as active sites.

[0048] FIG. 39A – FIG. 39B depicts various embodiments of the invention, interlayer CO32-as active sites.

[0049] FIG. 40 depicts various embodiments of the invention, potential mechanisms for CO2binding.

[0050] FIG. 41 depicts various embodiments of the invention, rational material design strategy: second metal doping.

[0051] FIG. 42A – FIG. 42C depicts various embodiments of the invention, rational material design strategy: second metal doping.

[0052] FIG. 43A – FIG. 43C depicts various embodiments of the invention, rational material design strategy: second metal doping.

[0053] FIG.44A – FIG.44B depicts various embodiments of the invention, metal doped- PTMHs.

[0054] FIG.45A – FIG.45B depicts various embodiments of the invention, metal doped- PTMHs.

[0055] FIG.46A – FIG.46B depicts various embodiments of the invention, metal doped- PTMHs.

[0056] FIG.47A – FIG.47B depicts various embodiments of the invention, cycle stability under O2environment.

[0057] FIG.48 depicts various embodiments of the invention.

[0058] FIG.49 depicts various embodiments of the invention, synthesis for PTMHs.

[0059] FIG. 50A – FIG. 50C depicts various embodiments of the invention, DAC performances on PTMHs. Effect of Porosity & Metal Doping (FIG. 50A), Effect of Humidity (FIG.50B), and DAC Sorption Products (FIG.50C).

[0060] FIG.51A – FIG.51C depicts various embodiments of the invention, potential CO2binding mechanisms (FIG.51A), cycle stability (FIG.51B), and key metrics vs. existing sorbents (FIG.51C).4886-5761-4062.1Page 7 of 164094876-000018WOPT

[0061] FIG. 52A – FIG. 52C depicts in accordance with various embodiments of the invention, (FIG.52A) XRD patterns (dashed lines represent peak positions for α-NiFe0.2(OH)x), 52B) N2adsorption-desorption isotherms, and (FIG. 52C) pore size distributions derived from BJH analysis of the desorption branches of PNH samples.

[0062] FIG. 53A – FIG. 53B depicts in accordance with various embodiments of the invention, Bright field transmission electron microscopy (TEM) images of α-NiCe0.1(OH)x-no AMOST (FIG.53A) and α-NiCe0.1(OH)x(FIG.53B).

[0063] FIG. 54 depicts in accordance with various embodiments of the invention, DAC capacities of various porous nickel hydroxides plotted as a function of BET surface area. Adsorption measurements were carried out at 25 °C under 400 ppm CO2, 2.1 kPa H2O (67% RH), balance N2. Dashed line represents a linear regression for the adsorption capacities of the Ce-free sorbents.

[0064] FIG.55 depicts in accordance with various embodiments of the invention, possible adsorption mechanisms mediating CO2binding onto PNH materials including (1) CO2binding in the form of interstitial bicarbonates within anion interlayers, (2) CO2adsorption onto surface hydroxyls, and (3) CO2binding enabled by the molecular adsorption of water.

[0065] FIG. 56A – FIG. 56C depicts in accordance with various embodiments of the invention, (FIG.56A) Powder X-ray diffraction patterns, (FIG.56B) S 2p XPS spectra, and (FIG. 56C) FT-IR spectra of α-Ni(OH)2and α-Ni(OH)2-SO42-samples obtained at 30 °C under an Ar purge after a 2 h, 200 °C thermal pretreatment under Ar.

[0066] FIG. 57A – FIG. 57C depicts in accordance with various embodiments of the invention, (FIG. 57A) DAC adsorption capacity as a function of water pressure for the three α- Ni(OH)2materials tested; adsorption under 400 ppm CO2at 25 °C, (FIG.57B) Effect of adsorption temperature on α-NiCe0.1(OH)xDAC capacities under dry and humid (2.1 kPa water) conditions, and (FIG. 57C) water adsorption isotherms for α-NiCe0.1(OH)xat 25, 50, and 75 °C, and DAC capacities at the corresponding adsorption temperatures and water pressures. The horizontal dashed line represents the estimated water monolayer coverage for α- NiCe0.1(OH)xat 3.6 molecules / nm2.

[0067] FIG. 58 depicts in accordance with various embodiments of the invention, CO2adsorption energies of PNH materials measured using microcalorimetry at incrementally increased4886-5761-4062.1Page 8 of 164094876-000018WOPTCO2pressure at 30 °C. Samples were thermally pretreated for 2 hours under vacuum at 200 °C prior to CO2adsorption.

[0068] FIG. 59A – FIG. 59B depicts in accordance with various embodiments of the invention, (FIG. 59A) FTIR spectra of α-Ni(OH)2measured under 400 ppm CO2without water vapor (dry), 400 ppm CO2and 2.1 kPa H2O (humid), and 400 ppm CO2and 2.1 kPa D2O (humid D2O). (FIG.59B) Evolution in FTIR spectral data over α-Ni(OH)2upon switching from a stream containing 400 ppm CO2and 2.1 kPa D2O (humid D2O) to one containing only 400ppm CO2(spectra are reported either 5 or 30 minutes after switching to a dry stream). Reported spectra are background subtracted with those measured under Ar before exposure to CO2.

[0069] FIG. 60 depicts in accordance with various embodiments of the invention, Depiction of the proposed effect of hydration on the free energies of (bi)carbonates formed through CO2binding onto metal hydroxide surfaces.

[0070] FIG. 61A – FIG. 61B depicts in accordance with various embodiments of the invention, (FIG. 61A) Average adsorption rates for α-NiCe0.1(OH)xas a function of relative humidity of the feed stream. Rates were calculated from breakthrough curves measured at 25°C under 400 ppm CO2. (FIG. 61B) Cyclic DAC performance of α-NiCe0.1(OH)xover 5 cycles. Adsorption conditions: 25°C, 400 ppm CO2, balance N2. Regeneration conditions: 100°C for 2 hours under 2.1 kPa H2O, 20 kPa O2, balance Ar.

[0071] FIG.62 depicts in accordance with various embodiments of the invention, Earth- abundant porous nickel hydroxides synthesized using aqueous miserable organic solvent treatments are activated by surface water to reversibly adsorb ultradilute CO2from humid ambient air. High-valent doping with cerium is used to significantly improve DAC capacities by amplifying surface basicity.

[0072] FIG. 63 depicts in accordance with various embodiments of the invention, XRD patterns of β-Ni(OH)2-T, non-porous β-Ni(OH)2and α-Ni(OH)2. Yellow triangle symbol represents the assigned diffraction peaks from α-Ni(OH)2impurity in non-porous β-Ni(OH)2.

[0073] FIG. 64 depicts in accordance with various embodiments of the invention, XRD pattern of α-NiCe0.1(OH)xand α-NiCe0.1(OH)x-no AMOST.

[0074] FIG. 65 depicts in accordance with various embodiments of the invention, N2adsorption-desorption isotherms of α-NiCe0.1(OH)xand α-NiCe0.1(OH)x-no AMOST.4886-5761-4062.1Page 9 of 164094876-000018WOPT

[0075] FIG.66 depicts in accordance with various embodiments of the invention, FT-IR spectra of α-Ni(OH)2and α-NiCe0.1(OH)x.

[0076] FIG.67 depicts in accordance with various embodiments of the invention, Water vapor adsorption isotherms at different temperature of α-Ni(OH)2and α-NiCe0.1(OH)x.

[0077] FIG. 68 depicts in accordance with various embodiments of the invention, XPS spectra of Ni 2p region of α-Ni(OH)2and α-NiCe0.1(OH)x.

[0078] FIG. 69 depicts in accordance with various embodiments of the invention, N2adsorption-desorption isotherm of α-Ni(OH)2-SO42-and α-Ni(OH)2.

[0079] FIG. 70 depicts in accordance with various embodiments of the invention, CO2concentration profile from switching humid CO2(67% RH) to dry CO2on a humid CO2(67% RH) saturated α-Ni(OH)2.

[0080] FIG. 71 depicts in accordance with various embodiments of the invention, CO2breakthrough curves at 25 °C under different humidity level. Asterisks on each branch represents the point at adsorption half time. Sorbents are α-NiCe0.1(OH)xafter 200 °C 2h pretreatment under Ar.

[0081] FIG. 72A – FIG. 72D depicts in accordance with various embodiments of the invention, High-resolution TEM and IFFT images of α-NiCe0.1(OH)x-no AMOST (FIG.72A, FIG. 72B) and α-NiCe0.1(OH)x(FIG.72C, FIG.72D). The corresponding d-spacing of the lattice fringe represents (101) plane of Ce(OH)3.

[0082] FIG. 73A – FIG. 73B depicts in accordance with various embodiments of the invention, Proposed crystal structure of Ni(OH)2(FIG. 73A) and Ce(OH)3(FIG. 73B) in α- NiCe0.1(OH)x.

[0083] FIG. 74A – FIG. 74B depicts in accordance with various embodiments of the invention, proposed integrated ramp DACM process (FIG. 74A) and isothermal DACM process (FIG.74B).

[0084] FIG.75 depicts in accordance with various embodiments of the invention, proposed schematic for Ni-based oxides as DFMs to achieve DACM process.

[0085] FIG. 76A – FIG. 76C depicts in accordance with various embodiments of the invention, (FIG. 76A) gas profiles of CO2and CH4during a ramp methanation process on Ni0.7Ce0.3Oxafter DAC (FIG.76B) H2-TPR profiles of NiCeOx; Gas flow: 50 ml min-1, 10% H2 / Ar; Sample are thermally pretreated under 350°C under Ar; (FIG. 76C) CH4produced in 5 ramp4886-5761-4062.1Page 10 of 164094876-000018WOPTDACM cycles for NiCeOxwith various Ce loadings; adsorption condition: 25 °C, 400 ppm CO2, 2.1 kPa water and balance N2, methanation condition: ramp from 30 °C to 230 °C with 10 °C / min ramp rate and keep isothermal for additional 1 hour, under 10% H2 / Ar. Experimental details are described in experimental section.

[0086] FIG. 77A – FIG. 77C depicts in accordance with various embodiments of the invention, a) DAC adsorption capacity of NiCeOxwith various Ce loading at 25 °C, under dry and humid (2.1 kPa water) conditions; b) CO2-TPD profiles of NiCeOx; samples are pre-adsorbed with humid (2.1 kPa) 400 ppm CO2for 3 hours. Blue and orange curves represent the weakly bounded CO2and strongly bounded CO2from devolution of experimental measured curve c) Percentage of weakly bounded CO2and strongly bounded CO2from CO2-TPD profiles for NiCeOx.

[0087] FIG. 78A – FIG. 78B depicts in accordance with various embodiments of the invention, (FIG. 78A) difference FT-IR spectra of Ni0.7Ce0.3Oxand NiO at 30 °C, after 30min humid (2.1 kPa D2O) 400 ppm CO2adsorption; (FIG. 78B) difference FT-IR spectra of Ni0.7Ce0.3Oxat 30 °C after 30 min dry and humid (2.1 kPa D2O) 400 ppm CO2adsorption; samples are thermally pretreated under 350 °C under Ar purge. Background spectra at 30 °C before CO2introduction was subtracted.

[0088] FIG. 79A – FIG. 79B depicts in accordance with various embodiments of the invention, proposed schematics for Ni-based oxides as DFMs to achieve DACM process. (FIG. 79A): desorption-diffusion-reaction mechanism; (FIG. 79B): reactively desorbed mechanism by H-spillover or CO2-spillover.

[0089] FIG.80 depicts in accordance with various embodiments of the invention, carbon product profiles of CO2-saturated Ni0.8Ce0.2Oxusing 10% H2 / Ar (dashed line) and pure Ar (solid line) purging at 230 °C; sample was firstly thermally pretreated at 350 °C under Ar purge, and then pre-reduced under 10% H2 / Ar and saturated with dry 400 ppm CO2, balanced N2at 230 °C. Number shown under curves represents the cumulative amount of carbon products during 10 min purging.

[0090] FIG. 81A – FIG. 81C depicts in accordance with various embodiments of the invention, (FIG. 81A) DAC capacity of Ni0.7Ce0.3Ox,Ni0.7Ce0.3Ox-air and Ni0.7Ce0.3Ox-O2; adsorption condition: 400 ppm CO2, 2.1 kPa water, balanced N2at 25 °C; (FIG.81B) XPS spectra of NiCeOxfor Ni 2p3 / 2region; (FIG. 81C) CO2-TPD profile of Ni0.7Ce0.3Ox,Ni0.7Ce0.3Ox-air and Ni0.7Ce0.3Ox-O2; samples pre-adsorbed CO2at 25 °C for 3 hours using 400 ppm CO2, 2.1 kPa4886-5761-4062.1Page 11 of 164094876-000018WOPTwater, balanced N2stream. Number shown under curves represents the cumulative amount of CO2desorbed during CO2-TPD.

[0091] FIG. 82A – FIG. 82B depicts in accordance with various embodiments of the invention, (FIG. 82A) Gas profiles during isothermal DACM at 230 °C in 5 cycles; (FIG. 82B) CO2adsorbed / CH4produced amount of Ni0.7Ce0.3Oxduring isothermal DACM in 5 cycles; 0.035 g of Ni0.7Ce0.3Oxwas thermally pretreated at 350 °C Ar for 2 hours and then pre-reduced under 10% H2 / Ar at 230 °C.

[0092] FIG. 83A – FIG. 83B depicts in accordance with various embodiments of the invention, XRD diffraction patterns (FIG. 83A), and N2adsorption-desorption isotherms (FIG. 83B) of NiCeOx, Samples are pretreated for 2 hours under vacuum at 350 °C.

[0093] FIG. 84 depicts in accordance with various embodiments of the invention, DAC capacity during DAC stage (step 1), CO2desorbed and CH4formed during temperature ramp stage (step 3) on 2ndcycle of Ni0.8Ce0.2Oxin 5 cycles using 200 °C methanation temperature.

[0094] FIG. 85 depicts in accordance with various embodiments of the invention, DAC capacity during DAC stage (step 1), CO2desorbed and CH4formed during temperature ramp stage (step 3) on 2ndcycle DACM of NiCeOxwith various Ce loadings.

[0095] FIG.86 depicts in accordance with various embodiments of the invention, BJH pore size distribution from desorption branch of NiCeOxat different Ce loadings.

[0096] FIG. 87 depicts in accordance with various embodiments of the invention, difference FT-IR spectra of Ni0.7Ce0.3Oxby applying temperature desorption under Ar.; samples are y thermally pretreated under 350 °C under Ar purge, and then cooled to 30 °C, following by 30min humid (2.1 kPa D2O) 400 ppm CO2adsorption. After that, an Ar purge at 30 °C was conducted for 30 min. Sample temperature was then heated with the ramp rate of 10 °C / min. Sample was kept isothermal when it reached 50, 150, 250 °C for 30 min for stabilization of surface carbonates to obtain IR spectra. Each spectra was obtained at the end of the isothermal 30 min step. Background spectra at each temperature before CO2introduction was subtracted.

[0097] FIG. 88 depicts in accordance with various embodiments of the invention, CO2- TPD profile of Ni0.7Ce0.3Ox; samples were pre-saturated by humid (2.1kPa water) CO2and dry CO2before TPD.

[0098] FIG. 89 depicts in accordance with various embodiments of the invention, XRD pattern of Ni0.7Ce0.3Ox, Ni0.7Ce0.3Ox-air and Ni0.7Ce0.3Ox-O2.4886-5761-4062.1Page 12 of 164094876-000018WOPT

[0099] FIG. 90 depicts in accordance with various embodiments of the invention, XPS spectra of Ni0.7Ce0.3Oxand Ni0.7Ce0.3Ox-air for O 1s region.

[0100] FIG. 91 depicts in accordance with various embodiments of the invention, XPS spectra of Ni0.7Ce0.3Ox, Ni0.7Ce0.3Ox-air and CeO2for Ce 3d region.

[0101] FIG. 92 depicts in accordance with various embodiments of the invention, CO2desorption amount from CO2-TPD and corresponding strongly / weakly bounded CO2amount from deconvolution curve of Ni0.7Ce0.3Oxusing different adsorption time.

[0102] FIG. 93A – FIG. 93B depicts various embodiments of the invention, porous transition metal hydroxides: a new class of DAC sorbents.

[0103] FIG. 94A – FIG. 94B depicts various embodiments of the invention, porous transition metal hydroxides: a new class of DAC sorbents.

[0104] FIG. 95A – FIG. 95B depicts various embodiments of the invention, moisture activation: a new paradigm for direct air capture.

[0105] FIG.96A – FIG.96B depicts various embodiments of the invention, carbon capture and conversion. Segregated beds and dual-component dual-function (FIG. 96A), and single- component dual-function (FIG.96B).

[0106] FIG. 97 depicts various embodiments of the invention, single component carbon capture and conversion.

[0107] FIG. 98A – FIG. 98B depicts various embodiments of the invention, capture and conversion can also be run at steady state, 0.015 g oxide, 10 sccm H2, 40 sccm 400 ppm CO2 / N2.

[0108] FIG. 99 depicts in accordance with various embodiments of the invention, schematic of moisture swing adsorption process over nickel hydroxides.

[0109] FIG. 100A – FIG. 100B depicts in accordance with various embodiments of the invention, (FIG.100A) CO2gas profiles during Ar desorption step with different moisture content, and (FIG.100B) equilibrium CO2capacity and desorption capacity from 2-hour Ar purge using Ni(OH)2-T sorbents. (FIG.100B) Moisture-purge is feasible for effectively desorbing CO2over β-Ni(OH)2-T.

[0110] FIG. 101 depicts in accordance with various embodiments of the invention, equilibrium CO2capacity and desorption capacity from Ar purge using Ni(OH)2-T, NiCe0.3(OH)x- T and NiO.4886-5761-4062.1Page 13 of 164094876-000018WOPT

[0111] FIG. 102A – FIG. 102B depicts in accordance with various embodiments of the invention, (FIG.102A) MSA Cycle stability using Ni(OH)2sorbents. Cycle 7 applied an overnight (17 hours) humid Ar desorption step. (FIG. 102B) Average MSA working capacity at different humidity levels using Ni(OH)2sorbents.

[0112] FIG. 103 depicts in accordance with various embodiments of the invention, adsorption breakthrough curves of dry CO2after 2-hour humid Ar desorption at different humidity in 3rd cycle.

[0113] FIG. 104A – FIG. 104B depicts in accordance with various embodiments of the invention, different operation processes for DAC. Temperature Swing Adsorption (FIG. 104A), and Moisture Swing Adsorption (FIG.104B).

[0114] FIG. 105 depicts in accordance with various embodiments of the invention, proposed MSA processes.

[0115] FIG. 106A – FIG. 106B depicts in accordance with various embodiments of the invention, MSA feasibility study.

[0116] FIG. 107A – FIG. 107B depicts in accordance with various embodiments of the invention, MSA using α-Ni(OH)2.

[0117] FIG. 108A – FIG. 108B depicts in accordance with various embodiments of the invention, (FIG. 108A) Illustration of the layered double hydroxide (LDH) structure, and (FIG. 108B) depiction of LDH delamination by aqueous miscible organic solvent treatment (AMOST). Adapted from (Q.Wang, D. O’hare, Chem. Commun.2013, 49, 6301-6303).

[0118] FIG. 109 depicts in accordance with various embodiments of the invention, Illustration of α-Ni(OH)2and β-Ni(OH)2crystal structures. Reprinted with permission from (J. Yao, Y. Li, R. Huang, J. Jiang, S. Xiao, J. Yang, Ionics (Kiel).2021, 27, 65-74).

[0119] FIG. 110A – FIG. 110B depicts in accordance with various embodiments of the invention, gas profiles of CO2and CH4during ramp methanation process on Ni-based oxides after DAC (FIG.110A); and DAC capacity and gas produced during temperature ramp and isothermal at 230oC using pure NiO in 3 cycles (FIG.110B). DETAILED DESCRIPTION OF THE INVENTION

[0120] All references cited herein are incorporated by reference in their entirety as though fully set forth. Unless defined otherwise, technical and scientific terms used herein have the same4886-5761-4062.1Page 14 of 164094876-000018WOPTmeaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0121] One skilled in the art will recognize many methods and materials similar or equivalent to those described herein, which could be used in the practice of the present invention. Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, various features of embodiments of the invention. Indeed, the present invention is in no way limited to the methods and materials described. For purposes of the present invention, the following terms are defined below. For convenience, certain terms employed herein, in the specification, examples and appended claims are collected here.

[0122] Unless stated otherwise, or implicit from context, the following terms and phrases include the meanings provided below. Unless explicitly stated otherwise, or apparent from context, the terms and phrases below do not exclude the meaning that the term or phrase has acquired in the art to which it pertains. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should be understood that this invention is not limited to the particular methodology, protocols, and reagents, etc., described herein and as such can vary. The definitions and terminology used herein are provided to aid in describing particular embodiments, and are not intended to limit the claimed invention, because the scope of the invention is limited only by the claims.

[0123] As used herein the term “comprising” or “comprises” is used in reference to compositions, methods, systems, articles of manufacture, apparatus, and respective component(s) thereof, that are useful to an embodiment, yet open to the inclusion of unspecified elements, whether useful or not. It will be understood by those within the art that, in general, terms used herein are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). Although the open- ended term “comprising,” as a synonym of terms such as including, containing, or having, is used herein to describe and claim the invention, the present invention, or embodiments thereof, may alternatively be described using alternative terms such as “consisting of” or “consisting essentially of.”4886-5761-4062.1Page 15 of 164094876-000018WOPT

[0124] Unless stated otherwise, the terms “a” and “an” and “the” and similar references used in the context of describing a particular embodiment of the application (especially in the context of claims) can be construed to cover both the singular and the plural. The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (for example, “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the application and does not pose a limitation on the scope of the application otherwise claimed. The abbreviation, “e.g.” is derived from the Latin exempli gratia, and is used herein to indicate a non-limiting example. Thus, the abbreviation “e.g.” is synonymous with the term “for example.” No language in the specification should be construed as indicating any non- claimed element essential to the practice of the application.

[0125] “Optional" or “optionally” means that the subsequently described circumstance may or may not occur, so that the description includes instances where the circumstance occurs and instances where it does not.

[0126] In some embodiments, the numbers expressing quantities of reagents, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.4886-5761-4062.1Page 16 of 164094876-000018WOPT

[0127] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and / or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

[0128] As used herein the term “electron donating group” is well-known in the art and generally refers to a functional group or atom that pushes electron density away from itself, towards other portions of the molecule, e.g., through resonance and / or inductive effects. Non- limiting examples of electron-donating groups include ORc, NRcRd, alkyl groups, wherein Rcand Rdare each independently H, optionally substituted alkyl, optionally substituted heteroalkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted cyclyl, or optionally substituted heterocyclyl.

[0129] As used herein the term “electron withdrawing group” is well-known in the art and generally refers to a functional group or atom that pulls electron density towards itself, away from other portions of the molecule, e.g., through resonance and / or inductive effects. Non-limiting examples of electron withdrawing groups include NO2, F, Cl, Br, I, CF3, CN, CO2Ra, C(=O)NRaRb, C(=O)Ra, SO2Ra, SO2ORa, SO2NRaRb, PO3RaRb, or NO, wherein Raand Rbare each independently H, optionally substituted alkyl, optionally substituted heteroalkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted cyclyl, or optionally substituted heterocyclyl.

[0130] As used herein, the term “alkyl” means a straight or branched, saturated aliphatic radical having a chain of carbon atoms. Cxalkyl and Cx-Cyalkyl are typically used where X and Y indicate the number of carbon atoms in the chain. For example, C1-C6alkyl includes alkyls that have a chain of between 1 and 6 carbons (e.g., methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, and the like). Alkyl represented along with another radical (e.g., as in arylalkyl) means a straight or branched, saturated alkyl divalent radical having the number of atoms indicated or when no atoms are indicated means a bond, e.g., (C6-C10)aryl(C0- C3)alkyl includes phenyl, benzyl, phenethyl, 1-phenylethyl 3-phenylpropyl, and the like.4886-5761-4062.1Page 17 of 164094876-000018WOPTBackbone of the alkyl can be optionally inserted with one or more heteroatoms, such as N, O, or S.

[0131] In preferred embodiments, a straight chain or branched chain alkyl has 30 or fewer carbon atoms in its backbone (e.g., C1-C30for straight chains, C3-C30for branched chains), and more preferably 20 or fewer. Likewise, preferred cycloalkyls have from 3-10 carbon atoms in their ring structure, and more preferably have 5, 6 or 7 carbons in the ring structure. The term “alkyl” (or “lower alkyl”) as used throughout the specification, examples, and claims is intended to include both “unsubstituted alkyls” and “substituted alkyls”, the latter of which refers to alkyl moieties having one or more substituents replacing a hydrogen on one or more carbons of the hydrocarbon backbone.

[0132] Unless the number of carbons is otherwise specified, “lower alkyl” as used herein means an alkyl group, as defined above, but having from one to ten carbons, more preferably from one to six carbon atoms in its backbone structure. Likewise, “lower alkenyl” and “lower alkynyl” have similar chain lengths. Throughout the application, preferred alkyl groups are lower alkyls. In preferred embodiments, a substituent designated herein as alkyl is a lower alkyl.

[0133] Non-limiting examples of substituents of a substituted alkyl can include halogen, hydroxy, nitro, thiols, amino, azido, imino, amido, phosphoryl (including phosphonate and phosphinate), sulfonyl (including sulfate, sulfonamido, sulfamoyl and sulfonate), and silyl groups, as well as ethers, alkylthios, carbonyls (including ketones, aldehydes, carboxylates, and esters),- CF3, -CN and the like.

[0134] As used herein, the term “alkenyl” refers to unsaturated straight-chain, branched- chain or cyclic hydrocarbon radicals having at least one carbon-carbon double bond. Cxalkenyl and Cx-Cyalkenyl are typically used where X and Y indicate the number of carbon atoms in the chain. For example, C2-C6alkenyl includes alkenyls that have a chain of between 2 and 6 carbons and at least one double bond, e.g., vinyl, allyl, propenyl, isopropenyl, 1-butenyl, 2-butenyl, 3- butenyl, 2-methylallyl, 1-hexenyl, 2-hexenyl, 3- hexenyl, and the like). Alkenyl represented along with another radical (e.g., as in arylalkenyl) means a straight or branched, alkenyl divalent radical having the number of atoms indicated. Backbone of the alkenyl can be optionally inserted with one or more heteroatoms, such as N, O, or S.

[0135] As used herein, the term “alkynyl” refers to unsaturated hydrocarbon radicals having at least one carbon-carbon triple bond. Cxalkynyl and Cx-Cyalkynyl are typically used4886-5761-4062.1Page 18 of 164094876-000018WOPTwhere X and Y indicate the number of carbon atoms in the chain. For example, C2-C6alkynyl includes alkynls that have a chain of between 2 and 6 carbons and at least one triple bond, e.g., ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, isopentynyl, 1,3-hexa-diyn-yl, n-hexynyl, 3-pentynyl, 1-hexen-3-ynyl and the like. Alkynyl represented along with another radical (e.g., as in arylalkynyl) means a straight or branched, alkynyl divalent radical having the number of atoms indicated. Backbone of the alkynyl can be optionally inserted with one or more heteroatoms, such as N, O, or S.

[0136] The terms “alkylene,” “alkenylene,” and “alkynylene” refer to divalent alkyl, alkelyne, and alkynylene” radicals. Prefixes Cxand Cx-Cyare typically used where X and Y indicate the number of carbon atoms in the chain. For example, C1-C6alkylene includes methylene, (—CH2—), ethylene (—CH2CH2—), trimethylene (—CH2CH2CH2—), tetramethylene (— CH2CH2CH2CH2—), 2-methyltetramethylene (—CH2CH(CH3)CH2CH2—), pentamethylene (— CH2CH2CH2CH2CH2—) and the like).

[0137] As used herein, the term “alkylidene” means a straight or branched unsaturated, aliphatic, divalent radical having a general formula =CRaRb. Non-limiting examples of Raand Rbare each independently hydrogen, alkyl, substituted alkyl, alkenyl, or substituted alkenyl. Cxalkylidene and Cx-Cyalkylidene are typically used where X and Y indicate the number of carbon atoms in the chain. For example, C2-C6alkylidene includes methylidene (=CH2), ethylidene (=CHCH3), isopropylidene (=C(CH3)2), propylidene (=CHCH2CH3), allylidene (=CH— CH=CH2), and the like).

[0138] The term “heteroalkyl”, as used herein, refers to straight or branched chain, or cyclic carbon-containing radicals, or combinations thereof, containing at least one heteroatom. Suitable heteroatoms include, but are not limited to, O, N, Si, P, Se, B, and S, wherein the phosphorous and sulfur atoms are optionally oxidized, and the nitrogen heteroatom is optionally quaternized. Heteroalkyls can be substituted as defined above for alkyl groups.

[0139] As used herein, the term “halogen” or “halo” refers to an atom selected from fluorine (F), chlorine (Cl), bromine (Br) and iodine (I). The term “halogen radioisotope” or “halo radioisotope” refers to a radionuclide of an atom selected from fluorine (F), chlorine (Cl), bromine (Br) and iodine (I).4886-5761-4062.1Page 19 of 164094876-000018WOPT

[0140] In some embodiments, “iodo” refers to the iodine atom (I) when it is used in the context of a halo functional group or halogen functional group or as a halo substituent or halogen substituent.

[0141] In some embodiments, “bromo” refers to the bromine atom (Br) when it is used in the context of a halo functional group or halogen functional group or as a halo substituent or halogen substituent.

[0142] In some embodiments, “chloro” refers to the chlorine atom (Cl) when it is used in the context of a halo functional group or halogen functional group or as a halo substituent or halogen substituent.

[0143] In some embodiments, “fluoro” refers to the fluorine atom (F) when it is used in the context of a halo functional group or halogen functional group or as a halo substituent or halogen substituent.

[0144] A “halogen-substituted moiety” or “halo-substituted moiety”, as an isolated group or part of a larger group, means an aliphatic, alicyclic, or aromatic moiety, as described herein, substituted by one or more “halo” atoms, as such terms are defined in this application. For example, halo-substituted alkyl includes haloalkyl, dihaloalkyl, trihaloalkyl, perhaloalkyl and the like (e.g. halosubstituted (C1-C3)alkyl includes chloromethyl, dichloromethyl, difluoromethyl, trifluoromethyl (-CF3), 2,2,2-trifluoroethyl, perfluoroethyl, 2,2,2-trifluoro-l,l-dichloroethyl, and the like).

[0145] The term “aryl” refers to monocyclic, bicyclic, or tricyclic fused aromatic ring system. Cxaryl and Cx-Cyaryl are typically used where X and Y indicate the number of carbon atoms in the ring system. For example, C6-C12aryl includes aryls that have 6 to 12 carbon atoms in the ring system. Exemplary aryl groups include, but are not limited to, pyridinyl, pyrimidinyl, furanyl, thienyl, imidazolyl, thiazolyl, pyrazolyl, pyridazinyl, pyrazinyl, triazinyl, tetrazolyl, indolyl, benzyl, phenyl, naphthyl, anthracenyl, azulenyl, fluorenyl, indanyl, indenyl, naphthyl, phenyl, tetrahydronaphthyl, benzimidazolyl, benzofuranyl, benzothiofuranyl, benzothiophenyl, benzoxazolyl, benzoxazolinyl, benzthiazolyl, benztriazolyl, benztetrazolyl, benzisoxazolyl, benzisothiazolyl, benzimidazolinyl, carbazolyl, 4aH carbazolyl, carbolinyl, chromanyl, chromenyl, cinnolinyl, decahydroquinolinyl, 2H,6H-1,5,2-dithiazinyl, dihydrofuro[2,3 b]tetrahydrofuran, furanyl, furazanyl, imidazolidinyl, imidazolinyl, imidazolyl, 1H-indazolyl, indolenyl, indolinyl, indolizinyl, indolyl, 3H-indolyl, isatinoyl, isobenzofuranyl, isochromanyl,4886-5761-4062.1Page 20 of 164094876-000018WOPTisoindazolyl, isoindolinyl, isoindolyl, isoquinolinyl, isothiazolyl, isoxazolyl, methylenedioxyphenyl, morpholinyl, naphthyridinyl, octahydroisoquinolinyl, oxadiazolyl, 1,2,3- oxadiazolyl, 1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, oxazolidinyl, oxazolyl, oxindolyl, pyrimidinyl, phenanthridinyl, phenanthrolinyl, phenazinyl, phenothiazinyl, phenoxathinyl, phenoxazinyl, phthalazinyl, piperazinyl, piperidinyl, piperidonyl, 4-piperidonyl, piperonyl, pteridinyl, purinyl, pyranyl, pyrazinyl, pyrazolidinyl, pyrazolinyl, pyrazolyl, pyridazinyl, pyridooxazole, pyridoimidazole, pyridothiazole, pyridinyl, pyridyl, pyrimidinyl, pyrrolidinyl, pyrrolinyl, 2H-pyrrolyl, pyrrolyl, quinazolinyl, quinolinyl, 4H-quinolizinyl, quinoxalinyl, quinuclidinyl, tetrahydrofuranyl, tetrahydroisoquinolinyl, tetrahydroquinolinyl, tetrazolyl, 6H-1,2,5-thiadiazinyl, 1,2,3-thiadiazolyl, 1,2,4-thiadiazolyl, 1,2,5-thiadiazolyl, 1,3,4- thiadiazolyl, thianthrenyl, thiazolyl, thienyl, thienothiazolyl, thienooxazolyl, thienoimidazolyl, thiophenyl and xanthenyl, and the like. In some embodiments, 1, 2, 3, or 4 hydrogen atoms of each ring can be substituted by a substituent.

