Plasmon-enhanced alkane dehydrogenation

Abstract

Methods for the dehydrogenation of an alkane to a product are provided, comprising exposing an alkane to heat and light in the presence of a nanostructured photocatalyst comprising a plasmonic metal and a dopant metal, wherein the light generates localized surface plasmon resonances in the nanostructured photocatalyst and the alkane undergoes dehydrogenation to produce a product.

Description

Atty. Dkt. No. 00100-0408-PCTPLASMON-ENHANCED ALKANE DEHYDROGENATIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Patent Application No. 63 / 715,383, filed November 1, 2024, the entire contents of which are incorporated herein by reference.BACKGROUND

[0002] Propylene is a key building block in the chemical industry, notably as a precursor for acetone, acrylonitrile, and polypropylene manufacturing. Currently, propylene production is dominated by steam cracking of naphtha, a highly energy intensive process which is limited by low thermodynamic yields (-15%) while producing a mixture of byproducts. These limitations have led to the increased popularity of direct catalytic propane dehydrogenation (PDH), yielding the targeted olefin exclusively. Additionally, due to the increase of shale gas resources in the United States, direct propane dehydrogenation to propylene has become more economically and societally relevant. Taking advantage of domestic natural gas reserves beyond heating and electric power generation could reduce the need for crude oil resources and have positive implications for the energy transition.

[0003] PDH can be performed in the presence of an oxidant, such as molecular oxygen, but selectivity challenges between the desired olefin and carbon oxides are substantial. Non- oxidative PDH is an alternative to using additional oxidants but requires much higher temperatures to achieve substantial rates. The high temperatures of non-oxidative PDH can lead to catalyst deactivation through sintering or catalyst inhibition through accumulation of carbaceous deposits (coke) on the active catalytic surface. Advancements in PDH technologies have seen the emergence of industrial catalysts such as CrOx and Pt-based thermocatalysts. Although these catalysts have been optimized to operate at the thermodynamic limit while increasing their stability and selectivity, the deposition of coke requires regeneration of the catalyst for sustained operation, which can lead to downtime in industrial facilities. These factors contribute significantly to the environmental impact and operational challenges of propane dehydrogenation chemistry which leads to a high carbon footprint and a significant reliance on fossil fuels both as a feedstock and energy source.Atty. Dkt. No. 00100-0408-PCTSUMMARY

[0004] Provided are methods for converting alkanes (e.g., propane) to products (e.g., propylene), using certain photocatalysts activated with both heat and light. The present disclosure is illustrated by reference to an Example 1 , below, in which a CuPt photocatalyst was synthesized and investigated to study the impact of generating localized surface plasmon resonances in the photocatalyst on propane dehydrogenation kinetics. Using the present methods which involve exposing the propane to both heat and light in the presence of the CuPt photocatalyst, it was found that the propylene formation rate increased by 200% as compared to the method conducted in the absence of the light. Additional experiments were conducted to reveal the photocatalytic mechanism which, without wishing to be bound to any particular theory, is thought to involve the generation of plasmon-induced hot holes that localize at Pt sites. The present disclosure is further illustrated by reference to Example 2, below, which further demonstrates use of a variety' of illustrative photocatalysts in the present methods to produce olefins and aromatic compounds.

[0005] In an embodiment, a method for dehydrogenation of an alkane to a product comprises exposing an alkane to heat and light in the presence of a nanostructured photocatalyst comprising a plasmonic metal and a dopant metal, wherein the light generates localized surface plasmon resonances in the nanostructured photocatalyst and the alkane undergoes dehydrogenation to produce a product.

[0006] Other principal features and advantages of the disclosure will become apparent to those skilled in the art upon review' of the follow ing drawings, the detailed description, and the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Illustrative embodiments of the disclosure will hereafter be described with reference to the accompanying drawings.

[0008] FIGS. 1 A-1D. Synthesis and characterization of CuPt / SiO2 dilute plasmonic alloys. FIG. 1 A shows a Strong Electrostatic Adsorption synthesis scheme for synthesizing CuPt / SiO2 catalysts. CuPt alloy nanoparticles are supported on high surface area SiO2. FIG. IB shows diffuse reflectance UV-vis spectroscopy of CuPto.oo SiCh. FIG. 1C shows CO diffuse reflectance infrared Fourier transform spectroscopy of CuPto.oi4 / Si02 showcasing PtAtty. Dkt. No. 00100-0408-PCT ensemble sites. FIG. ID shows CO Diffuse reflectance infrared fourier transform spectroscopy of CuPto.ooi4 / Si02 showcasing single atom sites.

[0009] FIGS. 2A-2D. Photocatalytic propane dehydrogenation on CuPt / SiO2. FIG. 2A shows CuPto.ooi4 thermocatalytic and photocatalytic propylene formation rates from 400-520 °C, light conditions were 585 nm ± 50 nm, 188 mW. FIG. 2B shows CuPtoou thermocatalytic and photocatalytic propylene formation rates from 400-520 °C, light conditions were 585 nm ± 50 nm, 188 mW. FIG. 2C shows representative mass spectra of the propylene trace (m / z = 42) on CuPto 0014 at 520 °C, with the highlighted section showing the light-enhanced propylene formation rate. FIG. 2D shows propylene formation rate as a function of Pt:Cu ratio under light and dark conditions. Gas composition: 8 kPa propane and 4 kPa hydrogen balanced by Ar, total flow rate was 50 ml / min.

