Complex multicationic catalysts for co2 conversion

Abstract

The present invention relates to a multi cationic high-entropy (HEO) oxide catalysts comprising at least 5 metal cations. The catalysts are used to reduce carbon dioxide to methane, methanol and carbon monoxide.

Description

[0001] Complex multicationic catalysts for CO2 conversion

[0002] Field

[0003] The present invention relates to a multi cationic entropy oxide catalyst.

[0004] Background

[0005] With the ever-growing need for a dynamic energy economy that can utilize local renewable sources, catalyst development has required a fundamental shift away from ones developed for processes utilizing centralized fossil fuels to smaller-scale processes utilizing decentralized local resources and / or waste streams (e.g. CO2). New catalytic materials that are more selective, more active, and more stable than the status quo are needed, and they need to be specifically tunable to an ever-growing set of specific conversion reactions. Therefore, a material class with a large parametric space coupled to a material synthesis platform to easily tune properties is a Holy Grail for catalyst design.

[0006] The modifier "high-entropy" has been coined to describe the extreme configurational entropy of one such emerging class of materials. The unique properties of high-entropy materials (HEMs) originate in the homogeneous incorporation of >5 equimolar cations into a single crystalline phase. High-entropy alloys (HEAs), having been discovered over a decade before many other high-entropy material classes, have been applied and explored for a wide range of catalytic processes. These efforts have shown that high-entropy forms could play a pivotal role in catalyst design. Specifically, chemical compositions in HEAs were achievable that were previously limited by miscibility barriers. In the case of catalytic decomposition of ammonia, this allowed for theoretically targeted optimal catalyst compositions to be realized in material design and synthesis. Additionally, lattice distortions from different atomic sizes allow for thermodynamically non-equilibrium states resulting in reduced energy barriers for surface chemical processes. Finally, the increased sluggish diffusion kinetics as well as entropy stabilization results in enhanced stability.

[0007] As the general category of high-entropy materials has expanded to include oxides and other classes, the complexity and range of structures have grown, including the discovery of high- entropy oxide forms of structures like rock salt, fluorite, spinel, and garnet. However, as more complex oxide structures are being adapted to high-entropy forms, it is currently heavily discussed how one defines a material as "high-entropy" and if the criteria for HEA can be directly applied to other materials. A universal configurational entropy value for HEMs called the entropic metric (EM) was proposed8, where sublattices can be taken into account. Following this definition, materials with EM < 1 are "low-entropy", 1 < EM < 1.5 are "medium entropy", and EM > 1.5 are "high-entropy". By using this metric, the number of cations needed to qualify as "high-entropy" varies depending on structure. For example, spinel oxide structure A2BO4 with three different A cations (with equimolar concentration) and four different B cations (with equimolar concentration) has an EM > 1.5 and is thus "high-entropy", while A2BO4 with two different A cations (with equimolar concentration), and five different B cations (with equimolar concentration) has 1 < EM < 1.5 and is classified as medium entropy. However, in literature the descriptor "high-entropy" is far from consistently applied and is evolving.

[0008] Despite the increasing interest in HEOs for both fundamental understanding and their applications, HEOs have so far only been evaluated for a relatively narrow patchwork of heterogenous catalytic systems. The development of HEOs for catalysis is further complicated by the fact that the most common synthesis method for HEOs, solid-state synthesis, is often not suitable for heterogeneous catalysis because of the resulting low porosity and poor control of morphology and particle size of the synthesis product. Recently, different porous high- entropy precursors to high-entropy oxides have been developed, where it was shown that porosity and morphology could be maintained from the precursor through heat treatments to produce HEOs. Examples of such precursors are layered double hydroxides (LDHs), which have been shown to readily adapt to high-entropy forms with as many as 10 cations being incorporated, and which can also easily be tailored to incorporate a wide range of combinations of cations. Similarly, high-entropy hydroxides and other hydroxycarbonate structures have also been shown to be adaptable to high-entropy forms, where a large combination of cations can also be used to direct synthesis to produce a variety of oxide structures. Additionally, high- entropy glycerolate precursors can be used to synthesize complex morphologies for HEOs, including mesoporous spheres, with a solvothermal synthesis method. However, it is unknown whether these high-entropy materials can provide a benefit to some of the most pressing catalytic reactions, where the discovery of new active materials are needed.