[0146] The term “heteroaryl” refers to an aromatic 5-8 membered monocyclic, 8-12 membered fused bicyclic, or 11-14 membered fused tricyclic ring system having 1-3 heteroatoms if monocyclic, 1-6 heteroatoms if bicyclic, or 1-9 heteroatoms if tricyclic, said heteroatoms selected from O, N, or S (e.g., carbon atoms and 1-3, 1-6, or 1-9 heteroatoms of N, O, or S if monocyclic, bicyclic, orrespectively. Cxheteroaryl and Cx-Cyheteroaryl are typically used where X and Y indicate the number of carbon atoms in the ring system. For example, C4-C9heteroaryl includes heteroaryls that have 4 to 9 carbon atoms in the ring system. Heteroaryls include, but are not limited to, those derived from benzo[b]furan, benzo[b] thiophene, benzimidazole, imidazo[4,5-c]pyridine, quinazoline, thieno[2,3-c]pyridine, thieno[3,2-b]pyridine, thieno[2, 3-b]pyridine, indolizine, imidazo[l,2a]pyridine, quinoline, isoquinoline, phthalazine, quinoxaline, naphthyridine, quinolizine, indole, isoindole, indazole, indoline, benzoxazole, benzopyrazole, benzothiazole, imidazo[l,5-a]pyridine, pyrazolo[l,5-a]pyridine, imidazo[l,2- a]pyrimidine, imidazo[l,2-c]pyrimidine, imidazo[l,5-a]pyrimidine, imidazo[l,5-c]pyrimidine, pyrrolo[2,3-b]pyridine, pyrrolo[2,3cjpyridine, pyrrolo[3,2-c]pyridine, pyrrolo[3,2-b]pyridine, pyrrolo[2,3-d]pyrimidine, pyrrolo[3,2-d]pyrimidine, pyrrolo [2,3-b]pyrazine, pyrazolo[l,5- a]pyridine, pyrrolo[l,2-b]pyridazine, pyrrolo[l,2-c]pyrimidine, pyrrolo[l,2-a]pyrimidine, pyrrolo[l,2-a]pyrazine, triazo[l,5-a]pyridine, pteridine, purine, carbazole, acridine, phenazine, phenothiazene, phenoxazine, l,2-dihydropyrrolo[3,2,l-hi]indole, indolizine, pyrido[l,2-a]indole,4886-5761-4062.1Page 21 of 164094876-000018WOPT2(lH)-pyridinone, benzimidazolyl, benzofuranyl, benzothiofuranyl, benzothiophenyl, benzoxazolyl, benzoxazolinyl, benzthiazolyl, benztriazolyl, benztetrazolyl, benzisoxazolyl, benzisothiazolyl, benzimidazolinyl, carbazolyl, 4aH-carbazolyl, carbolinyl, chromanyl, chromenyl, cinnolinyl, decahydroquinolinyl, 2H,6H-1,5,2-dithiazinyl, dihydrofuro[2,3-b]tetrahydrofuran, furanyl, furazanyl, imidazolidinyl, imidazolinyl, imidazolyl, 1H-indazolyl, indolenyl, indolinyl, indolizinyl, indolyl, 3H-indolyl, isatinoyl, isobenzofuranyl, isochromanyl, isoindazolyl, isoindolinyl, isoindolyl, isoquinolinyl, isothiazolyl, isoxazolyl, methylenedioxyphenyl, morpholinyl, naphthyridinyl, octahydroisoquinolinyl, oxadiazolyl, 1,2,3- oxadiazolyl, 1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, oxazolidinyl, oxazolyl, oxepanyl, oxetanyl, oxindolyl, pyrimidinyl, phenanthridinyl, phenanthrolinyl, phenazinyl, phenothiazinyl, phenoxathinyl, phenoxazinyl, phthalazinyl, piperazinyl, piperidinyl, piperidonyl, 4-piperidonyl, piperonyl, pteridinyl, purinyl, pyranyl, pyrazinyl, pyrazolidinyl, pyrazolinyl, pyrazolyl, pyridazinyl, pyridooxazole, pyridoimidazole, pyridothiazole, pyridinyl, pyridyl, pyrimidinyl, pyrrolidinyl, pyrrolinyl, 2H-pyrrolyl, pyrrolyl, quinazolinyl, quinolinyl, 4H- quinolizinyl, quinoxalinyl, quinuclidinyl, tetrahydrofuranyl, tetrahydroisoquinolinyl, tetrahydropyranyl, tetrahydroquinolinyl, tetrazolyl, 6H-1,2,5-thiadiazinyl, 1,2,3-thiadiazolyl, 1,2,4-thiadiazolyl, 1,2,5-thiadiazolyl, 1,3,4-thiadiazolyl, thianthrenyl, thiazolyl, thienyl, thienothiazolyl, thienooxazolyl, thienoimidazolyl, thiophenyl and xanthenyl. Some exemplary heteroaryl groups include, but are not limited to, pyridyl, furyl or furanyl, imidazolyl, benzimidazolyl, pyrimidinyl, thiophenyl or thienyl, pyridazinyl, pyrazinyl, quinolinyl, indolyl, thiazolyl, naphthyridinyl, 2-amino-4-oxo-3,4-dihydropteridin-6-yl, tetrahydroisoquinolinyl, and the like. In some embodiments, 1, 2, 3, or 4 hydrogen atoms of each ring may be substituted by a substituent.

[0147] The term “cyclyl” or “cycloalkyl” refers to saturated and partially unsaturated cyclic hydrocarbon groups having 3 to 12 carbons, for example, 3 to 8 carbons, and, for example, 3 to 6 carbons. Cxcyclyl and Cx-Cycycyl are typically used where X and Y indicate the number of carbon atoms in the ring system. For example, C3-C8cyclyl includes cyclyls that have 3 to 8 carbon atoms in the ring system. The cycloalkyl group additionally can be optionally substituted, e.g., with 1, 2, 3, or 4 substituents. C3-C10cyclyl includes cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclohexenyl, 2,5-cyclohexadienyl, cycloheptyl, cyclooctyl, bicyclo[2.2.2]octyl,4886-5761-4062.1Page 22 of 164094876-000018WOPTadamantan-l-yl, decahydronaphthyl, oxocyclohexyl, dioxocyclohexyl, thiocyclohexyl, 2- oxobicyclo [2.2.1]hept-l-yl, and the like.

[0148] Aryl and heteroaryls can be optionally substituted with one or more substituents at one or more positions, for example, halogen, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, amino, nitro, sulfhydryl, imino, amido, phosphate, phosphonate, phosphinate, carbonyl, carboxyl, silyl, ether, alkylthio, sulfonyl, ketone, aldehyde, ester, a heterocyclyl, an aromatic or heteroaromatic moiety, -CF3, -CN, or the like.

[0149] The term “heterocyclyl” refers to a nonaromatic 4-8 membered monocyclic, 8-12 membered bicyclic, or 11-14 membered tricyclic ring system having 1-3 heteroatoms if monocyclic, 1-6 heteroatoms if bicyclic, or 1-9 heteroatoms if tricyclic, said heteroatoms selected from O, N, or S (e.g., carbon atoms and 1-3, 1-6, or 1-9 heteroatoms of N, O, or S if monocyclic, bicyclic, or tricyclic, respectively). Cxheterocyclyl and Cx-Cyheterocyclyl are typically used where X and Y indicate the number of carbon atoms in the ring system. For example, C4-C9heterocyclyl includes heterocyclyls that have 4-9 carbon atoms in the ring system. In some embodiments, 1, 2 or 3 hydrogen atoms of each ring can be substituted by a substituent. Exemplary heterocyclyl groups include, but are not limited to piperazinyl, pyrrolidinyl, dioxanyl, morpholinyl, tetrahydrofuranyl, piperidyl, 4-morpholyl, 4-piperazinyl, pyrrolidinyl, perhydropyrrolizinyl, 1,4- diazaperhydroepinyl, 1,3-dioxanyl, 1,4-dioxanyland the like.

[0150] The terms “bicyclic” and “tricyclic” refers to fused, bridged, or joined by a single bond polycyclic ring assemblies.

[0151] The term “cyclylalkylene” means a divalent aryl, heteroaryl, cyclyl, or heterocyclyl.

[0152] As used herein, the term “fused ring” refers to a ring that is bonded to another ring to form a compound having a bicyclic structure when the ring atoms that are common to both rings are directly bound to each other. Non-exclusive examples of common fused rings include decalin, naphthalene, anthracene, phenanthrene, indole, furan, benzofuran, quinoline, and the like. Compounds having fused ring systems can be saturated, partially saturated, cyclyl, heterocyclyl, aromatics, heteroaromatics, and the like.

[0153] As used herein, the term “carbonyl” means the radical —C(O)—. It is noted that the carbonyl radical can be further substituted with a variety of substituents to form different carbonyl groups including acids, acid halides, amides, esters, ketones, and the like.4886-5761-4062.1Page 23 of 164094876-000018WOPT

[0154] The term “carboxy” means the radical —C(O)O—. It is noted that compounds described herein containing carboxy moieties can include protected derivatives thereof, i.e., where the oxygen is substituted with a protecting group. Suitable protecting groups for carboxy moieties include benzyl, tert-butyl, and the like. The term "carboxyl" means –COOH.

[0155] The term “cyano” means the radical —CN.

[0156] The term, “heteroatom” refers to an atom that is not a carbon atom. Particular examples of heteroatoms include, but are not limited to nitrogen, oxygen, sulfur and halogens. A “heteroatom moiety” includes a moiety where the atom by which the moiety is attached is not a carbon. Examples of heteroatom moieties include —N=, —NRN—, —N+(O-)=, —O—, —S— or —S(O)2—, —OS(O)2—, and —SS—, wherein RNis H or a further substituent.

[0157] The term “hydroxy” means the radical —OH.

[0158] The term “imine derivative” means a derivative comprising the moiety —C(NR)— , wherein R comprises a hydrogen or carbon atom alpha to the nitrogen.

[0159] The term “nitro” means the radical —NO2.

[0160] An “oxaaliphatic,” “oxaalicyclic”, or “oxaaromatic” mean an aliphatic, alicyclic, or aromatic, as defined herein, except where one or more oxygen atoms (—O—) are positioned between carbon atoms of the aliphatic, alicyclic, or aromatic respectively.

[0161] An “oxoaliphatic,” “oxoalicyclic”, or “oxoaromatic” means an aliphatic, alicyclic, or aromatic, as defined herein, substituted with a carbonyl group. The carbonyl group can be an aldehyde, ketone, ester, amide, acid, or acid halide.

[0162] As used herein, the term, “aromatic” means a moiety wherein the constituent atoms make up an unsaturated ring system, all atoms in the ring system are sp2hybridized and the total number of pi electrons is equal to 4n+2. An aromatic ring can be such that the ring atoms are only carbon atoms (e.g., aryl) or can include carbon and non-carbon atoms (e.g., heteroaryl).

[0163] As used herein, the term “substituted” refers to independent replacement of one or more (typically 1, 2, 3, 4, or 5) of the hydrogen atoms on the substituted moiety with substituents independently selected from the group of substituents listed below in the definition for “substituents” or otherwise specified. In general, a non-hydrogen substituent can be any substituent that can be bound to an atom of the given moiety that is specified to be substituted. Examples of substituents include, but are not limited to, acyl, acylamino, acyloxy, aldehyde, alicyclic, aliphatic, alkanesulfonamido, alkanesulfonyl, alkaryl, alkenyl, alkoxy, alkoxycarbonyl,4886-5761-4062.1Page 24 of 164094876-000018WOPTalkyl, alkylamino, alkylcarbanoyl, alkylene, alkylidene, alkylthios, alkynyl, amide, amido, amino, aminoalkyl, aralkyl, aralkylsulfonamido, arenesulfonamido, arenesulfonyl, aromatic, aryl, arylamino, arylcarbanoyl, aryloxy, azido, carbamoyl, carbonyl, carbonyls including ketones, carboxy, carboxylates, CF3, cyano (CN), cycloalkyl, cycloalkylene, ester, ether, haloalkyl, halogen, halogen, heteroaryl, heterocyclyl, hydroxy, hydroxyalkyl, imino, iminoketone, ketone, mercapto, nitro, oxaalkyl, oxo, oxoalkyl, phosphoryl (including phosphonate and phosphinate), silyl groups, sulfonamido, sulfonyl (including sulfate, sulfamoyl and sulfonate), thiols, and ureido moieties, each of which may optionally also be substituted or unsubstituted. In some cases, two substituents, together with the carbon(s) to which they are attached to, can form a ring.

[0164] Substituents may be protected as necessary and any of the protecting groups commonly used in the art may be employed. Non-limiting examples of protecting groups may be found, for example, in Greene et al., Protective Groups in Organic Synthesis, 3rd Ed. (New York: Wiley, 1999).

[0165] The terms “alkoxyl” or “alkoxy” as used herein refers to an alkyl group, as defined above, having an oxygen radical attached thereto. Representative alkoxyl groups include methoxy, ethoxy, propyloxy, tert-butoxy, n-propyloxy, iso-propyloxy, n-butyloxy, iso-butyloxy, and the like. An “ether” is two hydrocarbons covalently linked by an oxygen. Accordingly, the substituent of an alkyl that renders that alkyl an ether is or resembles an alkoxyl, such as can be represented by one of -O-alkyl, -O-alkenyl, and -O-alkynyl. Aroxy can be represented by –O-aryl or O- heteroaryl, wherein aryl and heteroaryl are as defined below. The alkoxy and aroxy groups can be substituted as described above for alkyl.

[0166] The term “aralkyl”, as used herein, refers to an alkyl group substituted with an aryl group (e.g., an aromatic or heteroaromatic group).

[0167] The term “alkylthio” refers to an alkyl group, as defined above, having a sulfur radical attached thereto. In preferred embodiments, the “alkylthio” moiety is represented by one of -S-alkyl, -S-alkenyl, and -S-alkynyl. Representative alkylthio groups include methylthio, ethylthio, and the like. The term “alkylthio” also encompasses cycloalkyl groups, alkene and cycloalkene groups, and alkyne groups. “Arylthio” refers to aryl or heteroaryl groups.

[0168] The term “sulfinyl” means the radical —SO—. It is noted that the sulfinyl radical can be further substituted with a variety of substituents to form different sulfinyl groups including sulfinic acids, sulfinamides, sulfinyl esters, sulfoxides, and the like.4886-5761-4062.1Page 25 of 164094876-000018WOPT

[0169] The term “sulfonyl” means the radical —SO2—. It is noted that the sulfonyl radical can be further substituted with a variety of substituents to form different sulfonyl groups including sulfonic acids (-SO3H), sulfonamides, sulfonate esters, sulfones, and the like.

[0170] The term “thiocarbonyl” means the radical —C(S)—. It is noted that the thiocarbonyl radical can be further substituted with a variety of substituents to form different thiocarbonyl groups including thioacids, thioamides, thioesters, thioketones, and the like.

[0171] As used herein, the term “amino” means -NH2. The term “alkylamino” means a nitrogen moiety having at least one straight or branched unsaturated aliphatic, cyclyl, or heterocyclyl radicals attached to the nitrogen. For example, representative amino groups include —NH2, —NHCH3, —N(CH3)2, —NH(C1-C10alkyl), —N(C1-C10alkyl)2, and the like. The term “alkylamino” includes “alkenylamino,” “alkynylamino,” “cyclylamino,” and “heterocyclylamino.” The term “arylamino” means a nitrogen moiety having at least one aryl radical attached to the nitrogen. For example —NHaryl, and —N(aryl)2. The term “heteroarylamino” means a nitrogen moiety having at least one heteroaryl radical attached to the nitrogen. For example —NHheteroaryl, and —N(heteroaryl)2. Optionally, two substituents together with the nitrogen can also form a ring. Unless indicated otherwise, the compounds described herein containing amino moieties can include protected derivatives thereof. Suitable protecting groups for amino moieties include acetyl, tertbutoxycarbonyl, benzyloxycarbonyl, and the like.

[0172] The term “aminoalkyl” means an alkyl, alkenyl, and alkynyl as defined above, except where one or more substituted or unsubstituted nitrogen atoms (—N—) are positioned between carbon atoms of the alkyl, alkenyl, or alkynyl. For example, an (C2-C6) aminoalkyl refers to a chain comprising between 2 and 6 carbons and one or more nitrogen atoms positioned between the carbon atoms.

[0173] The term "alkoxyalkoxy" means –O-(alkyl)-O-(alkyl), such as –OCH2CH2OCH3, and the like.

[0174] The term “alkoxycarbonyl" means –C(O)O-(alkyl), such as –C(=O)OCH3, – C(=O)OCH2CH3, and the like.

[0175] The term “alkoxyalkyl" means -(alkyl)-O-(alkyl), such as -- CH2OCH3, – CH2OCH2CH3, and the like.4886-5761-4062.1Page 26 of 164094876-000018WOPT

[0176] The term “aryloxy" means –O-(aryl), such as –O-phenyl, –O-pyridinyl, and the like.

[0177] The term “arylalkyl" means -(alkyl)-(aryl), such as benzyl (i.e., –CH2phenyl), – CH2-pyrindinyl, and the like.

[0178] The term “arylalkyloxy" means –O-(alkyl)-(aryl), such as –O-benzyl, –O–CH2- pyridinyl, and the like.

[0179] The term “cycloalkyloxy" means –O-(cycloalkyl), such as –O-cyclohexyl, and the like.

[0180] The term “cycloalkylalkyloxy" means –O-(alkyl)-(cycloalkyl, such as – OCH2cyclohexyl, and the like.

[0181] The term “aminoalkoxy" means –O-(alkyl)-NH2, such as –OCH2NH2, – OCH2CH2NH2, and the like.

[0182] The term “mono- or di-alkylamino" means –NH(alkyl) or –N(alkyl)(alkyl), respectively, such as –NHCH3, –N(CH3)2, and the like.

[0183] The term "mono- or di-alkylaminoalkoxy" means –O-(alkyl)-NH(alkyl) or –O- (alkyl)-N(alkyl)(alkyl), respectively, such as –OCH2NHCH3, –OCH2CH2N(CH3)2, and the like.

[0184] The term “arylamino" means –NH(aryl), such as –NH-phenyl, –NH-pyridinyl, and the like.

[0185] The term “arylalkylamino" means –NH-(alkyl)-(aryl), such as –NH-benzyl, – NHCH2-pyridinyl, and the like.

[0186] The term “alkylamino" means –NH(alkyl), such as –NHCH3, –NHCH2CH3, and the like.

[0187] The term “cycloalkylamino" means –NH-(cycloalkyl), such as –NH-cyclohexyl, and the like.

[0188] The term “cycloalkylalkylamino" –NH-(alkyl)-(cycloalkyl), such as –NHCH2- cyclohexyl, and the like.

[0189] It is noted in regard to all of the definitions provided herein that the definitions should be interpreted as being open ended in the sense that further substituents beyond those specified may be included. Hence, a C1alkyl indicates that there is one carbon atom but does not indicate what are the substituents on the carbon atom. Hence, a C1alkyl comprises methyl (i.e., — CH3) as well as —CRaRbRcwhere Ra, Rb, and Rccan each independently be hydrogen or any other4886-5761-4062.1Page 27 of 164094876-000018WOPTsubstituent where the atom alpha to the carbon is a heteroatom or cyano. Hence, CF3, CH2OH and CH2CN are all C1alkyls.

[0190] Unless otherwise stated, structures depicted herein are meant to include compounds which differ only in the presence of one or more isotopically enriched atoms. For example, compounds having the present structure except for the replacement of a hydrogen atom by a deuterium or tritium, or the replacement of a carbon atom by a13C- or14C-enriched carbon are within the scope of the invention.

[0191] In various embodiments, compounds of the present invention as disclosed herein may be synthesized using any synthetic method available to one of skill in the art. Non-limiting examples of synthetic methods used to prepare various embodiments of compounds of the present invention are disclosed in the Examples section herein.

[0192] In various embodiments, “moisture swing adsorption” (MSA) refers to a technique that uses changes in the moisture content of the inlet stream to capture and release carbon dioxide (CO2) from a gas stream (e.g., ambient air) onto a solid sorbent (e.g., a sorbent of the present invention). In some embodiments, moisture swing adsorption (MSA) comprises the following steps: 1. Prehumidification: In some embodiments, the solid sorbent of the present invention is hydrated with water or water vapor to enable the subsequent effective CO2adsorption. In some embodiments, hydration of the solid sorbent leads to the formation of carbonates on the solid sorbent. 2. CO2adsorption: The solid sorbent is contacted with a gas stream (e.g., ambient air) and CO2in the gas stream is adsorbed on the solid sorbent. In some embodiments, during CO2adsorption, the formation of carbonates occur on the solid sorbent, and water on the surface of the solid sorbent starts to desorb, and reduction of water molecules around hydroxide sites facilitates the hydrolysis of carbonates. In some embodiments, the solid sorbent becomes at least partially saturated with CO2and bicarbonates become the dominate species effectively replacing the carbonates and adsorbed water. 3. Rehumidification: The solid sorbent is contacted with a humid inert gas. In some embodiments, contacting the solid sorbent with a humid inert gas rehumidifies the solid sorbent, which leads to the conversion of bicarbonates to carbonates, and CO2is released from the solid sorbent. In some embodiments, the humidified solid sorbent is ready for the next cycle of CO2adsorption. In some embodiments, the adsorption of CO2is carried out under dry conditions and desorption under wet conditions, and in other embodiments the converse occurs i.e. adsorption occurs under wet conditions and desorption under dry conditions. In some4886-5761-4062.1Page 28 of 164094876-000018WOPTembodiments, this MSA process is carried out isothermally i.e. at a single temperature, and in other embodiments it can be carried out non-isothermally i.e. with the adsorption step occurring at one temperature and the desorption occurring at another temperature.

[0193] In various embodiments, “pressure swing adsorption” (PSA) refers to a technique that is used to separate some gas species from a mixture of gas species (e.g., air or ambient air) using different pressures for the adsorption and desorption steps according to the species’ molecular characteristics and affinity of an adsorbent material (e.g., a sorbent of the present invention). In some embodiments, the method operates at ambient temperature and a sorbent (e.g., a sorbent of the present invention) is used to capture a gas species (e.g., carbon dioxide), preferentially adsorbing the gas species (e.g., carbon dioxide) at high pressure. The process then swings to low pressure to desorb the adsorbed gas species from the sorbent. In some embodiments, the pressure swing adsorption (PSA) process is based on the phenomenon that under high pressure, gases tend to be trapped onto solid surfaces, i.e., to be adsorbed. In some embodiments, the higher the pressure, the more gas is adsorbed. In some embodiments, when the pressure is dropped, the gas is released, or desorbed. For example, if a gas mixture (e.g., ambient air) is passed under pressure through a vessel containing an adsorbent (e.g., a sorbent of the present invention) that attracts carbon dioxide more strongly than oxygen, or other gases in the mixture, a fraction of carbon dioxide will be adsorbed by the sorbent, and the gas exiting the vessel will be richer in oxygen than the mixture entering the vessel. When the sorbent reaches the limit of its capacity to adsorb carbon dioxide, it can be regenerated by decreasing the pressure, thus releasing the adsorbed carbon dioxide. The sorbent is then ready for another cycle of adsorbing carbon dioxide from the gas mixture (e.g., ambient air) and producing an oxygen-enriched gas mixture. In some other embodiments, the process may involve both a temperature and a pressure swing, i.e. adsorption of CO2may occur at a particular pressure and temperature, and desorption at a different temperature and pressure.

[0194] In various embodiments, “vacuum swing adsorption” (VSA) refers to a technique that is used to separate some gas species form a mixture of gas species (e.g., air or ambient air) at ambient or higher pressures. The process then swings to a vacuum to regenerate the adsorbent material (e.g., sorbent of the present invention).

[0195] In various embodiments, “temperature swing adsorption” (TSA) refers to a technique that uses heat to regenerate an adsorbent material (e.g., a sorbent of the present4886-5761-4062.1Page 29 of 164094876-000018WOPTinvention) and / or separate some gas species from a mixture of gas species (e.g., air or ambient air). In some embodiments, in a TSA process adsorption generally occurs at a lower temperature, may be even room temperature, and desorption occurs at higher temperatures.

[0196] In various embodiments “ambient air” refers to atmospheric air or air from the atmosphere. In some embodiments, the atmosphere is earth’s atmosphere. In some embodiments, ambient air comprises about 78% nitrogen, about 21% oxygen, about 0.93% argon, about 0.04% carbon dioxide, and about 0% to about 4% water or water vapor. In some embodiments, ambient air may further comprise at least one pollutant. In some embodiments, ambient air may further comprise at least one other gas. In some embodiments, the at least one other gas is for example neon, helium, hydrogen, krypton, nitrous oxide, xenon, ozone, or iodine, or any combination thereof. In some embodiments, ambient air may further comprise for example tiny solid and / or liquid particles commonly referred to as aerosols. These aerosols may comprise for example, dust, spores, pollen, salt from sea water or sea spray, volcanic ash, smoke, and / or other pollutants.

[0197] In various embodiments “carbon dioxide (CO2) sorbent” refers to a material that can adsorb and / or bind carbon dioxide (CO2). In some embodiments, the adsorption and / or binding is reversible. In some embodiments, the carbon dioxide (CO2) sorbent is designed to be regenerated. In some embodiments, the carbon dioxide (CO2) sorbent is a carbon dioxide (CO2) solid sorbent. In some embodiments, a carbon dioxide (CO2) sorbent of the present invention comprises at least one transition metal hydroxide. In some embodiments, a carbon dioxide (CO2) sorbent of the present invention comprises at least one transition metal oxide.

[0198] In various embodiments “ambient temperature” refers to the average temperature of an environment and can be any temperature. In some embodiments, the ambient temperature is 0oC – 75oC. In some embodiments, the ambient temperature is 0oC to 50oC. In some embodiments, the ambient temperature is 10oC to 50oC. In some embodiments, the ambient temperature is 20oC to 50oC. In some embodiments, the ambient temperature is 20oC to 40oC. In some embodiments, the ambient temperature is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, or 75oC.4886-5761-4062.1Page 30 of 164094876-000018WOPT

[0199] In various embodiments “ambient pressure” refers to the pressure of the surrounding air, gas, or liquid in contact with an object in a specific location. For example, typical pressure at sea level is 14.7 pounds per square inch.

[0200] In various embodiments “ambient humidity” refers to the amount of moisture (e.g. water or water vapor) in the air in a particular environment. In some embodiments, the ambient humidity is expressed in the form of a relative humidity.

[0201] In various embodiments “relative humidity” refers to the amount of water or water vapor in the air, relative to the temperature of the air. In some embodiments, the relative humidity is 0% - 100%. In some embodiments, the relative humidity is less than 100%. In some embodiments, the relative humidity is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100%.

[0202] In various embodiments “room temperature” refers to a temperature range to which most people find comfortable, for example, a comfortable indoors temperature. In some embodiments, a room temperature is an ambient temperature. In some embodiments, a room temperature is not an ambient temperature. In some embodiments, the room temperature is 20oC to 27oC. In some embodiments, the room temperature is 20, 21, 22, 23, 24, 25, 26, or 27oC. In some embodiments, the room temperature is 20oC to 50oC. In some embodiments, the room temperature is 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50oC. In some embodiments, the room temperature is 20oC to 40oC. In some embodiments, the room temperature is 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40oC. In some embodiments, the room temperature is 20oC to 30oC. In some embodiments, the room temperature is 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30oC.

[0203] In various embodiments “flue gas” refers to the gas exiting to the atmosphere via a flue, where a flue is for example a pipe, channel, or chimney for conveying the gases resulting from combustion of a material from, for example, a fireplace, oven, furnace, boiler, steam generator, cement plant, and / or power plant. In some embodiments, combustion of fossil fuels is a source of flue gas. In some embodiments, the composition of flue gas depends on what is being4886-5761-4062.1Page 31 of 164094876-000018WOPTburned. For example, in some embodiments, the flue gas comprises nitrogen, carbon dioxide, water vapor, and / or oxygen. In some embodiments, flue gas may further comprise at least one pollutant. In some embodiments, the pollutant is or comprises particulate matter (e.g., soot), carbon monoxide, nitrogen oxides, or sulfur oxides, or any combination thereof.

[0204] In various embodiments “natural gas” refers to a naturally occurring mixture of gaseous hydrocarbons. In some embodiments, the natural gas comprises methane and other alkanes. In some embodiments, the natural gas further comprises carbon dioxide, nitrogen, hydrogen sulfide, helium, or water vapor, or any combination thereof.

[0205] In various embodiments “exhaust gas” refers to gas that is emitted from an engine resulting from the combustion of fuels such as natural gas, gasoline, diesel fuel, fuel oil, biodiesel blends, or coal. In some embodiments, the exhaust gas comprises nitrogen, carbon dioxide, and / or water vapor. In some embodiments, exhaust gas may further comprise at least one pollutant. In some embodiments, the pollutant is or comprises particulate matter (e.g., soot), carbon monoxide, hydrocarbons, nitrogen oxides, sulfur oxides, or any combination thereof.

[0206] In various embodiments “biogas” refers to gas produced from raw materials such as for example agricultural waste, manure, municipal waste, plant material, vegetation, sewage, green waste, wastewater, and / or food waste. In some embodiments, biogas is produced by anerobic digestion with anaerobic organisms in an anaerobic digester or bioreactor. In some embodiments, the biogas comprises methane, and / or carbon dioxide. In some embodiments, the biogas further comprises hydrogen sulfide, water vapor, and / or siloxanes.

[0207] Chapter 1

[0208] Porous Transition Metal Hydroxides (PTMHs).

[0209] Low-cost direct air capture (DAC) technologies are urgently needed to mitigate CO2emissions and avert adverse effects of climate change. Solid sorbent-based technologies have shown promise for DAC applications, but existing classes of DAC solid sorbents have been estimated to carry high sorbent costs for traditional capture materials such as supported amines, metal-organic frameworks, zeolite and alkaline earth-metal oxides (e.g., MgO / CaO), mainly due to inherent limitations such as poor thermal / oxidative stability, weak water tolerance, slow kinetics, and high regeneration energy penalty. Herein, we successfully developed novel and inventive porous transition metal hydroxides (PTMHs) as new DAC solid sorbents. The porous transition metal hydroxides (PTMHs) of the present invention are highly porous, cost-effective,4886-5761-4062.1Page 32 of 164094876-000018WOPTwater-tolerant, thermally and oxidatively stable solid materials. PTMHs can efficiently capture trace CO2under ambient temperature and humid conditions. The presence of water vapor under simulated air flow is critical to enhancing DAC capacity. The strong correlation between BET surface areas and DAC capacity are observed, highlighting the significance of PTMH porous structures. In addition, by rationally doping metals, the DAC capacity of PTMHs can be enhanced by approximately 50% to 1.35 mmol CO2 / g sorbent compared to single-metal hydroxides. Without being bound by theory, in situ FTIR data suggests bicarbonate / carbonate species as main products of adsorption. The materials exhibit stable working capacities and no degradation during multiple adsorption-desorption cycles when using a 100 °C, 2 hour regeneration under an O2-containing inert gas purge. Our findings reveal that PTMHs can serve as a new class of solid DAC sorbents that can efficiently and cyclically capture ambient CO2under humid conditions for multiple cycles; these PTMH sorbents are also significantly less expensive and more tunable compared to existing DAC sorbents.

[0210] Porous Nickel-Based Metal Hydroxides (PNMHs).

[0211] The summarized key metrics of current Direct Air Capture (DAC) solid sorbents are qualitatively shown in a radar plot (FIG.1). The existing classes of DAC solid sorbents, namely supported amines, metal-organic frameworks, zeolite and alkali earth-metal oxides (e.g., MgO / CaO) have been widely explored to optimize sorbent performances. While many of the current DAC solid sorbents show promising DAC performances, the high estimated DAC sorbent costs based on current development status indicate the necessity of finding a new class of DAC sorbents.

[0212] Herein, we have successfully developed novel and inventive porous nickel-based metal hydroxides (PNMHs), which are a subclass of our novel and inventive porous transition metal hydroxides (PTMHs) discussed above. These porous nickel-based metal hydroxides (PNMHs) of the present invention are a new class of direct air capture (DAC) sorbents. In some embodiments, the porous nickel-based metal hydroxides (PNMHs) of the present invention have an α-polymorph structure. In various embodiments, the nickel-based metal hydroxides (PNMHs) of the present invention can have various polymorph structures, including without limitation alpha polymorphs (α polymorphs), and beta polymorphs (β polymorphs), and mixtures and / or combinations thereof. The porous nickel-based metal hydroxides (PNMHs) of the present invention are highly porous (e.g., ~800 m2 / g BET surface area), highly cost-effective, water4886-5761-4062.1Page 33 of 164094876-000018WOPTtolerant, thermally stable solid materials. In various embodiments, the PTMHs and PNMHs of the present invention are capable of efficiently capturing CO2in ambient air under room temperature, ambient temperature, ambient humidity, ambient pressure, and / or humid environment. A strong correlation between water adsorbed amount and DAC capacity was found on PNMHs in a range of relative humidity levels and temperatures. The nature of active sites is most likely associated with nickel hydroxide surface layers. In-situ FT-IR spectra suggested the formation of carbonate / bicarbonate species as sorption products. The clear correlation was observed between Brunauer-Emmett-Teller (BET) surface area and humid DAC capacity under high humidity level, while the different Ni(OH)2polymorphs have negligible effect. We also demonstrated the feasible material design strategy of enhancing DAC capacity of porous Ni(OH)2by introducing Ce3+, obtaining 45% enhancement and 1.35 mmol / g DAC capacity, likely due to more nucleophilic hydroxide / hydroxyls towards CO2binding from cerium (Ce) introduction. The work of the present invention described herein suggests porous nickel-based metal hydroxides can serve as a new platform for DAC of carbon dioxide and demonstrates its extended potential for optimizing DAC performance from an effective material design strategy.