[0010] FIGS. 3A-3F. Mechanistic insights into photocatalytic propane dehydrogenation with a CuPto.oo4 / Si02dilute plasmonic alloy. FIG. 3A.shows a wavelength dependent study on CuPtooo4 / Si02with constant light intensity of 105 mW cm'2.. FIG. 3B shows an Arrhenius plot of CuPto.oou / SiCh under light and dark conditions, activation energies were extracted for both catalytic processes FIG. 3C shows a power dependent study of CuPto.i SiChto disentangle photothermal and non-thermal effects in plasmonic propane dehydrogenation. FIG. 3D shows CsHs partial pressure and FIG. 3E shows H2 partial pressure impacted rates collected at 500 °C. FIG. 3F shows the kinetic isotope studies comparing the olefin formation rates from 2,2-C3HeD2-H2 isotope-labeled dehydrogenation to determine the kinetic isotope effect (KIE) under light and dark conditions on CuPtsA (205: 1) and CuPtens (70: 1) at 460 °C (SA = single atom; ens = ensemble). The increased KIE value observed on CuPtsA suggests the presence of vibrationally excited states, further validating the contribution of photochemical processes during the reaction.

[0011] FIGS. 4A-4B. Photocatalytic propane dehydrogenation on other Cu-based dilute alloys. FIG. 4A shows photocatalytic and thermocatalytic propylene formation rate of CuRho.004 in the range of 460-520 °C. FIG. 4B shows the photocatalytic propylene formation rate of CuPt, CuRh and CuNi at 460 °C.

[0012] FIG. 5A shows the thermocatalytic and photocatalytic benzene formation rates of silica-supported Cu, CuPt (205: 1), and Pt photocatalysts — with equivalent Pt loadings to the CuPt (205: 1) sample — at 520 °C, highlighting the synergy between Cu and Pt sites in propane dehydroaromatization. Light condition: 585±50 nm, 1.12 W cm'2light intensity .Atty. Dkt. No. 00100-0408-PCTGas composition: 8 kPa propane and 4 kPa hydrogen balanced by Ar, total flow rate is 50 seem. FIG. 5B shows benzene rate enhancement under light versus dark conditions as a function of wavelength, where the rate enhancement mirrors the UV-vis spectra, highlighting the role of LSPR in promoting benzene formation.

[0013] FIG. 6A illustrates the propane dehydroaromatization mechanism by varying the saturation of C3 species (propane, propylene and propyne) over Cu catalyst. FIF. 6B schematic illustration based on varying the saturation of C3 species, where isolated Pt sites promote C-H activation, converting alkanes to olefins, while Cu sites catalyze subsequent olefin-to-alkyne conversion and alky ne cyclization reactions, thus highlighting the bifunctionality of Cu-Pt. (Extra C.3 species and H2 are omitted for simplicity.)

[0014] FIG. 7A shows thermocatalytic and photocatalytic benzene formation rate from ethylene / acetylene on Cu and from acetylene on Ag , showcasing the use of Cu as a light- assisted C2 trimerization catalyst. FIG. 7B shows C2-C4 alkane dehydroaromatization on CuPtsA (205: 1) at 500 °C, showcasing the generalizability of this light-assisted dehydroaromatization process.

[0015] FIG. 8A shows the production of the H2 by-product under light illumination when using a CuPt photocatalyst for ethane dehydrogenation. FIG. 8B shows thermocatalytic and photocatalytic H2 formation rate from 500-560 °C using the CuPt photocatalyst. FIG. 8C shows the activation barrier for H2 formation using the CuPt photocatalyst.

[0016] FIG. 9 shows thermocataly tic and photocatalytic benzene formation rate at 590 °C using two CuPt photocatalysts.

[0017] FIG. 10A shows the production of benzene under light illumination when using a AgPt photocatalyst for propane dehydroaromatization. FIG. 10B shows thermocatalytic and photocatalytic benzene formation rate from 400-520 °C using the AgPt photocatalyst. FIG. 10C shows the activation barrier for benzene formation using the AgPt photocatalyst.

[0018] FIG. 11 A shows propane and butane / propylene and butene (C3: C4=l : 1) crosscoupling over CuPtsA at 440 °C . Light condition: 585±75 nm, 1.65 W cm'2light intensity. Quantification of toluene and benzene formation rates and toluene / benzene ratios under both conditions. FIG. 1 IB shows propane and butane co-flow, C butane, and D propane over CuPtsA at 440 °C.Atty. Dkt. No. 00100-0408-PCTDETAILED DESCRIPTION

[0019] Methods are provided which comprise exposing an alkane to heat and light in the presence of a photocatalyst comprising a plasmonic metal and a dopant metal, to convert the alkane to a product. As discussed in the Example, below, the conversion is a chemical reaction that is believed to involve dehydrogenation of the alkane which is greatly enhanced by localized surface plasmon resonances (LSPRs) generated in the photocatalyst by the light.

[0020] A variety of alkanes may be used in the present methods. The alkane may be a linear alkane, a branched alkane, or a cyclic alkane. The alkane may have various numbers of carbon atoms, e.g., from 2 to 10, including 3, 4, 5, 6, 7, 8, 9, carbon atoms or a range between any of these values. The alkane may be unsubstituted by w hich it is meant that the alkane contains no heteroatoms. Illustrative alkanes include ethane, propane, butane, pentane, hexane, and cyclohexane, although alkanes having a greater number of carbons may be used. Illustrative branched alkanes such as 2-methylpropane and isobutane may also be used. A single type of alkane or multiple, different types of alkanes (e.g., propane and butane) may be used.

[0021] Products which may be produced by the present methods include olefins. The olefin may be that corresponding to the alkane being used, i.e., an olefin having the same number of carbon atoms as the alkane. For example, propane may be converted to propylene by the present methods. Similarly, ethane may be converted to ethylene by the present methods. However, as illustrated in Example 2, below', other products that involve an elementary step of C-C bond cleavage and C-C bond coupling may be produced, including other olefins that have a different number of carbon atoms as the alkane (e.g., butene) and aromatic compounds (e.g., benzene, toluene). The formation of such higher hydrocarbons can be enhanced by adjusting certain conditions being used in the present methods, including temperature, flow' rate (e.g., when using a continuous flow' reactor), and amount of alkane. For example, higher temperatures (e.g., above 500 °C), lower flow rates, and higher amounts of alkane generally facilitate the formation of higher hydrocarbons.