[0009] With carbon dioxide being a waste product from many local sources like cement plants or other industrial processes, its valorization to hydrocarbons is a promising path to reaching a net-zero carbon emission economy, even opening a path towards maintaining many activities that require hydrocarbons as high-density energy carriers like fuels. The methanation of CO2 is thermodynamically favorable at low temperatures, but kinetic limitations at these temperatures result in the need for a catalyst to achieve acceptable conversion rates. The most widely used catalyst (nickel on alumina) requires high reaction temperatures, while low-temperature conversion, often defined as a reaction temperature <300°C, generally requires an expensive noble metal like ruthenium or rhodium.

[0010] Recently, medium and high-entropy oxides have been used to derive Ni-Co metallic methanation catalysts. However, the process for generating catalytically active metallic sites also resulted in the loss of the "high-entropy" form in the support as well as severe loss in porosity. Ultimately this means that any synergy between the active site and the high-entropy support was not possible to be observed. These studies show very little enhanced catalytic properties compared to metallic nickel or metallic nickel-cobalt on various oxide supports, and it remained unknown whether HEOs could provide any benefit to such a reaction.

[0011] Based on the above-mentioned state of the art, the objective of the present invention is to provide means and methods to obtain multi cationic enhanced entropy oxides with high CO2 and NOXconversion rates in low temperatures. This objective is attained by the subject-matter of the independent claims of the present specification, with further advantageous embodiments described in the dependent claims, examples, figures and general description of this specification.

[0012] Summary of the Invention

[0013] A first aspect of the invention relates to a multi cationic oxide catalyst comprising at least 5 metal cations.

[0014] A second aspect of the invention relates to a method for preparing a multi cationic oxide catalyst comprising the steps of a. providing a cationic precursor comprising at least 5 metal cations, b. calcinating said cationic precursor, in particular to a temperature in the range of 250-700 °C. yielding a multi cationic oxide catalyst.

[0015] A third aspect of the invention relates to a method for converting CO2 or NOX, particularly for converting CO2, using hydrogen or ammonia, in the presence of an active multi cationic oxide catalyst according the first and second aspect of the invention.

[0016] Terms and definitions

[0017] General

[0018] For purposes of interpreting this specification, the following definitions will apply and whenever appropriate, terms used in the singular will also include the plural and vice versa. In the event that any definition set forth below conflicts with any document incorporated herein by reference, the definition set forth shall control.

[0019] The terms “comprising”, “having”, “containing”, and “including”, and other similar forms, and grammatical equivalents thereof, as used herein, are intended to be equivalent in meaning and to be open-ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. For example, an article “comprising” components A, B, and C can consist of (i.e., contain only) components A, B, and C, or can contain not only components A, B, and C but also one or more other components. As such, it is intended and understood that “comprises” and similar forms thereof, and grammatical equivalents thereof, include disclosure of embodiments of “consisting essentially of” or “consisting of.”

[0020] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit, unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the disclosure, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure.

[0021] Reference to “about” a value or parameter herein includes (and describes) variations that are directed to that value or parameter per se. For example, description referring to “about X” includes description of “X.”

[0022] As used herein, including in the appended claims, the singular forms “a”, “or” and “the” include plural referents unless the context clearly dictates otherwise.

[0023] "And / or" where used herein is to be taken as specific recitation of each of the two specified features or components with or without the other. Thus, the term "and / or" as used in a phrase such as "A and / or B" herein is intended to include "A and B," "A or B," "A" (alone), and "B" (alone). Likewise, the term "and / or" as used in a phrase such as "A, B, and / or C" is intended to encompass each of the following aspects: A, B, and C; A, B, or C; A or C; A or B; B or C; A and C; A and B; B and C; A (alone); B (alone); and C (alone).

[0024] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art (e.g., in cell culture, molecular genetics, nucleic acid chemistry, hybridization techniques and biochemistry, organic synthesis). Standard techniques are used for molecular, genetic, and biochemical methods (see generally, Sambrook et al., Molecular Cloning: A Laboratory Manual, 4th ed. (2012) Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. and Ausubel et al., Short Protocols in Molecular Biology (2002) 5th Ed, John Wiley & Sons, Inc.) and chemical methods.

[0025] The term near equimolar in the context of the present specification relates to a non- equimolar that satisfy the entropic metric. The more cations the more non-equimolar concentration will still satisfy the entropic metric. The equipmolarity is defined by:

[0026] 100% / (number of elements) *0.5. The term rare earth metal in the context of the present specification relates to the 17 elements belonging to the group 3 elements with the exception of actinium, and the lanthanoids.