[0213] Porous Nickel-Based Metal Hydroxides (PNMHs) - Chemical Composition and Structures

[0214] Textural properties of Porous Nickel-Based Metal Hydroxide (PNMH) samples were estimated from N2adsorption-desorption isotherms. Regardless of chemical composition, the samples show the type-IV isotherm shape with a H3-type hysteresis, similar with other Aqueous Miscible Organic Solvent Treatment (AMOST) assisted layered double hydroxides (LDHs) pore properties. Without being bound by theory, this featured hysteresis loop may come from the non- rigid aggregates of plate-like particles. The textural properties of the PNMH samples are shown in Table 1. α-Ni(OH)2has the highest BET surface area at 820 m2 / g, which to the best of our knowledge, is the highest porosity among reported porous nickel-based hydroxides. Cerium (Ce) doping of α-Ni(OH)2provides a slightly lower surface area (766 m2 / g), while the addition of iron cation further reduces the porosity (476 m2 / g). Without being bound by theory, this indicates the addition of Ce3+provides a negligible effect on pore properties of α-Ni(OH)2, while the strong particle aggregation in NiFe LDHs, may be due to the Fe3+stabilized the layer stacking even after a sufficient ethanol redispersion for delamination. The derived pore size distribution is shown in FIG.2B, suggesting our PNMHs are mesopore-dominated, with most pore width at 3-6 nm.4886-5761-4062.1Page 34 of 164094876-000018WOPT

[0215] Table 1. Textural and CO2 Adsorption Properties of PNMHs. Sample BET Pore Dry DAC Humid DAC

[0216] The XRD pattern of our synthesized porous α-Ni(OH)2(FIG. 2C) demonstrates a crystallized structure, exhibiting the characteristic Bragg diffraction of typical LDHs or α- Ni(OH)2. The strong diffraction peaks at 2θ ~23°, 34°, 60°, corresponding to (006), (012), (110)4886-5761-4062.1Page 35 of 164094876-000018WOPTplanes respectively. Without being bound by theory, another common characteristic Bragg diffraction peak for plane (003) of α-Ni(OH)2with CO32-in the interlayer should typically exhibit an intense peak at 11°, (40) while there is only a small shoulder on our α-Ni(OH)2. α-NiCe0.1(OH)xshows very similar XRD pattern with α-Ni(OH)2with slightly lower crystallinity. FIG. 10 shows the XRD pattern comparison for α-NiCe0.1(OH) before and afx ter Aqueous Miscible Solvent Treatment (AMOST), with a more prominent diffraction peak shown at 11° without AMOST. Without being bound by theory this likely represents the high delamination degree / smaller crystallite sizes from the influence of AMOST. A new diffraction peak is present at 28° after Ce3+doping, attributed to (101) plane of Ce(OH)3. Without being bound by theory, this suggests the heterogenous nature of α-NiCe0.1(OH)xand at least a fraction of Ce3+present in a separate phase as Ce(OH)3. In contrast, Fe3+doping leads to a much more crystallized structure by forming LDHs rather than α-NiCe0.1(OH)x. There is no additional diffraction peak observed, suggesting the excellent doping homogeneity from Fe3+. The most intense diffraction peak of (003) plane appears at ~11°, along with other featured diffraction peaks same with α-Ni(OH)2, evidencing the formation of NiFe-LDHs as well as the isostructural feature between NiFe-LDHs and α-Ni(OH)2. The 2-theta angle for (003) plane at 11° also reveals the presence of carbonate ion in the interlayer. The more crystallized structure of NiFe0.2-LDHs is consistent with structures that are less porous than α-Ni(OH)2. Without being bound by theory, these results suggest a more ordered and stable layered structures of α-Ni(OH)2from introduction of Fe3+.

[0217] FT-IR spectra (FIG.11) was obtained for understanding the chemical composition of our PNMH samples. Without being bound by theory, the characteristic peaks at 2974 cm-1suggests C-H stretching likely from the existence of trace ethanol molecules in the interlayer even after thermal treatment at 200 °C. The vibration mode of the intercalated carbonate anions exhibits two bands at 1462 and 1356 cm−1.

[0218] Porous Nickel-Based Metal Hydroxides (PNMHs) - Effect of Water

[0219] Direct Air Capture (DAC) of carbon dioxide has not been considered as a viable option on bulk metal hydroxides due to their poor reactivity. Surprisingly, we found that enhanced DAC capacity can be obtained on our PNHMs in the presence of water vapor in the feed CO2stream. FIG.3B shows the breakthrough curve of 400 ppm CO2over α-Ni(OH)2under both humid and dry conditions from a fixed bed reactor setup. Dry CO2starts to breakthrough only slightly later than the inert N2flow, representing a relatively low CO2capacity (0.07 mmol / g), while a4886-5761-4062.1Page 36 of 164094876-000018WOPTsurprising 13-fold enhancement of DAC capacity (0.92 mmol / g) was observed in the water co- feed CO2stream. This unexpected and significant increase in DAC capacity of our PNHMs under wet or humid conditions makes using metal hydroxides a practical and commercially viable option for DAC of carbon dioxide. A more systematic analysis of the relationship between relative humidity and DAC capacity is shown in FIG. 3A. Generally, without being bound by theory, a monotonically higher DAC capacity is observed at higher humidity and a plateau is reached in the range of high humidity level (67%-92% RH). Within this humidity range, DAC capacity has the clear order: α- NiCe0.1(OH)x> α-Ni(OH)2> NiFe0.2-LDHs. Without being bound by theory, the lower DAC capacity of NiFe-LDHs is likely due to NiFe-LDHs having a lower surface area compared to α- NiCe0.1(OH)xor α-Ni(OH)2. Addition of Ce3+leads to a surprising enhancement (47%) in DAC capacity regardless of textural properties.

[0220] However, the same trends in DAC capacity are not retained under dry conditions. The two PNMH samples with metal doping shows better performance while α-Ni(OH)2exhibits the lowest DAC capacity. Surprisingly, under dry conditions NiFe-LDHs outperforms α-Ni(OH)2with only half exposed surface area. Without being bound by theory, a possible explanation of these two different trends under dry and humid conditions may be related to the nature of active sites towards CO2. Without being bound by theory, we hypothesize that the metal hydroxides (M- OHs) can serve as the potential active sites to react with low-concentrations of CO2, resulting in formation of carbonate / bicarbonate species. (FIG. 4). Without being bound by theory, the reactivity between CO2and the hydroxides depend on its nucleophilicity, which is likely affected by the doping metal. Specifically in our case, Fe3+as well as Ce3+are higher valency cations than Ni2+.Without being bound by theory, such partial substitution may lead to a more nucleophilic nature of the molecular-bonded hydroxide sites in the PNMHs. This increase in nucleophilicity may assist in enhancing DAC capacity under dry conditions allowing for higher CO2affinity on active sites.

[0221] To understand the unexpected and significant increase in DAC capacity of our PNHMs under wet or humid conditions, we explored the nature of the active sites in an effort to better understand the CO2adsorption mechanism. Without being bound by theory, we hypothesized CO2is likely adsorbed on the metal hydroxide layers. However, the CO32--contained interlayer can also potentially provide active sites towards CO2. Without being bound by theory, this CO32--contained interlayer may chemically react with CO2in the presence of water to form4886-5761-4062.1Page 37 of 164094876-000018WOPTbicarbonate species. Without being bound by theory, FIG.4 suggests the hypothesized schematics of reaction among CO32-, CO2,and water. To elucidate this pathway for CO2adsorption, we synthesized an anion-exchanged α-Ni(OH)2using SO42-. α-Ni(OH)2-SO42-has very similar N2adsorption-desorption isotherm shape (FIG. 12) and slightly lower BET surface area (702 m2 / g, Table 1) compared to α-Ni(OH)2. The XRD pattern (FIG.5A) of α-Ni(OH)2-SO42-demonstrated the unchanged crystal structure after anion-exchange. XPS spectra of S 2p (FIG.5B) showed an apparent peak in α-Ni(OH)2-SO42-at 168.5 eV, while there is no peak in α-Ni(OH)2, evidencing the presence of sulfate ion after ion exchange. FT-IR spectra of α-Ni(OH)2-SO42-(FIG.5C) also suggests the presence of SO42-from the new band at 1110 cm-1, attributed to the stretching mode of sulfate ion. Additionally, the FT-IR spectra of α-Ni(OH)2-SO42-also shows the weaker carbonate ion peaks, illustrating the fact of partial ion exchange between CO32-and SO42-. The reduction ratio of peak intensity of CO32-after normalization is estimated roughly at 50%. According to literature reports, CO32-intercalated layered double hydroxides may exhibit limited anion-exchange capability using traditional exchange methods, as CO32-generally leads to strong bindings with metal hydroxide layers. If the adsorption route in our PNMHs involves intercalated carbonate, α-Ni(OH)2-SO42-should show a much lower DAC capacity as the anion-exchange partially substitutes the hypothesized active sites by a CO2-inert anion (i.e., SO42-anion). However, much to our surprise no reduction was observed on DAC capacity under humid conditions (67% Relative Humidity) on α-Ni(OH)2-SO42-, which is inconsistent with bicarbonate formation via an intercalated CO32-mechanism. (FIG.5D). Without being bound by theory, this result suggests the adsorption mechanism on the PNMHs of the present invention is not directly associated with interlayer anions.

[0222] The effect of adsorption temperature on α-NiCe0.1(OH)xwas evaluated under both dry and humid conditions (67% Relative Humidity) (FIG. 6A). Under dry conditions, DAC capacity only shows a small reduction at higher adsorption temperature, likely originating from the nature of low heat of adsorption / weak binding for CO2on M-OH sites. In contrast, DAC capacity under humid conditions is sensitive to adsorption temperature, significantly dropping from 1.35 mmol / g (25 °C) to 0.48 mmol / g (50 °C) and 0.25 mmol / g (75 °C). Without being bound by theory, the more predominant reduction of DAC capacity under humid conditions likely indicates the different adsorption mechanism / routes under dry and humid conditions. In view of the unexpected and significant increase in DAC capacity of our PNHMs under wet or humid4886-5761-4062.1Page 38 of 164094876-000018WOPTconditions, without being bound by theory we hypothesize that the difference is possibly associated with a temperature effect on water adsorption capacity. FIG. 6B shows the effect of temperature on water vapor adsorption isotherm of α-NiCe0.1(OH)x. At 25 °C, a type II isotherm was obtained, suggesting a monolayer-multilayer adsorption of water on α-NiCe0.1(OH)x. The increase of adsorbed water quantity with water vapor pressure starts to slightly level off at ~0.5 kPa (16% RH) and then appears to show a sharp increase without reaching a plateau at higher water vapor pressure. Without being bound by theory, this may suggest the completion of a monolayer of water molecules at ~0.5 kPa and starts to build up multilayer adsorption / water condensation at higher humidity levels. By comparing the effect of humidity level on DAC capacity and water adsorption capacity at 25 °C, it is observed that both consistently increase with higher humidity at similar extent below 2.1 kPa. (FIG.6B). Surprisingly, the change of adsorption temperature also suggests a similarly good correlation between water vapor and CO2capacity (FIG.6A), indicating that the large deviation of DAC capacity under dry and humid condition in terms of adsorption temperature may mainly come from water adsorption quantity. These results strongly evidences the correlation between the amount of water adsorbed and DAC capacity on PNMHs. From these observations, without being bound by theory we hypothesized several possibilities for the observed beneficial role of water on the PNMHs of the present invention. Without being bound by theory, we hypothesize that non-stoichiometric surface hydroxyls may be formed during hydroxylation of nickel hydroxide surface, which can potentially serve as additional active sites for DAC of carbon dioxide, similar with lattice hydroxide sites. (FIG. 4) However, DAC capacity under humid conditions is not saturated at ~0.5 kPa and it was more prominently promoted at higher humidity level (FIG.6B), suggesting the monolayer of adsorbed water is not sufficient for maximizing DAC capacity. Without being bound by theory, the indication of required multilayer water adsorption may also suggest the water-induced surface hydroxyls are likely not the only reason for water promotion effect. Without being bound by theory we hypothesize that CO2dissolution into surface adsorbed water may facilitate the acid-base interactions between hydroxides / hydroxyls and CO2molecules. Therefore, it is possible that the surface adsorbed water may exhibit as a suitable media for effective CO2reaction with hydroxides. Surprisingly, we discovered that a moderate humidity level can behave as a promoter for achieving reasonable DAC capacity on PNMHs of the present invention, while the presence of humidity in air flow is detrimental for most metal-organic frameworks (MOFs).4886-5761-4062.1Page 39 of 164094876-000018WOPT

[0223] Porous Nickel-Based Metal Hydroxides (PNMHs) - Effect of Surface Area and Polymorphs

[0224] To elucidate the role of polymorphs and textural properties on DAC capacity of Ni(OH)2, another three Ni(OH)2were prepared using typical precipitation methods without carbonate ion assistance. For generating the porous structure, soft organic template, octylamine, was used for the synthesis. For comparison, a non-porous Ni(OH)2was obtained without soft template applied during the synthesis. The different polymorphs of nickel hydroxides, β-Ni(OH)2, were obtained from organic template-assisted precipitation methods, evidenced by XRD patterns (FIG.13). The intense characteristic peaks at 19°, 33° and 39° are attributed to typical β-Ni(OH)2crystal diffraction features. Similar with α-Ni(OH)2, Ce3+addition leads to lower crystallinity as well as the formation of Ce(OH)3as the occurrence of (101) plane characteristic peak at 28°. Non- porous Ni(OH)2shows a co-existence of α and β polymorphs from XRD diffraction pattern. Despite the assistance from organic soft template, less porous β-Ni(OH)2were obtained from this approach, which shows 200-250 m2 / g of BET surface area. FIG.7 shows the correlation between BET surface area and humid DAC capacity (67% Relative Humidity) of our prepared samples. According to FIG.7, we note that the non-Ce containing samples show a clear linear correlation between DAC capacity and surface area, regardless of polymorphs of nickel hydroxides. The data point close to original point is from non-porous Ni(OH)2. Almost no DAC capacity was found on this non-porous Ni(OH)2sample due to a highly limited surface area. According to FIG.7, Fe3+introduction does not deviate the DAC performance, showing the limited effect of enhancing humid DAC capacity from homogeneous Fe3+doping. In contrast, the two samples using Ce3+doping, show a strongly deviation upwards of the correlation line, along with a slight reduction of the BET surface area. Without being bound by theory, this demonstrates the promotion role of Ce3+is independent of nickel polymorph, and does not originate from expanding the porosity. In addition, very similar water vapor adsorption isotherm shape and quantity between α- NiCe0.1(OH)xand α-Ni(OH)2(FIG. 14) suggests that the DAC capacity enhancement from Ce3+is also not affiliated with water adsorption capability. From the XRD pattern, in the two Ce3+containing samples, Ce3+is likely partially present in the form of Ce(OH)3, deposited on the bulk Ni(OH)2surface. According to our Ni 2p XPS results (FIG.15), the peak at 855.3eV in α-Ni(OH)2shifts to 855.65 eV in α-NiCe0.1(OH)x. Without being bound by theory, the shift toward higher binding energy represents the potential partial electron transfer out of Ni2+from Ce3+introduction,4886-5761-4062.1Page 40 of 164094876-000018WOPTwhich may lead to more positively charged environment around Ni2+. This increase in the positively charged environment around Ni2+may result in the higher nucleophilicity of metal hydroxides which enhances the CO2affinity under both dry and humid environments. These results suggest that the material design strategy focused on maximizing the nucleophilicity of hydroxides is important to optimize DAC performance of PNMHs.

[0225] Porous Nickel-Based Metal Hydroxides (PNMHs) - Surface Chemistry: CO2, H2O and OH-

[0226] To further confirm the proposed reaction mechanism and formed surface species, in-situ FT-IR experiments were carried out on α-Ni(OH)2. After exposure to dry 400 ppm CO2, a series of new bands between 1000-1700 cm-1were observed, representing the formation of surface species during DAC. Without being bound by theory, this suggests PNMHs may belong to chemisorbents from the chemical interactions with CO2, likely forming the carbonate / bicarbonate species on hydroxide sites. Symmetric and asymmetric modes for HCO3- / CO32-are widely reported between 1000-1700 cm-1from different carbonate types and bands may shift due to different metal identities and coordination environment. FIG.8A showed difference FT-IR spectra of α-Ni(OH)2after exposure to CO2environment. In dry CO2conditions, without being bound by theory the bands at 1680 and 1645 cm-1are most likely associated with asymmetric modes of HCO3-, which typically has wavenumber range falling between 1600-1680 cm-1on metal-based nucleophiles reported in the literature. Without being bound by theory, the three adjacent bands (1473, 1435 and 1387 cm-1) at lower wavenumbers likely can be attributed to symmetric bands of CO32-. H2O co-feed simulated air stream led to significantly higher peak intensity for these assigned bands, which is consistent with our data herein showing a significantly higher DAC capacity under a humid environment. However, H-O-H bending mode at 1600-1700 cm-1exhibits a strong peak from adsorbed water on wafer and gas-phase water vapor, inhibiting the potential band observation from bicarbonates in the same region. Without being bound by theory, the IR spectrum obtained using deuterium oxide co-feed CO2may provide additional information for humid CO2adsorption. The new intense band at 1205 cm-1is attributed to the D-O-D bending mode, at the same time, the region between 1600-1700 cm-1was revealed without effect of H-O-H bending. Interestingly, the two bands generally associated with bicarbonates showed no prominent enhancement of absorbance than when compared to the absorbance under dry conditions, while the three bands (1473, 1435 and 1387 cm-1) associated with carbonates exhibited much higher intensity,4886-5761-4062.1Page 41 of 164094876-000018WOPTsuggesting the formation of carbonate species are strongly enhanced over bicarbonate species under humidity co-feed conditions. The band position for the three bands assigned with CO32-is unchanged using humid (D2O) versus dry / humid (H2O), which without being bound by theory is also consistent with the non-bicarbonate band assignment. In contrast, the two new peaks (1618, 1585 cm-1) at slightly lower wavenumber (compared to 1680, 1645 cm-1) appeared, which without being bound by theory may be associated with deuterated bicarbonates. Without being bound by theory the co-existence of protonated bicarbonate and deuterated bicarbonate is understandable as during D2O-adsorption, the uncompleted H-D exchange can lead to the surface being partially deuterated. Such phenomenon seems counterintuitive that water environment leads to unfavored bicarbonate formation. However, it was previously reported in several studies that humid conditions favor the formation of carbonates and dry conditions lead to decomposition of carbonates to form bicarbonates and hydroxide ions in ion-exchange resins. Without being bound by theory this moisture swing adsorption mechanism may explain why our PNHMs of the present invention form a greater number of carbonates rather than bicarbonates under humid conditions. To better understand the mechanism of equilibrium shifted by humidity and band assignments on CO32- / HCO3-, a following dry 400 ppm CO2purge was performed on a D2O-CO2saturated sample. (FIG.8B) The same operation was conducted using a fixed-bed reactor setup and showed slightly more CO2adsorbed on α-Ni(OH)2(~0.1 mmol / g) during the humid CO2to dry CO2switch. Without being bound by theory, this result seemed to indicate that it may not be possible to purge out adsorbed humid CO2using dry CO2purge. On the contrary, additional CO2was observed to be adsorbed on the α-Ni(OH)2surface. Without being bound by theory, this observation follows previous reports in the literature as mentioned above where dry conditions were reported to decompose CO32-into HCO3- and OH-, thereby forming additional active sites for CO2adsorption. This was evidenced by the FT-IR spectra shown in FIG.8B. During dry CO2purge, the D-O-D bending mode was weakened by the removal of gas phase / weakly adsorbed D2O. In addition, the absorbance of three bands at 1473, 1435 and 1387 cm-1were reduced, and the bands between 1645 and 1680 cm-1were increased. Without being bound by theory, these observations indicate a conversion of carbonates to bicarbonates by reducing D2O concentration within pores. Without being bound by theory these observations suggest that the surface chemistry in PNHMs during DAC of carbon dioxide may be similar to moisture swing adsorption reported on ion-exchange resins.4886-5761-4062.1Page 42 of 164094876-000018WOPT

[0227] Porous Nickel-Based Metal Hydroxides (PNMHs) - Cycle Stability

[0228] The cyclic stability of α-NiCe0.1(OH)xwas evaluated in the fixed bed reactor for multiple cycles (FIG. 9). The typical regeneration method under dry Ar purge at elevated temperature was performed. Under the regeneration temperature of 150 °C, it performed a stable working capacity ~1.05 mmol / g after the fresh DAC capacity at 1.35 mmol / g.

[0229] Porous Nickel-Based Metal Hydroxides PNMHs – Summary

[0230] In summary, the work described herein provides Porous Nickel-Based Metal Hydroxides (PNMHs) of the present invention as a new class of DAC solid sorbents. The synthesis procedure is straightforward, and the low manufacturing costs make PNMHs very competitive alternatives to current DAC solid sorbent materials such as amine-supported materials, zeolites, and MOFs. The excellent performance of PNMHs under humid conditions demonstrates the feasibility of using PNMHs for direct air capture of carbon dioxide from ambient air without the need for additional costly dehumidification steps which are generally required when using water- sensitive zeolites and MOFs. In addition, metal doping of the PNMHs was shown to be an effective strategy to enhance DAC performance of PNMHs. This demonstrated the extended potential for optimizing DAC performance of PNMHs by rational material design. Excellent cycle stability was demonstrated under mild regeneration temperatures and O2-containing environment. Based on the results and observations herein we believe that PNMHs may open a new avenue to low-cost DAC solid sorbents, thereby improving the economic viability of DAC of carbon dioxide from ambient air.

[0231] Porous Transition Metal Oxides (PTMOs)

[0232] Low-cost direct air capture (DAC) technologies are urgently needed to mitigate CO2emissions and avert adverse effects of climate change. Solid sorbent-based technologies have shown promise for DAC applications, but high sorbent costs for traditional capture materials such as supported amines and metal-organic frameworks that represent a large fraction of the overall DAC cost limit their widespread use. Some metal oxides such as MgO and CaO were recently explored as potential DAC solid sorbents, however, these materials require very high regeneration temperatures and long adsorption times. Herein, we report novel and inventive porous transition metal oxides (PTMOs) that can capture CO2from air at ambient temperatures. These PTMO materials exhibit promising DAC capacities that increase under humid environments. By rationally doping metals in terms of metal identity, concentration and doping method, the sorption4886-5761-4062.1Page 43 of 164094876-000018WOPTperformance of PTMOs can be significantly enhanced to ~0.75 mmol CO2 / g sorbent. Without being bound by theory, in-situ FTIR data suggests the formation of multiple carbonate species on PTMOs during DAC. The porous transition metal oxides (PTMOs) of the present invention can be subjected to several temperature swing adsorption cycles. Overall, our findings reveal that PTMOs can serve as a new class of solid DAC sorbents that are significantly less expensive and more tunable compared to existing classes of sorbents.

[0233] Porous Transition Metal Oxides (PTMOs) - Characterization

[0234] The textural properties of Porous Transition Metal Oxides (PTMOs) of the present invention were evaluated using N2adsorption-desorption isotherms shown in FIG.16 and derived pore properties were provided in Table 2. The high surface area (>200 m2 / g) nickel-based oxides were produced. Typical type-IV isotherm was observed to suggest a mesopore-dominated structure. Similar BET surface area and pore volume were obtained for samples regardless of Ce to Ni molar ratio except for the case of pure CeO2. Without being bound by theory a possible reason for less porous CeO2is the soft template may not be able to very effectively form a complex under acid conditions with Ce4+compared to Ni2+.The similar pore properties of these materials can help compare CO2adsorption performances without any effects from different pore properties.

[0235] Table 2. Textural and CO2 adsorption properties of PTMOs Sample BET surface area Pore volume Humid DAC capacity (m2 / g) (cm3 / g) (pelletized sample) (mmol / g)

[0236] XRD pattern of Ce10NiOH and Ce10NiO are shown in FIG.17. For the sample of Ce10NiOH, the diffraction peaks at 19° and 33° correspond to Ni(OH)2and peaks at 29°, 47° and 56° correspond to Ce(OH)4, representing the formation of mixed nickel and cerium hydroxides. After calcination at high temperature, the mixed metal hydroxides were converted to oxide phase, evidenced by the existence of peaks at 37°, 43° and 62° assigned to crystalline NiO.

[0237] Porous Transition Metal Oxides (PTMOs) – CO2Capture Performance

[0238] CO2adsorption isotherm of Ce10NiO was measured between 35-250 °C shown in FIG.18. It indicated a sharp increase of CO2uptake at relatively low CO2concentration, followed4886-5761-4062.1Page 44 of 164094876-000018WOPTby a gradual increase at higher pressures. The higher adsorption temperature reduced the overall adsorption capacity and flattened the increasing trend at higher pressures. Without being bound by theory, this isotherm may suggest the existence of strong chemical bindings of CO2on Ce10NiO, leading to the sharp increase at low pressure region under dry CO2conditions. This feature supports PTMOs become as DAC sorbent candidates.

[0239] Water tolerance is a very important property for CO2capture sorbents especially for DAC. The comparison of DAC capacity using dry and humid (66% relative humidity) 400 ppm CO2flow is shown in FIG. 19 using Ce10NiO powder sorbents. The significant increase in DAC capacity of PTMOs of the present invention under humid conditions is surprising and unexpected. This increase in DAC capacity of the inventive PTMOs is particularly important since many currently known DAC sorbents, such as zeolites and MOFs, exhibit a decrease in DAC capacity under humid conditions. This feature gives PTMOs of the present invention significant advantages over currently known DAC sorbents for practical applications of DAC of CO2ambient air.

[0240] The effect of Ce doping concentration on humid DAC capacity of PTMOs of the present invention is shown in FIG.20. It should be noted that the CeO2has lower surface area (120 m2 / g) than the other nickel-oxide based sorbents (250 m2 / g) studied, which without being bound by theory may partially contribute to the observed decrease in DAC performance. Without being bound by theory, the best Ce to Ni molar ratio of the PTMOs studied for maximum DAC capacity suggested the existence of synergistic effect between Ce and Ni in the oxide frameworks.

[0241] The cyclic stability of Ce10NiO powder was evaluated in a fixed bed reactor for 5 consecutive cycles. Under the regeneration temperature of 250 °C, it performed a stable working capacity at 0.5 mmol / g after the fresh DAC capacity at 0.68 mmol / g. Without being bound by theory, the ~25% capacity drop in the second cycle may suggest a small portion of strongly adsorbed CO2cannot desorb at this desorption conditions. Without being bound by theory, the stable working capacity in multiple cycles may be beneficial in terms of sorbent costs of DAC process.

[0242] FT-IR difference spectra were performed on Ce10NiO powder under dry and humid conditions, as shown in FIG.22. The appearance of five peaks noted by the vertical dashed lines indicated the surface species after CO2introduction. The significantly larger peak area from humid conditions suggests the consistency of higher DAC capacity in humid conditions than dry conditions observed from CO2breakthrough measurements. Without being bound by theory, the4886-5761-4062.1Page 45 of 164094876-000018WOPTmost likely assignments of these surface species may be related to carbonates and / or bicarbonates. This suggests that the active sites of PTMOs could be oxygen atoms in the oxide frameworks of the PTMOs.

[0243] Integrated Direct Air Capture and Methanation on Porous Transition Metal Oxides (PTMOs)

[0244] Low-cost direct air capture (DAC) technologies are urgently needed to mitigate CO2emissions and avert adverse effects of climate change. CO2capture and utilization has gained increased attention from offering alternative pathways of production of value-added chemicals. However, an integrated DAC and conversion process is not widely explored. We show herein that low-cost and highly tunable porous transition metal oxides (PTMOs) can capture CO2from simulated air at ambient temperature, with enhanced DAC capacity under humid environment. The CO2adsorption capacity of these materials can be tuned through aliovalent doping, with optimal adsorption capacities achieved at intermediate dopant loadings. Moreover, a subsequent methanation process after DAC is achieved under a diluted hydrogen flow at intermediate reaction temperature (200-300 °C). Overall, our findings reveal that PTMOs can serve as a new class of solid DAC sorbents that are significantly less expensive and more tunable. Furthermore, the feasibility to directly convert captured CO2from air into methane within a single component bed sets PTMOs apart from existing classes of sorbents (FIG.26A – FIG.26B).

[0245] Chapter 2

[0246] Surface Hydration of Porous Nickel Hydroxides Facilitates the Reversible Adsorption of CO2 from Ambient Air

[0247] Direct air capture (DAC) technologies operating under humid ambient conditions employ sorbent materials containing both an organic as well as an inorganic component, with sorbents that are purely inorganic in composition for the most part operating hundreds of degrees above room temperature. In this work, we report porous metal hydroxides as a novel class of water- tolerant, oxidatively and hydrothermally stable low-temperature sorbents that exhibit competitive DAC working capacities over consecutive temperature swing adsorption-desorption cycles in the presence of steam and oxygen. Aqueous miscible organic solvent treatments are used to exfoliate layered nickel double hydroxides to create highly porous structures that capture CO2in the form of bicarbonates under dry conditions, and carbonates under wet conditions. Water exerts a facilitative rather than an inhibiting effect on CO2binding, with the presence of hydrating4886-5761-4062.1Page 46 of 164094876-000018WOPTmultilayers serving to stabilize carbonate species – akin to moisture swing adsorbents – except for the fact that the presence of water vapor results in an increase, not decrease, in DAC capacity. High-valent doping with cerium is used to improve DAC capacities under humid conditions by amplifying surface basicity, evidencing porous nickel hydroxides specifically (and porous metal hydroxides more generally) as a novel class of robust, earth-abundant DAC sorbents.

[0248] Introduction

[0249] Climate change mitigation remains the defining challenge facing mankind in the 21stcentury. There is growing consensus that reversing the already calamitous trends in anthropogenic CO2emissions is predicated on the use of negative emissions technologies that extract CO2directly out of the atmosphere (National Academies of Sciences, Engineering and Medicine, Negative Emissions Technologies and Reliable Sequestration: A Research Agenda; The National Academies Press: Washington, DC, 2019; M. Erans, E. S. Sanz-Pérez, D. P. Hanak, Z. Clulow, D. M. Reiner, G. A. Mutch, Energy Environ. Sci.2022, 15, 1360–1405). Over and above reversing emissions trends, the intentional removal of CO2from air using direct air capture (DAC) technologies also helps address adverse effects of distributed sources that account for up to two- thirds of global CO2emissions (D. L. Damm, A. G. Fedorov, Energy Convers. Manag. 2008, 49, 1674–1683). Temperature swing adsorption (TSA) processes are highly attractive for DAC due in part to the fact that they apply work to concentrated CO2rather than the dilute feed containing only 400 parts-per-million (ppm) of carbon dioxide (Ryan P.Lively and Matthew J. Realff, R. P. Lively, M. J. Realff, AIChE J. 2016, 62, 3699–3705). A variety of solid sorbent materials have been evaluated in this context including zeolites, metal-organic frameworks (MOFs), supported amines, and bulk metal oxides. Each of these existing classes of sorbent materials, however, suffer from specific limitations that encumber their practical use. Zeolites, for instance, although hydrothermally stable, are highly unselective to CO2in the presence of water vapor (D. Fu, Y. Park, M. E. Davis, Angew. Chemie - Int. Ed.2022, 61, 1–6; A. Kumar, D. G. Madden, M. Lusi, K. J. Chen, E. A. Daniels, T. Curtin, J. J. Perry, M. J. Zaworotko, Angew. Chemie - Int. Ed.2015, 54, 14372–14377). Hybrid, organic-inorganic sorbents such as MOFs and supported amines exhibit limited stability in the presence of oxygen, with the latter also suffering from leaching of organics that oftentimes degrades DAC performance over time (S. Bose, D. Sengupta, T. M. Rayder, X. Wang, K. O. Kirlikovali, A. K. Sekizkardes, T. Islamoglu, O. K. Farha, Adv. Funct. Mater.2023, 2307478; P. Bollini, S. Choi, J. H. Drese, C. W. Jones, Energy and Fuels 2011, 25, 2416–2425).4886-5761-4062.1Page 47 of 164094876-000018WOPT

[0250] Calcium and magnesium oxides are the most commonly investigated oxide-based CO2capture sorbents. These oxides are relatively inexpensive compared to supported amine systems, and possess high theoretical CO2adsorption capacities that can exceed values of 15 mmol CO2per gram of sorbent (M. A. Naeem, A. Armutlulu, Q. Imtiaz, F. Donat, R. Schäublin, A. Kierzkowska, C. R. Müller, Nat. Commun. 2018, 9, 2408; F. Donat, C. R. Müller, Curr. Opin. Green Sustain. Chem. 2022, 36, 100645). CO2forms very strongly bound carbonates on these sorbents, however, requiring temperatures in excess of 400 °C for their conversion back to oxides (V. Hiremath, H. J. Kwon, I. S. Jung, S. Kwon, S. H. Kwon, S. G. Lee, H. C. Lee, J. G. Seo, ChemSusChem 2019, 12, 2810–2818; V. Nikulshina, D. Hirsch, M. Mazzotti, A. Steinfeld, Energy 2006, 31, 1715–1725). These sorbents are also hampered by slow adsorption kinetics resulting from diffusion limitations, as demonstrated in the literature. Rausis et al., for instance, reported slow carbonation kinetics under DAC conditions for MgO, with only 16 wt% of the sorbent being carbonated in an entire year (K. Rausis, A. R. Stubbs, I. M. Power, C. Paulo, Int. J. Greenh. Gas Control 2022, 119, 103701). CaO sorbents can also be limited by adsorption kinetics; a stream of 500 ppm CO2at temperatures as high as 300 °C still requires 100 minutes for 35wt% carbonation (V. Nikulshina, M. E. Gálvez, A. Steinfeld, Chem. Eng. J.2007, 129, 75–83). Alkaline-earth metal oxides therefore appear to not be viable low-temperature DAC sorbents due to the lack of sizeable working capacities under ambient conditions.

[0251] More generally, to the best of our knowledge, no oxide or hydroxide-based DAC sorbent has been reported to date in the literature that operates efficaciously at close to room temperatures. This, despite the fact that hydroxide groups in other classes of materials such as MOFs have been shown to capture CO2at low temperatures. Dong et al., for instance, attributed the reasonable DAC capacity of MOF-808 – 0.21 mmol CO2 / g at 25 °C – to the formation of intramolecular hydrogen bonds between neighboring Zr-OH sites (H. Dong, L. Li, C. Li, 2023, 14, 8507-8513). The Wade and Ho groups reported DAC capacities greater than 2 mmol / g at 27 °C over benzotriazolate MOFs bearing Ni / Zn-hydroxyls (C. E. Bien, K. K. Chen, S. C. Chien, B. R. Reiner, L. C. Lin, C. R. Wade, W. S. W. Ho, J. Am. Chem. Soc.2018, 140, 12662–12666; Z. Cai, C. E. Bien, Q. Liu, C. R. Wade, Chem. Mater.2020, 32, 4257–4264). These prior studies support the feasibility of using hydroxyl groups for low-temperature DAC applications specifically, and the potential use of surface hydroxyls ubiquitous on bulk (hydr)oxide surfaces for CO2capture more generally. Our own group previously reported the interaction of CO2formed in-situ under4886-5761-4062.1Page 48 of 164094876-000018WOPTcatalytic ethane oxidation conditions with unsupported NiO samples prepared using a solid-state decomposition procedure (X. Zhao, Q. Ning, L. C. Grabow, J. D. Rimer, P. Bollini, J. Catal.2022, 416, 423–438). Owing to their high tunability and hydrothermal stability, combined with their low manufacturing costs, bulk oxides and hydroxides are in principle more ideal carriers of oxygen- containing nucleophiles for DAC applications compared to MOFs that tend to inherently be more susceptible to degradation (S. Walia, S. Balendhran, H. Nili, S. Zhuiykov, G. Rosengarten, Q. H. Wang, M. Bhaskaran, S. Sriram, M. S. Strano, K. Kalantar-Zadeh, 2013, 58, 1443-1489).