[0022] As noted above, the photocatalyst comprises a plasmonic metal and a dopant metal. The plasmonic metal refers to a metal that, w hen in the form of the photocatalysts described herein (including the nanoparticles described below ), is capable of coupling w ith the light being used so as to excite a localized surface plasmon resonance (LSPR) therein. An illustrative plasmonic metal is copper (Cu), but other plasmonic metals may be used, e g.,Atty. Dkt. No. 00100-0408-PCT gold (Au), and silver (Ag). The dopant metal refers to a different type of metal than the plasmonic metal. The dopant metal may be selected on the basis of its ability to adsorb the alkane being used in the present methods. Illustrative dopant metals include platinum group metals such as platinum (Pt), but other dopant metals may be used, e.g., palladium (Pd), nickel (Ni), ruthenium (Ru), rhodium (Rh), cobalt (Co), iron (Fe). The term “dopant” is used since the amount of the dopant metal in the photocatalyst is significantly less than the plasmonic metal. The particular plasmonic metal and dopant metal, as well as their relative amounts, may be further selected so that the dopant metal is incorporated in the photocatalyst as isolated, single metal atoms distributed throughout a solid matrix formed of the plasmonic metal, or the surface thereof. As described in the Example, below, CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) may be used to confirm that the dopant metal is in the form of isolated, single metal atoms in the photocatalyst. Otherwise, the composition and plasmonic metal / dopant metal amounts may be selected to achieve a desired result, e.g., maximum conversion of the alkane, maximum yield / selectivity of a particular product, minimum coke formation, etc.

[0023] Illustrative plasmonic metal and dopant metal combinations include CuPt, AgPt, AuPt, CuRh, AgRh, AuRh, CuPd, AgPd, AuPd. CuRu, AgRu, AuRu. CuNi, AgNi. and AuNi, as well as those described in the Example, below. Illustrative relative amounts that result in dopant metal incorporation as isolated, single atoms are provided in the Example, below. This includes use of a molar ratio of (plasmonic metal): (dopant metal) of from 1000: 1 to 200:1, from 900: 1 to 300: 1, and from 800: 1 to 400: 1.

[0024] A single type of plasmonic metal or multiple, different types of plasmonic metal may be used. A single type of dopant metal or multiple, different types of dopant metal may be used. A single type of photocatalyst or multiple, different types of photocatalysts may be used.

[0025] The photocatalysts may be nanostructured, i.e., in the form of a plurality of nanoparticles, i.e., individual, distinct particles having nanoscale dimensions. The nanoparticles may be characterized by their size and shape. Each of the three dimensions of the nanoparticles is nanoscale, e.g., 100 nm or less. This includes 50 nm or less, 25 nm or less, 10 nm or less, or in a range of from 1 nm to 10 nm. The three dimensions may be of similar magnitude to each other such that the nanoparticles may be spherical in shape and the size may refer to a diameter of the nanoparticles. However, “spherical” does not meanAtty. Dkt. No. 00100-0408-PCT perfectly spherical, e.g., the nanoparticles may be faceted. The nanoparticles may assume other shapes (e.g., cubic, pyramidal, ovoid, etc.). For non-spherical shapes, the size may be taken as the largest cross-sectional dimension of the nanoparticles, which may be within any of the dimensions described above. The sizes / dimensions in this paragraph may refer to an average value.

[0026] The photocatalysts may be provided on a support material, e.g., such as a metal oxide (e.g., SiCh). The amount of the photocatalyst relative to the support material may be selected to achieve the desired results as set forth above. An illustrative SiCh-supported CuPt nanoparticle photocatalyst is shown in FIG. 1A. As also shown in FIG. 1 A and further described in Example 1, below', the photocatalysts may be synthesized using strong electrostatic adsorption, follow ed by EE reduction. This synthetic technique includes the use of a pretreated nanoparticulate silica support, which is a unique feature of the illustrative photocatalysts.

[0027] As noted above, the present methods are carried out using both heat and light. Regarding heat, the particular temperature being used depends upon the photocatalyst and the alkane, and selection may be made with reference to a desired result as set forth above. However, present methods may be carried out using temperatures that are significantly less than those used in existing alkane dehydrogenation techniques. Illustrative temperatures include those no greater than 600 °C, no greater than 575 °C, no greater than 550 °C, or in a range of from 400 °C to 530 °C. Regarding light, the wavelength (or range thereof) is selected so as to generate the LSPRs in the selected photocatalyst as described above. Thus, the particular wavelength(s) depends upon the selected photocatalyst. However, light having wavelength(s) in the visible portion of the electromagnetic spectrum may be used. The intensity / power of the light may be selected based on a desired result as set forth above.

[0028] Other reactants may be used in the present methods. These reactants may be combined with the selected alkane to form a reactant mixture (e.g., a gaseous reactant mixture) which is exposed to the heat and the light as described above. The additional reactants may be alkenes, including alkenes corresponding to any of the alkanes described herein. Alkenes include, e.g., ethylene, propylene, butene, etc. An inert gas may be included in the reactant mixture. However, generally, the reactant mixture is free of O2 and any oxy gen-containing compound (however, this does not preclude the use of a metal oxide support material as described above). The amounts (e.g., partial pressure) of the alkane andAtty. Dkt. No. 00100-0408-PCT other reactants (if present) in the reactant mixture may be selected to achieve a desired result as set forth above. Similarly, when using a flow reactor, the flow rate of the alkane and any other reactants (if present) may be selected to achieve a desired result as set forth above.