[0027] The term base metal in the context of the present specification relates to non-ferrous metals excluding precious metals including silicon, iron, nickel, lead, zinc, copper, cerium, aluminium, tin, tungsten, molybdenum, tantalum, cobalt, bismuth, cadmium, titanium, zirconium, antimony, manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium, niobium, rhenium and thallium and their alloys.

[0028] The term noble metal in the context of the present specification relates to metallic chemical elements, generally resistant to corrosion. Examples include gold, platinum, ruthenium, rhodium, palladium, osmium, iridium, silver.

[0029] The term alkaline earth metal in the context of the present specification relates to group 2 elements including beryllium, magnesium, calcium, strontium, barium, and radium.

[0030] Any patent document cited herein shall be deemed incorporated by reference herein in its entirety.

[0031] Detailed Description of the Invention

[0032] A first aspect of the invention relates to a multi cationic oxide catalyst comprising at least 5 metal cations.

[0033] In certain embodiments, the multi cationic oxide catalyst comprises at least 6 metal cations. Multi cationic oxide catalysts show increased performances in CO2 conversion to methane, methanol or C2H4 hydrocarbons.

[0034] In certain embodiments, the multi cationic oxide catalyst comprises at least 7 metal cations.

[0035] Multi cationic oxide catalysts comprising at least 7 metal cations retain the mixed metal oxide structure before and after the reaction. Additionally, multi cationic oxide catalysts show a higher reducibility and a broad operating temperature regime, providing a more stable catalyst that is suitable for use in a wide range of conversion reactions.

[0036] In certain embodiments, the multi cationic oxide catalyst comprises 7 metal cations.

[0037] Multi cationic oxide catalysts comprising 7 cations allow for stabilising dispersed catalytic active sites and strong support interaction. They further increase concentration and stability of oxygen vacancies, acidic sites, or basic sides.

[0038] In certain embodiments, the multi cationic oxide catalyst comprises 5 to 16 metal cations.

[0039] In certain embodiments, the multi cationic oxide catalyst comprises 5 to 15 metal cations.

[0040] In certain embodiments, the multi cationic oxide catalyst comprises 5 to 14 metal cations. In certain embodiments, the multi cationic oxide catalyst comprises 5 to 13 metal cations.

[0041] In certain embodiments, the multi cationic oxide catalyst comprises 5 to 12 metal cations.

[0042] In certain embodiments, the multi cationic oxide catalyst comprises 5 to 11 metal cations.

[0043] In certain embodiments, the multi cationic oxide catalyst comprises 5 to 10 metal cations.

[0044] In certain embodiments, the multi cationic oxide catalyst comprises 6 to 16 metal cations.

[0045] In certain embodiments, the multi cationic oxide catalyst comprises 6 to 15 metal cations.

[0046] In certain embodiments, the multi cationic oxide catalyst comprises 6 to 14 metal cations.

[0047] In certain embodiments, the multi cationic oxide catalyst comprises 6 to 13 metal cations.

[0048] In certain embodiments, the multi cationic oxide catalyst comprises 6 to 12 metal cations.

[0049] In certain embodiments, the multi cationic oxide catalyst comprises 6 to 11 metal cations.

[0050] In certain embodiments, the multi cationic oxide catalyst comprises 6 to 10 metal cations.

[0051] In certain embodiments, the multi cationic oxide catalyst comprises 7 to 16 metal cations.

[0052] In certain embodiments, the multi cationic oxide catalyst comprises 7 to 15 metal cations.

[0053] In certain embodiments, the multi cationic oxide catalyst comprises 7 to 14 metal cations.

[0054] In certain embodiments, the multi cationic oxide catalyst comprises 7 to 13 metal cations.

[0055] In certain embodiments, the multi cationic oxide catalyst comprises 7 to 12 metal cations.

[0056] In certain embodiments, the multi cationic oxide catalyst comprises 7 to 11 metal cations.

[0057] In certain embodiments, the multi cationic oxide catalyst comprises 7 to 10 metal cations.

[0058] In certain embodiments, the multi cationic oxide catalyst comprises a homogenous distribution.

[0059] The cations of the multi cationic oxide catalyst are arbitrarily distributed within the structure in a given phase.

[0060] In certain embodiments, the metal cations with the same valence are equimolar.

[0061] In certain embodiments, the metal cations with the same valence are near equimolar.