[0252] Surface area limitations of (hydr)oxide powders can potentially be overcome through the use of layered double hydroxides (LDHs) – a class of highly tunable metal hydroxides that carry the requisite porosity for DAC applications, and that are characterized by a two- dimensional structure comprised of cationic metal hydroxide and charge-balancing anion interlayers (FIG.108A) (Q. Wang, D. Ohare, Chem. Rev.2012, 112, 4124–4155). We demonstrate herein the first example of the use of LDH-derived solid sorbents to deliver competitive DAC equilibrium and working adsorption capacities, oxidative and hydrothermal stability, recyclability, water tolerance, and CO2selectivity. We use an aqueous miscible organic solvent treatment (AMOST) protocol developed by O’Hare and co-workers (Q. Wang, D. O’hare, Chem. Commun. 2013, 49, 6301–6303) to synthesize a high surface area hydroxide with the requisite gravimetric adsorption site density, and use doping with high-valent metals to accentuate the nucleophilicity of (hydr)oxide active sites toward CO2adsorption. Hydroxide groups that adsorb CO2in these materials exhibit much stronger tolerance to oxidation compared with nitrogen moieties in supported amine sorbents, likely due to the fact that unlike organic-inorganic hybrid materials, the adsorbing functional group in the material reported is itself inherently rich in oxygen (M. E. Zick, S. M. Pugh, J. Lee, A. C. Forse, P. J. Milner, 2022, 61, e202206718). α-polymorphs of nickel hydroxides reported here represent the first example of a low-temperature DAC sorbent that is purely inorganic in composition, yet functions effectively from the standpoint of capture and release from humid DAC feedstreams. Results presented pave the way for exploiting a novel class of relatively inexpensive hydroxide sorbents that could help address persistent limitations associated with existing classes of DAC sorbents.

[0253] Results and Discussion

[0254] Direct Air Capture Performances of Nickel Hydroxides4886-5761-4062.1Page 49 of 164094876-000018WOPT

[0255] Nickel is a common component in LDH materials containing divalent and trivalent metal cations. Nickel hydroxides have two polymorphs: α-Ni(OH)2, which has a hydrotalcite-like structure and contains solely divalent cations, and β-Ni(OH)2, which has a similar layered structure as α-Ni(OH)2but without charge compensating anions and water molecules in the interlayer region, leading to a more compact layered structure as shown in FIG. 109 (D. S. Hall, D. J. Lockwood, C. Bock, B. R. MacDougall, Proc. R. Soc. A Math. Phys. Eng. Sci.2015, 471). β-nickel hydroxides synthesized using co-precipitation in the absence of any template were found to carry α-Ni(OH)2impurities (FIG. 63) and minimal porosity (3.3 m2 / g surface area and 0.01 cc / g pore volume, Table 3), albeit with clear characteristic diffraction peaks at 19, 33, and 39° attributable to the β-Ni(OH)2phase (J. Shi, E. Wu, Microporous Mesoporous Mater. 2013, 168, 188–194). These textural and diffraction results are consistent with mixed nickel hydroxide phases reported previously that were synthesized using chemical precipitation methods (D. S. Hall, D. J. Lockwood, C. Bock, B. R. MacDougall, Proc. R. Soc. A Math. Phys. Eng. Sci. 2015, 471). The low porosity of this β-nickel hydroxide sample results in an exceedingly low equilibrium CO2adsorption capacity under humid DAC conditions (<0.01 mmol / g, Table 3). Significant porosity was incorporated into the β-nickel hydroxide samples when applying the same co-precipitation method in the presence of an octylamine template. The templated β-Ni(OH)2-T sample was found to carry a BET surface area of 240 m2 / g and a pore volume of 0.44 cc / g. The surface area obtained for this sample is within the 200-250 m2 / g range reported in prior studies employing analogous soft template-assisted (hydr)oxide syntheses (J. Shi, E. Wu, Microporous Mesoporous Mater. 2013, 168, 188–194; M. Li, U. Tumuluri, Z. Wu, S. Dai, ChemSusChem 2015, 8, 3651–3660). The higher porosity of these samples resulted in a significantly greater equilibrium DAC capacity of 0.31 mmol / g under a 67% relative humidity stream (Table 3). These results suggest the potential for significantly improving DAC capacities by increasing nickel hydroxide porosity. To achieve further improvements in surface area and DAC capacity, α-Ni(OH)2samples were synthesized and subjected to an aqueous miscible organic solvent treatment (AMOST) protocol for delaminating layered double hydroxide structures. AMOST – reported by O’Hare and co-workers – has been shown to be an effective strategy for improving the porosity of LDH materials by redispersing wet samples into water-soluble solvents such as acetone and ethanol prior to drying (Q. Wang, D. O’hare, Chem. Commun.2013, 49, 6301–6303). Treatment with water-soluble solvents can extract water molecules out of LDH interlayers, thereby minimizing hydrogen bonding interactions and4886-5761-4062.1Page 50 of 164094876-000018WOPTreducing the extent of particle aggregation during the drying step (FIG. 108B) (Q. Wang, D. O’hare, Chem. Commun. 2013, 49, 6301–6303). The use of solvent re-dispersion to improve porosity through delamination has been demonstrated previously for non-Ni containing materials such as Mg-Al LDHs (C. Chen, A. Wangriya, J. C. Buffet, D. O’Hare, Dalt. Trans. 2015, 44, 16392–16398), as well as Ni-Ti LDHs for which a surface area of 492 m2 / g was achieved using an AMOST-assisted procedure (A. Pastor, C. Chen, G. de Miguel, F. Martin, M. Cruz-Yusta, J. C. Buffet, D. O’Hare, I. Pavlovic, L. Sánchez, Chem. Eng. J.2022, 429, 132361), which points to the feasibility of producing highly porous metal hydroxide structures using this technique.

[0256] The powder diffraction pattern of the synthesized α-Ni(OH)2sample in FIG.52A shows diffraction peaks at 2θ values of 22, 33.7, and 60° corresponding, respectively, to the (006) basal, (012), and (110) planes of α-Ni(OH)2(Z. Zhang, H. Huo, L. Wang, S. Lou, L. Xiang, B. Xie, Q. Wang, C. Du, J. Wang, G. Yin, Chem. Eng. J.2021, 412, 128617). AMOST-subjected α- Ni(OH)2samples in this work exhibit much higher surface areas and pore volumes – 820 m2 / g and 1.56 cc / g, respectively – compared to templated and non-templated β-nickel hydroxide samples, and also exhibit a correspondingly high DAC capacity of 0.92 mmol / g under humid conditions. To the best of our knowledge, this represents, to date, both the highest surface area achieved for a nickel hydroxide sample, as well as the first report presenting a non-alkaline earth metal hydroxide with competitive adsorption capacity and kinetics for direct air capture at close to room temperatures. Note that unlike the sorbents reported in our study, alkaline earth metal oxide sorbents may exhibit higher adsorption capacities such as 4 mmol / g at room temperature, but take extended times – sometimes up to a year – to realize this capacity (K. Rausis, A. R. Stubbs, I. M. Power, C. Paulo, Int. J. Greenh. Gas Control 2022, 119, 103701) rendering them impractical for low-temperature DAC specifically, and also CO2capture at close to ambient temperatures more generally. The much smaller timescales for CO2diffusion and adsorption onto the PNH materials reported here, combined with the competitive equilibrium adsorption capacities presented, create an opportunity for exploiting nucleophilic oxygen / hydroxyl groups on extended surfaces for the purposes of capturing CO2directly from humid ambient air. Next, we demonstrate further improvements in DAC performance through the use of aliovalent doping to rationally tune acid- base properties of hydroxide surfaces.

[0257] Table 3. Textural properties of PNH samples tested in our study, and their CO2adsorption capacities in the absence and presence of humidity. Adsorption conditions:4886-5761-4062.1Page 51 of 164094876-000018WOPT25 °C, 400 ppm CO2, 2.1 kPa H2O (67% RH) / balance N2. Pre-treatment conditions: 200 °C, 2 h Ar purge. BET Pore Dry Humid l surface l DAC DAC )

[0258] DAC Performance of Doped Nickel Hydroxides

[0259] Three types of porous nickel hydroxide (PNH) samples were investigated in this work - α-nickel hydroxides (α-Ni(OH)2), non-templated β-nickel hydroxides (β-Ni(OH)2), and templated β-nickel hydroxides (β-Ni(OH)2-T). Owing to their low surface areas and poor DAC performance, non-templated nickel hydroxides were not further evaluated in our study. Without being bound by theory, we hypothesized, consistent with density functional theory (DFT)- derived postulates put forth by the Metiu group (H. Metiu, S. Chrétien, Z. Hu, B. Li, X. Sun, J. Phys. Chem. C 2012, 116, 10439–10450; E. W. McFarland, H. Metiu, Chem. Rev.2013, 113, 4391–4427), that doping with metals carrying a higher valency compared to nickel will result in a net basicity on4886-5761-4062.1Page 52 of 164094876-000018WOPTthe surface that will in turn increase significantly the binding energy of CO2. Per this postulate, when a high-valent dopant such as cerium substitutes into the NiO(H) matrix, it brings in more valence electrons compared to the nickel atom it displaces. Regardless of whether these excess electrons are delocalized onto the adjacent nickel atom or not, the excess valence electrons brought in by the high-valent dopant results in the creation of net basicity on the (hydr)oxide surface relative to the undoped surface. Without being bound by theory, we hypothesized that doping of the α-nickel hydroxide sample with cerium – carrying either a +3 or a +4 valency – could result in a net basicity on the surface that would be reflected in the form of more nucleophilic oxygen or hydroxide moieties that would in turn bind CO2more strongly. Iron was also tested as an alternative dopant that could take on an oxidation state of either +2 (acting as an aliovalent dopant) or +3 (acting as a high-valent dopant).

[0260] Ce / Fe doped samples are referred to with their corresponding target mole fractions included in the nomenclature. For example, a 10 mole % Ce-doped α-nickel hydroxide sample is referred to as α-NiCe0.1(OH)x. The synthesized α-NiCe0.1(OH)xsample exhibits similar X-ray diffraction peak positions as α-Ni(OH)2, but appears to be less crystalline than its unary counterpart (FIG.52A). Delamination, like doping, lowers the crystallinity of the cerium-containing sample, as indicated by the presence of a more prominent diffraction peak at 11° assigned to the (003) plane of samples. Samples containing interlayer carbonates not subjected to the ethanol AMOST step (FIG.64) (Z. Liu, R. Ma, M. Osada, N. Iyi, Y. Ebina, K. Takada, T. Sasaki, J. Am. Chem. Soc. 2006, 128, 4872–4880). Similar reductions in (003) peak intensity have previously been reported in other studies on nickelate layered double hydroxides after delamination steps such as AMOST or ultrasound treatment (A. Pastor, C. Chen, G. de Miguel, F. Martin, M. Cruz-Yusta, J. C. Buffet, D. O’Hare, I. Pavlovic, L. Sánchez, Chem. Eng. J. 2022, 429, 132361; S. Sanati, Z. Rezvani, Ultrason. Sonochem. 2018, 48, 199–206). Delamination of the sample with ethanol results in a much larger surface area compared to the Ni-Ce hydroxide sample not subjected to AMOST (FIG. 65), pointing to the effectiveness of AMOST in generating the requisite surface area for DAC applications. The delamination of Ni-Ce hydroxide resulting from ethanol treatment can be demonstrated directly from its effect on particle morphology inferred from the TEM images shown in FIG.53A – FIG.53B.

[0261] Whereas α-NiCe0.1(OH)xobtained without being subjected to AMOST treatment in ethanol shows strongly aggregated particles, the α-NiCe0.1(OH)x-6h sample subjected to AMOST4886-5761-4062.1Page 53 of 164094876-000018WOPTexhibits a flower-like nanosheet morphology, aligning with images for AMOST-assisted LDHs reported previously by other groups (A. Pastor, C. Chen, G. de Miguel, F. Martin, M. Cruz-Yusta, J. C. Buffet, D. O’Hare, I. Pavlovic, L. Sánchez, Chem. Eng. J. 2022, 429, 132361; X. Zhu, C. Chen, H. Suo, Q. Wang, Y. Shi, D. O’Hare, N. Cai, Energy 2019, 167, 960–969; S. Shang, A. Hanif, M. Sun, Y. Tian, Y. S. Ok, I. K. M. Yu, D. C. W. Tsang, Q. Gu, J. Shang, J. Hazard. Mater. 2019, 373, 285–293). Next, we discuss the effect of Ce introduction on the structure of nickel hydroxide.

[0262] The diffraction peak attributable to the (101) plane of Ce(OH)3that appears at 28° upon introduction of cerium (FIG. 52A) (Y. Wang, G. Wang, L. Zhang, Z. Jin, T. Zhao, Dalt. Trans.2019, 48, 17660–17672) suggests that not all of the cerium substitutes isomorphously into the NiO matrix. Unlike the demonstrably heterogenous α-NiCe0.1(OH)xmaterial in which a fraction of the cerium is present as a separate Ce(OH)xphase, the α-NiFe0.2(OH)xmaterial is significantly more crystalline than the single component α-Ni(OH)2sample (FIG. 52A). The absence of additional diffraction peaks upon introduction of Fe suggests minimal formation of crystalline Fe(OH)xphases, and the sharper diffraction peaks, including the appearance of a clear (003) peak at 11°, suggests the formation of a much more crystalline α-Ni hydroxide phase upon doping with Fe. Besides, (003) and (006) basal plane peaks in α-NiFe0.2(OH)xthat appear shifted to higher 2T values compared to α-Ni(OH)2suggest a shorter basal spacing, consistent with lesser delamination and a greater extent of stacking for the Fe-containing sample. (012) and (110) diffraction peaks are also shifted to slightly higher 2T values, likely originating from lattice substitution of Fe3+ions carrying a smaller ionic radius (0.0645 nm) compared to Ni2+ones (0.069 nm). Note that the similar positions of Fe and Ni in the periodic table imply that the minimal shift in diffraction peak position is expected even if the entirety of the Fe were isomorphously substituted into the NiO LDH framework. In fact, the similar ionic radii of Fe and Ni may constitute part of the reason for the more effective substitution of Fe and the concomitant absence of diffraction peaks corresponding to crystalline Fe(OH)3. Without being bound by theory, we posit that unlike Ce3+ / 4+ions that have a negligible effect on pore properties of the synthesized hydroxide, strong particle aggregation is retained in the NiFe LDH samples, presumably due to Fe3+-induced stabilization of layer stacking that is resistant to delamination upon redispersion in ethanol.4886-5761-4062.1Page 54 of 164094876-000018WOPT

[0263] Consistent with the X-ray diffraction results, the α-Ni(OH)2and α-NiCe0.1(OH)xsamples exhibit similar pore characteristics including surface area and pore diameter, unlike the much more crystalline α-NiFe0.2(OH)xsample that exhibits a lower surface area (476 m2 / g), albeit with a similar pore diameter (Table 3 and FIG.52B, FIG.52C). The lower surface area of the Fe- containing sample reinforce our assertion that it is in fact the delamination of the LDH structure that enables the creation of very high surface areas for the α-Ni(OH)2and α-NiCe0.1(OH)xsamples (820 and 766 m2 / g, respectively). The more ordered and stable layered structure formed upon introduction of Fe into α-Ni(OH)2in fact disfavors the creation of the requisite degree of porosity for DAC applications. Textural properties of samples reported here, including a type-IV isotherm with an H3-type hysteresis loop, mirrors prior reports on LDH samples subjected to AMOST protocols (Q. Wang, D. O’hare, Chem. Commun.2013, 49, 6301–6303; A. Pastor, C. Chen, G. de Miguel, F. Martin, M. Cruz-Yusta, J. C. Buffet, D. O’Hare, I. Pavlovic, L. Sánchez, Chem. Eng. J. 2022, 429, 132361). The mesoporosity corresponding to this hysteresis loop could also potentially originate from the presence of non-rigid aggregates of plate-like particles present in a layered material (M. Thommes, K. Kaneko, A. V. Neimark, J. P. Olivier, F. Rodriguez-Reinoso, J. Rouquerol, K. S. W. Sing, Pure Appl. Chem. 2015, 87, 1051–1069). FTIR spectra of the α- Ni(OH)2and α-NiCe0.1(OH)xsamples contain infrared bands at 2974 cm-1likely corresponding to C-H stretching vibrations originating from residual interlayer ethanol molecules recalcitrant to thermal treatment at 200 °C, and also point to the presence of intercalated carbonate anions that exhibit symmetric stretching bands at 1378 cm−1(FIG. 66) (A. Pastor, C. Chen, G. de Miguel, F. Martin, M. Cruz-Yusta, J. C. Buffet, D. O’Hare, I. Pavlovic, L. Sánchez, Chem. Eng. J.2022, 429, 132361; Z. Liu, R. Ma, M. Osada, N. Iyi, Y. Ebina, K. Takada, T. Sasaki, J. Am. Chem. Soc.2006, 128, 4872–4880; N. Iyi, T. Sasaki, J. Colloid Interface Sci.2008, 322, 237–245).

[0264] FIG.54 shows a compilation of DAC capacities in the presence of water vapor for the various unary and binary α and β nickel hydroxides as a function of their corresponding BET surface areas. DAC capacities for all samples devoid of Ce were found to be linearly correlated with surface area irrespective of crystal structure, Ni / Fe content, and AMOST treatment, suggesting that variations in DAC capacity in these samples can be attributed entirely to changes in surface area and the corresponding concomitant alterations in adsorption site density, and not to the tuning of acid-base properties that result from changes in coordination environments of active oxygens or hydroxyls. Doping with Fe fails to result in an enhancement in DAC performance on4886-5761-4062.1Page 55 of 164094876-000018WOPTa per unit surface area basis despite the highly crystalline nature of the sample and the absence of diffraction peaks associated with crystalline Fe(OH)x. In contrast, every Ce-containing nickel hydroxide sample tested exhibits a disproportionately higher adsorption capacity compared to the corresponding non-Ce analogues at equivalent surface areas (FIG.54). Specifically, the templated Ce-Ni β-hydroxide sample was found to exhibit a significantly larger adsorption capacity compared to the Ni β-hydroxide sample (0.48 versus 0.31 mmol CO2 / g) despite carrying a slightly smaller BET surface area (228 versus 240 m2 / g). Moreover, the Ce-Ni α-hydroxide sample subjected to AMOST manifested the highest DAC capacity of all materials tested (1.35 mmol CO2 / g), and also, to the best of our knowledge, the highest DAC capacity measured at reasonable timescales reported to date in the literature under ambient conditions for materials that are either oxidic or hydroxidic in composition. Improvements in DAC capacity are significant; for example, a 47% increase in adsorption capacity was noted upon doping α-Ni(OH)2with cerium. These improvements in DAC performance are unlikely to be a consequence of CeOxdomains formed upon addition of Ce to α-Ni(OH)2because areal CO2adsorption capacities for Ce(OH)3-T are much lower than those for α-NiCe0.1(OH)x(0.0009 versus 0.0018 mmol CO2 / m2). Differences in water adsorption or hydroxyl formation are also not likely to be contributing factors to these improvements, as reflected in near-identical water adsorption isotherms for the α-Ni(OH)2and α- NiCe0.1(OH)xsamples (FIG.67). We therefore ascribe the larger DAC capacities for Ce-containing samples to the effect of high-valent doping, consistent with the aforementioned hypothesis that substitution with high-valent dopants increase the basicity of the nickel (hydr)oxide surface. Our XPS results provide further corroboration of the fact that doping alters binding characteristics of the hydroxide surface. The Ni 2p peak in the XPS data shown in FIG.68 shifts to higher binding energies from 855.3 eV for α-Ni(OH)2to 855.65 eV for α-NiCe0.1(OH)x, indicating partial electron transfer out of the Ni2+ion upon Ce3+introduction; such electron transfer would be consistent with more electron rich (i.e. more basic) oxygen / hydroxyl moieties. These more basic moieties would in turn explain the higher DAC capacities under both dry and humid conditions upon introduction of cerium. Similar changes in Ni 2p binding energy have been reported by Liu et al. to result in lower overpotentials for oxygen evolution reaction catalysis over Ce(OH)3-containing and Ce- doped NiFe-LDH materials (M. Liu, K. A. Min, B. Han, L. Y. S. Lee, Adv. Energy Mater. 2021, 11, 1–11). The basis for the limited effect of Fe doping on adsorption capacities noted in FIG.54 remain ambiguous, but could be attributed to the versatility of Fe, which, unlike Ce, can exist in4886-5761-4062.1Page 56 of 164094876-000018WOPTeither a +2 or a +3 oxidation state. Note that doping with either of the elements considered – Fe or Ce – increase DAC capacities on a per unit area basis under dry conditions, but only the latter results in an improvement in performance under wet conditions (Table 3). Importantly, all Ni- hydroxide samples tested in our work, regardless of chemical composition or crystal structure, benefit from the presence of humidity in the feed stream. We next discuss the effect of water present on nickel hydroxide surfaces on CO2binding characteristics.

[0265] Effect of Water on CO2 Binding

[0266] Consistent with prior reports (B. Zhang, Y. Duan, K. Johnson, J. Chem. Phys.2012, 136, 4516), we find that metal hydroxides are not optimal candidate sorbents for CO2capture under dry conditions owing to the minimal binding that they exhibit in the absence of humidity. This conclusion changes, however, when evaluating this class of sorbents in the presence of water vapor, prompting questions as to the basis for the favorable role of water on CO2binding. Three potential types of sites were considered in our analysis of CO2adsorption data (FIG. 55) – interlayer carbonates, surface hydroxyls, and adsorbate species stabilized by surface water. Interlayer carbonates can react chemically with CO2in the presence of water to form bicarbonate species, akin to low pressure CO2adsorption mechanisms proposed previously over sodium / potassium carbonate impregnated sorbents that form bicarbonate species in the presence of water vapor (J. V. Veselovskaya, V. S. Derevschikov, T. Y. Kardash, O. A. Stonkus, T. A. Trubitsina, A. G. Okunev, Int. J. Greenh. Gas Control 2013, 17, 332–340; N. Masoud, V. Clement, T. Van Haasterecht, M. Fü, J. P. Hofmann, J. H. Bitter, Cite This Ind. Eng. Chem. Res 2022, 61, 14211-14221; N. Masoud, G. Bordanaba-Florit, T. Van Haasterecht, J. H. Bitter, Cite This Ind. Eng. Chem. Res 2021, 60, 13749–13755). To test the contribution of interlayer carbonates to CO2adsorption, an SO42-- exchanged α-Ni(OH)2sample was synthesized by redispersing the α-Ni(OH)2wet cake obtained after washing with DI water into an aqueous sodium sulfate solution for 48 hours at room temperature. The sulfate exchanged sample was found to exhibit a similar powder X-ray diffraction pattern and porosity as the native α-Ni(OH)2sample (FIG.56A and FIG.69). Sulfate ion exchange can be evidenced by the appearance of an S 2p peak at 168.35 eV in the XPS spectrum of the α-Ni(OH)2-SO42-sample that is absent in the case of the α-Ni(OH)2sample (FIG. 56B), as well as the appearance of a new infrared band at 1115 cm-1attributable to the asymmetric stretching mode of the sulfate anion and the concomitant loss of carbonate symmetric stretching bands at 1378 cm-1(H. Zhang, X. Wen, Y. Wang, J. Solid State Chem. 2007, 180, 1636–1647).4886-5761-4062.1Page 57 of 164094876-000018WOPTRoughly half the area of the carbonate band at 1378 cm-1was lost during ion exchange, suggesting significant but partial exchange of carbonate species with sulfate anions despite the limited propensity toward anion-exchange suggested by the strong binding of carbonates onto metal hydroxide layers evidenced previously using experiment and theory (Z. Liu, R. Ma, M. Osada, N. Iyi, Y. Ebina, K. Takada, T. Sasaki, J. Am. Chem. Soc.2006, 128, 4872–4880; X. Wang, H. Zhao, L. Chang, Z. Yu, Z. Xiao, S. Tang, C. Huang, J. Fan, S. Yang, ACS Omega 2022, 7, 39169–39180). The involvement of interlayer carbonates in CO2adsorption would require that adsorption capacities drop significantly upon sulfate ion exchange. Similar DAC capacities measured pre versus post ion exchange (0.92 versus 0.99 mmol CO2 / g), however, appear to eliminate the potential involvement of interlayer carbonates in CO2adsorption (pathway (1), FIG. 55), and suggest that CO2may instead bind to either surface hydroxyls or other sites that are 'activated' in the presence of water (pathways (2) and (3), FIG. 55). Note that the strong correlation between DAC capacities and BET surface areas captured in FIG. 54, and the positive influence of delamination of the layered structure on CO2capture performance, both provide further corroboration of the participation of surface, not interlayer sites, in CO2adsorption.

[0267] The presence of water has a significant favorable effect on the CO2adsorption capacities of all nickel hydroxide materials tested. CO2adsorption capacities increased with water partial pressures upto 2.1 kPa water before plateauing out or decreasing slightly at higher pressures (FIG.57A). The presence of water could either a) merely increase the density of adsorption sites present or b) alter not only the density but also the CO2binding characteristics of these sites. The much greater sensitivities of adsorption capacities to adsorption temperature under humid conditions compared to under dry conditions (FIG.57B) suggest a significant increase in binding energy in the presence of water versus in its absence. As an example, adsorption capacities of α- NiCe0.1(OH)xdecrease by a factor of 81% when increasing the adsorption temperature from 25 to 75 °C under 2.1 kPa water vapor, but only by 28% for the same change in temperature under dry conditions. The larger changes in adsorption capacity under humid conditions could also be caused by the lower water loadings encountered at higher temperatures under wet conditions, unlike under dry conditions where the surface has minimal amounts of water regardless of adsorption temperature. The presence of water vapor affects not only the adsorption capacity values but also our interpretation of the effect of doping on CO2binding. Under dry conditions, α-NiFe0.2(OH)xand α-NiCe0.1(OH)xcapture more CO2on a per unit area basis compared to α-Ni(OH)2(Table 3),4886-5761-4062.1Page 58 of 164094876-000018WOPTunlike under humid conditions, where only the Ce, not the Fe-containing material, exhibits higher areal DAC capacities (FIG. 54). Adsorption energies under dry conditions measured using adsorption microcalorimetry are shown in FIG.58 and demonstrate that the higher DAC capacities on the Fe and Ce-doped materials result from stronger binding compared to the unary α-Ni hydroxide sample. Adsorption energies over a wide range of surface coverages follow the order α- NiFe0.2(OH)x> α-NiCe0.1(OH)x> α-Ni(OH)2 / α-Ni(OH)2-SO42--- identical to the order of areal DAC capacities under dry conditions. These adsorption calorimetry data provide strong evidence of the enhanced CO2adsorption strength upon doping with Fe or Ce, potentially resulting from the expected enhancement in basicity of hydroxide moieties in the presence of high-valent dopants. The contrasting effects of doping in the presence versus the absence of water vapor demonstrate a unique role of water in facilitating CO2binding. These significant changes in binding energy could originate either from the creation of hydroxyls generated by the dissociative adsorption of water (pathway (2), FIG.55), or the direct involvement of molecularly adsorbed water in CO2binding (pathway (3), FIG. 55). Analysis of water adsorption isotherms measured over α-NiCe0.1(OH)xprovides insights that help further differentiate between these two adsorption pathways. A type II water isotherm indicative of monolayer-multilayer adsorption was measured at 25 °C, with an inflection in the 0.45-0.55 kPa range corresponding to a transition from mono to multilayer adsorption (FIG.57C). Surface hydroxylation, unlike water adsorption, is necessarily constrained to the nickel hydroxide surface, and hence should cease to provide improvements in DAC adsorption performance past the water vapor pressure where hydroxyl / water monolayers are formed. In sharp contrast with such an expectation, DAC capacities continue to increase significantly even above pressures that result in monolayer coverages of water (FIG.57C).

[0268] Not only do multilayer water adsorption capacities continue to favorably impact CO2adsorption, but in fact seem to provide a marker for adsorption capacities. DAC capacities shown in FIG.57C track quantitatively with water adsorption at multiple pressures at 25 °C and at multiple adsorption temperatures at 2.1 kPa water. The strong correlation between the quantities of bound water and CO2adsorbed over a wide range of mono and multilayer coverages suggest a role of molecular water clusters in enhancing CO2binding onto nickel hydroxide surfaces (pathway (3), FIG.55). Note that the involvement of molecular water in CO2binding does not in and of itself negate the participation of surface hydroxyls; rather, CO2binding could still occur over surface hydroxyls in a manner that is facilitated by either molecular water or hydrogen-4886-5761-4062.1Page 59 of 164094876-000018WOPTbonded water clusters. A possible means for the facilitative role of water is the formation of a particular type of precursor species in water that then coordinates to the hydroxide surface, akin to the mechanism for CO2binding onto hydroxide-bearing polyamine-Cu(II) hybrid sorbents proposed recently by the Sengupta group (H. Chen, H. Dong, Z. Shi, A. K. SenGupta, Sci. Adv. 2023, 9,eadg1956). The favorable effect of water vapor up to relative humidity values of 60% on CO2adsorption was interpreted in their work to result from acid-base interactions not between surface sites and CO2, but instead between surface hydroxides and carbonic acid, the latter of which was pre-formed through CO2dissolution into the adsorbed water phase. Adsorbed water also appears to enable CO2binding onto nickel hydroxide samples tested in our study, although its precise role, which could potentially include solvation of bound species or the formation of unidentified precursors to these bound species, remain ambiguous, and constitute the focus of current and future investigation. We note that the facilitative role of water in CO2adsorption sensed here contrast with hydroxide-bearing MOFs that can exhibit only limited tolerance to water, as well as an outsized propensity toward degradation in the presence of oxygen (C. E. Bien, K. K. Chen, S. C. Chien, B. R. Reiner, L. C. Lin, C. R. Wade, W. S. W. Ho, J. Am. Chem. Soc.2018, 140, 12662–12666; M. E. Zick, S. M. Pugh, J. Lee, A. C. Forse, P. J. Milner, 2022, 61, e202206718). Nickel hydroxides reported here, in contrast, are highly water-tolerant – as demonstrated in FIG.57A – FIG.57C – and highly oxidatively stable – as discussed in section 3.5. We next probe, using infrared spectroscopy, the speciation of adsorbed CO2under dry and humid conditions.

[0269] Adsorbate Speciation under Dry and Humid Conditions

[0270] In-situ FT-IR measurements over α-Ni(OH)2under 400 ppm CO2reveals a series of infrared bands between 1000 and 1700 cm-1that correspond to carbonate and bicarbonate species (FIG.59A). Symmetric and asymmetric stretching modes for (bi)carbonate species in the 1000-1700 cm-1wavenumber range have been reported widely in the literature, and band positions can vary with metal (hydr)oxide identity and surface coordination environment (C. E. Bien, K. K. Chen, S. C. Chien, B. R. Reiner, L. C. Lin, C. R. Wade, W. S. W. Ho, J. Am. Chem. Soc.2018, 140, 12662–12666; X. Zhao, Q. Ning, L. C. Grabow, J. D. Rimer, P. Bollini, J. Catal.2022, 416, 423–438; M. Li, U. Tumuluri, Z. Wu, S. Dai, ChemSusChem 2015, 8, 3651–3660; K. Coenen, F. Gallucci, B. Mezari, E. Hensen, M. van Sint Annaland, J. CO2 Util.2018, 24, 228–239). We assign bands at 1645 and 1680 cm-1detected in the presence of 400 ppm CO2without any water vapor to4886-5761-4062.1Page 60 of 164094876-000018WOPTasymmetric stretching modes for HCO3- species that have been reported previously to appear in the 1580-1680 cm-1range during CO2adsorption over a variety of hydroxyl-bearing materials including MOFs, reducible bulk metal oxides, and hydrotalcites (K. Rausis, A. R. Stubbs, I. M. Power, C. Paulo, Int. J. Greenh. Gas Control 2022, 119, 103701; C. E. Bien, K. K. Chen, S. C. Chien, B. R. Reiner, L. C. Lin, C. R. Wade, W. S. W. Ho, J. Am. Chem. Soc. 2018, 140, 12662– 12666; Z. Cai, C. E. Bien, Q. Liu, C. R. Wade, Chem. Mater. 2020, 32, 4257–4264; M. Li, U. Tumuluri, Z. Wu, S. Dai, ChemSusChem 2015, 8, 3651–3660; K. Coenen, F. Gallucci, B. Mezari, E. Hensen, M. van Sint Annaland, J. CO2 Util. 2018, 24, 228–239). The three bands at lower wavenumbers –1387, 1435, and 1473 cm-1– can be assigned to O-C-O stretching modes for CO32-species (K. Rausis, A. R. Stubbs, I. M. Power, C. Paulo, Int. J. Greenh. Gas Control 2022, 119, 103701; M. Li, U. Tumuluri, Z. Wu, S. Dai, ChemSusChem 2015, 8, 3651–3660; K. Yoshikawa, H. Sato, M. Kaneeda, J. N. Kondo, J. CO2 Util.2014, 8, 34–38). The inclusion of 2.1 kPa water vapor in the 400 ppm CO2-containing stream results in a significant increase in each of the aforementioned carbonate and bicarbonate bands (FIG. 59A), consistent with the much higher DAC capacities under humid compared to under dry conditions (Table 3 and FIG. 57A). These infrared bands, however, are rendered challenging to discern due to the presence of H-O-H bending vibrations in the 1600-1700 cm-1range when co-feeding H2O. These bands become more apparent when using D2O co-feeds instead of H2O co-feeds because D-O-D bending modes appear as a distinguishable band near 1205 cm-1rather than the 1600-1700 cm-1range that now appears well- defined and distinct from H-O-H bending vibrations previously obfuscating key infrared features (FIG.59A). Positions of bands associated with carbonates that are devoid of hydrogen / deuterium are unaffected by the introduction of D2O, unlike bands assigned to hydrogen / deuterium- containing bicarbonates that redshift from 1645 and 1680 cm-1to 1585 and 1618 cm-1, respectively, providing corroborating evidence for our assignments. These effects of H-D substitution are also consistent with previously reported IR band redshifts for KDCO3and KHCO3powders calculated using DFT and measured experimentally (W. W. Rudolph, D. Fischer, G. Irmer, 2006, 60, 130– 144). The co-existence of both protonated and deuterated bicarbonates in the presence of D2O is not entirely unexpected since surface hydroxyls need not be completely exchanged with deuterium; infrared band intensities at 1645 and 1680 cm-1are minor compared to those at 1585 and 1618 cm-1, suggesting that the surface is mostly (but not completely) deuterated.4886-5761-4062.1Page 61 of 164094876-000018WOPT

[0271] Intriguingly, the three bands at 1387, 1435, and 1473 cm-1assigned to carbonate species were amplified disproportionately upon introduction of D2O compared to the bands at 1645 and 1680 cm-1ascribed to bicarbonate species, with the latter showing increasing water:carbon ratios (X. Shi, H. Xiao, K. Kanamori, A. Yonezu, K. S. Lackner, X. Chen, Joule 2020, 4, 1823– 1837). The authors also deconvoluted the effect of solvation from that of the carbonate- bicarbonate reaction equilibrium, and found that while both surface species were solvatively stabilized to a similar extent in the absence of water, solvation preferentially stabilizes carbonate over little growth in intensity upon switching to humid conditions. The introduction of D2O therefore appears to favor the formation of carbonates rather than bicarbonates despite the fact that the formation of bicarbonates involves hydrolysis of carbonates by means of the following reaction: (X. Shi, H. Xiao, X. Chen, K. S. Lackner, Chem. - A Eur. J.2016, 22, 18326–18330). ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ଷଶି^ ^ଶ^ ՜ ^^ଷି^ ^ ^^ିEq. (1) If the adsorbatespeciation, one expect water to to bicarbonate to carbonate molar ratios. The predominance of carbonates under wet conditions, and bicarbonates under dry conditions, appears to suggest factors other than the carbonate-bicarbonate reaction equilibrium determining adsorbate speciation.