[0029] The present methods may be carried out using a variety of reactor systems, including that which is described in the Example, below. Regarding the reactor system described in the Example, below, which is a continuous flow reactor system, the amount of photocatalyst and the method for packing the continuous flow reactor is adjusted to maximize light interaction with the material. This is a different approach, e.g., as compared to existing methods that do not make use of light.

[0030] As further described in the Example below, in at least in some embodiments, the method is able to achieve high values of alkane conversion. In embodiments, the present method is characterized by a rate of product (e.g., olefin, aromatic compound) formation that is at least 200% greater than achieved by the same method conducted in the absence of the light. This includes at least 250% and at least 275% greater. These values may refer to a type of reaction (e.g., alkane dehydrogenation-to-olefin, alkane dehydroaromatization-to-aromatic compound). These values may further refer to a specific alkane (e.g., ethane, propane) or a specific product (e.g., ethylene, propylene, butene, benzene, toluene), including reference to a specific reaction (e.g., ethane-to-ethylene, propane-to-propylene, ethane-to-benzene, propane- to-benzene, propane-to-butene). These values may further refer to a particular set of conditions including a temperature at any value or range of values disclosed herein, a wavelength of light at any value or range of values disclosed herein, and a (plasmonic metal): (dopant metal) molar ratio at any value or range of values disclosed herein. It is unexpected that the present methods were able to achieve such high conversions since alkane dehydrogenation is known to be a challenging reaction. In addition, there is no basis for predicting outcomes for alkane dehydrogenation reactions based on other types of chemical reactions that are fundamentally different such as alkyne hydrogenation reactions.EXAMPLE

[0031] Example 1

[0032] Introduction

[0033] This Example describes the investigation of Cu-based dilute plasmonic alloys for propane dehydrogenation and found that, in the presence of light, combined with thermalAtty. Dkt. No. 00100-0408-PCT heating, the propylene formation rate increased at least 200% compared to dark thermocatalytic conditions. To understand the photocatalytic mechanism, wavelength and power-dependent studies were performed, and the results show a clear trend in propylene formation at the localized surface plasmon resonance (LSPR), suggesting nonthermal contributions are significant in the light-enhancement of propane dehydrogenation rates. Further kinetic studies vary ing propane and H2 partial pressures revealed that light did not alter the first-order dependence of the dehydrogenation process on propane. The observed negative rate order with respect to H2 indicated the inhibitory nature of FL in the dehydrogenation process and suggested that deep dehydrogenation leading to coke formation was not significant in the dilute CuPt alloys. Additionally, CuRh and CuNi dilute plasmonic alloys were tested to demonstrate the generalizability of thermal catalysts for this reaction with the ability to contrast the impact of dopant identity on PDH. This Example sheds light on the efficiency of plasmon enhancement based on the nature of the active sites and has the potential to extend to earth abundant metals, an approach that may be applied to other industrially relevant reactions.

[0034] Methods

[0035] Synthesis of Dilute Plasmonic Alloys. CuPt / SiO2,CuRh / SiO2 and CuNi / SiCh photocatalysts were synthesized through a Strong Electrostatic Adsorption (S.E.A.) synthesis method. Briefly, as illustrated in FIG. 1A, this method involved depositing metal complexes on negatively charged hydroxyl groups on high surface area (280m2 / g) silica support. To prepare the support for ideal metal cation adsorption, nanoparticulate S1O2 was first pretreated with a dropwise addition of 33% Ammonium Hydroxide in milliQ water until a pH of 10 was reached. The P.Z.C. of the nanoparticulate silica was determined to be at pH 3, allowing for a high deprotonation of surface hydroxyl groups at pH 10. The solution was centrifuged at 5000 r.c.f. for 10 minutes at three intervals after the solution was stirred for 6 hours. The washed silica was dried overnight in the oven at 70 °C.

[0036] 1 g of pretreated silica w as added to a 250 mL round bottom flask w ith a stir bar and 100 mL of milliQ water. NH4OH was added dropwise until a pH of 10 was reached and the solution was equilibrated for 1 hour. Further dropwise addition of base was added as needed to maintain the pH. A mixed metal solution with appropriate mols of [CU(NHS)4(H2O)2](NO3)2, [Pt(NH3)4(H2O)2](NO3)2, or RhCls metal cations w as added dropwise with an automatic syringe pump (1 mL / min for 10 min) and the solution was stirredAtty. Dkt. No. 00100-0408-PCT for an hour. The metal complex / SiO? solution was centrifuged at 5000 r.c.f. for 5 minutes before washing with milliQ water three subsequent times. The clear supernatant and light blue colored powder indicated that the Cu complex had successfully adsorbed onto the metal oxide support. The precatalyst was set to air dry overnight at room temperature before further drying in the oven at 70 °C for 4 hours.

[0037] To produce the zerovalent bimetallic nanoparticles, the precatalyst was reduced under 30 seem of hydrogen at 350 °C for 1 hour with a furnace ramp of 10 °C / min.

[0038] Table 1, below, shows the ratios of each metal in the photocatalysts as determined using ICP-OES.

[0039] Table 1. Composition of CuPt / SiCh and CuRh / SiCh photocatalysts.

[0040] Material Characterization.