[0062] Near equimolar ratios improve performance of the catalyst, i.e. improved reducibility of the catalytically active metal site and increase oxygen defect, acidic sites and basic sites in the lattice.

[0063] In certain embodiments, the multi cationic oxide catalyst comprises an entropic metric of >1.15.

[0064] In certain embodiments, the multi cationic oxide catalyst comprises an entropic metric in the range of < 2.5 to >1.15. In certain embodiments, the metal cations are selected from the groups of rare earth metal cations, noble metal cations, base metal cations, and alkaline earth metal cations.

[0065] In certain embodiments, the metal cations are selected from the groups of from base metal cations and alkaline earth metal cations.

[0066] In certain embodiments, the metal cations are selected from the group of rare earth metal cations.

[0067] In certain embodiments, the metal cations are selected from the group of noble metal cations.

[0068] In certain embodiments, the metal cations are selected from the group of base metal cations.

[0069] In certain embodiments, the metal cations are selected from the group of alkaline earth metal cations.

[0070] In certain embodiments, the metal cations are selected from Al, Cr, Fe, Ga, In, Ho, Y, Er, Yb, Ce, Mg, Co, Ni, Zn, Mn, Cu, Ca, Sr or Si.

[0071] The selection of the metal cations affects the preference to specific products. Therefore the specific selection of metal cations directs to different final products. Additionally the different metal cations and their combinations can change available oxygen vacancies, basic sites, and acidic sites which also can direct the different reaction pathways to get different products.

[0072] In certain embodiments, the metal cations are selected from Al, Cr, Fe, Mg, Co, Ni or Zn.

[0073] The metal cations are catalytically active for CO2 conversion, particularly for CO2 methanation. Having metal cations Al, Cr, Fe, Mg, Co, Ni, Cu or Zn, particularly Al, Cr, Fe, Mg, Co, Ni or Zn in the multi cationic oxide catalyst improves the catalyst stability and lowers the process conditions to achieve a high selectivity and conversion for CO2 methanation.

[0074] In certain embodiments, the metal cations are selected from Al, Ca, Co, Cr, In, Ni, Ho, Zn or Ce, Cr, Cu, Er, Fe, Ga, In, Ni, Y, Zn, particularly Al, Ca, Ce, Co, Cr, Cu, Er, Fe, Ga, In, Ni, Y or Zn.

[0075] In certain embodiments, the metal cations are Al, Ca, Co, Cr, In, Ni, Ho, Zn or Ce, Cr, Cu, Er, Fe, Ga, In, Ni, Y, Zn, particularly Al, Ca, Co, Cr, In, Ni, Zn or Ce, Cr, Cu, Er, Fe, Ga, In, Y, Zn.

[0076] The metal cations are catalytically active for CO2 conversion, particularly for CO2 conversion to methanol.

[0077] Having metal cations Al, Ca, Co, Cr, In, Mg, Ni, Ho, Zn or Ce, Cr, Cu, Er, Fe, Ga, In, Y, Zn, particularly Al, Ca, Co, Cr, In, Ni, Zn or Ce, Cr, Cu, Er, Fe, Ga, In, Y, Zn present in the multi cationic oxide catalyst improves catalyst stability and results in increased methanol yields compared to non-high entropy counterparts. In certain embodiments, the base metal cations are selected from Al, Ce, Co, Cr, Mg, Mn, Si, Sr or Zn.

[0078] The metal cations are catalytically active for CO2 conversion, particularly for CO2 conversion to C2H4 hydrocarbons.

[0079] In certain embodiments, the metal cations are selected from Al, Ca, Ce, Cr, Ho, Cu, Fe, Ga, Mg, Mn, Ni or Zn, particularly Al, Ca, Ce, Cu, Cr, Fe, Ga, Mg, Mn, Ni or Zn, more particularly Al, Ca, Ce, Cr, Fe, Ga, Mg, Mn, Ni or Zn.

[0080] The metal cations are catalytically active for CO2 conversion, particularly for CO2 conversion to CO.

[0081] In certain embodiments, the metal cations are selected from Co2+, Co3+, Ni2+, Ni3+, Zn2+, Zn3+, Mn2+, Mn3+, Al2+, Al3+, Cr2+, Cr3+, Fe2+, Fe3+Ga3+, ln3+, Ho3+, Y3+, Er3+, Yb3+, Ce3+, Ce4+, Mg2+, Ca2+, Sr2+, Cu2+, Cu1+' orSi4+.