[0272] The preferential formation of carbonates in the presence of water has been reported widely in the open literature (FIG. 60). Gankanda et al. (A. Gankanda, D. M. Cwiertny, V. H. Grassian, J. Phys. Chem. C 2016, 120, 19195–19203), for instance, evidenced the progressive solvation of carbonates with increasing relative humidities over copper and zinc oxide nanoparticles by identifying unique infrared bands at 1385 and 1490 cm-1that increased in intensity relative to unsolvated carbonates. Preferential formation of carbonates have also been proposed in the context of moisture swing adsorption processes over ion exchange resins that involve adsorption of CO2under dry conditions and desorption under humid conditions (X. Shi, H. Xiao, K. Kanamori, A. Yonezu, K. S. Lackner, X. Chen, Joule 2020, 4, 1823–1837; X. Shi, H. Xiao, K. S. Lackner, X. Chen, Angew. Chemie 2016, 128, 4094–4097; X. Shi, H. Xiao, H. Azarabadi, J. Song, X. Wu, X. Chen, K. S. Lackner, Angew. Chemie - Int. Ed. 2019, 2–25). The Chen group used MD simulations to study the effect of up to 10 molecules of water per molecule of adsorbate on free energy changes for carbonate-bicarbonate interconversion over ion exchange resins containing quaternary ammonium salts. They reported that the free energy of carbonates4886-5761-4062.1Page 62 of 164094876-000018WOPTrelative to bicarbonates decreased monotonically with bicarbonate species with increasing water to carbon ratios (X. Shi, H. Xiao, K. S. Lackner, X. Chen, Angew. Chemie 2016, 128, 4094–4097). These simulations not only suggest solvation to be a predominant factor affecting CO2speciation in confined environments but also solvation affects the stability of carbonates more sensitively upon initial addition of water molecules than surplus hydration provided at higher water to carbon ratios. For instance, according to these calculations, preferential solvation ceases to affect carbonate stability above 20 molecules of water per carbonate ion (X. Shi, H. Xiao, K. S. Lackner, X. Chen, Angew. Chemie 2016, 128, 4094–4097). Adsorbate valency also plays a determinative role in solvative stabilization, as shown by Shi et al. in the study of the hydrolysis of a variety of mono, di, and trivalent ions. Their conclusion that the preferential solvation of carbonate species extends to other divalent (and even trivalent ions) but not monovalent ions suggests that the difference in valency between divalent carbonate and monovalent bicarbonate anions could constitute a potential basis for the stabilization proposed in our work (X. Shi, H. Xiao, X. Chen, K. S. Lackner, Chem. - A Eur. J. 2016, 22, 18326–18330). Analogies between CO2capture by porous nickel hydroxides reported here and moisture swing adsorption proposed by the Lackner group also extend to wet to dry transients (T. Wang, K. S. Lackner, A. Wright, Environ. Sci. Technol. 2011, 45, 6670–6675). Purging a sample under 400 ppm CO2and 2.1 kPa D2O with a stream containing 400 ppm CO2in the absence of D2O resulted in a monotonic decrease in carbonate coverage, and a concurrent monotonic increase in bicarbonate coverage (FIG. 59B), suggesting that the stabilization of carbonates at high water loadings is indeed reversible, akin to moisture swing adsorbents that respond reversibly to changes in humidity under isothermal conditions (X. Shi, H. Xiao, K. S. Lackner, X. Chen, Angew. Chemie 2016, 128, 4094–4097; T. Wang, K. S. Lackner, A. Wright, Environ. Sci. Technol.2011, 45, 6670–6675). Not only does the adsorbate speciation mirror that observed in moisture swing adsorption, but so do adsorption capacities, as evidenced by the fact that some CO2(0.04 mmol CO2 / g) is adsorbed upon switching from humid to dry conditions (FIG.70). These results capture the analogous nature of carbonate- bicarbonate interconversion chemistry sensed in our experiments versus those reported under wet conditions on other classes of sorbents, but also point to some intriguing differences between the adsorption chemistry prevalent on nickel hydroxide surfaces under wet versus dry conditions. Importantly, we note that the solvative stabilization of carbonates under humid conditions has thus far, to the best of our knowledge, been exploited for moisture swing applications only, not4886-5761-4062.1Page 63 of 164094876-000018WOPTtemperature swing adsorption applications that are more commonly evaluated for direct air capture; to the best of our knowledge, the work on porous nickel hydroxides reported here represents the first instance of its application in realizing viable temperature swing adsorption capacities for DAC applications. Adsorption in the form of carbonates enables not only the reversible adsorption of CO2at low temperatures but also rapid adsorption kinetics and robust cyclic stability under aggressive oxidative conditions, as discussed next.

[0273] Adsorption Kinetics and Cyclic Oxidative Stability

[0274] In addition to equilibrium adsorption capacities, adsorption kinetics that determine DAC working capacities are another key performance metric, with rapid kinetics enabling shorter cycle times and minimizing DAC costs (H. Azarabadi, K. S. Lackner, Appl. Energy 2019, 250, 959–975). In fact, one of the primary limitations of inorganic metal oxide or hydroxide sorbents such as MgO and CaO are the slow adsorption kinetics that adversely affect the performance of these materials at room- temperature. The PNH materials reported here, on the other hand, exhibit uptake kinetics that compare favorably with other classes of organic-inorganic hybrid sorbents such as supported amines that represent the state-of-the-art for temperature swing DAC applications. The average adsorption rate for α-NiCe0.1(OH)xcalculated based on the adsorption half time compares favorably with values reported previously for a variety of supported amine sorbents listed in Table 7. Note that the different techniques and flow conditions used in these studies render quantitative comparison challenging to conduct and limited in rigor; the data nevertheless still strongly support the viability of practical operation over nickel hydroxides with sufficiently fast adsorption cycles. As shown in FIG.61A, the relative humidity of the CO2feed stream has little effect on the adsorption uptake rate, meaning that humid streams still benefit from larger equilibrium capacities without adverse effects on uptake kinetics that could potentially result as a consequence of adsorbed water multilayer formation. An exception to this trend appears to be the data point at the lowest relative humidity tested (27%). Comparison of the breakthrough curves at different relative humidities (FIG. 71) indicates that the outlet CO2concentration at the adsorption half time is significantly higher for the run at 27% relative humidity. A likely cause of these poorer kinetics is the more gradual progression of the water adsorption front at lower water vapor pressures, thereby potentially leading to a larger fraction of the CO2being adsorbed at later rather than earlier times in the breakthrough experiment. A more detailed analysis of dynamic breakthrough phenomena is needed in order to fully explain these trends in adsorption kinetics.4886-5761-4062.1Page 64 of 164094876-000018WOPTCrucially though, adsorption timescales consistently remain of a similar order of magnitude as those exhibited by supported amines, and orders of magnitude smaller than those for many of the previously reported oxide sorbents that only operate efficaciously at higher temperatures.

[0275] Cyclic stability of DAC sorbents under oxidative conditions is another key factor determining sorbent lifetime and total cost. Sorbents such as supported amine materials containing an organic component are inherently susceptible to oxidative and hydrothermal degradation at 75 °C after 12 hours of aging under air at 105 °C (Y. Meng, J. Jiang, A. Aihemaiti, T. Ju, Y. Gao, J. Liu, S. Han, ACS Appl. Mater. Interfaces 2019, 11, 33781–33791). Gebald et al. reported a 30% loss in DAC capacity for amine-functionalized nanofibrilated cellulose sorbents after treatment for 15 hours under a humid 20% O2in N2stream at90 °C (C. Gebald, J. A. Wurzbacher, P. Tingaut, A. Steinfeld, Environ. Sci. Technol. 2013, 47, 10063–10070). Carneiro et al. recently suggested that the presence of water vapor can accelerate the oxidative degradation rate of alumina supported PEI by a factor of two compared to under dry conditions (J. S. A. Carneiro, G. Innocenti, H. J. Moon, Y. Guta, L. Proaño, C. Sievers, M. A. Sakwa-Novak, E. W. Ping, C. W. Jones, Angew. Chemie 2023, 135, e202302887). Other potentially irreversible side reactions such as urea formation and leaching of organics further complicate the use of supported amine sorbents despite their competitive adsorption capacities and kinetics. PNHs are expected to serve as a highly robust platform for cyclic experiments in the presence of oxygen given the fact that surface oxygen / hydroxyl groups that capture CO2are already rich in oxygen and hence less susceptible to oxidation. α-NiCe0.1(OH)xexhibits excellent cyclability when regenerated at 100 °C under a stream containing 2.1 kPa steam and 20 kPa O2(FIG.61B). Imperceptible extents of degradation were observed over the course of 5 temperature swing adsorption-desorption cycles, with the adsorption capacity remaining stable at a value of 1.25 mmol CO2 / g. Adsorption kinetics also remained robust to cycling, with the adsorption rate remaining close to a value of 0.028 mmol g-1min-1. The consistent performance noted over 5 cycles despite the rather aggressive hydrothermal and oxidative conditions used during regeneration suggests that the α-NiCe0.1(OH)xsamples tested here are viable candidates for DAC applications. Such stable cyclic performance could extend broadly to other formulations within this novel class of inorganic sorbents – sorbents that thus far appear to compare favorably on every apparent performance metric of relevance to DAC applications.

[0276] Conclusion4886-5761-4062.1Page 65 of 164094876-000018WOPT

[0277] Aqueous miscible organic solvent treatment of nickelate layered double hydroxide structures yield high surface area porous nickel hydroxides (PNHs) that capture CO2under dry conditions, and exhibit competitive DAC capacities when exposed to humid air streams. Both of the high-valent dopants tested – Fe and Ce – result in an increase in areal adsorption capacity under dry conditions, unlike under wet conditions, where only doping with Ce results in DAC capacity enhancement. Unlike many other classes of DAC sorbents, the presence of humidity has a significant favorable effect on equilibrium DAC capacities and a minimal impact on adsorption kinetics for all PNH sorbents tested, with adsorption kinetics shown to compare favorably with supported amine sorbents heavily evaluated in the open literature. The favorable effect of water on DAC performance manifests over a wide range of mono and multilayer water coverages, and appears to originate from the preferential stabilization of carbonates in the presence of adsorbed water. Infrared spectra confirm the transformation of bicarbonate species formed on PNH surfaces under dry conditions to carbonate species under humid conditions, akin to changes in adsorbate speciation in moisture swing adsorbents reported previously. The cerium-doped alpha nickel hydroxide sample reported here exhibits a DAC capacity of 1.25 mmol / g that remains unaltered over 5 consecutive temperature swing adsorption-desorption cycles in the presence of oxygen and steam, successfully manifesting the high degree of hydrothermal and oxidative stability expected of sorbent formulations that are purely inorganic in composition. This study – the first one, to the best of our knowledge, to report robust, water-tolerant DAC performance at close to room temperatures for a sorbent that is purely inorganic in composition – demonstrates the potential for circumventing the use of expensive, hydrothermally and oxidatively unstable organic components for DAC processes currently constrained by prohibitive sorbent costs.

[0278] Chapter 3

[0279] Integrated Direct Air Capture and In-situ Methanation using Porous Nickel- cerium Oxides as Single-component Dual Function Materials

[0280] Integrated direct air capture of CO2and in-situ conversion is an emerging process aiming to find energy-efficient methods to convert ambient air to valuable products. Dual function materials (DFMs), typically composed of at least two components, are important to achieve both CO2sorption and catalytic methanation functions in a single bed. Traditional DFMs for applications of integrated carbon capture and methanation are suffered from high methanation temperature (>300 °C) and use of noble catalysts, owing to strongly bounded CO2species and long4886-5761-4062.1Page 66 of 164094876-000018WOPTdistance between adsorption and catalytic sites. Herein we report the first single-component dual function material, porous nickel-based oxides, that can achieve efficient DAC (25 °C) and low- temperature in-situ methanation (230 °C). Unreduced Ni-O serves as CO2binding sites and reduced metallic Ni enables activation of H2for hydrogenation. Incorporation of Ce regulates electronic properties of Ni-O to increase Ni3+content and therefore facilitate the non- stoichiometric oxygen content, resulting in enhanced basicity and mitigated reducibility of Ni-O, eventually leading to significant enhancements of DACM key metrics including CH4productivity and cycle stability. Ni0.7Ce0.3Oxas the first example of single-component DFMs without use of noble catalyst can perform low-temperature DACM (230 °C), and show the stable, excellent CH4productivity (0.8-0.9 mmol / g) and selectivity (100%) obtained over 5 adsorption-methanation cycles. The reactively desorbed pathway is observed on this system, which (bi)carbonates are converted directly to methane without need of desorbing into gas phase before hydrogenation. The unique proximity between adsorption / catalytic sites in such single-component DFM NiCeOxlikely enables and enhances the reactive desorption mechanism. This work sheds light on the advanced design strategy of DFMs for integrated carbon capture and methanation process.

[0281] Introduction

[0282] There is a growing consensus that climate changes need to be mitigated by developing negative emission technologies such as direct air capture (DAC). The destination of captured carbon is considered for either sequestration or utilization. Carbon capture and sequestration (CCS) aims to permanently store captured CO2underground, however, currently limited at wide implementations by high costs of deployments and operations (compression and transportation of CO2) (Budinis, S.; Krevor, S.; Dowell, N. Mac; Brandon, N.; Hawkes, A. An Assessment of CCS Costs, Barriers and Potential. Energy Strateg. Rev. 2018, 22, 61–81) and potential risks of leakage (Gholami, R.; Raza, A.; Iglauer, S. Leakage Risk Assessment of a CO2 Storage Site: A Review. Earth-Science Rev.2021, 223, 103849) though with some debates. Carbon capture and utilization (CCU) aims to use captured CO2as feedstock to produce valuable chemicals and renewable fuels. However, traditional CCU may require desorption, purification and compression of captured CO2before applying subsequent catalytic conversions (Zhang, Y.; Zhao, S.; Li, L.; Feng, J.; Li, K.; Huang, Z.; Lin, H. Integrated CO2 Capture and Utilization: A Review of the Synergistic Effects of Dual Function Materials. Catal. Sci. Technol. 2024). Integrated CO2capture and utilization (ICCU), which can directly process catalytic reaction4886-5761-4062.1Page 67 of 164094876-000018WOPTwithout additional pretreatments after CO2capture within a single bed, is considered as a more cost-effective and energy-efficient process than typical CCU, recently attracting more attentions from researchers (Lv, Z.; Chen, S.; Huang, X.; Qin, C. Recent Progress and Perspective on Integrated CO2 Capture and Utilization. Curr. Opin. Green Sustain. Chem.2023, 40, 100771).

[0283] To achieve both functions in a single bed, dual function materials (DFMs), typically consist of two active components for achieving both adsorption and catalytic conversion respectively, are the key to affect process performances (Jo, S.; Cruz, L.; Shah, S.; Wasantwisut, S.; Phan, A.; Gilliard-Abdulaziz, K. L. Perspective on Sorption Enhanced Bifunctional Catalysts to Produce Hydrocarbons. ACS Catal.2022, 12 (13), 7486–7510). Among multiple pathways of thermo-catalytic conversion of CO2, CO2methanation is among the most exothermic reactions, making it potentially energy-efficient and thermodynamically favored at low temperature. Integrated carbon capture and methanation (ICCM) has been widely explored using both concentrated CO2(10% CO2) and diluted CO2(400ppm CO2) as CO2feedstock (Zhang, Y.; Zhao, S.; Li, L.; Feng, J.; Li, K.; Huang, Z.; Lin, H. Integrated CO2 Capture and Utilization: A Review of the Synergistic Effects of Dual Function Materials. Catal. Sci. Technol.2024; Liu, G.; Sun, S.; Sun, H.; Zhang, Y.; Lv, J.; Wang, Y.; Zeng, J.; Yan, Z.; Wu, C. Integrated CO2 Capture and Utilisation: A Promising Step Contributing to Carbon Neutrality. Carbon Capture Sci. Technol. 2023, 7, 100116). The favored DFMs for ICCM process can efficiently capture CO2at desired temperature and conditions, and then in-situ convert captured CO2to methane under H2environment at high temperature. Various DFMs composed of different sorbents and catalysts have been researched for ICCM process. Regarding the methanation component, Ru is verified as best CO2methanation catalyst regarding catalytic activity and selectivity and widely implemented in DFMs to provide highly active catalytic sites, despite its high costs as a noble metal (Chen, J.; Xu, Y.; Liao, P.; Wang, H.; Zhou, H. Recent Progress in Integrated CO2 Capture and Conversion Process Using Dual Function Materials: A State-of-the-Art Review. Carbon Capture Sci. Technol. 2022, 4, 100052).

[0284] Ni is earth-abundant and much more affordable transition metal and reported as most active non-noble metal catalysts towards CO2methanation (Lee, W. J.; Li, C.; Prajitno, H.; Yoo, J.; Patel, J.; Yang, Y.; Lim, S. Recent Trend in Thermal Catalytic Low Temperature CO2 Methanation: A Critical Review. Catal. Today 2021, 368, 2–19). In terms of sorption components, alkali and alkaline earth metal oxides including Na2O, BaO, CaO, MgO have been commonly4886-5761-4062.1Page 68 of 164094876-000018WOPTutilized in DFMs due to their high theoretical CO2capacity and strong surface basicity allowing robust CO2binding to obtain sufficient CO2adsorption capacity and high selectivity towards other gas impurities. However, strongly bounded CO2in the form of carbonates on these oxides generally results in higher temperature requirement for the following steps in utilization than that from traditional CO2methanation using continuous CO2flow as carbon source. For example, Ru / CaO supported on γ-Al2O3was reported by Bermejo-López et al. that over 500 °C of reduction temperature is required for fully decomposition from carbonate to oxides during ICCU (Bermejo- López, A.; Pereda-Ayo, B.; González-Marcos, J. A.; González-Velasco, J. R. Mechanism of the CO2 Storage and in Situ Hydrogenation to CH4. Temperature and Adsorbent Loading Effects over Ru-CaO / Al2O3 and Ru-Na2CO3 / Al2O3 Catalysts. Appl. Catal. B Environ. 2019, 256, 117845). Jo et al. reported no CO2desorption or methanation is observed on Ni / CaO at 400 °C during H2purge despite considerable amount of carbonates formed in the former adsorption step (Jo, S. Bin; Woo, J. H. Lee, J. H.; Kim, T. Y.; Kang, H. I.; Lee, S.C.; Kim, J. C. A Novel Integrated CO2 Capture and Diret Methanation Process Using Ni / CaO Catal-Sorbents. Sustain. Energy Fuels 2020, 4 (9), 4679-4687. In comparison, traditional CO2methanation can be achieved at much lower temperature (180-300 °C) using Ni / Ru supported catalysts (Lee, W. J.; Li, C.; Prajitno, H.; Yoo, J.; Patel, J.; Yang, Y.; Lim, S. Recent Trend in Thermal Catalytic Low Temperature CO2 Methanation: A Critical Review. Catal. Today 2021, 368, 2–19). Such higher methanation temperature for DFMs leads not only higher energy demand, but also lower CH4selectivity due to the potential side products of CO from reverse-water-gas-shift (RWGS) reaction. Na and Mg- based oxides were reported with weaker CO2binding, however, also require 300-450 °C for ICCM process reported in ICCU process regardless of applied catalysts (Jeong-Potter, C.; Farrauto, R. Feasibility Study of Combining Direct Air Capture of CO2 and Methanation at Isothermal Conditions with Dual Function Materials. Appl. Catal. B Environ.2021, 282, 119416; Kosaka, F.; Liu, Y.; Chen, S. Y.; Mochizuki, T.; Takagi, H.; Urakawa, A.; Kuramoto, K. Enhanced Activity of Integrated CO2Capture and Reduction to CH4under Pressurized Conditions toward Atmospheric CO2Utilization. ACS Sustain. Chem. Eng. 2021, 9 (9), 3452–3463). Therefore, discovery of adsorption sites for appropriate CO2binding strength is required to allow low temperature ICCM process.

[0285] Reported DFMs for applications of integrated direct air capture and methanation (DACM) are limited. As poor DAC kinetics and capacities from CaO which is applied widely in4886-5761-4062.1Page 69 of 164094876-000018WOPTDFMs for ICCU using concentrated CO2feed, Na / K-based sorbents are typically utilized instead. Kosaka et al. reported the feasibility of using Ni-Na / γ-Al2O3for isothermal DACM process (capture and methanation occur at same temperature) and obtained stable but limited performances (0.11 mmol CH4 / g DFMs) in multiple adsorption-methanation cycles, along with very high operation temperature (450 °C), mainly due to low CO2adsorption capacity and catalytic activity for the DFMs (Kosaka, F.; Liu, Y.; Chen, S. Y.; Mochizuki, T.; Takagi, H.; Urakawa, A.; Kuramoto, K. Enhanced Activity of Integrated CO2Capture and Reduction to CH4under Pressurized Conditions toward Atmospheric CO2Utilization. ACS Sustain. Chem. Eng.2021, 9 (9), 3452–3463). Lee and Otomo reported the use of Ru for enhanced catalytic activity and achieved DACM process (0.191 mmol CH4 / g DFMs) at relatively mild methanation temperature at 300 °C using Ru-K2CO3 / K-β″ alumina (Lee, J.; Otomo, J. Low-Temperature Activated Direct Air Capture Methanation Using K-Β″ Alumina. Ind. Eng. Chem. Res. 2023, 62 (31), 12096–12108). Farrauto group reported multiple DACM works using Ru-Na2O / γ-Al2O3and at similar moderate methanation temperature (300-320 °C) obtained stable and best DACM performances so far (0.4- 1.07 mmol CH4 / g DFMs, range represented performances in different works) (Lin, Y. (Iris); Abdallah, M. J.; Peters, J. E.; Luo, T.; Sheng, H.; Chen, Y. L.; Farrauto, R. J. Aging Studies of Dual Functional Materials for CO2 Direct Air Capture with in Situ Methanation under Simulated Ambient Conditions: Ru Thrifting for Cost Reduction. Chem. Eng. J.2024, 479, 147495; Jeong- Potter, C.; Abdallah, M.; Sanderson, C.; Goldman, M.; Gupta, R.; Farrauto, R. Dual Function Materials (Ru+Na2O / Al2O3) for Direct Air Capture of CO2 and in Situ Catalytic Methanation: The Impact of Realistic Ambient Conditions. Appl. Catal. B Environ.2022, 307, 120990; Abdallah, M.; Lin, Y. (Iris); Farrauto, R. Laboratory Aging of a Dual Function Material (DFM) Washcoated Monolith for Varying Ambient Direct Air Capture of CO2 and in Situ Catalytic Conversion to CH4. Appl. Catal. B Environ.2023, 339, 123105). However, practical implementations of DACM are likely only feasible if we can further reduce the energy consumption and overall process costs, which highly catalytic active DFMs without use of precious metal is urgently needed.

[0286] We herein report a novel single-component DFM, porous nickel-based oxides that enable the accomplishments of room-temperature DAC and low-temperature (230 °C) in-situ methanation. Incorporation of Ce into NiO rationally regulates electronic structures of Ni-O lattice to significantly enhance DACM performance including CH4productivity and cycle stability. Low methanation temperature requirement (230 °C) for NiCeOxis remarkable compared with literature4886-5761-4062.1Page 70 of 164094876-000018WOPTreported DFMs using more active Ru as catalytic component. Without being bound by theory, we hypothesize that this is mainly attributed to the proximity between CO2binding and hydrogenation sites, which is a unique feature of NiCeOxas single-component DFMs over typical DFMs loaded with two active components by impregnation. The work described herein explores the way of using cost-effective transition metal oxides as DFMs and rationally tuning their electronic structures to enhance performances of DACM process.

[0287] Results and discussion

[0288] Porous NiO as Single-component DFMs for ramp DACM

[0289] Typical DFMs require two active components for both sorption and catalysis functions, and potential use of porous support for loading highly dispersed active sites. Such DFMs may theoretically have fewer active components for each function and lower performances. For example, Ru-Na2O / γ-Al2O3reported from Farruato group loads only 6.1-10% Na2O, which can be a limiting factor for achieving higher CO2storage capacity and catalytic activity. Herein we report a novel single-component DFM, porous NiO that enables the accomplishments of both functions on this material during low-temperature (230 °C) DACM process (FIG.75). Dilute CO2adsorption can occur on Ni-O sites in forming (bi)carbonates (equation 2) and methanation is completed by assistance of reduced Ni sites, which H2can dissociatively adsorb on metallic nickel (equation 3) and subsequently react with (bi)carbonates on Ni-O to undergo methanation (equation 4). ^^ െ ^ ^ ^^ଶ՜ ^^െ^^ଷEq. (2) ^ଶ^ ʹ^^ ՜ ʹ^^ െ ^כEq. (3) ͺ^^ െ ^כ^ ^^^^ଷ՜ ͺ^^ ^ ^^ െ ^ ^ ʹ^ଶ^ ^ ^^ସ^^^ Eq. (4)

[0290] Porous nickel hydroxides are synthesized using soft template-assisted precipitation methods and corresponding porous NiO are obtained after thermal pretreatment at 350 °C under inert atmosphere. The crystal structure of pure NiO is evidenced by XRD patterns (FIG. 83A), which shows sharp diffraction peaks at 37, 43 and 62.5° corresponding to (100), (200) and (220) planes of cubic NiO crystalline phase, respectively. There is additional metallic Ni phase existing in the pure NiO as corresponding diffraction peaks located at 44.5 and 51.8°, attributed to (111) and (200) planes of cubic structure of metallic Ni. The formation of metallic Ni represents the4886-5761-4062.1Page 71 of 164094876-000018WOPTpartial reduction of NiO to Ni under Ar calcination similar with prior reports (Altay, M. C.; Eroglu, S. Non-Isothermal Reduction Behavior of NiO in Undiluted Ar and CH4 Atmospheres. Int. J. Miner. Process.2016, 149, 50–55). Such NiO shows high BET surface area at 176 m2 / g (FIG.83B and Table 6) and have similar porosity with Shi and Wu reported porous NiO (158 m2 / g, calcined at 350 °C in open air) with same synthesis procedure. NiO is not a traditional DAC sorbent, however, our group previously reported that NiO enables strong CO2binding by forming carbonates on non-stoichiometric oxygen, even under ultradilute CO2concentration (0.05 mmol / g at 400 ppm CO2) (Zhao, X.; Ning, Q.; Grabow, L. C.; Rimer, J. D.; Bollini, P. Carbonate Dimorphism, and the Reinterpretation of Rates of Lattice and Excess Oxygen-Driven Catalytic Cycles. J. Catal.2022, 416, 423–438). We evaluated pure NiO sample with much higher porosity is capable to achieve reasonable DAC capacity (0.28 mmol / g), and the presence of humidity in CO2stream enhances DAC capacity to 0.44 mmol / g. The moderate DAC capacity enables sufficient CO2stored on the surface and allows us to evaluate the feasibility of hydrogenation of carbonated NiO in DACM process.

[0291] Integrated ramp DACM was then performed over NiO for evaluating its feasibility as DFMs and the process schematic is demonstrated in experimental section (FIG.74A), similar with literature reported ramp DACM (Chen, J.; Xu, Y.; Liao, P.; Wang, H.; Zhou, H. Recent Progress in Integrated CO2 Capture and Conversion Process Using Dual Function Materials: A State-of-the-Art Review. Carbon Capture Sci. Technol.2022, 4, 100052). The typical gas profile for porous nickel-based oxides of CO2and CH4during the methanation (step 3-4 in FIG.74A) is shown for demonstration of ramp DACM process (FIG.74A). During the temperature ramp stage, a portion of weakly bounded CO2is desorbed without hydrogenation and considered as unused CO2, before approaching to light-off temperature (~150 °C) of CO2methanation. When it reaches light-off temperature, CH4signal is detected immediately and reaches peak at 230 °C with minimal CO2desorbed in this stage. An experimental attempt for using methanation temperature at 200 °C leads to lower carbon products than DAC capacity in all cycles, indicating incomplete removal of surface carbonates at 200 °C within one hour. (FIG. 84). Metallic Ni as catalytic actives can be formed simultaneously from reduction of Ni-O, as well as from the initial thermal pretreatment under Ar verified by XRD pattern (FIG.83A). Subsequently, the isothermal stage at 230 °C leads to gradually decreased CH4production due to less remained CO2on Ni-O surfaces. Generally, the sum of CO2desorbed and CH4formed is equal to CO2adsorbed in DAC stage, representing all4886-5761-4062.1Page 72 of 164094876-000018WOPTadsorbed CO2leaves the oxide surface during hydrogenation at 230 °C. We note that 1stcycle data may show slightly more carbon products than CO2adsorbed likely due to gas products from non- desorbed carbonates or remaining impurities (NO3-) may contribute to mass 15 during hydrogenation process, and a good carbon balance is obtained in the 2ndand following cycles. (FIG.85) This also suggests that there is minimal side carbon product such as CO formed, which is typically inevitable in most Ni-containing DFMs due to the higher operation temperature and high activity of Ni for RWGS reaction. Pure NiO presents relatively low methane productivity (0.38 mmol CH4 / g) in the 1stcycle, however, almost completely loss of performances (<0.01 mmol CH4 / g) in the following two cycles. (FIG. 110A – FIG. 110B). Such degradation can be mainly attributed to over-reduction of Ni-O, as evidenced by H2-TPR curve that TPR peak of pure NiO occurs at 230 °C representing most Ni-O is likely reduced to metallic Ni under this hydrogenation temperature. (FIG.76B) Such reduction would almost fully remove Ni-O, which is responsible for providing adsorption sites, and eventually leading minimal CH4productivity in the following cycles. The low methane productivity and poor cycle stability clearly makes pure NiO less favored as DFMs for ramp DACM process. Nevertheless, we successfully achieve reasonable DAC capacity at room temperature and produce methane over porous NiO at low methanation temperature, suggesting the feasibility of applying NiO as DFMs for DACM process.

[0292] Several limitations are needed to be addressed to make porous nickel-based oxides a practical DFM for DACM process including: (1) increase DAC capacity. Higher DAC capacity can directly increase the amount of CO2utilized in the following methanation step to increase CH4productivity; (2) promote cycle stability. Pure NiO exhibits highly reducible features and most Ni- O cannot persist under hydrogenation conditions, making cyclic operations not feasible; (3) rational increase CO2binding strength. From the gas profile (FIG. 77A), unused CO2should be minimized by making CO2bounded sufficiently strong, allowing most of the adsorbed CO2to undergo methanation rather than desorption. Over strongly bounded CO2may in turn result in increased methanation temperature to utilize these stable carbonates.

[0293] To address these issues, without being bound by theory, we hypothesized that high valency doping can increase net basicity on the surface, as suggested by the Metiu group using density function theory (DFT) calculation and our work about enhancement of nickel hydroxides DAC capacity from high-valency dopant, that will in turn increase CO2adsorption capacity and CO2binding strength. We speculated Ce, as a higher valency dopant of 3+ / 4+, can incorporate into4886-5761-4062.1Page 73 of 164094876-000018WOPTNi-O lattice, making oxygen sites more nucleophilic and resulting in enhanced CO2interactions with Ni-O sites.

[0294] Incorporation of Ce remarkably enhances DACM performances

[0295] From incorporating 10-30% molar ratio of Ce into NiO, NiCeOxshows monotonically decreased crystallinity of NiO and enhanced diffraction peaks of CeO2at 28.5, 47.5 and 57° corresponding to (111), (220) and (311) planes. (FIG. 83A) The occurrence of CeO2diffraction peaks represents Ce loading leads to the formation of separated CeO2phase, suggesting the heterogeneous doping from Ce, even at lowest Ce loading at 10%. This may be partially due to the large difference of ion radius between Ni2+and Ce3+ / Ce4+, leading to direct replacement of Ni2+by Ce3+ / Ce4+less favorable. Ce incorporation leads to slightly enhanced BET surface area (220-250 m2 / g) compared with pure NiO (176 m2 / g). (Table 6 and FIG.83B) Type II isotherm is generally observed for all materials except pure CeO2exhibiting type IV isotherm according to IUPAC reports (Thommes, M.; Kaneko, K.; Neimark, A. V.; Olivier, J. P.; Rodriguez-Reinoso, F.; Rouquerol, J.; Sing, K. S. W. Physisorption of Gases, with Special Reference to the Evaluation of Surface Area and Pore Size Distribution (IUPAC Technical Report). Pure Appl. Chem.2015, 87 (9–10), 1051–1069). BJH pore size distribution (FIG. 86) from desorption branch represents these materials containing mainly mesopores with a portion of micropores, and contribution of micropores is increased from increasing Ce incorporation. Without being bound by theory, the general trend of shrinking pore size and increasing BET surface area from increased Ce loading may be attributed to the dispersion of nanocrystalline CeO2over NiO lattice.