[0041] STEM micrographs were collected on a JEOL ARM200 instrument with 200 kV electrons after dropcasting 5uL of sample dispersed in milliQ water onto a carbon grid. DRUVS measurements were performed with an Agilent Cary5000 UV-visible spectrometer equipped with a Praying Mantis Diffuse Reflection Accessory (Harrick Scientific Inc.). The sample was placed into the sample chamber of the Cary5000. The sample was packed flat into the sample holder to ensure a relatively smooth surface. DRIFTS measurements were performed with a ThermoFischer Nicolet-550 equipped with an MCT detector. Before DRIFTS experiments, the catalyst had to be reduced at 350 °C under hydrogen for 1 hour (10 °C / min ramp rate). The catalyst was then dosed with CO (10% in Ar) until all platinum group metal (PGM) sites were saturated. The catalyst under CO atmosphere was heated to 110 °C before cooling and purging the cell with Ar until all free gaseous CO was displaced whileAtty. Dkt. No. 00100-0408-PCT collecting spectra every 5 minutes, leaving behind features for bound surface CO. Multi-peak fitting with a mixed Gaussian / Lorentzian line shape was performed using Origin software to differentiate the various Cu and Pt sites in the CuPt samples, with the FWHM determined as described in De Castro, L., et al., J. Phys. Chem. C 2022, 126 (27), 11111-11128, and fixed during the peak fitting process. ICP-OES measurements were performed on a Thermo iCAP 7600 ICP-OES instrument through the Quantitative Bio-element Imaging Center at Northwestern. XPS spectra were collected on a NEXSA G2 instrument to determine elemental composition and oxidation states of the bimetallic plasmonic catalysts.

[0042] Plasmonic Propane Dehydrogenation. 5 mg of CuPGM / SiO2 photocatalyst was loaded on top of 3 mm steel metal disks into a commercial packed-bed reactor (Harrick Scientific Inc.) with a flat quartz window. The sample was illuminated with a spot size of 0.545 cm2with a broadband supercontinuum source (NKT FUI-15) with laser output coupled through a variable bandwidth tunable filter (N.K.T. SuperK Varia). The laser wavelength was set to match the Cu nanoparticle's LSPR at 585 nm with a bandwidth of ±50 nm, the power was controlled with a neutral density filter. 10% Propane in Argon (4 seem), Hydrogen (2 seem), and Argon (44 seem) were flowed through stainless steel piping into the photoreactor and monitored in real time with a mass spectrometer (Hiden HPR-20). Photo and thermal experiments were conducted between 250-520 °C, and temperatures were controlled with an Eazy zone heater (X). Propylene product (m / z = 42) was detected along with reactants such as propane (m / z = 43), hydrogen (m / z = 2), and argon (m / z = 40). The propylene partial pressure was used to determine the catalytic conversion and product formation rate during light and dark conditions. This rate was normalized by the moles of dopant metal in the catalyst for each sample based off ICP-OES data (see Table 1, above).

[0043] Wavelength dependent studies were performed at 585 nm ±25 nm with a power of 50 mW. Wavelength ranged between 400 nm and 800 nm with 50 nm increments. Power dependence studies were performed with 585 nm ±50 nm with powers ranging between 50 mW-200 mW in 25 mW increments.

[0044] The propylene formation rate was calculated using a propylene calibration curve to convert partial pressure into mole percentage. The mole percentage was further converted to the rate of propylene production (Equation 1) by converting it to the molar ratio. Eq 1uation 1) 7Atty. Dkt. No. 00100-0408-PCT

[0045] where Ap (for light on partial pressure, the light off partial pressure is subtracted) corresponds to the molar ratio obtained by converting the propylene (m / z = 42) partial pressure using the propylene calibration curve; f represents the flow rate; and npGM corresponds to the moles of platinum group metals (either Rh or Pt), as determined from the ICP data. Selectivity is given by Equation 2 below: (Equation 2)

[0046] where ntrepresents the moles of produced hydrocarbon and i corresponds to the carbon numbers of the produced hydrocarbon species.

[0047] Results and Discussion

[0048] Synthesizing plasmonic alloys down to the single atom limit. Dilute plasmonic alloy photocatalysts were synthesized through a strong electrostatic adsorption (SEA) synthetic procedure (FIG. 1 A), in which positively charged metal cations adsorb onto a negatively charged metal oxide surface of interest by controlling the pH relative to the support's point of zero charge (PZC). Due to the indiscriminate nature of electrostatic binding, an assortment of metals and supports are amenable to this synthetic method, allowing the deposition of multiple metals concurrently. The composition of the bimetallic nanoparticles can be controlled by adjusting the concentration of the metal cation precursor solutions. In this Example, copper-based catalysts supported on SiCh supports were studied due to their relatively high surface area and low concentration of reactive Bronsted and Lewis sites.

[0049] For CuPt nanoparticles, the average particle size was determined to be 2.98 ± 0.03 nm by bright-held transmission electron microscopy (TEM; data not shown). CuPt / SiCh generally exhibited localized surface plasmon resonances at 585 nm as determined with diffuse reflectance UV-Vis spectroscopy (DRUVS; FIG. IB). To understand the effect of dilute dopant sites on photocatalytic reactivity in dilute plasmonic alloys, two CuPt / SiCh systems were synthesized: one CuPt / SiCh system approaching the single atom (SA) limit and another CuPt / SiCh system in which ensemble (ens) platinum sites dominated, referred to herein as CuPto.oou / SiCh, and CuPto.oitySiCh, respectively. Dilute solute metals (Pt in this Example) can either segregate to the surface or stay within the subsurface (which limits their catalytic contribution), depending on whether the segregation energy of the solute dopant element in the copper solvent host was negative or positive. Similarly, aggregation energiesAtty. Dkt. No. 00100-0408-PCT determine whether alloyants prefer to isolate throughout the copper host as single atoms or aggregate into ensemble sites. In the case of CuPt, the aggregation energy favors the isolation of Pt single atoms in the Cu host. To deduce the nature of the catalyst surface, carbon monoxide (CO) was used to titrate the catalyst surface, and the C-0 bond stretching frequency was monitored using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Due to the back-bonding nature of the CO-metal bond, C-0 stretching is highly sensitive to its surrounding coordination environment, making it a common chemical probe to determine metal site identity in heterogeneous catalysis and organometallic chemistry. CODRIFTS showed that CuPto.ouhad two main features, a ~ 2124 cm’1peak attributed to linearly bound CO on Cu and a broad peak centered at -2021 cm’1attributed to CO bound on Pt ensembles (FIG. 1C). By contrast, for CuPto.0014, in which Pt was isolated as single atom sites, linearly bound CO on Cu was still apparent at 2124 cm’1, but there was no CO vibrational frequency indicative of Pt ensembles. Instead, a new spectral feature at -2113 cm’1emerged, representative of CO bound on isolated Pt atoms in the Cu host (FIG. ID). It is worth noting that the distribution and dispersion of active sites become more complex under catalytic conditions, as adsorbates may stabilize isolated metal sites and cause reverse segregation to the surface or isolated sites aggregation, even when theory predicts segregation to the bulk or isolation as thermodynamically more favorable in the absence of adsorbates.