[0082] In certain embodiments, one of the metal cations is an alkaline earth metal.

[0083] In certain embodiments, the alkaline earth metal cation is Mg, Ca or Sr.

[0084] In certain embodiments, the alkaline earth metal cation is Ca and Mg.

[0085] In the conversions of CO2 to methanol the alkaline earth metal cation is Ca.

[0086] In certain embodiments, the multi cationic oxide catalyst comprises 7 metal cations and an oxide anion.

[0087] In certain embodiments, the multi cationic oxide catalyst is selected from (Mg, Co, Ni, Zn)(AI, Cr, Fe) Ox , and (Mg, Co, Ni, Zn, Mn) Ox.

[0088] In certain embodiments, x in Oxis 25 wt% to 35 wt%.

[0089] In certain embodiments, the multi cationic oxide catalyst is (Mg, Co, Ni, Zn)(AI, Cr, Fe) Ox.

[0090] In certain embodiments, the multi cationic oxide catalyst can be doped.

[0091] A second aspect of the invention relates to a method for preparing a multi cationic oxide catalyst comprising the steps of a. providing a cationic precursor comprising at least 5 metal cations, b. calcinating said cationic precursor, in particular to a temperature in the range of 250-700 °C. yielding a multi cationic oxide catalyst. In certain embodiments, the cationic precursor is prepared comprising the steps of a. dissolving metal nitrates in water, yielding a solution, b. autoclaving the solution, yielding a cationic precursor.

[0092] In certain embodiments, the cationic precursor is calcinated to a temperature in the range of 350 to 500 °C.

[0093] In certain embodiments, the cationic precursor is calcinated at a rate of 2 °C per minute until a temperature of 450 °C is reached.

[0094] In certain embodiments, the cationic double hydroxide precursor is calcinated for 2 h under air.

[0095] In certain embodiments, the metal cations have an oxidation state of +111 or +11.

[0096] In certain embodiments, the metal cations have an oxidation state +111 are equimolar to each other.

[0097] In certain embodiments, the metal cations have an oxidation state +11 are equimolar to each other.

[0098] A third aspect of the invention relates to a method for converting CO2 or NOX, particularly for converting CO2, using hydrogen or ammonia, in the presence of an active multi cationic oxide catalyst according to the first aspect or second aspect of the invention.

[0099] In certain embodiments, the method yields methane, methanol, CO, C2-C4 hydrocarbons or nitrogen.

[0100] In certain embodiments, the method yields methane, methanol, CO, C2-C4 hydrocarbons.

[0101] In certain embodiments, the method yields methane, methanol or CO.

[0102] In certain embodiments, the method comprises the step of reducing the active multi cationic oxide catalyst under hydrogen.

[0103] In certain embodiments, the method is conducted at a temperature in the range of 200 to 450 °C.

[0104] In certain embodiments, the method is conducted at a temperature in the range of 200 to 380 °C.

[0105] In certain embodiments, the method is conducted at a temperature in the range of 250 to 380 °C.

[0106] In certain embodiments, the reaction of the method has the ratio of H2 and CO2 is 1 to 6.5.

[0107] In certain embodiments, the reaction of the method has the ratio of H2 and CO2 is 2 to 6.5.

[0108] In certain embodiments, the reaction of the method has the ratio of H2 and CO2 is 3 to 6.5. In certain embodiments, the metal cations are selected from Al, Cr, Fe, Mg, Co, Ni or Zn for converting CO2 into methane.

[0109] A catalyst comprising these metal cations obtained high methane selectivity.

[0110] In certain embodiments, the metal cations are selected from Al, Ca, Ce, Co, Cr, Cu, Er, Fe, Ga, In, Ni, Y or Zn for converting CO2 into methanol.

[0111] In certain embodiment, the metal cations are selected from Al, Ca, Co, Cr, In, Ni and Zn or Ce, Cr, Cu, Er, Fe, Ga, In, Y and Zn for converting CO2 into methanol.

[0112] A catalyst comprising these metal cations obtained high methanol selectivity, while suppressing CO formation, resulting in high yields for methanol.

[0113] In certain embodiments, the metal cations are selected from Al, Ce, Co, Cr, Mg, Mn, Si, Sr or Zn for converting CO2 into C2-C4 hydrocarbons.

[0114] In certain embodiments, the metal cations are selected from Al, Ca, Ce, Cr, Fe, Ga, Mg, Mn, Ni or Zn for converting CO2 into CO.