[0296] NiCeOxwith different Ce loadings, as well as pure NiO and CeO2were evaluated and compared for DAC capacities using both dry and humid simulated air streams (FIG. 77A). The incorporation of Ce significantly enhances of DAC capacities, which Ni0.7Ce0.3Oxexhibits much higher CO2adsorption capacity under humid conditions (1.05 mmol / g) than pure NiO (0.43 mmol / g) and pure CeO2(0.15 mmol / g). Despite variations of textural properties among these materials (Table 4), this conclusion is not changed after normalizations based on BET surface area, evidencing the synergistic effect of Ce incorporation on CO2adsorption. Besides, the presence of mild humidity (67% RH) in 400 ppm CO2stream generally enhances DAC capacity for all materials, consistent with our work showing a moisture promotion effect of CO2adsorption on porous Ni(OH)2.The promotion from humidity is likely from the adsorbed surface cluster water as media to enhance acid-base interactions between dissolved CO2and Ni-O. This feature not only4886-5761-4062.1Page 74 of 164094876-000018WOPTbenefits for higher CO2adsorption capacity, but also suggests good water tolerance allowing practical use of NiCeOxunder more realistic conditions. To the best of our knowledge, this is the first report using transition metal oxides for DAC applications and DAC capacity of Ni0.7Ce0.3Oxis over 1 mmol / g which is comparable with existing classes of sorbents such as zeolites and amine- supported materials.

[0297] To elucidate CO2binding strength on NiCeOxat various Ce loadings, CO2-TPD were performed after pre-adsorbing humid (2.1 kPa) 400 ppm CO2(FIG.77B). CO2-TPD is widely used to characterize the basicity of oxygen nucleophiles. The experimentally measured profiles consist of two major CO2desorption peaks, roughly deconvoluted to weakly bounded (peak around 110 °C) and strongly bounded CO2(peak around 230 °C). The corresponding calculated contribution (FIG. 77C) indicates that increase of Ce loading leads to significant increased percentage of strongly adsorbed CO2. 70% strongly adsorbed CO2is observed on Ni0.7Ce0.3Oxwhile pure NiO and CeO2shows 35% and 21% respectively, suggesting the origin of strongly bounded CO2from modified Ni-O lattice instead of contribution from Ce-O sites. Note that bed maximum temperature is set at 250 °C for CO2-TPD, leading a portion of adsorbed CO2remained on the surface at the end of the measurements. For example, total desorbed CO2amount is 0.83 mmol / g for Ni0.7Ce0.3Ox, slightly lower than its DAC capacity (1.05 mmol / g). The enhanced Ni- O basicity from Ce incorporation can partially explain the remarkable enhancement of DAC capacity, enabling part of inactive Ni-O sites in pure NiO capable for dilute CO2binding.

[0298] To evaluate the reducibility of Ni-O changes from Ce incorporation, H2-TPR experiments were performed for all NiCeOxmaterials as well as pure NiO and CeO2, indicating the reduction extent of NiO to metallic Ni, which is necessary for CO2methanation (FIG.76B). All Ce-containing samples exhibited remarkably less reducible oxygen, which the major reduction peak is in the range of 300-390 °C, much higher than that from pure NiO (230 °C). Higher Ce loading also increases light-off temperature of reduction. Such results suggests that NiCeOxcan exhibit much greater resistance towards Ni-O reduction, resulting in most Ni-O survived under hydrogenation conditions (10% H2, 230 °C) during ramp DACM and likely result in better cycle stability.

[0299] In-situ Fourier transformed-infrared spectroscopy (FT-IR) was conducted to gain insight into CO2-induced surface species during DAC process. The difference spectra before and after CO2adsorption represents the formation of surface species from CO2introduction. D2O was4886-5761-4062.1Page 75 of 164094876-000018WOPTused as humidity source to avoid curve overlapping in the region around 1600 cm-1from H2O, replaced by D2O bending peaks shown between 1150-1250 cm-1where no CO2-related species shows bends around this region.At close to room temperature (30 °C) and simulated humid air adsorption condition, NiO represents three dominant CO2-induced peaks at 1620 cm-1attributed to bicarbonates, 1485 and 1355 cm-1attributed to asymmetric and symmetric monodentate carbonates, respectively. These assignments are reported for (bi)carboantes on different metal oxides (Taifan, W.; Boily, J. F.; Baltrusaitis, J. Surface Chemistry of Carbon Dioxide Revisited. Surf. Sci. Rep.2016, 71 (4), 595–671). The observed CO2-induced surface species represents dilute CO2 is chemisorbed over Ni-O surfaces to form (bi)carbonates. At the same adsorption condition, Ni0.7Ce0.3Oxexhibits more intense, along with obviously broader bands around monodentate regions. We therefore assigned two additional bands at 1572 cm-1and 1295 cm-1attributed to bidentate carbonates. From CO2-TPD results (FIG.77B), Ni0.7Ce0.3Oxexhibits significantly more strongly bounded CO2than NiO, which may be attributed to the additional bidentate carbonates formation observed in IR spectra upon Ce incorporation. To evidence if bidentate carbonates are recalcitrant to thermal desorption, an in-situ FT-IR experiment of temperature desorption over Ni0.7Ce0.3Oxafter humid 400 ppm adsorption was conducted (FIG.87). Ar purge at 30 °C almost does not change the surface species and purge at 50 °C leads to reduction of monodentate carbonates (1360, 1487 cm-1) while bidentate carbonates (1578, 1295 cm-1) exhibit minimal decomposition. When the sample is heated towards 150 °C, bands for monodentate carbonates are reduced at significant extent and most bidentate carbonates remain on the surface. The disproportional reduction of monodentate and bidentate carbonates suggest their different thermal stabilities and indicates favored formation of bidentate carbonates on Ni0.7Ce0.3Oxmay be the key for prevailing strongly bound CO2observed from CO2-TPD. Purging Ar at 250 °C decomposed most carbonates of both types on surface, consistent with major desorption peak at about 230 °C for strongly bound CO2observed in CO2-TPD curves (FIG.77B).

[0300] The effect of water in CO2-induced surface species was examined by FT-IR spectra. Humidity presented in CO2stream leads to significantly enhanced DAC capacity (FIG.77A), as well as changing the type of surface species. (FIG.78B) Bicarbonates (1620 cm-1) may contribute significantly higher under dry condition than that under humid condition, leading the broad peak shifts toward higher wavenumber. This is consistent with carbonate / bicarboantes equilibrium shift by tuning the environment humidity, widely reported in literature regarding moisture swing4886-5761-4062.1Page 76 of 164094876-000018WOPTadsorption of CO2(Shi, X.; Xiao, H.; Kanamori, K.; Yonezu, A.; Lackner, K. S.; Chen, X. Moisture-Driven CO2 Sorbents. Joule 2020, 4 (8), 1823–1837). Humid environments makes carbonates favored in the equilibrium and minimizes the formation of bicarbonates, while at dry environments, bicarbonates and hydroxyls can be formed from hydrolysis of carbonates (Shi, X.; Xiao, H.; Lackner, K. S.; Chen, X. Capture CO 2 from Ambient Air Using Nanoconfined Ion Hydration . Angew. Chemie 2016, 128 (12), 4094–4097). Such favored formation of bicarbonates under dry condition is consistent with IR results on Ni-O surfaces, along with CO2-TPD peaks presented at much lower temperature from corresponding CO2-TPD curves (FIG. 88), as bicarbonates are generally considered as least thermal stable among all carbonate types. Besides, monodentate carbonates becomes less dominant surface species under dry condition, while bidentate carbonates contribute at greater extent. The remarkably less strongly bound CO2formed on Ni0.7Ce0.3Oxin the absence of water with dominated bidentate carbonates is not consistent with our hypothesis that bidentate carbonate is more thermally stable than monodentate carbonates. Further study is required to explore if the effect of water in enhancing CO2binding strength can be achieved without affecting carbonate types.

[0301] From the discussed changes of properties, NiCeOxwith increase in DAC capacity, CO2binding strength and limiting the reducibility of Ni-O, is supposed to eventually result in enhancing CH4productivity and cycle stability and perform as a better DFM for DACM process. We experimentally evaluate ramp DACM performances for NiCeOx and the comparison of ramp DACM cycle stability of NiCeOx and pure NiO (FIG. 76C) suggests that Ce incorporation considerably enhances DACM performances. The highest CH4productivity is obtained on Ni0.7Ce0.3Ox(0.83 mmol / g), and there is a monotonically increasing trend of CH4productivity with increasing Ce loading. The increased CH4productivity of NiCeOxis likely a result from both higher DAC capacity (FIG. 77A) and stronger CO2binding on Ni-O surfaces (FIG. 77B, FIG. 77C). Cycle stability of CH4productivity follows the same trend that Ni0.7Ce0.3Oxexhibits most stable performances (0.8-0.9 mmol / g) within 5 cycles while pure NiO shows minimal CH4produced (<0.01 mmol / g) after 1stcycle, mainly attributed to more resistant Ni-O towards reduction under hydrogenation conditions. And there is not an observably lower catalytic activity from less reduction (less metallic Ni) in NiCeOxas a good carbon balance obtained in all samples under same hydrogenation condition after 1stcycle. (FIG.84) These performances are concluded4886-5761-4062.1Page 77 of 164094876-000018WOPTthat rational incorporation of Ce into porous NiO successfully tackle the limitations of pure NiO as DFMs for DACM.

[0302] Reactively desorption of CO2to methane

[0303] Despite the fact that adsorption and methanation functions are achieved by two different components separately on typical DFMs, the question that how surface bounded CO2on adsorption components is utilized by methanation component in the following hydrogenation step still remains unambiguous. Two potential reaction pathways can exist during the hydrogenation of carbonated DFMs (FIG. 74A – FIG. 74B): (1) decomposition of carbonates to gas phase CO2, followed by diffusion and transport to catalytic active sites and react with activated H atom to form CH4; (2) activated H atom on catalytic active sites directly react with carbonates to produce CH4. And the preferably latter mechanism theoretically requires proximity between carbonates and catalytic sites to enable the direct reaction of reactant species on two distinct sites. However, traditional DFMs loading sorbents and catalysts on supports using impregnation have very limited control on the dispersion, leading unfavored (2) mechanism over those DFMs.

[0304] NiCeOxas a single-component DFM may have intrinsic advantages in terms of proximity between sorbents and catalysts, as catalytically active metallic Ni is formed from Ni-O lattices, therefore enabling every catalytic active site surrounded by unreduced Ni-O. Comparing with literature reported methanation temperature in DACM process, most DFM needs 300-450 °C to activate the methanation and clean the carbonate surface, even in the use of more active catalysts like Ru. However, NiCeOxis capable to light-off the reaction at around 150 °C and fully recover the carbonate surface at 230 °C. To elucidate the origin of lower methanation temperature, we performed purge experiments (FIG.80) using H2-containing and inert gas stream for pre-reduced and 400 ppm CO2saturated NiCeOxsample at 230 °C. Pure Ar purge leads to negligible CO2desorbed (0.02 mmol / g), while 10% H2 / Ar purge leads to considerable CH4produced immediately (0.21 mmol / g). Such more effective formation of C1 products from H2 / Ar indicates that in a DACM process, adsorbed CO2in the form of (bi)carbonates undergoes direct reaction with activated H on metallic Ni without need of desorbing into gas phase CO2initially. Some literature suggested H-spillover, or CO2-spillover / migration may assist this mechanism (FIG. 79A – FIG. 79B) (Porta, A.; Visconti, C. G.; Castoldi, L.; Matarrese, R.; Jeong-Potter, C.; Farrauto, R.; Lietti, L. Ru-Ba Synergistic Effect in Dual Functioning Materials for Cyclic CO2 Capture and Methanation. Appl. Catal. B Environ. 2021, 283, 119654; Wu, X.; Chang, R.; Tan, M.; Tao, L.;4886-5761-4062.1Page 78 of 164094876-000018WOPTFan, Q.; Hu, X.; Ling, H.; Åhl, M.; Cheung, O.; Liu, W. Applied Catalysis B : Environmental An Investigation of the Ni / Carbonate Interfaces on Dual Function Materials in Integrated CO2 Capture and Utilisation Cycles. 2023, 338 (June)). The more effective removal of surface carbonates by hydrogenation than desorption is also evidenced by near 100% carbon balance from ramp ICCU process in 2ndcycle (FIG. 85), representing complete removal of carbonates by hydrogenation at 230 °C, while CO2is not fully released under Ar purge as CO2desorption amount from CO2-TPD (0.83 mmol / g) is smaller than DAC capacity (1.05 mmol / g) at a slightly higher temperature at 250 °C.

[0305] Non-stoichiometric Ni-O sites for strong CO2binding

[0306] To track the origin of Ni-O sites for stronger CO2binding, besides inert environment calcination to obtain nickel-based oxides from hydroxides, we thermally treated Ni0.7Ce0.3(OH)xin the presence of simulated air (21% O2, balanced N2) and pure O2at the same °C) to obtain Ni0.7Ce0.3Ox-air and Ni0.7Ce0.3Ox-O2and compare with Ni0.7Ce0.3Ox(calcined under Ar) sample. Calcination under oxygen-containing atmosphere tends to make metal oxides more crystalline and form more ordered metal-oxygen lattice with less surface deficiency, as oxygen insertion can potentially vanish partial reduction of NiO which occurs under Ar calcination. Hop et al. reported the increased non-stoichiometry of NiOxunder Ar atmosphere versus air / O2calcination for LaSrNiOx evidenced by increased chemisorbed oxygen / lattice oxygen ratio and decreased Ni3+ / Ni2+ratio from XPS data (Hop, D. H.; Chung, R. B. K.; Heo, Y. W.; Kim, J. J.; Lee, J. H. Oxygen Nonstoichiometry and Electrical Properties of La2–XSrxNiO4+δ (0 ≤ x ≤ 0.5). J. Korean Ceram. Soc. 2020, 57 (4), 416–422). XRD diffraction patterns of Ni0.7Ce0.3Ox, Ni0.7Ce0.3Ox-air and Ni0.7Ce0.3Ox-O2(FIG.89) indicates the enhanced crystallinity for both NiO and CeO2phases from calcination in oxygen atmosphere. The disappearance of metallic Ni diffraction peak for Ni0.7Ce0.3Ox-air and Ni0.7Ce0.3Ox-O2is also consistent with favored formation of ordered Ni-O lattice from oxygen. The more stoichiometric Ni-O lattice is also evidenced by deconvoluted XPS spectra of O1s. There are three major peaks located at 529.1 eV, 531 eV and 531.9 eV which represents the surface lattice oxygen, surface adsorbed (non- stoichiometric) oxygen and weakly chemisorbed oxygen (including adsorbed water and carbonates), respectively (FIG.90). Increased surface lattice oxygen to non-stoichiometric oxygen ratio is shown with increased O2concentration of calcination atmosphere. (Table 4) In terms of the CO2binding properties, a remarkably drop of humid DAC capacity is observed for 4886-5761-4062.1Page 79 of 164094876-000018WOPTNi0.7Ce0.3Ox-air (0.39 mmol / g) and Ni0.7Ce0.3Ox-O2(0.22 mmol / g) comparing with Ni0.7Ce0.3Ox(1.05 mmol / g), even with the consideration of porosity change (203 m2 / g for Ni0.7Ce0.3Ox-O2, 180 m2 / g for Ni0.7Ce0.3Ox-air and 250 m2 / g for Ni0.7Ce0.3Ox, Table 6), indicating the significant differences of CO2binding characteristics among samples calcined in different atmospheres. (FIG. 81B) This feature is further evaluated by their CO2-TPD profiles (FIG. 81C). Calcination under oxygen-containing atmosphere significantly lowers basicity of Ni-O sites, resulting in almost disappearance of the strongly bounded CO2peak observed on Ni0.7Ce0.3Ox. Without being bound by theory, we therefore speculate the strong CO2binding sites are likely originated from non- stoichiometric oxygen, as a strong correlation between reduced non-stoichiometric oxygen content and vanishment of strongly bounded CO2for air / oxygen-calcined samples. Such hypothesis was previously reported by Zhao et al. (Zhao, X.; Ning, Q.; Grabow, L. C.; Rimer, J. D.; Bollini, P. Carbonate Dimorphism, and the Reinterpretation of Rates of Lattice and Excess Oxygen-Driven Catalytic Cycles. J. Catal. 2022, 416, 423–438) that non-stoichiometric oxygen sites enables irreversible strong CO2binding over NiO surface. Besides, the significantly decreased Ni3+ / Ni2+ratio is found on Ni0.7Ce0.3Ox-air and Ni0.7Ce0.3Ox-O2by XPS Ni2p3 / 2data (FIG.81B and Table 4), consist with more stoichiometric NiO lattice formation.

[0307] The comparisons among samples with different calcination atmosphere points out that electronic structures of Ni-O are the origin for tuning of CO2binding properties, and this helps us further understand Ce promotion effect in the system. We discussed the unique effect of Ce incorporation in tuning properties of Ni-O for enhancing DACM performances, attributed by increase of Ni-O basicity to enhance both CO2binding strength and DAC capacity, and mitigate the reducibility of Ni-O to enhance the cycle stability. A more detailed analysis for electronic structure changes by Ce incorporation is presented by XPS data for Ni2p3 / 2and Ce3d regions. (FIG. 81B, Table 4). Incorporation of Ce increases Ni3+ / Ni2+ratio from 1.43 for pure NiO to 3.47 for Ni0.7Ce0.3Ox. Besides, Ce incorporation evidently shift the Ni3+peak to higher binding energy (+0.4 eV). This demonstrates lower electron density on Ni after Ce incorporation, likely due to the electron transfer from Ni center to Ce center. This electron transfer between Ni and Ce can be further evidenced by looking into oxidation states of Ce, which surface Ce4+ / Ce3+ratio (2.91) of Ni0.7Ce0.3Oxis considerably lower than that from pure CeO2(3.48) as Ce accepts electrons from Ni. (FIG.91 and Table 4) And oxygen atmosphere calcination rollbacks the electron transfer from Ce, suggested by Ce4+ / Ce3+ratio at 3.26 for Ni0.7Ce0.3Ox-air and Ni0.7Ce0.3Ox-O2. This4886-5761-4062.1Page 80 of 164094876-000018WOPTphenomenon from Ce incorporation is consistent with Liu et al. reports for the same higher binding energy shift from Ce interfacing on NiFe-LDHs, as well as our previous report on Ce doping in α- Ni(OH)x(Liu, M.; Min, K. A.; Han, B.; Lee, L. Y. S. Interfacing or Doping? Role of Ce in Highly Promoted Water Oxidation of NiFe-Layered Double Hydroxide. Adv. Energy Mater.2021, 11 (33), 1–11). We conclude that both inert calcination atmosphere (versus oxygen-containing calcination) and Ce doping can increase Ni3+ratio and therefore increased non-stoichiometry of Ni-O lattice, resulting in enabling and enhancing strongly bounded CO2over non-stoichiometric oxygen sites from Ni-O.

[0308] Table 4. Surface composition of NiCeOxwith various Ce loadings by deconvoluted XPS spectra. Samples Surface Surface lattice Surface Ce4+ / oxygen / absorbed Ce3+

[0309] Operation methods of DACM

[0310] All DACM experiments discussed above were performed based on ramp DACM process (FIG. 74A), which achieves DAC at room temperature and methanation at high temperature (230 °C). Isothermal process (achieve both capture and methanation at high temperature) is generally more favorable in process aspect from its process simplicity and capability for continuous operation, and was previously proposed and achieved by many works for4886-5761-4062.1Page 81 of 164094876-000018WOPTICCM process. For example, Kosaka et al. (Kosaka, F.; Liu, Y.; Chen, S. Y.; Mochizuki, T.; Takagi, H.; Urakawa, A.; Kuramoto, K. Enhanced Activity of Integrated CO2Capture and Reduction to CH4under Pressurized Conditions toward Atmospheric CO2Utilization. ACS Sustain. Chem. Eng. 2021, 9 (9), 3452–3463) reported an isothermal DACM process at 450 °C using Ni / Na-γ-Al2O3as DFMs and obtained 0.1 mmol / g CH4productivity per cycle. Jeong-Potter and Farrauto reported Ru / Na2O-γ-Al2O3can achieve 0.2 mmol / g DAC capacity and 0.15 mmol / g CH4productivity during isothermal DACM at 320 °C. We performed similar isothermal DACM process at 230 °C for Ni0.7Ce0.3Ox(FIG. 74B) and a stable CH4productivity of 0.21 mmol / g is obtained in 5 consecutive cycles (FIG. 82A – FIG. 82B). The much lower CH4productivity per cycle in isothermal DACM is mainly from the lower DAC capacity of Ni0.7Ce0.3Oxat elevated temperature. Slightly enhanced methanation kinetics (sharper CH4peaks) during cycles are observed, likely attributed to additional formation of reduced Ni when expose materials to 10% H2 / Ar at later cycles. In addition, isothermal operation needs much shorter cycle time (30 min for adsorption and 15 min for methanation) than ramp process (3 hours for adsorption, 1.5 hour for ramping bed temperature and methanation), as less steps needed and faster adsorption kinetic at elevated temperature. Although all the process parameters applied here are for bench-scale study without optimization, this generally suggests the shorter cycle time from isothermal operation which is beneficial for higher overall productivity in multi-step chemical processes. However, in terms of large-scale DAC, room-temperature air needs to be blown into reactor at high flow rates and pre-heating large volume air is necessary for isothermal process to keep high reactor temperature, which can be significantly energy intensive and impractical (Lin, Y. (Iris); Abdallah, M. J.; Peters, J. E.; Luo, T.; Sheng, H.; Chen, Y. L.; Farrauto, R. J. Aging Studies of Dual Functional Materials for CO2 Direct Air Capture with in Situ Methanation under Simulated Ambient Conditions: Ru Thrifting for Cost Reduction. Chem. Eng. J.2024, 479, 147495). Besides, though it takes longer adsorption time for ramp DACM process to reach equilibrated CO2loading at room temperature, partial loading of CO2(30 min DAC) can lead to lower fraction of weakly bounded CO2(13%), than that (26%) from equilibrated CO2loading (3 hours DAC) from CO2-TPD profiles. (FIG. 92) This represents CO2preferentially adsorbs on the strong binding sites rather than weaker sites in the early adsorption stage, indicating the possibility of applying non-equilibrium CO2loading during DAC step to shorten the cycle time and enhance overall CH4productivity during long cycles on NiCeOx.4886-5761-4062.1Page 82 of 164094876-000018WOPT

[0311] Table 5 compares DACM performances reported in prior literature and from the work described herein as exemplified by embodiments of the present invention. We notice that existing literature reported ramp DACM majorly in using Ru-based DFMs, likely to reduce the methanation temperature, enhance CO2selectivity toward CH4, as well as the cycle stability as dispersed Ni particles tends to undergo sintering at high temperature. We highlight our NiCeOxcan achieve remarkable DACM performances using cost-effective Ni as the catalytic component with low methanation temperature at 230 °C, while most literature performed hydrogenation over 300 °C. In addition, NiCeOx exhibits among the best CH4productivity (0.8-0.9 mmol CH4 / g DFMs pre cycle) and shows good tolerance towards water during adsorption stage. Performances for isothermal DACM are also compared and both NiCeOxand reported DFMs show restricted CH4productivity as limited CO2adsorbed under high temperature and very dilute CO2feed. Considering the energy requirement for heating the inlet air, isothermal DACM is likely less competitive versus ramp DACM operation at this moment.

[0312] Table 5. Comparison of DACM operating conditions and performances reported in prior literature and this work. DFMs CO2Methanation CO2CH4CO2 Work condition conversion er .; t g. –4886-5761-4062.1Page 83 of 164094876-000018WOPTK2CO3 / Al2O325°C, 400 Pure H2,1.1 1.0898%,Veselovskaya, J. V; (two 100% Lysikov, A. I.; 2 ts ly : on . e ir on . 2 8 o, ) d c s. 04886-5761-4062.1Page 84 of 164094876-000018WOPT1% Ru-10% 25°C, 400 15% H2 / N2,1.03 0.658.3%,Abdallah, M.; Lin, 100% Y. (Iris); Farrauto, N 2 i h l ng n l. .; . r t , e4886-5761-4062.1Page 85 of 164094876-000018WOPT6.1%Na2O / 320°C, 15% H2 / N2,0.21 0.1782%,Jeong-Potter, C.; 100% Farrauto, R. 4 i h l of t 2 at . 6 .; y d CS g. – e .

[0313] Conclusions

[0314] Porous nickel cerium mixed oxides can be applied as a single-component DFMs for DACM process that capture CO2over Ni-O sites to form (bi)carbonates at room temperature and subsequently hydrogenation of carbonates by assistance of metallic Ni under dilute H2stream4886-5761-4062.1Page 86 of 164094876-000018WOPTat high temperature. Ce incorporation remarkably enhances DACM performances in both CH4productivity and cycle stability, attributed to higher DAC capacity, increased CO2binding strength and decreased Ni-O reducibility. Tuning properties of Ni-O sites from Ce loading is originated by increased Ni3+ / Ni2+ratio from electron transfer out of Ni center to Ce. Such feature increases non- stoichiometric oxygen site density and therefore enhances net basicity of Ni-O sites. Ramp DACM performances of NiCeOxshows excellent CH4productivity and stability in 5 consecutive cycles using low methanation temperature at 230 °C, while most previouly reported ICCM process using higher methanation temperature over 300 °C even in the assistance of precious metal. The low methanation temperature is mainly attributed by moderate CO2binding strength, as well as the proximity between adsorption and hydrogenation sites, which the latter can enhance the reactively desorption pathway, existing in our systems evidenced by significantly enhanced removal of carbonates in the presence of H2. This work reports a first-of-this-kind, single-component DFM for application of DACM composed of affordable transition metal oxides, sheding light on advanced design strategy of high-performance and cost-effective DFMs.

[0315] Table 6 Textural properties of pure NiO, CeO2and NiCeOxtested in our study, and their CO2 adsorption capacities in the absence and presence of humidity. Adsorption conditions: 25 °C, 400 ppm CO2, 2.1 kPa H2O (67% RH) / balance N2. Pre-treatment conditions: 350 °C, 2 hour Ar purge. Sample BET Pore Dry Humid CH4ty ab4886-5 6 - 06 .Page 87 of 16409 8 6-0000 8 O TCeO2118 0.16 0.1 0.15 / atw.bsecond number shown here represents the 3rdcycle data.

[0316] Chapter 4

[0317] Moisture-Driven Desorption of CO2Over Metal-Oxygen Interfaces For Room-Temperature Direct Air Capture

[0318] Introduction

[0319] Moisture swing adsorption (MSA) receives increasing attentions from its capability for achieving unique non-energy driven sorption cycles, which can significantly reduce energy consumption compared with traditional temperature swing adsorption. MSA process aims for capturing dry CO2at room temperature and releasing CO2under humid environment. MSA for DAC was firstly proposed and developed by Lackner’s group in 2009, applying ion-exchanged resins with quaternary ammonium ions as solid adsorbents, which anions act as strong base, bearing hydroxide sites as counter ions for strong binding of CO2from dilute concentration (Shi, X.; Xiao, H.; Azarabadi, H.; Song, J.; Wu, X.; Chen, X.; Lackner, K. S. Sorbents for the Direct Capture of CO2 from Ambient Air. Angewandte Chemie - International Edition 2019, 2–25). This class of materials is researched and widely reported as only effective adsorbents responsive to moisture swing CO2sorption cycles.

[0320] Reaction mechanisms of moisture swing for DAC have been proposed. In brief, the driving force of CO2sorption cycle is based on CO2affinity change at different hydration levels originated from carbonates / bicarbonates equilibrium shift. This phenomenon was demonstrated theoretically and experimentally by Shi et al. (Shi, X.; Xiao, H.; Kanamori, K.; Yonezu, A.; Lackner, K. S.; Chen, X. Moisture-Driven CO2 Sorbents. Joule 2020, 4 (8), 1823–183; Shi, X.; Xiao, H.; Chen, X.; Lackner, K. S. The Effect of Moisture on the Hydrolysis of Basic Salts. Chemistry - A European Journal 2016, 22 (51), 18326–18330; Shi, X.; Xiao, H.; Lackner, K. S.; Chen, X. Capture CO2 from Ambient Air Using Nanoconfined Ion Hydration. Angewandte Chemie International Edition 2016, 55 (12), 4026–4029) , reporting that the reduced availability4886-5761-4062.1Page 88 of 164094876-000018WOPTof water molecules promotes the hydrolysis of CO32-, producing lower valent ions in protonated form (HCO3-) and OH- ions. The additional forming hydroxide ion is capable to bind additional CO2for generating moisture swing capacity. Such benchmark CO32--IER sorbents provide 0.2-0.4 mmol / g working capacity based on prior reports from closed-loop setup. Though the non-energy driven sorption cycles from MSA are very attractive from operation standpoint, the relatively poor DAC performances represent the urgent needs of MSA sorbent material developments.

[0321] There are recently growing research interests in developing advanced MSA sorbents based on CO32--IER sorbents. The use of other active anion pairs rather than traditional CO32- / HCO3-is a research direction (Song, J.; Zhu, L.; Shi, X.; Liu, Y.; Xiao, H.; Chen, X. Moisture Swing Ion-Exchange Resin-PO4 Sorbent for Reversible CO2 Capture from Ambient Air. Energy and Fuels 2019, 33 (7), 6562–6567). Shi et al. reported a modelling study to represent MSA behavior may be generally applicable for other divalent / trivalent anion pairs, but not monovalent ion pairs (Shi, X.; Xiao, H.; Chen, X.; Lackner, K. S. The Effect of Moisture on the Hydrolysis of Basic Salts. Chemistry - A European Journal 2016, 22 (51), 18326–183300). This prediction was recently experimentally explored by Hegarty et al., suggesting the use of new anion pairs and their different thermodynamic and kinetics behavior in affecting DAC performances (Hegarty, J.; Shindel, B.; Sukhareva, D.; Barsoum, M. L.; Farha, O. K.; Dravid, V. Expanding the Library of Ions for Moisture-Swing Carbon Capture. Environ Sci Technol 2023, 57 (50), 21080– 21091). Zhu et al. reported a similar study and highlighted the basicity of anions is highly correlated with CO2swing capacity, as well as remarkable effect of water confinement with pore characteristics (Zhu, Y.; Booth, A.; Hatzell, K. B. Confinement Effects on Moisture-Swing Direct Air Capture. Environ Sci Technol Lett 2024, 11 (2), 89–94). The broader anion libraries further expand the applicability of MSA for DAC process. Besides different anion pairs, MSA sorbents are also optimized from ammonium cation part. For example, reported by Wang et al., traditional single quaternary ammonium cation can be switched to diamine-based double quaternary ammonium cation, which can result in doubling the density of hydroxide sites leading improvement of DAC swing capacity (3.41 mmol / g) (Wang, X.; Chen, Y.; Xu, W.; Lindbråthen, A.; Cheng, X.; Chen, X.; Zhu, L.; Deng, L. Development of High Capacity Moisture-Swing DAC Sorbent for Direct Air Capture of CO2. Sep Purif Technol 2023, 324 (June), 124489). Other carrier materials rather than ion-exchanged resins are also developed for loading the hydroxide sites. Song et al. used a low-cost quaternized chitosan / poly(vinyl alcohol) hybrid aerogels with quaternary4886-5761-4062.1Page 89 of 164094876-000018WOPTammonium groups and hydroxide ions as MSA sorbents, with 0.18 mmol / g DAC working capacity reported (Song, J.; Liu, J.; Zhao, W.; Chen, Y.; Xiao, H.; Shi, X.; Liu, Y.; Chen, X. Quaternized Chitosan / PVA Aerogels for Reversible CO2 Capture from Ambient Air. Ind Eng Chem Res 2018, 57 (14), 4941–4948). Hou et al. reported the use of alternative low-cost support, quaternized bamboo cellulose can provide MSA working capacity of 0.18 mmol / g. Nicotera et al. recently reported the significant working capacity enhancement from use of highly porous quaternized graphene., reporting 2.3 mmol / g DAC capacity based on a TGA apparatus, which is the highest MSA working capacity up to date, along with a 7.5% capacity loss after 50 cycles. To conclude, most MSA sorbents developed based on IERs are still at 0.1-0.5 mmol / g DAC capacity, despite few exceptions using advanced material designs and different testing apparatus for evaluations. Future studies will be needed to evaluate the feasibility and reproducibility of these high-capacity sorbents.

[0322] The current development of MSA sorbents is highly based on the benchmark CO32--IER sorbents. In the work described herein, we report the first example of using metal-oxygen interfaces for moisture swing response in DAC applications. As we reported herein, porous nickel- based (hydr)oxides are new classes of DAC sorbents and applicable for traditional TSA cycles. In- situ FTIR spectroscopy represents the formation of carbonates / bicarbonates is the main products for CO2binding from DAC. The analogous product species with IER system motivates the potential of MSA for porous metal (hydr)oxides for DAC applications. This feasibility study not only expands the universality of porous metal hydroxides for DAC applications, but also provides new insights in developing advanced MSA sorbents.

[0323] Results and Discussion

[0324] Proposed operations and mechanisms for MSA over for nickel-based oxygen nucleophiles

[0325] We discussed herein that porous nickel hydroxides exhibit limited CO2capacity from dry 400 ppm CO2stream adsorption, however, surface hydration can remarkably enhance CO2affinity to hydroxide sites leading over 10-fold DAC capacity enhancement using humid CO2stream. The facilitative role of water for CO2adsorption on Ni-OH surface is unique, while from typical IER system, surface adsorbed water only plays a role during desorption step, resulting in hydrolysis of CO32-to produce HCO3- and OH-. The very low CO2equilibrium capacity at dry conditions over nickel hydroxides illustrates the initial CO2loading on completely dry sorbents,4886-5761-4062.1Page 90 of 164094876-000018WOPTwhich is typically the initial state for IER system, is not applicable on metal-oxygen interfaces. Without being bound by theory, the proposed operation and hypothesized mechanism for MSA over nickel hydroxides is presented in FIG. 99. First, we applied a pre-humidification step to hydrate the Ni(OH)2, enabling the subsequent effective dry CO2adsorption over wetted Ni(OH)2due to the presence of surface water. During dry CO2adsorption, surface water starts to desorb, and the significant reduction of water molecules around hydroxide sites would facilitate the hydrolysis of initially formed carbonates, which the main surface species under humid CO2condition on Ni(OH)2 as we reported herein (FIG.57A – FIG.57C), resulting in a CO2-saturated phase with bicarbonates as the dominated species and limited amount of surface water at the end of the step. It is followed by a humid Ar purge step for re-humidification of the sorbents, leading the conversion of surface bicarbonates to carbonates along with CO2release from surface. The partially CO2-loaded, humidified Ni(OH)2is capable for next cycle dry CO2adsorption.