[0050] Photocatalytic propane dehydrogenation of CuPt dilute plasmonic alloys. CuPto.ooi SiCh and CuPto.ou / SiCh dilute plasmonic alloy photocatalysts were tested for their ability to enhance propane dehydrogenation under photoexcitation. Using a dilute plasmonic alloy architecture, the Pt-sites served as an adsorption site for propane while the plasmonic Cu host afforded the optical properties which make this system an effective photocatalyst. Although increasing Pt loading enhanced catalytic rates, it also slightly dampened the LSPR of the plasmonic host. Consequently, the ratio of Pt / Cu must be carefully selected to achieve maximum photocatalytic enhancements by modifying the propane adsorption energy while also reducing coke formation to achieve high propylene selectivity.

[0051] PDH was performed between 400-520 °C (FIGS. 2A and 2B) with and without photoexcitation at 585 nm to target the LSPR frequency of the CuPt photocatalysts. No reaction was observed below 400 °C under dark or light conditions. Above 520 °C, reaction rates decreased rapidly, likely due to nanoparticle sintering. Pt-ensembles on CuPto.014 exhibited a modest, and relatively constant, light-enhanced propylene formation rate of about 15% across all temperatures studied (data not shown). In contrast, the isolated Pt single atomsAtty. Dkt. No. 00100-0408-PCT of CuPto.0014 displayed significantly increased propylene formation rates compared to dark conditions at the same temperature. The largest degree of light-enhanced propylene formation on CuPtoooi4 was observed at temperatures below 460 °C but remained consistently higher than 50% across the entire temperature range of this study (data not shown). It is also noteworthy that light-enhanced propylene formation rates were equivalent to purely thermocatalytic rates 40 °C lower than the peak reactivity in the studies at 520 °C. These results indicate that, under photoexcitation, the nature of the Pt site (i.e., isolated single atoms or Pt ensembles) was more important to propylene formation rates than intrinsic Pt loading in plasmon-assisted PDH. Specifically, light-enhanced reaction rates for CuPt photocatalysts in the single atom regime were significant, with increased propylene formation under photoexcitation at reduced Pt loadings (FIG. 2D).

[0052] Mechanistic studies of plasmonic propane dehydrogenation. A Pt / Cu ratio (CuPto.004) in the single atom limit that could be reproduced for multiple dopant identities was chosen for further kinetic evaluation. To understand how light enhances propylene production, a series of experiments were performed to help discern the photocatalytic mechanisms. A wavelength dependence experiment was used to determine that the enhanced propylene production was heightened at photoexcitation frequencies overlapping the LSPR (FIG. 3 A). An Arrhenius plot was extracted for CuPto.004 over a 400 °C to 520 °C temperature range both in the dark and under light conditions ( = 585 nm + / - 50 nm, 188 mW). The overall activation energy was determined to be 68 kJ / mol under illumination and 99 kJ / mol in the dark. This clear reduction in the activation energy barrier indicated an electronic contribution of plasmon- induced hot carriers photochemical process (FIG.3B). Although both photothermal heating and non-thermal charge transfer mechanisms can contribute to enhanced photocatalytic rates in plasmonic catalytic processes, non-thermal mechanisms proceed through a new potential energy surface (PES) where a transient negative ion (TNI) state can be formed. This change in PES due to accessing a new electronic excited state redefines the reaction coordinate of the reaction, allowing for new7activation energies at different elementary7reaction steps. This new7reaction coordinate led to altered reactivity7and selectivity outcomes. Enhanced rates observed from plasmonic catalysts were most likely a mix of different enhancement processes, and disentangling these various contributions remains challenging. A power dependent study allowed correlation of which mechanism was the main contributor based off the fit of the plotted reactivity over increasing power. A linear fit is indicative of an electronic process, whereas an exponential fit is more likely to be indicative of a photothermal process. The linearAtty. Dkt. No. 00100-0408-PCT fitting with respect to the power intensity of the PDH rate on the CuPto.004 system indicated that the photoexcited mechanism was an electronic process. (FIG. 3C). These results along with the result that negligible light response was observed on Cu / SiCh (data not shown) indicated electronic contributions from non-thermal carriers, particularly hot carriers that localized the dilute Pt sites, played the primary role in the photochemical enhancement.. Further kinetic experiments of varying CsHs and H2 partial pressure were conducted to understand this plasmon-enhanced process. (FIGS. 3D-3E.) The formation rate of C3H6 exhibited a first-order dependence on the partial pressure of C?Hs under both dark and light conditions. The first- order dependence demonstrated that light did not change the rate-limiting step (RLS), with C- H activation being the RLS independent of photoexcitation. H2 has been reported to exhibit positive effect to reduce coke formation, and a positive rate order indicates the role of H2 in this process. However, a negative rate order was observed for H2 partial pressure that suggested an inhibitory effect of adding H2 under light and dark conditions, providing evidence that coke formation was negligible on the dilute CuPto.004 catalyst. In addition, kinetic isotope studies were performed comparing olefin formation from CH3CH2CH3 and CH3CD2CH3. Negligible changes in KIE values were observed on CuPtEns under both light and dark conditions, whereas an increased KIE was observed on CuPtsA, suggesting the presence of vibrationally excited states that facilitate C-H activation — a feature unique to photochemically dominated processes.