[0115] In certain embodiments, the metal cations are selected from Al, Ce, Co, Cu, Fe, Mg, or Mn for converting CO2 into nitrogen .The invention is further illustrated by the following examples and figures, from which further embodiments and advantages can be drawn. These examples are meant to illustrate the invention but not to limit its scope.

[0116] Description of the Figures

[0117] Fig. 1 shows the catalytic performance in respect to carbon dioxide conversion and methane selectivity for high-entropy oxides derived from various porous high- entropy precursors. Catalytic activity was screened using a fixed-bed reactor. The catalyst was initially reduced under H2 (F^ / Ar 1 / 5) at 450°C for 60 min. The gas was switched to a mix of H2 / CO2 with a molar ratio of 5.5 at 5 bar. The resulting gases were then fed into an FTIR-gas cell installed in a Bruker Alpha spectromete

[0118] Fig. 2 shows CO2 hydrogenation catalytic results for three HEO samples 5-cation (Co,AI,Cr,Fe,ln), 6-cation (Co,AI,Cr,Fe,ln,Ga) and 7-cation (Co,AI,Cr,Fe,ln,Fa,Ce). The reaction conditions were 1 : 3 : 1.5 : 0.75 CO2: H2: N2: He at 50barg using a fixed bed Flowrence XR fixed-bed reactor unit with sampling of the products by gas chromatography (Agilent 8890B). All samples showed catalytic activity for CO2 hydrogenation with a preference to methanol formation.

[0119] Fig. 3 a) and b) show (Top) Scanning electron micrographs of calcined multi-cationic oxides. (Middle) X-ray powder diffraction of precursors, calcined, and after reaction. (Bottom) Nitrogen adsorption and desorption isotherms with inset graph showing the distribution of the pore volume.

[0120] Fig. 4 shows (a) HAADF image and the elemental mapping for all cations, (b) XANES spectra taken at K-edge for Cr, Fe, Co, Ni, and Zn. The dotted line as the metal foil reference and the grey lines are the oxide reference for each element.

[0121] Fig. 5 shows various formulations with increasing amount of metals at a reaction temperature of 300 °C. The percent conversion tends to improve as the number of cations increase. The reaction conditions were 300°C and a flowrate of 14.5 mL min-1 (1 : 4 : 1.5 : 0.75 CO2 : H2 : N2 : He) at 50barg using a fixed bed Flowrence XR fixed-bed reactor unit with sampling of the products by gas chromatography (Agilent 8890B).

[0122] Fig 6 shows the stability of high performing materials (AICaCoCrlnNiZnOx) for methanol formation over time. The reaction conditions were 300°C and a flowrate of 14.5 mL min-1 (1 : 4 : 1.5 : 0.75 CO2 : H2 : N2 : He) at 50barg using a fixed bed Flowrence XR fixed-bed reactor unit with sampling of the products by gas chromatography (Agilent 8890B).

[0123] Description of the Tables

[0124] Table 1 shows sample name with description of number of cations, which cations, and synthesis method. List of samples and the measured chemical formulas. Materials with 7 cations were measured by WD-XRF while materials with less complex chemistry like the 5-cation and the 3-cation samples were measured by EDX. Ni-alumina samples was measured using combinatorial neutron imaging.

[0125] Table 2 shows BET surface area numbers before and after reaction. Measured pore volumes by BJH method before and after reaction.

[0126] Table 3 shows summary of medium and high-entropy oxides tested for CO2 methanation.

[0127] Table 4 shows the highest performing high-entropy oxide that led to methanol flow rates above 0.005 mol / (h*gCat). 15 mg per sample were loaded in fixed-bed reactor (Flowrence XR fixed-bed reactor unit). The reaction conditions were set to 50 barg and a flowrate of 14.5 mL min-1 (1 : 4 : 1.5 : 0.75 CO2 : H2 : N2 : He) with He as internal standard. 3 temperatures (250, 275 and 300 °C) were probed and the products were analysed by gas chromatography (Agilent 8890B). The same applies to the tables 5 to 8. Table 5 shows high-throughput screening data that resulted in greater than 80% selectivity for CO.

[0128] Table 6 shows high-throughput screening data that resulted in greater than 80% selectivity for CH4.

[0129] Table ? shows various formulations with increasing amount of metals at a reaction temperature of 300 °C. The percent conversion tends to improve as the number of cations increase.