[0326] Ni(OH)2-T, synthesized by template-assisted precipitation methods, is applied for the initial attempt of MSA-DAC capabilities. As reported herein, Ni(OH)2-T has porous structure with 240 m2 / g BET surface area, and equilibrium humid DAC capacity of 0.31 mmol / g. Using this operation method, dry DAC equilibrium capacity on a pre-humidified sample is lower (0.19 mmol / g). Desorption gas profiles from Ar purge is shown in FIG. 100A – FIG. 100B. Unlike widely reported MSA procedure which CO2concentration remains unchanged, a combination of pressure and moisture swing is applied in our experiments, which uses humid Ar as desorption purge stream. To evaluate the effect of water in the desorption step, Ar purge with / without water over CO2-saturated surface was applied and the CO2desorbed amount is monitored, which the difference between measured CO2profiles and blank response is used for integration to obtain CO2desorbed amount from the surface. A pure pressure swing (dry Ar purge) leads a small portion of CO2gradually desorbed (0.05 mmol / g), while water-co feed Ar purge exhibits much faster desorption kinetics in the initial stage, with the maximum CO2outlet concentration is higher than adsorption CO2stream (400 ppm). This represents the promoting role of water adsorption over CO2-saturated surface for CO2desorption, consistent with proposed mechanism of conversion from bicarbonates to carbonates resulting in release of CO2due to the stoichiometry change of surface species. The corresponding desorption capacity is represented in FIG. 100B. While pressure swing only leads 26% CO2desorbed from the surface within 2 hours, moisture swing4886-5761-4062.1Page 91 of 164094876-000018WOPTdesorbs additional 53% CO2which is close to the theoretical maximum moisture swing capacity of 50% from the change of stoichiometry from HCO3- to CO32-.

[0327] Effect of CO2binding strength on Moisture Swing Capability

[0328] Although Ni(OH)2-T demonstrates the majority of surface CO2from DAC can be effectively desorbed by MSA (moisture swing capacity / equilibrium DAC capacity ratio=0.79, FIG.100B), the relatively lower working capacity (0.15 mmol / g) limits its practical use. Based on the material design strategies described herein, a higher DAC capacity can be obtained over Ni- based oxygen interfaces by enhancing CO2binding strength via either Ce doping or use of Ni-O lattice rather than Ni-OH. We assess the MSA feasibility of NiO derived from Ni(OH)2-T, and NiCe0.3(OH)x-T. About 2-fold enhancement of equilibrium DAC capacity from NiCe0.3(OH)x-T and NiO originated from enhanced CO2binding strength (metal-oxygen nucleophilicity) as we extensively described herein (FIG.54). However, higher equilibrium DAC capacities does not lead same extent enhancement of desorption capacity of CO2from humid Ar purge (66% RH). NiO demonstrates slightly higher CO2desorption capacity (0.18 mmol / g). More surprisingly, NiCe0.3(OH)x-T exhibits even lower desorption capacity (0.12 mmol / g) than that from Ni(OH)2-T (0.15 mmol / g). This is likely from insufficient driving force from hydrolysis for interrupting strong chemical binding of CO2on NiCe-OH interfaces. We note that the strategy for enhance equilibrium DAC capacity by increasing CO2affinity of oxygen nucleophiles can have the trade-off effect restricting the extent of CO2desorption from MSA.

[0329] Enhanced Moisture Swing Adsorption from Highly Porous Ni(OH)2

[0330] Expanding porosity of nickel hydroxides is considered as another strategy to enhance DAC capacity from our work as described herein. Carbonate-assisted co-precipitation method with AMOST can more efficiently create highly porous Ni(OH)2, along with much higher humid DAC capacity. To assess if this strategy can enhance MSA working capacity, multiple MSA cycles were performed over Ni(OH)2and corresponding adsorption capacities from each cycle are shown in FIG. 102A – FIG. 102B. First cycle captures 0.79 mmol / g on initial pre-humidified empty sorbents representing the equilibrium CO2loadings. The subsequent 2-6 cycles show relatively stable CO2capacities within range of 0.34-0.45 mmol / g, demonstrating a significant higher MSA working capacity than Ni(OH)2-T due to its higher equilibrium DAC capacity and no significant decrease of desorption extent. We note that there are likely sorption kinetic limitations existing in the process. Extended humid Ar purge time at 7th cycle (17 hours) increases adsorption4886-5761-4062.1Page 92 of 164094876-000018WOPTcapacity to 0.52 mmol / g, representing the 2-hour desorption does not completely regenerate the sorbent to equilibrium state. The limited kinetic is present during adsorption step as well, indicated by adsorption breakthrough curves (FIG. 103) showing C / C0at 0.9-0.95 at the end of 1-hour adsorption. The relatively poor adsorption kinetics can limit the sorbent performances and its practical use, which may be due to dense surface adsorbed water layers, as suggested by slower adsorption kinetics from higher humidity level, which higher water vapor pressure can significantly increase surface water loadings on Ni(OH)2(FIG.57A – FIG.57C ). Further studies focused on mechanisms of kinetics limitation and strategies for enhancements are necessary.

[0331] The major role of water in the MSA cycles over Ni-OH sites is from two aspects.First, sorbents are required to be sufficiently hydrated before CO2adsorption to enhance CO2binding (FIG.57C), which hydration extent is highly correlated with humidity level (FIG.102B). Second, water plays the key role in altering surface (bi)carbonates equilibrium for facilitatingCO2desorption, which the adsorbed water amount affectedby humidity level may determine theextent of MSA. To evaluate the effect of humidity level on MSA cycle performances, Ar desorption streams with multiple moisture content are applied in multi-cycle runs and the corresponding average DAC working capacity is shown in FIG.102B. The absence of water leadsminimal working capacityis expected as very limited CO2binding capability over Ni-OH surfacereported before (FIG. 57A). Low RH value at 25% performs relatively low DAC working capacity (0.18 mmol / g), likely due to its lower equilibrium CO2loading caused by insufficient pre-humidification at 25% RH. The desorption step is likely not strongly affected by the low humidity as considerable swing extent of 0.75 obtained at this condition (equilibrium CO2capacity is 0.24 mmol / g). The higher humidity 66% and 93% RH remarkably enhances MSA working capacity to 0.37 mmol / g. The considerable MSA working capacities obtained from multiple cycles are comparable with reports from traditional IER sorbents, suggesting nickel hydroxides as a feasible MSA sorbent candidate.

[0332] Conclusions

[0333] Porous nickel hydr(oxides) of the present invention as described herein are newDAC sorbentplatforms applicable for multiple TSA sorption cycles. In the work of the presentinvention described herein, porous Ni(OH)2isevaluated for its MSA feasibility for DACapplications. Our material is able to perform considerable MSA working capacities at room4886-5761-4062.1Page 93 of 164094876-000018WOPTtemperature by switching between dry CO2and humid Ar stream. CO2binding strength on oxygen nucleophiles are strongly correlated with MSA swing capability, which stronger CO2binding strength alleviates the efficiency of desorption from moisture introduction. Ni(OH)2with higher porosity, synthesized by AMOST methods, can remarkably enhance MSA capacity. Moisture content in desorption stream have multiple effects; for adsorption stage, low humidity leads lower surface hydration level would result in less CO2adsorbed on surfaces in following adsorption step, however, high humidity causes dense surface water layer inhibiting CO2adsorption kinetics. We highlight that this is the first example of metal-oxygen nucleophiles responsive to moisture swing of CO2, providing further insights for advanced MSA sorbent design and mechanistic hints for moisture swing behaviors.

[0334] Various Non-Limiting Embodiments of the Invention

[0335] Embodiments include those listed below.

[0336] Embodiment 1. A solid sorbent for direct air capture of carbon dioxide, the solid sorbent comprising: at least one transition metal hydroxide.

[0337] Embodiment 2. The solid sorbent of embodiment 1, wherein the at least one transition metal hydroxide comprises at least one transition metal selected from the group consisting of nickel (Ni), cerium (Ce), iron (Fe), and any combination thereof.

[0338] Embodiment 3. The solid sorbent of embodiment 1 or embodiment 2, wherein the at least one transition metal hydroxide is porous, non-porous, or combination thereof.

[0339] Embodiment 4. The solid sorbent of any one of embodiments 1-3, wherein the at least one transition metal hydroxide is porous.

[0340] Embodiment 5. The solid sorbent of any one of embodiments 1-4, wherein the at least one transition metal hydroxide comprises at least one polymorph.

[0341] Embodiment 6. The solid sorbent of any one of embodiments 1-5, wherein the at least one transition metal hydroxide is selected from Ni(OH)2.

[0342] Embodiment 7. The solid sorbent of any one of embodiments 1-6, wherein the at least one transition metal hydroxide is α-Ni(OH)2, β-Ni(OH)2, or combination thereof.

[0343] Embodiment 8. The solid sorbent of any one of embodiments 1-7, further comprising at least one dopant.

[0344] Embodiment 9. The solid sorbent of embodiment 8, wherein the at least one dopant comprises cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo),4886-5761-4062.1Page 94 of 164094876-000018WOPTmanganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), vanadium (V), or any combination thereof.

[0345] Embodiment 10. The solid sorbent of embodiment 8, wherein the at least one dopant comprises cerium (Ce), iron (Fe), or combination thereof.

[0346] Embodiment 11. The solid sorbent of embodiment 8, wherein the at least one dopant is a cationic dopant.

[0347] Embodiment 12. The solid sorbent of embodiment 11, wherein the cationic dopant is selected from Ce3+, Fe3+, or combination thereof.

[0348] Embodiment 13. The solid sorbent of any one of embodiments 8-12, wherein the solid sorbent is a layered double hydroxide (LDH).

[0349] Embodiment 14. The solid sorbent of embodiments 1-4, wherein the at least one transition metal hydroxide is an anion-exchanged transition metal hydroxide.

[0350] Embodiment 15. The solid sorbent of embodiment 14, wherein the anion- exchanged transition metal hydroxide is α-Ni(OH)2-SO42-.

[0351] Embodiment 16. The solid sorbent of any one of embodiments 1-5, wherein the at least one transition metal hydroxide is at least one mixed transition metal hydroxide.

[0352] Embodiment 17. The solid sorbent of embodiment 16, wherein the at least one mixed transition metal hydroxide comprises at least two transition metals selected from the group consisting of nickel (Ni), cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo), manganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), vanadium (V), and any combination thereof.

[0353] Embodiment 18. The solid sorbent of embodiment 16, wherein the at least one mixed transition metal hydroxide comprises at least two transition metals selected from the group consisting of nickel (Ni), cerium (Ce), iron (Fe), and any combinations thereof.

[0354] Embodiment 19. The solid sorbent of any one of embodiments 1-18, wherein the solid sorbent is a solid adsorbent.

[0355] Embodiment 20. The solid sorbent of any one of embodiments 1-18, wherein the solid sorbent is a solid chemisorbent.

[0356] Embodiment 21. The solid sorbent of any one of embodiments 1-20, further comprising water or water vapor.4886-5761-4062.1Page 95 of 164094876-000018WOPT

[0357] Embodiment 22. A direct air capture (DAC) system for capture, removal, separation, and / or adsorption of carbon dioxide (CO2) from ambient air comprising: a reaction chamber, wherein the reaction chamber comprises an air intake opening, an air exhaust opening; and the solid sorbent of any one of embodiments 1-21 positioned in the reaction chamber.

[0358] Embodiment 23. The system of embodiment 22, further comprising a substrate material positioned in the reaction chamber, wherein the substrate material structurally supports the solid sorbent.

[0359] Embodiment 24. The system of embodiment 23, wherein the solid sorbent is impregnated in the substrate material.

[0360] Embodiment 25. The system of embodiment 23, wherein the solid sorbent is dispersed in the substrate material.

[0361] Embodiment 26. The system of embodiment 23, wherein the solid sorbent is deposited on the substrate material.

[0362] Embodiment 27. The system of embodiment 23, wherein the solid sorbent is coated on the substrate material.

[0363] Embodiment 28. The system of any one of embodiments 23-27, wherein the substate material comprises ceramic, metal, organic material, inorganic material, or any combination thereof.

[0364] Embodiment 29. The system of any one of embodiments 23-28, wherein the substrate material comprises cordierite, alumina, silica / alumina, silicon carbide (SiC), titania, silica, magnesia, zirconia, carbon, or any combination thereof.

[0365] Embodiment 30. The system of any one of embodiments 23-29, wherein the substrate material is in monolithic form.

[0366] Embodiment 31. The system of any one of embodiments 22-30, further comprising a mechanism, device, or equipment for introducing water or water vapor into the reaction chamber.

[0367] Embodiment 32. The system of any one of embodiments 22-31, further comprising a mechanism, device, or equipment for contacting the solid sorbent with water or water vapor.

[0368] Embodiment 33. The system of any one of embodiments 22-32, further comprising a mechanism, device, or equipment for heating the reaction chamber.4886-5761-4062.1Page 96 of 164094876-000018WOPT

[0369] Embodiment 34. The system of any one of embodiments 22-33, further comprising a mechanism, device, or equipment for heating the solid sorbent.

[0370] Embodiment 35. The system of any one of embodiments 22-34, further comprising a mechanism, device, or equipment for cooling the reaction chamber.

[0371] Embodiment 36. The system of any one of embodiments 22-35, further comprising a mechanism, device, or equipment for cooling the solid sorbent

[0372] Embodiment 37. The system of any one of embodiments 22-36, further comprising an air movement mechanism, device, or equipment positioned to move ambient air through the reaction chamber utilizing the air intake opening and air exhaust opening.

[0373] Embodiment 38. The system of any one of embodiments 22-37, further comprising an air movement mechanism, device, or equipment configured to contact ambient air with the solid sorbent positioned in the reaction chamber.

[0374] Embodiment 39. The system of any one of embodiments 22-38, further comprising a mechanism, device, or equipment for desorbing or removing the adsorbed carbon dioxide from the solid sorbent.

[0375] Embodiment 40. The system of embodiment 39, wherein the mechanism, device, or equipment comprises a compressor, vacuum pump, or combination thereof.

[0376] Embodiment 41. The system of any one of embodiments 22-40, further comprising a mechanism, device, or equipment for reducing the pressure in the reaction chamber.

[0377] Embodiment 42. The system of any one of embodiments 22-41, further comprising a mechanism, device, or equipment for increasing the pressure in the reaction chamber.

[0378] Embodiment 43. The system of any one of embodiments 22-42, further comprising a mechanism, device, or equipment for performing pressure swing adsorption, vacuum swing adsorption, temperature swing adsorption, moisture swing adsorption, or any combination thereof.

[0379] Embodiment 44. A direct air capture (DAC) method for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from ambient air, comprising: providing a solid sorbent of any one of embodiments 1-21; and contacting the solid sorbent with ambient air.4886-5761-4062.1Page 97 of 164094876-000018WOPT

[0380] Embodiment 45. The method of embodiment 44, further comprising capturing and / or removing, and / or separating, and / or adsorbing carbon dioxide from the ambient air.

[0381] Embodiment 46. The method of embodiment 44 or embodiment 45, further comprising contacting the solid sorbent with water or water vapor before contacting the solid sorbent with ambient air.

[0382] Embodiment 47. The method of any one of embodiments 44-46, wherein the ambient air comprises water or water vapor.

[0383] Embodiment 48. The method of any one of embodiments 44-47, wherein the ambient air has a relative humidity of greater than 10%.

[0384] Embodiment 49. The method of any one of embodiments 44-47, wherein the ambient air has a relative humidity of greater than 50%.

[0385] Embodiment 50. The method of any one of embodiments 44-47, wherein the ambient air has a relative humidity of greater than 70%.

[0386] Embodiment 51. The method of any one of embodiments 44-47, wherein the ambient air has a relative humidity of 100% or less.

[0387] Embodiment 52. The method of any one of embodiments 44-47, wherein the ambient air is contacted with the solid sorbent at ambient temperature, ambient humidity, or ambient pressure, or any combination thereof.

[0388] Embodiment 53. The method of any one of embodiments 44-52, further comprising adsorbing carbon dioxide from the ambient air onto the solid sorbent.

[0389] Embodiment 54. The method of any one of embodiments 44-53, further comprising desorbing or removing the carbon dioxide from the solid sorbent.

[0390] Embodiment 55. The method of embodiment 54, wherein desorbing or removing the carbon dioxide from the solid sorbent comprises adjusting or changing pressure applied to the solid sorbent, adjusting or changing temperature of the solid sorbent, adjusting or changing vacuum applied to the solid sorbent, adjusting or changing moisture level of the solid sorbent, or any combination thereof.

[0391] Embodiment 56. A material assembly for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from ambient air, comprising: a substrate; and a solid sorbent of any one of embodiments 1-21.4886-5761-4062.1Page 98 of 164094876-000018WOPT

[0392] Embodiment 57. The material assembly of embodiment 56, wherein the substrate structurally supports the solid sorbent.

[0393] Embodiment 58. The material assembly of embodiment 56 or embodiment 57, wherein the solid sorbent is impregnated in the substrate,

[0394] Embodiment 59. The material assembly of embodiment 56 or embodiment 57, wherein the solid sorbent is dispersed in the substrate,

[0395] Embodiment 60. The material assembly of embodiment 56 or embodiment 57, wherein the solid sorbent is deposited on the substrate,

[0396] Embodiment 61. The material assembly of embodiment 56 or embodiment 57, wherein the solid sorbent is coated on the substrate.

[0397] Embodiment 62. The material assembly of any one of embodiments 56-61, wherein the substate comprises ceramic, metal, organic material, inorganic material, or any combination thereof.

[0398] Embodiment 63. The material assembly of any one of embodiments 56-62, wherein the substrate comprises cordierite, alumina, silica / alumina, silicon carbide (SiC), titania, silica, magnesia, zirconia, carbon, or any combination thereof.

[0399] Embodiment 64. The material assembly of any one of embodiments 56-63, wherein the substrate is in monolithic form.

[0400] Embodiment 65. A solid sorbent for direct air capture of carbon dioxide, the solid sorbent comprising: at least one transition metal oxide.

[0401] Embodiment 66. The solid sorbent of embodiment 65, wherein the at least one transition metal oxide comprises at least one transition metal selected from the group consisting of nickel (Ni), cerium (Ce), iron (Fe), and any combination thereof.

[0402] Embodiment 67. The solid sorbent of embodiment 65 or embodiment 66, wherein the at least one transition metal oxide is porous, non-porous, or combination thereof.

[0403] Embodiment 68. The solid sorbent of any one of embodiments 65-67, wherein the at least one transition metal oxide is porous.

[0404] Embodiment 69. The solid sorbent of any one of embodiments 65-68, wherein the at least one transition metal oxide comprises at least one polymorph.

[0405] Embodiment 70. The solid sorbent of any one of embodiments 65-69, wherein the at least one transition metal oxide is selected from NiO, CeO2, or combination thereof.4886-5761-4062.1Page 99 of 164094876-000018WOPT

[0406] Embodiment 71. The solid sorbent of any one of embodiments 65-70, further comprising at least one dopant.

[0407] Embodiment 72. The solid sorbent of embodiment 71, wherein the at least one dopant comprises cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo), manganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), vanadium (V), or any combination thereof.

[0408] Embodiment 73. The solid sorbent of embodiment 71, wherein the at least one dopant comprises cerium (Ce), iron (Fe), or combination thereof.

[0409] Embodiment 74. The solid sorbent of embodiment 71, wherein the at least one dopant is a cationic dopant.

[0410] Embodiment 75. The solid sorbent of embodiment 74, wherein the cationic dopant is selected from Ce3+, Fe3+, or combination thereof.

[0411] Embodiment 76. The solid sorbent of any one of embodiments 65-69, wherein the at least one transition metal oxide is at least one mixed transition metal oxide.

[0412] Embodiment 77. The solid sorbent of embodiment 76, wherein the at least one mixed transition metal oxide comprises at least two transition metals selected from the group consisting of nickel (Ni), cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo), manganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), vanadium (V), and any combination thereof.

[0413] Embodiment 78. The solid sorbent of embodiment 76, wherein the at least one mixed transition metal oxide comprises at least two transition metals selected from the group consisting of nickel (Ni), cerium (Ce), iron (Fe), and any combinations thereof.

[0414] Embodiment 79. The solid sorbent of embodiment 76, wherein the at least one mixed transition metal oxide is selected from Ce4.4NiO, Ce10NiO, Ce20NiO, and combinations thereof.

[0415] Embodiment 80. The solid sorbent of any one of embodiments 65-79, wherein the solid sorbent is a solid adsorbent.

[0416] Embodiment 81. The solid sorbent of any one of embodiments 65-79, wherein the solid sorbent is a solid chemisorbent.

[0417] Embodiment 82. The solid sorbent of any one of embodiments 65-81, further comprising water or water vapor.4886-5761-4062.1Page 100 of 164094876-000018WOPT

[0418] Embodiment 83. A direct air capture (DAC) system for capture, removal, separation and / or adsorption of carbon dioxide (CO2) from ambient air comprising:

[0419] a reaction chamber, wherein the reaction chamber comprises an air intake opening, an air exhaust opening; and

[0420] the solid sorbent of any one of embodiments 65-82 positioned in the reaction chamber.

[0421] Embodiment 84. The system of embodiment 83, further comprising a substrate material positioned in the reaction chamber, wherein the substrate material structurally supports the solid sorbent.

[0422] Embodiment 85. The system of embodiment 84, wherein the solid sorbent is impregnated in the substrate material.

[0423] Embodiment 86. The system of embodiment 84, wherein the solid sorbent is dispersed in the substrate material.

[0424] Embodiment 87. The system of embodiment 84, wherein the solid sorbent is deposited on the substrate material.

[0425] Embodiment 88. The system of embodiment 84, wherein the solid sorbent is coated on the substrate material.

[0426] Embodiment 89. The system of any one of embodiments 84-88, wherein the substate material comprises ceramic, metal, organic material, inorganic material, or any combination thereof.

[0427] Embodiment 90. The system of any one of embodiments 84-89, wherein the substrate material comprises cordierite, alumina, silica / alumina, silicon carbide (SiC), titania, silica, magnesia, zirconia, carbon, or any combination thereof.

[0428] Embodiment 91. The system of any one of embodiments 84-90, wherein the substrate material is in monolithic form.

[0429] Embodiment 92. The system of any one of embodiments 83-91, further comprising a mechanism, device, or equipment for introducing water or water vapor into the reaction chamber.

[0430] Embodiment 93. The system of any one of embodiments 83-92, further comprising a mechanism, device, or equipment for contacting the solid sorbent with water or water vapor.4886-5761-4062.1Page 101 of 164094876-000018WOPT

[0431] Embodiment 94. The system of any one of embodiments 83-93, further comprising a mechanism, device, or equipment for heating the reaction chamber.

[0432] Embodiment 95. The system of any one of embodiments 83-94, further comprising a mechanism, device, or equipment for heating the solid sorbent.

[0433] Embodiment 96. The system of any one of embodiments 83-95, further comprising a mechanism, device, or equipment for cooling the reaction chamber.

[0434] Embodiment 97. The system of any one of embodiments 83-96, further comprising a mechanism, device, or equipment for cooling the solid sorbent

[0435] Embodiment 98. The system of any one of embodiments 83-97, further comprising an air movement mechanism, device, or equipment positioned to move ambient air through the reaction chamber utilizing the air intake opening and air exhaust opening.

[0436] Embodiment 99. The system of any one of embodiments 83-98, further comprising an air movement mechanism, device, or equipment configured to contact ambient air with the solid sorbent positioned in the reaction chamber.

[0437] Embodiment 100. The system of any one of embodiments 83-99, further comprising a mechanism, device, or equipment for desorbing or removing the adsorbed carbon dioxide from the solid sorbent.

[0438] Embodiment 101. The system of embodiment 100, wherein the mechanism, device, or equipment comprises a compressor, vacuum pump, or combination thereof.

[0439] Embodiment 102. The system of any one of embodiments 83-101, further comprising a mechanism, device, or equipment for reducing the pressure in the reaction chamber.

[0440] Embodiment 103. The system of any one of embodiments 83-102, further comprising a mechanism, device, or equipment for increasing the pressure in the reaction chamber.

[0441] Embodiment 104. The system of any one of embodiments 83-103, further comprising a mechanism, device, or equipment for performing pressure swing adsorption, vacuum swing adsorption, temperature swing adsorption, moisture swing adsorption, or any combination thereof.

[0442] Embodiment 105. A direct air capture (DAC) method for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from ambient air, comprising: providing a4886-5761-4062.1Page 102 of 164094876-000018WOPTsolid sorbent of any one of embodiments 65-82; and contacting the solid sorbent with ambient air.

[0443] Embodiment 106. The method of embodiment 105, further comprising capturing and / or removing and / or separating and / or adsorbing carbon dioxide from the ambient air.

[0444] Embodiment 107. The method of embodiment 105 or embodiment 106, further comprising contacting the solid sorbent with water or water vapor before contacting the solid sorbent with ambient air.

[0445] Embodiment 108. The method of any one of embodiments 105-107, wherein the ambient air comprises water or water vapor.

[0446] Embodiment 109. The method of any one of embodiments 105-108, wherein the ambient air has a relative humidity of greater than 10%.

[0447] Embodiment 110. The method of any one of embodiments 105-108, wherein the ambient air has a relative humidity of greater than 50%.

[0448] Embodiment 111. The method of any one of embodiments 105-108, wherein the ambient air has a relative humidity of greater than 70%.

[0449] Embodiment 112. The method of any one of embodiments 105-108, wherein the ambient air has a relative humidity of 100% or less.

[0450] Embodiment 113. The method of any one of embodiments 105-108, wherein the ambient air is contacted with the solid sorbent at ambient temperature, ambient humidity, or ambient pressure, or any combination thereof.

[0451] Embodiment 114. The method of any one of embodiments 105-113, further comprising adsorbing carbon dioxide from the ambient air onto the solid sorbent.

[0452] Embodiment 115. The method of any one of embodiments 105-113, further comprising desorbing or removing the carbon dioxide from the solid sorbent.

[0453] Embodiment 116. The method of embodiment 115, wherein desorbing or removing the carbon dioxide from the solid sorbent comprises adjusting or changing pressure applied to the solid sorbent, adjusting or changing temperature of the solid sorbent, adjusting or changing vacuum applied to the solid sorbent, adjusting or changing moisture level of the solid sorbent, or any combination thereof.4886-5761-4062.1Page 103 of 164094876-000018WOPT

[0454] Embodiment 117. A material assembly for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from ambient air, comprising: a substrate; and a solid sorbent of any one of embodiments 65-82.

[0455] Embodiment 118. The material assembly of embodiment 117, wherein the substrate structurally supports the solid sorbent.

[0456] Embodiment 119. The material assembly of embodiment 117 or embodiment 118, wherein the solid sorbent is impregnated in the substrate,

[0457] Embodiment 120. The material assembly of embodiment 117 or embodiment 118, wherein the solid sorbent is dispersed in the substrate,

[0458] Embodiment 121. The material assembly of embodiment 117 or embodiment 118, wherein the solid sorbent is deposited on the substrate,

[0459] Embodiment 122. The material assembly of embodiment 117 or embodiment 118, wherein the solid sorbent is coated on the substrate.

[0460] Embodiment 123. The material assembly of any one of embodiments 117-122, wherein the substate comprises ceramic, metal, organic material, inorganic material, or any combination thereof.

[0461] Embodiment 124. The material assembly of any one of embodiments 117-123, wherein the substrate comprises cordierite, alumina, silica / alumina, silicon carbide (SiC), titania, silica, magnesia, zirconia, carbon, or any combination thereof.

[0462] Embodiment 125. The material assembly of any one of embodiments 117-124, wherein the substrate is in monolithic form.

[0463] Embodiment 126. The system of any one of embodiments 83-104, further comprising a mechanism, device, or equipment for contacting hydrogen with the solid sorbent.

[0464] Embodiment 127. The system of any one of embodiments 83-104, further comprising a mechanism, device, or equipment for adding hydrogen to the reaction chamber.

[0465] Embodiment 128. The method of any one of embodiments 105-116, where in the method further comprises one or more methanation processes.

[0466] Embodiment 129. The method of any one of embodiments 105-116, further comprising contacting the captured, removed, adsorbed, and / or separated carbon dioxide with hydrogen under conditions effective to produce methane.4886-5761-4062.1Page 104 of 164094876-000018WOPT

[0467] Embodiment 130. The method of any one of embodiments 105-116, further comprising contacting the solid sorbent with hydrogen under conditions effective to produce methane.

[0468] Embodiment 131. The system of any one of embodiments 22-43, further comprising a mechanism, device, or equipment for contacting hydrogen with the solid sorbent.

[0469] Embodiment 132. The system of any one of embodiments 22-43, further comprising a mechanism, device, or equipment for adding hydrogen to the reaction chamber.

[0470] Embodiment 133. The method of any one of embodiments 44-55, where in the method further comprises one or more methanation processes.

[0471] Embodiment 134. The method of any one of embodiments 44-55, further comprising contacting the captured, removed, adsorbed, and / or separated carbon dioxide with hydrogen under conditions effective to produce methane.

[0472] Embodiment 135. The method of any one of embodiments 44-55, further comprising contacting the solid sorbent with hydrogen under conditions effective to produce methane.

[0473] Embodiments include those listed below.

[0474] In various embodiments, the solid sorbents of the present invention, including the methods, systems, and material assemblies comprising the solid sorbents, are not limited to Direct Carbon Capture (DAC) of carbon dioxide (CO2) from ambient air. In various embodiments, the solid sorbents of the present invention, including the methods, systems, and material assemblies comprising the solid sorbents, may be used to capture, remove, separate, and / or adsorb carbon dioxide (CO2) from any source or stream, such as a point source emission (stationary or mobile), or directly from ambient air (e.g., by Direct Air Capture (DAC)). The captured, removed, separated, and / or adsorbed carbon dioxide may be desorbed or removed from the solid sorbent and stored, and / or used in various other processes, including but not limited to methanation. In some embodiments, the captured carbon dioxide is not desorbed or removed from the solid sorbent, but instead remains on the solid sorbent. In some embodiments, the solid sorbent containing the adsorbed carbon dioxide is stored.

[0475] In various embodiments, the present invention provides a solid sorbent for capturing, removing, separating, and / or adsorbing carbon dioxide (CO2) from a gas, the solid sorbent comprising at least one transition metal hydroxide. In various embodiments, the present4886-5761-4062.1Page 105 of 164094876-000018WOPTinvention provides a system for capture, removal, separation, and / or adsorption of carbon dioxide (CO2) from a gas, the system comprising: a reaction chamber, wherein the reaction chamber comprises an air intake opening, an air exhaust opening; and the solid sorbent of the present invention described herein positioned in the reaction chamber, wherein the solid sorbent comprises at least one transition metal hydroxide. In various embodiments, the present invention provides a method for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from a gas, the method comprising: providing a solid sorbent of the present invention described herein, wherein the solid sorbent comprises at least one transition metal hydroxide; and contacting the solid sorbent with a gas. In various embodiments, the present invention provides a material assembly for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from a gas, the material assembly comprising: a substrate; and a solid sorbent of the present invention described herein, wherein the solid sorbent comprises at least one transition metal hydroxide. In some embodiments, the gas is a CO2-containing gas mixture. In some embodiments, the gas comprises carbon dioxide (CO2). In some embodiments, the gas is ambient air. In some embodiments, the gas further comprises water or water vapor. In some embodiments, the solid sorbent comprises water or water vapor.

[0476] In various embodiments, the present invention provides a solid sorbent for capturing, removing, separating, and / or adsorbing carbon dioxide (CO2) from a gas, the solid sorbent comprising at least one transition metal oxide. In various embodiments, the present invention provides a system for capture, removal, separation, and / or adsorption of carbon dioxide (CO2) from a gas, the system comprising: a reaction chamber, wherein the reaction chamber comprises an air intake opening, an air exhaust opening; and the solid sorbent of the present invention described herein positioned in the reaction chamber, wherein the solid sorbent comprises at least one transition metal oxide. In various embodiments, the present invention provides a method for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from a gas, the method comprising: providing a solid sorbent of the present invention described herein, wherein the solid sorbent comprises at least one transition metal oxide; and contacting the solid sorbent with a gas. In various embodiments, the present invention provides a material assembly for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from a gas, the material assembly comprising: a substrate; and a solid sorbent of the present invention described herein, wherein the solid sorbent comprises at least one transition metal oxide. In some4886-5761-4062.1Page 106 of 164094876-000018WOPTembodiments, the gas is a CO2-containing gas mixture. In some embodiments, the gas comprises carbon dioxide (CO2). In some embodiments, the gas is ambient air. In some embodiments, the gas further comprises water or water vapor. In some embodiments, the solid sorbent comprises water or water vapor.

[0477] In various embodiments, the Porous Transition Metal Oxides (PTMOs) of the present invention can serve as a new class of Direct Air Capture (DAC) solid sorbents. Without being bound by theory, in some embodiments, humidity and metal doping surprisingly and significantly enhances DAC performance. Without being bound by theory, in some embodiments, an integrated DAC and methanation process is feasible using PTMOs in a single-component bed. Without being bound by theory, in some embodiments, PTMOs are able to integrate DAC and utilization in a single-component bed.

[0478] In various embodiments, the Porous Transition Metal Hydroxides (PTMHs) of the present invention can serve as a new class of Direct Air Capture (DAC) solid sorbents. Without being bound by theory, DAC active sites are associated with metal hydroxide layers. The presence of humidity significantly and surprisingly enhances DAC capacity. Without being bound by theory, metal doping has been proved as a rational material design strategy.

[0479] Additional embodiments include those listed below.

[0480] Embodiment 136. A solid sorbent for direct air capture of carbon dioxide, the solid sorbent comprising: at least one transition metal hydroxide.

[0481] Embodiment 137. The solid sorbent of embodiment 136, wherein the at least one transition metal hydroxide comprises at least one transition metal selected from the group consisting of nickel (Ni), cerium (Ce), iron (Fe), and any combination thereof.

[0482] Embodiment 138. The solid sorbent of embodiment 136, wherein the at least one transition metal hydroxide is porous, or non-porous, or combination thereof.