[0053] Investigating the plasmon-assisted PDH CuPt vs. CuRh vs CuNi. Plasmon- assisted PDH activity' of two catalysts prepared with nearly identical loadings (Cu:M=250:l) of CuRh and CuPt (see Table 1, above) was compared to understand the role of alloy ant identity of photocatalytic enhancements and to shed light on the generalizability of light- assisted mechanisms of promising single atom alloy catalysts. CuPt and CuRh catalysts were prepared using SEA on SiCh and exhibited steady-state propylene formations rates of 6.6 mmmmolc3H6gPt'1s'1, 3.8 mmolc3H6gRh'1s’1and 2.3 mmol gxi-1s'1, respectively, at 460 °C in the dark (FIG. 4B).

[0054] In both CuPt and CuRh, the alloy ant identity and the level of dispersion (single atom vs. ensemble) were key contributors to the enhanced propylene formation rates, while the identity7of the alloy ant was predominantly a contributor that modified the potential energy surface of the elementary' steps along the propane dehydrogenation mechanism. Under photoexcitation, the alloyant may play an additional role in modifying the PES of plasmon- assisted PDH. Since both CuRh and CuPt showed light-enhanced propylene formation at the LSPR, understanding how the alloyant affected plasmonic PDH and the possibleAtty. Dkt. No. 00100-0408-PCT contributions of nonthermal charge carrier mechanisms with the adsorbate became an important consideration.

[0055]

[0056] Conclusions

[0057] This Example has described a facile method to synthesize dilute plasmonic alloy catalysts, and the activities of CuPt and CuRh nanoparticles dispersed on SiC>2 were tested for non-oxidative propane dehydrogenation under combined light and external heating conditions. Pt single-atom sites, as determined by CO DRIFTS, in the Cu host have been shown to enhance propylene formation rates beyond those achievable with dilute alloys that exhibit Pt ensembles at their surface. CuPt exhibited wavelength-dependent propylene formation with maximum rates at the localized surface plasmon resonance wavelength of 585 nm and a linear increase in propylene formation rates in power-dependence experiments. These results combined with a measured decrease in the apparent activation energy barrier under illumination are suggestive of contributions of photochemical mechanisms associated with nonthermal charge carriers. It was proposed that hot holes generated and localized at the surface of the dilute plasmonic alloy were the primary contributors to the plasmon-assisted propane dehydrogenation reaction.

[0058] The generalizability of light-assisted propane dehydrogenation was examined by varying dopants (Pt, Rh, and Ni), where light responses were also observed on CuRh and CuNi. This demonstrates both the broad applicability7of the method, including extension to earth-abundant elements such as Ni, Co. and Fe. This Example demonstrates the use of dilute plasmonic alloys for propane dehydrogenation as well as using active site engineering in plasmonic photocatalytic processes aiding in the transition to sustainable chemical manufacturing using renewable energy' sources such as visible light.

[0059] Additional information related to this Example, including data / information indicated as not being shown, may be found in U.S. Provisional Patent Application No. 63 / 715,383, fded November 1, 2024, which is incorporated by reference in its entirety.

[0060] Example 2

[0061] Additional experiments w ere conducted to explore light-assisted C-C coupling on Cu catalysts by varying the saturation level of Ch species (propane, propylene, and propyne). Benzene formation was not observed on Cu when using propane, likely due to the high C-HAtty. Dkt. No. 00100-0408-PCT activation barrier on pure Cu surfaces. In contrast, benzene formation occurred with propylene and propyne, with the latter exhibiting a clear light response, suggesting that with suitable starting materials (due to favorable Cu-adsorbate interactions reflected in orbital overlap), Cu itself can facilitate light-induced C-C coupling to produce benzene.

[0062] Additional experiments were conducted to investigate C2 (ethylene and acetylene) trimerization on Cu, using acetylene trimerization on Ag as a reference. A light response was observed only on Cu, not on Ag, further demonstrating the potential of Cu as a photocatalyst for C-C coupling reactions. Also examined was C2-C4 dehydroaromatization on CUPISA; benzene formation was absent with ethane but occurred with ethylene, propane, and butane, with the yield increasing with hydrocarbon chain length — likely due to a favorable entropic contribution from longer hydrocarbons.

[0063] The results of additional experiments using CuPto.004 (synthesized per Example 1) and ethane as the reactant (carried out per Example 1) are shown in FIGS. 8A-8C. These results further demonstrate use of the present photocatalysts in the present methods to dehydrogenate alkanes (here, ethane) to form olefins (here, ethylene). Specifically, FIG. 8A shows the production of the H2 by-product under light illumination; FIG. 8B shows H2 production as a function of temperature under both dark and light conditions; FIG. 8C shows the activation barrier for H2 formation. As shown in FIG. 9. the CuPt photocatalyst (synthesized per Example 1) is also able to dehydroaromatize ethane to benzene using the present methods at higher Pt loadings (CuPto.014) and higher temperatures (590°C).