[0130] Table 8 shows a 7- metal catalyst with a high selectivity toward methanol formation.

[0131] Examples

[0132] Example 1: Preparation of high-entropy oxides for CO2 conversion to methane

[0133] A series of porous medium- and high-entropy oxides were synthesized in order to evaluate their catalytic activity for CO2 methanation. 7-cation layered double hydroxides (HE-LDHs) were synthesized utilizing both a hydrothermal synthesis method, and a precipitation method. A 5-cation oxides derived from multi cationic spherical glycerolates were synthesized utilizing a solvothermal method. A 7-cation hydroxycarbonate was synthesized utilizing a precipitation method previously developed for high-entropy hydroxycarbonates. As a reference material, a low-entropy 3-cation LDH (Mg, Al, Ni) was also synthesized utilizing the hydrothermal method. Finally, nickel precipitated on alumina was used as an additional reference. A summary of the synthesized materials can be found in Table 1. All the oxides are named for the number of cations and type of precursor.

[0134] To form high-entropy layered double hydroxides (HE-LDHs) through a hydrothermal method [1], 1.25 mmol of magnesium nitrate hexahydrate (Mg(NO3)2 6H2O, Sigma-Aldrich, >98% purity), 1.25 mmol of zinc nitrate hexahydrate (Zn(NO3)2 6H2O, Sigma-Aldrich, >98% purity), 1.25 mmol of nickel nitrate hexahydrate (Ni(NO3)2 6H2O, Fluka, >97% purity), 1.25 mmol of cobalt nitrate hexahydrate (Co(NO3)2 6H2O, Sigma-Aldrich, >98% purity), 0.83 mmol of aluminium nitrate nonahydrate (AI(NO3)3 9H2O, Sigma-Aldrich, >98% purity), 0.83 mmol chromium nitrate nonahydrate (Cr(NO3)3 9H2O, Sigma-Aldrich, >99% purity), and 0.83mmol iron nitrate nonahydrate (Fe(NO3)3 9H2O, Sigma-Aldrich, >98% purity) were dissolved in 31.5 ml of deionized water. The solution was stirred with a magnetic stirrer for 30 minutes to ensure all nitrates were fully dissolved. 2.25 grams of urea (Sigma-Aldrich, 99% purity) was then added to the nitrate solution, and the solution was stirred for another 30 minutes. The solution was poured into stainless steel autoclaves with PTFE-lined vessels with a capacity of 50 ml. The autoclaves containing the solutions were placed in an oven under static conditions at 180 °C and 1 h. The autoclave was then cooled to room temperature. The solid fraction was collected by centrifuge.

[0135] As a reference material, a low-entropy 3-cation LDH (Mg, Al, Ni) was also synthesized utilizing the hydrothermal method. In this case, 3.75 mmol of magnesium nitrate hexahydrate, 1.25 mmol of nickel nitrate hexahydrate, and 2.5 mmol of aluminium nitrate nonahydrate were dissolved in 31.5 ml of deionized water. The addition of urea, the crystallization time, crystallization temperature, and the solid collection were kept the same as for the HE-LDH.

[0136] Crystallization times ranging from 1-4 h and temperatures ranging from 120-180°C were also used for a selected number of syntheses with 8 cations, to study these parameters' effect on the resulting crystalline phase. After the completion of the crystallization time, the autoclaves were cooled to room temperature. The solid fraction was collected by centrifuge and washed three times with deionized water. The obtained powder was left to dry in air in an oven at 120°C for 16 h.

[0137] The precipitation method to produce HE-LDH was similar to the one developed by Kim et al. [2] 1.16 mmol of magnesium nitrate hexahydrate, 1.16 mmol of zinc nitrate hexahydrate, 1.16 mmol of nickel nitrate hexahydrate, 1.16 mmol of cobalt nitrate hexahydrate, 0.83 mmol of aluminium nitrate nonahydrate, 0.83 mmol chromium nitrate nonahydrate, and 0.83 mmol iron nitrate nonahydrate were dissolved in 100 ml of deionized water (Solution A). Solution A was stirred with a magnetic stirrer for 30 minutes to ensure all nitrates were fully dissolved. A second solution (solution B) was prepared with 0.1 mole of NaOH and 0.04 mole of Na2COs in 100ml. Solution B was slowly dispensed into solution A until pH 10 was reached. To achieve a pH of 10, approximately 13.8 ml of Solution B was utilized. The precipitant was collected by centrifuge after stirring for 24 hours at room temperature.