[0483] Embodiment 139. The solid sorbent of embodiment 136, wherein the at least one transition metal hydroxide is selected from Ni(OH)2.

[0484] Embodiment 140. The solid sorbent of embodiment 136, further comprising at least one dopant.

[0485] Embodiment 141. The solid sorbent of embodiment 140, wherein the at least one dopant comprises cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo),4886-5761-4062.1Page 107 of 164094876-000018WOPTmanganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), or vanadium (V), or any combination thereof.

[0486] Embodiment 142. The solid sorbent of embodiment 136, further comprising water or water vapor.

[0487] Embodiment 143. The solid sorbent of embodiment 136, wherein the at least one transition metal hydroxide is at least one mixed transition metal hydroxide.

[0488] Embodiment 144. The solid sorbent of embodiment 143, wherein the at least one mixed transition metal oxide comprises at least two transition metals selected from the group consisting of nickel (Ni), cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo), manganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), vanadium (V), and any combination thereof.

[0489] Embodiment 145. The solid sorbent of claim 143, wherein the at least one mixed transition metal oxide is selected from Ce4.4NiO, Ce10NiO, or Ce20NiO, and any combination thereof.

[0490] Embodiment 146. A direct air capture (DAC) system for capture, removal, separation, and / or adsorption of carbon dioxide (CO2) from ambient air comprising: a reaction chamber, wherein the reaction chamber comprises an air intake opening, and an air exhaust opening; and the solid sorbent of embodiment 136 positioned in the reaction chamber.

[0491] Embodiment 147. The system of embodiment146, further comprising a mechanism, device, or equipment for introducing water or water vapor into the reaction chamber.

[0492] Embodiment 148. The system of embodiment 146, further comprising an air movement mechanism, device, or equipment configured to contact ambient air with the solid sorbent positioned in the reaction chamber.

[0493] Embodiment 149. The system of embodiment 146, further comprising a mechanism, device, or equipment for desorbing or removing the adsorbed carbon dioxide from the solid sorbent.

[0494] Embodiment 150. The system of embodiment 146, further comprising a mechanism, device, or equipment for performing pressure swing adsorption, vacuum swing adsorption, temperature swing adsorption, or moisture swing adsorption, or any combination thereof.4886-5761-4062.1Page 108 of 164094876-000018WOPT

[0495] Embodiment 151. A direct air capture (DAC) method for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from ambient air, comprising: providing a solid sorbent of embodiment 136; and contacting the solid sorbent with ambient air.

[0496] Embodiment 152. The method of embodiment 151, further comprising contacting the solid sorbent with water or water vapor before contacting the solid sorbent with ambient air.

[0497] Embodiment 153. The method of embodiment 151 or embodiment 152, further comprising desorbing or removing the carbon dioxide from the solid sorbent.

[0498] Embodiment 154. The method of embodiment 153, wherein desorbing or removing the carbon dioxide from the solid sorbent is performed by contacting the solid sorbent with an inert gas, wherein the inert gas comprises water or water vapor.

[0499] Embodiment 155. The method of embodiment 153, wherein desorbing or removing the carbon dioxide from the solid sorbent comprises adjusting or changing pressure applied to the solid sorbent, adjusting or changing temperature of the solid sorbent, adjusting or changing vacuum applied to the solid sorbent, or adjusting or changing moisture level of the solid sorbent, or any combination thereof.

[0500] Additional embodiments include those listed below.

[0501] Embodiment 156. A carbon dioxide (CO2) sorbent, comprising: at least one transition metal hydroxide.

[0502] Embodiment 157. The carbon dioxide (CO2) sorbent of embodiment 156, wherein the at least one transition metal hydroxide comprises at least one transition metal selected from the group consisting of nickel (Ni), cerium (Ce), iron (Fe), and any combination thereof.

[0503] Embodiment 158. The carbon dioxide (CO2) sorbent of embodiment 156 or embodiment 157, wherein the at least one transition metal hydroxide is porous, or non-porous, or combination thereof.

[0504] Embodiment 159. The carbon dioxide (CO2) sorbent of any one of embodiments 156-158, wherein the at least one transition metal hydroxide is porous.

[0505] Embodiment 160. The carbon dioxide (CO2) sorbent of any one of embodiments 156-159, wherein the at least one transition metal hydroxide comprises at least one polymorph.

[0506] Embodiment 161. The carbon dioxide (CO2) sorbent of any one of claims 156- 160, wherein the at least one transition metal hydroxide is selected from Ni(OH)2.4886-5761-4062.1Page 109 of 164094876-000018WOPT

[0507] Embodiment 162. The carbon dioxide (CO2) sorbent of any one of embodiments 156-161, wherein the at least one transition metal hydroxide is α-Ni(OH)2, or β-Ni(OH)2, or combination thereof.

[0508] Embodiment 163. The carbon dioxide (CO2) sorbent of any one of embodiments 156-162, further comprising at least one dopant.

[0509] Embodiment 164. The carbon dioxide (CO2) sorbent of embodiment 163, wherein the at least one dopant comprises cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo), manganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), or vanadium (V), or any combination thereof.

[0510] Embodiment 165. The carbon dioxide (CO2) sorbent of embodiment 163, wherein the at least one dopant comprises cerium (Ce), or iron (Fe), or combination thereof.

[0511] Embodiment 166. The carbon dioxide (CO2) sorbent of embodiment 163, wherein the at least one dopant is a cationic dopant.

[0512] Embodiment 167. The carbon dioxide (CO2) sorbent of embodiment 166, wherein the cationic dopant is selected from Ce3+, Fe3+, Ce4+, or Fe2+, or any combination thereof.

[0513] Embodiment 168. The carbon dioxide (CO2) sorbent of any one of embodiments 163-167, wherein the solid sorbent is a layered double hydroxide (LDH).

[0514] Embodiment 169. The carbon dioxide (CO2) sorbent of any one of embodiments 156-159, wherein the at least one transition metal hydroxide is an anion-exchanged transition metal hydroxide.

[0515] Embodiment 170. The carbon dioxide (CO2) sorbent of embodiment 169, wherein the anion-exchanged transition metal hydroxide is α-Ni(OH)2-SO42-.

[0516] Embodiment 171. The carbon dioxide (CO2) sorbent of any one of embodiments 156-160, wherein the at least one transition metal hydroxide is at least one mixed transition metal hydroxide.

[0517] Embodiment 172. The carbon dioxide (CO2) sorbent of embodiment 171, wherein the at least one mixed transition metal hydroxide comprises at least two transition metals selected from the group consisting of nickel (Ni), cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo), manganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), vanadium (V), and any combination thereof.4886-5761-4062.1Page 110 of 164094876-000018WOPT

[0518] Embodiment 173. The carbon dioxide (CO2) sorbent of embodiment 171, wherein the at least one mixed transition metal hydroxide comprises at least two transition metals selected from the group consisting of nickel (Ni), cerium (Ce), iron (Fe), and any combinations thereof.

[0519] Embodiment 174. The carbon dioxide (CO2) sorbent of any one of embodiments 156-173, wherein the carbon dioxide (CO2) sorbent is a solid sorbent

[0520] Embodiment 175. The carbon dioxide (CO2) sorbent of any one of embodiments 156-173, wherein the carbon dioxide (CO2) sorbent is a solid adsorbent.

[0521] Embodiment 176. The carbon dioxide (CO2) sorbent of any one of embodiments 156-173, wherein the carbon dioxide (CO2) sorbent is a solid chemisorbent.

[0522] Embodiment 177. The carbon dioxide (CO2) sorbent of any one of embodiments 156-176, further comprising water or water vapor.

[0523] Embodiment 178. A direct air capture (DAC) system for capture, removal, separation, and / or adsorption of carbon dioxide (CO2) from ambient air comprising: a reaction chamber, wherein the reaction chamber comprises an air intake opening, and an air exhaust opening; and the carbon dioxide (CO2) sorbent of any one of embodiments 156-177 positioned in the reaction chamber.

[0524] Embodiment 179. The system of embodiment 178, further comprising a substrate material positioned in the reaction chamber, wherein the substrate material structurally supports the carbon dioxide (CO2) sorbent.

[0525] Embodiment 180. The system of embodiment 179, wherein the carbon dioxide (CO2) sorbent is impregnated in the substrate material.

[0526] Embodiment 181. The system of embodiment 179, wherein the carbon dioxide (CO2) sorbent is dispersed in the substrate material

[0527] Embodiment 182. The system of embodiment 179, wherein the carbon dioxide (CO2) sorbent is deposited on the substrate material.

[0528] Embodiment 183. The system of embodiment 179, wherein the carbon dioxide (CO2) sorbent is coated on the substrate material.

[0529] Embodiment 184. The system of any one of embodiments 179-183, wherein the substate material comprises ceramic, metal, organic material, or inorganic material, or any combination thereof.4886-5761-4062.1Page 111 of 164094876-000018WOPT

[0530] Embodiment 185. The system of any one of embodiments 179-183, wherein the substrate material comprises cordierite, alumina, silica / alumina, silicon carbide (SiC), titania, silica, magnesia, zirconia, or carbon, or any combination thereof.

[0531] Embodiment 186. The system of any one of embodiments 179-185, wherein the substrate material is in monolithic form.

[0532] Embodiment 187. The system of any one of embodiments 178-186, further comprising a mechanism, device, or equipment for introducing water or water vapor into the reaction chamber.

[0533] Embodiment 188. The system of any one of embodiments 178-187, further comprising a mechanism, device, or equipment for contacting the carbon dioxide (CO2) sorbent with water or water vapor.

[0534] Embodiment 189. The system of any one of embodiments 178-188, further comprising a mechanism, device, or equipment for heating the reaction chamber.

[0535] Embodiment 190. The system of any one of embodiments 178-189, further comprising a mechanism, device, or equipment for heating the carbon dioxide (CO2) sorbent.

[0536] Embodiment 191. The system of any one of embodiments 178-190, further comprising a mechanism, device, or equipment for cooling the reaction chamber.

[0537] Embodiment 192. The system of any one of embodiments 178-191, further comprising a mechanism, device, or equipment for cooling the carbon dioxide (CO2) sorbent.

[0538] Embodiment 193. The system of any one of embodiments 178-192, further comprising an air movement mechanism, device, or equipment positioned to move ambient air through the reaction chamber utilizing the air intake opening and air exhaust opening.

[0539] Embodiment 194. The system of any one of embodiments 178-193, further comprising an air movement mechanism, device, or equipment configured to contact ambient air with the carbon dioxide (CO2) sorbent positioned in the reaction chamber.

[0540] Embodiment 195. The system of any one of embodiments 178-194, further comprising a mechanism, device, or equipment for desorbing or removing the adsorbed carbon dioxide from the carbon dioxide (CO2) sorbent.

[0541] Embodiment 196. The system of embodiment 195, wherein the mechanism, device, or equipment comprises a compressor, or vacuum pump, or combination thereof.4886-5761-4062.1Page 112 of 164094876-000018WOPT

[0542] Embodiment 197. The system of any one of embodiments 178-196, further comprising a mechanism, device, or equipment for reducing the pressure in the reaction chamber.

[0543] Embodiment 198. The system of any one of embodiments 178-197, further comprising a mechanism, device, or equipment for increasing the pressure in the reaction chamber.

[0544] Embodiment 199. The system of any one of embodiments 178-198, further comprising a mechanism, device, or equipment for performing pressure swing adsorption, vacuum swing adsorption, temperature swing adsorption, or moisture swing adsorption, or any combination thereof.

[0545] Embodiment 200. A direct air capture (DAC) method for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from ambient air, comprising: providing a carbon dioxide (CO2) sorbent of any one of embodiments 156-177; and contacting the carbon dioxide (CO2) sorbent with ambient air.

[0546] Embodiment 201. The method of embodiment 200, further comprising capturing and / or removing, and / or separating, and / or adsorbing carbon dioxide from the ambient air.

[0547] Embodiment 202. The method of embodiment 200 or embodiment 201, further comprising contacting the carbon dioxide (CO2) sorbent with water or water vapor before or after contacting the solid sorbent with ambient air.

[0548] Embodiment 203. The method of any one of embodiments 200-202, wherein the ambient air comprises water or water vapor.

[0549] Embodiment 204. The method of any one of embodiments 200-203, wherein the ambient air has a relative humidity of greater than 10%.

[0550] Embodiment 205. The method of any one of embodiments 200-203, wherein the ambient air has a relative humidity of greater than 50%.

[0551] Embodiment 206. The method of any one of embodiments 200-203, wherein the ambient air has a relative humidity of greater than 70%.

[0552] Embodiment 207. The method of any one of embodiments 200-203, wherein the ambient air has a relative humidity of 100% or less.4886-5761-4062.1Page 113 of 164094876-000018WOPT

[0553] Embodiment 208. The method of any one of embodiments 200-203, wherein the ambient air is contacted with the carbon dioxide (CO2) sorbent at ambient temperature, ambient humidity, or ambient pressure, or any combination thereof.

[0554] Embodiment 209. The method of any one of embodiments 200-208, further comprising adsorbing carbon dioxide from the ambient air onto the carbon dioxide (CO2) sorbent.

[0555] Embodiment 210. The method of any one of embodiments 200-209, further comprising desorbing or removing the carbon dioxide from the carbon dioxide (CO2) sorbent.

[0556] Embodiment 211. The method of embodiment 210, wherein desorbing or removing the carbon dioxide from the carbon dioxide (CO2) sorbent comprises adjusting or changing pressure applied to the carbon dioxide (CO2) sorbent, adjusting or changing temperature of the carbon dioxide (CO2) sorbent, adjusting or changing vacuum applied to the carbon dioxide (CO2) sorbent, adjusting or changing moisture level of the carbon dioxide (CO2) sorbent, or adjusting or changing water or water vapor content of the carbon dioxide (CO2) sorbent, or any combination thereof.

[0557] Embodiment 212. A material assembly for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from ambient air, comprising: a substrate; and a carbon dioxide (CO2) sorbent of any one of embodiments 156-177.

[0558] Embodiment 213. The material assembly of embodiment 212, wherein the substrate structurally supports the carbon dioxide (CO2) sorbent.

[0559] Embodiment 214. The material assembly of embodiment 212 or embodiment 213, wherein the carbon dioxide (CO2) sorbent is impregnated in the substrate.

[0560] Embodiment 215. The material assembly of embodiment 212 or embodiment 213, wherein the carbon dioxide (CO2) sorbent is dispersed in the substrate.

[0561] Embodiment 216. The material assembly of embodiment 212 or embodiment 213, wherein the carbon dioxide (CO2) sorbent is deposited on the substrate.

[0562] Embodiment 217. The material assembly of embodiment 212 or embodiment 213, wherein the carbon dioxide (CO2) sorbent is coated on the substrate.

[0563] Embodiment 218. The material assembly of any one of embodiments 212-217, wherein the substate comprises ceramic, metal, organic material, or inorganic material, or any combination thereof.4886-5761-4062.1Page 114 of 164094876-000018WOPT

[0564] Embodiment 219. The material assembly of any one of embodiments 212-218, wherein the substrate comprises cordierite, alumina, silica / alumina, silicon carbide (SiC), titania, silica, magnesia, zirconia, or carbon, or any combination thereof.

[0565] Embodiment 220. The material assembly of any one of embodiments 212-219, wherein the substrate is in monolithic form.

[0566] Embodiment 221. A carbon dioxide (CO2) sorbent for direct air capture of carbon dioxide, the carbon dioxide (CO2) sorbent comprising: at least one transition metal oxide.

[0567] Embodiment 222. The carbon dioxide (CO2) sorbent of embodiment 221, wherein the at least one transition metal oxide comprises at least one transition metal selected from the group consisting of nickel (Ni), cerium (Ce), iron (Fe), and any combination thereof.

[0568] Embodiment 223. The carbon dioxide (CO2) sorbent of embodiment 221 or embodiment 222, wherein the at least one transition metal oxide is porous, or non-porous, or combination thereof.

[0569] Embodiment 224. The carbon dioxide (CO2) sorbent of any one of embodiments 221-223, wherein the at least one transition metal oxide is porous.

[0570] Embodiment 225. The carbon dioxide (CO2) sorbent of any one of embodiments 221-224, wherein the at least one transition metal oxide comprises at least one polymorph.

[0571] Embodiment 226. The carbon dioxide (CO2) sorbent of any one of embodiments 221-225, wherein the at least one transition metal oxide is selected from NiO, or CeO2, or combination thereof.

[0572] Embodiment 227. The carbon dioxide (CO2) sorbent of any one of embodiments 221-226, further comprising at least one dopant.

[0573] Embodiment 228. The carbon dioxide (CO2) sorbent of embodiment 227, wherein the at least one dopant comprises cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo), manganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), or vanadium (V), or any combination thereof.

[0574] Embodiment 229. The carbon dioxide (CO2) sorbent of embodiment 227, wherein the at least one dopant comprises cerium (Ce), or iron (Fe), or combination thereof.

[0575] Embodiment 230. The carbon dioxide (CO2) sorbent of embodiment 227, wherein the at least one dopant is a cationic dopant.4886-5761-4062.1Page 115 of 164094876-000018WOPT

[0576] Embodiment 231. The carbon dioxide (CO2) sorbent of embodiment 230, wherein the cationic dopant is selected from Ce3+, Fe3+, Ce4+, or Fe2+, or any combination thereof.

[0577] Embodiment 232. The carbon dioxide (CO2) sorbent of any one of embodiments 221-225, wherein the at least one transition metal oxide is at least one mixed transition metal oxide.

[0578] Embodiment 233. The carbon dioxide (CO2) sorbent of embodiment 232, wherein the at least one mixed transition metal oxide comprises at least two transition metals selected from the group consisting of nickel (Ni), cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo), manganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), vanadium (V), and any combination thereof.

[0579] Embodiment 234. The carbon dioxide (CO2) sorbent of embodiment 232, wherein the at least one mixed transition metal oxide comprises at least two transition metals selected from the group consisting of nickel (Ni), cerium (Ce), iron (Fe), and any combinations thereof.

[0580] Embodiment 235. The carbon dioxide (CO2) sorbent of embodiment 232, wherein the at least one mixed transition metal oxide is selected from Ce4.4NiO, Ce10NiO, or Ce20NiO, and any combinations thereof.

[0581] Embodiment 236. The carbon dioxide (CO2) sorbent of any one of embodiments 156-173, wherein the carbon dioxide (CO2) sorbent is a solid sorbent.

[0582] Embodiment 237. The carbon dioxide (CO2) sorbent of any one of embodiments 221-235, wherein the carbon dioxide (CO2) sorbent is a solid adsorbent.

[0583] Embodiment 238. The carbon dioxide (CO2) sorbent of any one of embodiments 221-235, wherein the solid sorbent is a solid chemisorbent.

[0584] Embodiment 239. The carbon dioxide (CO2) sorbent of any one of embodiments 221-238, further comprising water or water vapor.

[0585] Embodiment 240. A direct air capture (DAC) system for capture, removal, separation and / or adsorption of carbon dioxide (CO2) from ambient air comprising: a reaction chamber, wherein the reaction chamber comprises an air intake opening, and an air exhaust opening; and the carbon dioxide (CO2) sorbent of any one of embodiments 221-239 positioned in the reaction chamber.4886-5761-4062.1Page 116 of 164094876-000018WOPT

[0586] Embodiment 241. The system of embodiment 240, further comprising a substrate material positioned in the reaction chamber, wherein the substrate material structurally supports the carbon dioxide (CO2) sorbent.

[0587] Embodiment 242. The system of embodiment 241, wherein the carbon dioxide (CO2) sorbent is impregnated in the substrate material.

[0588] Embodiment 243. The system of embodiment 241, wherein the carbon dioxide (CO2) sorbent is dispersed in the substrate material.

[0589] Embodiment 244. The system of embodiment 241, wherein the carbon dioxide (CO2) sorbent is deposited on the substrate material.

[0590] Embodiment 245. The system of embodiment 241, wherein the carbon dioxide (CO2) sorbent is coated on the substrate material.

[0591] Embodiment 246. The system of any one of embodiments 241-245, wherein the substate material comprises ceramic, metal, organic material, or inorganic material, or any combination thereof.

[0592] Embodiment 247. The system of any one of embodiments 241-246, wherein the substrate material comprises cordierite, alumina, silica / alumina, silicon carbide (SiC), titania, silica, magnesia, zirconia, or carbon, or any combination thereof.

[0593] Embodiment 248. The system of any one of embodiments 241-247, wherein the substrate material is in monolithic form.

[0594] Embodiment 249. The system of any one of embodiments 240-248, further comprising a mechanism, device, or equipment for introducing water or water vapor into the reaction chamber.

[0595] Embodiment 250. The system of any one of embodiments 240-249, further comprising a mechanism, device, or equipment for contacting the carbon dioxide (CO2) sorbent with water or water vapor.

[0596] Embodiment 251. The system of any one of embodiments 240-250, further comprising a mechanism, device, or equipment for heating the reaction chamber.

[0597] Embodiment 252. The system of any one of embodiments 240-251, further comprising a mechanism, device, or equipment for heating the carbon dioxide (CO2) sorbent.

[0598] Embodiment 253. The system of any one of embodiments 240-252, further comprising a mechanism, device, or equipment for cooling the reaction chamber.4886-5761-4062.1Page 117 of 164094876-000018WOPT

[0599] Embodiment 254. The system of any one of embodiments 240-253, further comprising a mechanism, device, or equipment for cooling the carbon dioxide (CO2) sorbent.

[0600] Embodiment 255. The system of any one of embodiments 240-254, further comprising an air movement mechanism, device, or equipment positioned to move ambient air through the reaction chamber utilizing the air intake opening and air exhaust opening.

[0601] Embodiment 256. The system of any one of embodiments 240-255, further comprising an air movement mechanism, device, or equipment configured to contact ambient air with the carbon dioxide (CO2) sorbent positioned in the reaction chamber.

[0602] Embodiment 257. The system of any one of embodiments 240-256, further comprising a mechanism, device, or equipment for desorbing or removing the adsorbed carbon dioxide from the carbon dioxide (CO2) sorbent.

[0603] Embodiment 258. The system of embodiment 257, wherein the mechanism, device, or equipment comprises a compressor, or vacuum pump, or combination thereof.

[0604] Embodiment 259. The system of any one of embodiment 240-258, further comprising a mechanism, device, or equipment for reducing the pressure in the reaction chamber.

[0605] Embodiment 260. The system of any one of embodiments 240-259, further comprising a mechanism, device, or equipment for increasing the pressure in the reaction chamber.

[0606] Embodiment 261. The system of any one of embodiments 240-260, further comprising a mechanism, device, or equipment for performing pressure swing adsorption, vacuum swing adsorption, temperature swing adsorption, or moisture swing adsorption, or any combination thereof.

[0607] Embodiment 262. A direct air capture (DAC) method for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from ambient air, comprising: providing a carbon dioxide (CO2) sorbent of any one of embodiments 221-239; and contacting the carbon dioxide (CO2) sorbent with ambient air.

[0608] Embodiment 263. The method of embodiment 262, further comprising capturing and / or removing and / or separating and / or adsorbing carbon dioxide from the ambient air.4886-5761-4062.1Page 118 of 164094876-000018WOPT

[0609] Embodiment 264. The method of embodiment 262 or embodiment 263, further comprising contacting the carbon dioxide (CO2) sorbent with water or water vapor before contacting the carbon dioxide (CO2) sorbent with ambient air.

[0610] Embodiment 265. The method of any one of embodiments 262-264, wherein the ambient air comprises water or water vapor.

[0611] Embodiment 266. The method of any one of embodiments 262-265, wherein the ambient air has a relative humidity of greater than 10%.

[0612] Embodiment 267. The method of any one of embodiments 262-265, wherein the ambient air has a relative humidity of greater than 50%.

[0613] Embodiment 268. The method of any one of embodiments 262-265, wherein the ambient air has a relative humidity of greater than 70%.

[0614] Embodiment 269. The method of any one of embodiments 262-265, wherein the ambient air has a relative humidity of 100% or less.

[0615] Embodiment 270. The method of any one of embodiments 262-265, wherein the ambient air is contacted with the solid sorbent at ambient temperature, ambient humidity, or ambient pressure, or any combination thereof.

[0616] Embodiment 271. The method of any one of embodiments 262-270, further comprising adsorbing carbon dioxide from the ambient air onto the carbon dioxide (CO2) sorbent.

[0617] Embodiment 272. The method of any one of embodiments 262-270, further comprising desorbing or removing the carbon dioxide from the carbon dioxide (CO2) sorbent.

[0618] Embodiment 273. The method of embodiment 272, wherein desorbing or removing the carbon dioxide from the carbon dioxide (CO2) sorbent comprises adjusting or changing pressure applied to the carbon dioxide (CO2) sorbent, adjusting or changing temperature of the carbon dioxide (CO2) sorbent, adjusting or changing vacuum applied to the carbon dioxide (CO2) sorbent, or adjusting or changing moisture level of the carbon dioxide (CO2) sorbent, or any combination thereof.

[0619] Embodiment 274. A material assembly for capturing, separating, removing, and / or adsorbing carbon dioxide (CO2) from ambient air, comprising: a substrate; and a carbon dioxide (CO2) sorbent of any one of embodiments 221-239.4886-5761-4062.1Page 119 of 164094876-000018WOPT

[0620] Embodiment 275. The material assembly of embodiment 274, wherein the substrate structurally supports the carbon dioxide (CO2) sorbent.

[0621] Embodiment 276. The material assembly of embodiment 274 or embodiment 275, wherein the carbon dioxide (CO2) sorbent is impregnated in the substrate.

[0622] Embodiment 277. The material assembly of embodiment 274 or embodiment 275, wherein the carbon dioxide (CO2) sorbent is dispersed in the substrate.

[0623] Embodiment 278. The material assembly of embodiment 274 or embodiment 275, wherein the carbon dioxide (CO2) sorbent is deposited on the substrate.

[0624] Embodiment 279. The material assembly of embodiment 274 or embodiment 275, wherein the carbon dioxide (CO2) sorbent is coated on the substrate.

[0625] Embodiment 280. The material assembly of any one of embodiments 274-279, wherein the substate comprises ceramic, metal, organic material, or inorganic material, or any combination thereof.

[0626] Embodiment 281. The material assembly of any one of embodiments 274-280, wherein the substrate comprises cordierite, alumina, silica / alumina, silicon carbide (SiC), titania, silica, magnesia, zirconia, or carbon, or any combination thereof.

[0627] Embodiment 282. The material assembly of any one of embodiments 274-281, wherein the substrate is in monolithic form.

[0628] Embodiment 283. The system of any one of embodiments 240-261, further comprising a mechanism, device, or equipment for contacting hydrogen with the carbon dioxide (CO2) sorbent.

[0629] Embodiment 284. The system of any one of embodiments 240-261, further comprising a mechanism, device, or equipment for adding hydrogen to the reaction chamber.

[0630] Embodiment 285. The method of any one of embodiments 262-273, where in the method further comprises one or more methanation processes.

[0631] Embodiment 286. The method of any one of embodiments 262-273, further comprising contacting the captured, removed, adsorbed, and / or separated carbon dioxide with hydrogen under conditions effective to produce methane.

[0632] Embodiment 287. The method of any one of embodiments 262-273, further comprising contacting the carbon dioxide (CO2) sorbent with hydrogen under conditions effective to produce methane.4886-5761-4062.1Page 120 of 164094876-000018WOPT

[0633] Embodiment 288. The system of any one of embodiments 178-199, further comprising a mechanism, device, or equipment for contacting hydrogen with the carbon dioxide (CO2) sorbent.

[0634] Embodiment 289. The system of any one of embodiments 178-199, further comprising a mechanism, device, or equipment for adding hydrogen to the reaction chamber.

[0635] Embodiment 290. The method of any one of embodiments 200-211, where in the method further comprises one or more methanation processes.

[0636] Embodiment 291. The method of any one of embodiments 200-211, further comprising contacting the captured, removed, adsorbed, and / or separated carbon dioxide with hydrogen under conditions effective to produce methane.

[0637] Embodiment 292. The method of any one of embodiments 200-211, further comprising contacting the carbon dioxide (CO2) sorbent with hydrogen under conditions effective to produce methane.

[0638] Additional embodiments include those listed below.

[0639] Embodiment 293. A sorbent for removing, capturing, separating, and / or adsorbing carbon dioxide (CO2) from a gas source or a gas stream or a gas mixture, the sorbent comprising: at least one transition metal hydroxide.

[0640] Embodiment 294. The sorbent of embodiment 293, wherein the sorbent is a solid sorbent.

[0641] Embodiment 295. The sorbent of embodiment 293, wherein the sorbent is a carbon dioxide (CO2) sorbent.

[0642] Embodiment 296. The sorbent of embodiment 294, wherein the solid sorbent is a carbon dioxide (CO2) sorbent.

[0643] Embodiment 297. The sorbent of any one of embodiments 293-296, wherein the gas stream or gas mixture is ambient air, flue gas, natural gas, exhaust gas, or biogas, or any combination thereof.

[0644] Embodiment 298. The sorbent of any one of embodiments 293-296, wherein the gas stream or gas mixture comprises ambient air, flue gas, natural gas, exhaust gas, or biogas, or any combination thereof.4886-5761-4062.1Page 121 of 164094876-000018WOPT

[0645] Embodiment 299. The sorbent of any one of embodiments 293-296, wherein the gas source is ambient air, flue gas, natural gas, exhaust gas, or biogas, or any combination thereof.

[0646] Embodiment 300. The sorbent of any one of embodiments 293-296, wherein the gas source comprises ambient air, flue gas, natural gas, exhaust gas, or biogas, or any combination thereof.

[0647] Embodiment 301. The sorbent of any one of embodiments 293-300 wherein the at least one transition metal hydroxide comprises at least one transition metal selected from the group consisting of nickel (Ni), cerium (Ce), iron (Fe), and any combination thereof.

[0648] Embodiment 302. The sorbent of any one of embodiments 293-301, wherein the at least one transition metal hydroxide is porous, or non-porous, or combination thereof.

[0649] Embodiment 303. The sorbent of any one of embodiments 293-301, wherein the at least one transition metal hydroxide is porous.

[0650] Embodiment 304. The sorbent of any one of embodiments 293-303, wherein the at least one transition metal hydroxide comprises at least one polymorph.

[0651] Embodiment 305. The sorbent of any one of embodiments 293-304, wherein the at least one transition metal hydroxide is selected from Ni(OH)2.

[0652] Embodiment 306. The sorbent of any one of embodiments 293-305, wherein the at least one transition metal hydroxide is α-Ni(OH)2, or β-Ni(OH)2, or combination thereof.

[0653] Embodiment 307. The sorbent of any one of embodiments 203-306, further comprising at least one dopant.

[0654] Embodiment 308. The sorbent of embodiment 307, wherein the at least one dopant comprises cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo), manganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), or vanadium (V), or any combination thereof.

[0655] Embodiment 309. The sorbent of embodiment 307, wherein the at least one dopant comprises cerium (Ce), or iron (Fe), or combination thereof.

[0656] Embodiment 310. The sorbent of embodiment 307, wherein the at...

Claims

CLAIMS What is claimed is:

1. A solid sorbent for removing carbon dioxide (CO2) from a gas mixture, the solid sorbent comprising: at least one transition metal hydroxide.

2. The solid sorbent of claim 1, wherein the gas mixture comprises ambient air, flue gas, natural gas, exhaust gas, or biogas, or any combination thereof.

3. The solid sorbent of claim 1, wherein the at least one transition metal hydroxide comprises at least one transition metal selected from the group consisting of nickel (Ni), cerium (Ce), iron (Fe), and any combination thereof.

4. The solid sorbent of claim 1, wherein the at least one transition metal hydroxide is porous, or non-porous, or combination thereof.

5. The solid sorbent of claim 1, wherein the at least one transition metal hydroxide is selected from Ni(OH)2.

6. The solid sorbent of claim 1, further comprising at least one dopant.

7. The solid sorbent of claim 6, wherein the at least one dopant comprises cerium (Ce), iron, (Fe), aluminum (Al), niobium (Nb), molybdenum (Mo), manganese (Mn), cobalt (Co), copper (Cu), chromium (Cr), zinc (Zn), or vanadium (V), or any combination thereof.

8. The solid sorbent of claim 1, further comprising water or water vapor.

9. A system for removing carbon dioxide (CO2) from a gas mixture, the system comprising: a reaction chamber, wherein the reaction chamber comprises an inlet port, and an outlet port; and4886-5761-4062.1Page 161 of 164094876-000018WOPTthe solid sorbent of claim 1 positioned in the reaction chamber.

10. The system of claim 9, further comprising a mechanism, device, or equipment for introducing water or water vapor into the reaction chamber; and optionally further comprising a mechanism, device, or equipment configured to contact the gas mixture with the solid sorbent positioned in the reaction chamber; and optionally further comprising a mechanism, device, or equipment for desorbing or removing the adsorbed carbon dioxide from the solid sorbent.

11. The system of claim 9, wherein the gas mixture comprises ambient air, flue gas, natural gas, exhaust gas, or biogas, or any combination thereof.

12. The system of claim 9, further comprising a mechanism, device, or equipment for performing pressure swing adsorption, vacuum swing adsorption, temperature swing adsorption, or moisture swing adsorption, or any combination thereof.

13. A method for removing carbon dioxide (CO2) from a gas mixture, the method comprising: providing a solid sorbent of claim 1; and contacting the solid sorbent with a gas mixture.

14. The method of claim 13, further comprising contacting the solid sorbent with water or water vapor before contacting the solid sorbent with the gas mixture.

15. The method of claim 13 or claim 14, wherein the gas mixture comprises ambient air, flue gas, natural gas, exhaust gas, or biogas, or any combination thereof.

16. The method of claim 13 or claim 14, further comprising desorbing or removing the carbon dioxide from the solid sorbent.4886-5761-4062.1Page 162 of 164094876-000018WOPT17. The method of claim 16, wherein desorbing or removing the carbon dioxide from the solid sorbent is performed by contacting the solid sorbent with an inert gas, wherein the inert gas comprises water or water vapor.

18. The method of claim 16, wherein desorbing or removing the carbon dioxide from the solid sorbent comprises adjusting or changing pressure applied to the solid sorbent, adjusting or changing temperature of the solid sorbent, adjusting or changing vacuum applied to the solid sorbent, or adjusting or changing moisture level of the solid sorbent, or any combination thereof.4886-5761-4062.1Page 163 of 164094876-000018WOPT

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