[0064] The results of additional experiments using AgPto 2 (synthesized per Example 1) and propane as the reactant (carried out per Example 1) are show n in FIGS. 10A-10C. These results further demonstrate use of the present photocatalysts in the present methods to induce C-C reactions involving products and / or intermediate species formed when using alkane reactants (e.g., propane) to form aromatic compounds (e.g., benzene). Specifically, FIG. 10A show s the production of the benzene under light illumination; FIG. 10B shows benzene production as a function of temperature under both dark and light conditions; FIG. 10C shows the activation barrier for benzene formation. Similar results for AgPto.2 using ethane as the reactant (carried out per Example 1) to produce benzene were also obtained (data not shown).

[0065] Finally, additional experiments using CuPto.004 (synthesized per Example 1) were conducted by co-flowing propane and butane, as well as by flowing propane and butaneAtty. Dkt. No. 00100-0408-PCT separately as references. Reactions using propylene and butene as reactants (carried out according to Example 1) were also performed. The results are shown in FIG. 11 A-l ID and demonstrate the ability of the present photocatalysts and the present methods to induce C-C cross-coupling reactions, e.g., propane + propane to produce benzene; propane + butane to produce toluene; propylene + propylene to produce benzene; propylene + butene to produce toluene.

[0066] Additional information related to this Example, including data / information indicated as not being shown, may be found in U.S. Provisional Patent Application No. 63 / 715,383, filed November 1, 2024, which is incorporated by reference in its entirety.

[0067] The word "illustrative" is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "illustrative" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, "a" or "an" means "one or more.’'

[0068] If not already included, all numeric values of parameters in the present disclosure are proceeded by the term “about” which means approximately. This encompasses those variations inherent to the measurement of the relevant parameter as understood by those of ordinary skill in the art. This also encompasses the exact value of the disclosed numeric value and values that round to the disclosed numeric value.

[0069] The foregoing description of illustrative embodiments of the disclosure has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosure. The embodiments were chosen and described in order to explain the principles of the disclosure and as practical applications of the disclosure to enable one skilled in the art to utilize the disclosure in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the claims appended hereto and their equivalents.

[0070] In recognition of the inherent nature of chemical synthesis, throughout the present disclosure, terms and phrases such as “absence,” “free,” “does not comprise,” etc. encompass, but do not require a perfect absence of the referenced entity.

[0071] The term “type” as used herein refers to chemical formula such that a single type means the same chemical formula and different type means different chemical formula.Atty. Dkt. No. 00100-0408-PCTSimilarly, use of “more’' as in “one or more'’ refers to use of different types of the relevant entity.

[0072] Terms such as “comprising” and the like may be replaced with terms such as “consisting” and the like.

Claims

Atty. Dkt. No. 00100-0408-PCTWHAT IS CLAIMED IS:1 . A method for dehydrogenation of an alkane to a product, the method comprising exposing an alkane to heat and light in the presence of a nanostructured photocatalyst comprising a plasmonic metal and a dopant metal, wherein the light generates localized surface plasmon resonances in the nanostructured photocatalyst and the alkane undergoes dehydrogenation to produce a product.

2. The method of claim 1, wherein the dopant metal is incorporated as isolated, single atoms distributed in the plasmonic metal.

3. The method of claim 1, wherein the plasmonic metal and the dopant metal are present in the nanostructured photocatalyst at a (plasmonic metal): (dopant metal) molar ratio of from 1000: 1 to 200: 1.

4. The method of claim 1, wherein the nanostructured photocatalyst is in the form of a plurality of nanoparticles distributed on a surface of a support material.

5. The method of claim 1, wherein the plasmonic metal is selected from Cu, Au, Ag, or a combination thereof and the dopant metal is selected from Pt, Pd, Ni, Ru, Rh, Fe, Co, or a combination thereof.

6. The method of claim 1, wherein the nanostructured photocatalyst comprises nanostructured CuPt, CuPd, CuRh, Cu Ni, or a combination thereof.

7. The method of claim 6. wherein the nanostructured photocatalyst is in the form of a plurality of nanoparticles distributed on a surface of a metal oxide support material.

8. The method of claim 1, wherein the alkane is ethane, propane, butane, pentane, hexane, cyclohexane, 2-methylpropane, isobutane, or a combination thereof.

9. The method of claim 1, wherein the product comprises an olefin corresponding to the alkane.

10. The method of claim 1, wherein the product comprises an aromatic compound.Atty. Dkt. No. 00100-0408-PCT11. The method of claim 1, wherein the method is carried out at a temperature of no greater than 600°C.

12. The method of claim 11, wherein the light is visible light.

13. The method of claim 1. wherein the method does not comprise use of O2 and does not comprise use of an oxygen-containing compound.

14. The method of claim 1, wherein the dopant metal is incorporated as isolated, single atoms distributed in the plasmonic metal; the plasmonic metal is selected from Cu, Au, Ag, or a combination thereof and the dopant metal is selected from Pt, Pd, Ni, Ru, Rh, Fe, Co, or a combination thereof; and the nanostructured photocatalyst is in the form of a plurality of nanoparticles distributed on a surface of a metal oxide support material.

15. The method of claim 14, wherein the method is carried out at a temperature of no greater than 600°C and the light is visible light.

16. The method of claim 14, wherein the alkane is ethane, propane, or a combination thereof and the product comprises ethylene, propylene, butene, benzene, or a combination thereof.

17. The method of claim 14, wherein the nanostructured photocatalyst comprises nanostructured CuPt. CuPd, CuRh, CuNi, or a combination thereof.

18. The method of claim 17, wherein the method is carried out at a temperature of no greater than 600°C and the light is visible light.

19. The method of claim 18, wherein the alkane is ethane, propane, or a combination thereof and the product comprises ethylene, propylene, butene, benzene, or a combination thereof20. The method of claim 19, wherein the method is characterized by a rate of formation of the product that is at least 200% greater than that achieved by the method conducted in absence of the light.

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