[0138] A 7-cation hydroxocarbonate was synthesized utilizing a precipitation method previously developed for high-entropy hydroxocarbonates. [3] 2 mmol of aluminium nitrate nonahydrate, 2 mmol iron nitrate nonahydrate, 2 mmol chromium nitrate nonahydrate, 0.75 mmol magnesium nitrate hexahydrate, 0.75 mmol of zinc nitrate hexahydrate, 0.75 mmol of nickel nitrate hexahydrate, 0.75 mmol of cobalt nitrate hexahydrate were mixed in 40 mL of deionized water and stirred for 30 minutes with a magnetic stirrer. A second solution (Solution B) was prepared with 0.06 mol of ammonium bicarbonate (99% purity, Sigma-Aldrich) and 75 mL of deionized water. The metal nitrate solution was added dropwise to Solution B, and then stirred overnight at room temperature. The resulting precipitant was collected by centrifuge.

[0139] The 5-cation hollow oxides derived from high-entropy glycerates were synthesized utilizing a method similarly described in Gongalves et al. [4] 0.4 mmol of each of nickel nitrate hexahydrate, zinc nitrate hexahydrate, magnesium nitrate hexahydate, cobalt nitrate hexahydrate, and manganese nitrate hexahydrate (Mn(NO3)2 6H2O, Sigma-Aldrich, >98% purity) was dissolved in 40 ml of isopropanol and stirred with a magnetic stirrer for 2 hours. Then 8 ml of glycerol (99.5% purity, Sigma-Aldrich) was added to the solution and stirred for another 30 minutes. The solution was transferred to a PTFE-lined stainless-steel autoclave where the crystallization temperature and time were 180°C and 10 hours. The precipitant was collected by centrifuge.

[0140] Nickel precipitated on alumina was used as an additional reference, and the synthesis has been previous described elsewhere. [5]

[0141] All precursors were dried overnight at 60 °C and then heat treated to 450°C (2°C / min ramp) in a muffle furnace for 2 hours under air.

[0142] Example 2: Assessment of Catalytic Performance

[0143] Reduction of CO2 by hydrogen takes place on an active catalyst. A simple assessment of the activity of a catalyst is to follow the conversion as a function of temperature. Catalytic activity screenings were conducted using a fixed-bed reactor. Figure 1 gives an overview of the catalytic results of the screened materials. All materials were active for conversion of CO2 to methane except for the low-entropy reference material (3-cation LDH). Among the tested materials, there was a wide range of performances especially in the low temperature regimes (< 300°C) where the performance can be rated as 7-cation LDH (hydrothermal) > 7-cation LDH (precipitation) > 7-cation hydroxycarbonate > Ni-Alumina reference > 5-cation spherical glycerolate > 3-cation low entropy LDH. The 7-cation LDH (hydrothermally synthesized) showed superior performance at all temperature ranges for CO2 conversion and selectivity to methane. There also was similar trend for selectivity to methane formation with 7-cation LDH (hydrothermal) > 7-cation LDH (precipitation) > 7-cation hydroxycarbonate > Ni-Alumina reference > 5-cation spherical glycerolate / 3-cation low entropy LDH, where methane was not observed for the 5-cation spherical glycerolate-derived oxide and the low-entropy LDH-derived oxide below 300°C. The highest performing materials were generally ones with over six cations.

[0144] Ni-LDHs are known to be active in CO2 methanation; however, we did not observe any activity for the reference 3-cation LDH. This is likely due to the lower reduction temperature used in this study. For example, reduction temperatures are often higher (>600°C) to generate the metallic active sites (i.e. NiO) in LDH-derived catalysts and in this study the reduction was lower and conducted at 450°C. The activation and reaction conditions appears to greatly affect the 3-cation low-entropy LDH, but not the 7-cation LDHs which were active, despite moderate activation / reduction temperatures. Example 3: Material Characterization

[0145] Catalytic Activity Screening

[0146] Catalytic activity screenings were conducted using a fixed-bed reactor. Approximately 0.2 g of the material was placed between quartz wool in a 5mm diameter stainless steel reactor. The catalyst was initially reduced under H2 (1 bara, 4.5 Purity Pangas) at 450°C for 60 min with a flow of 290 ml / min (H2 / Ar 1 / 5). The gas was switched to a mix of H2 / CO2 (flow of 330ml / min) with a molar ratio of 5.5 at 5 bar which would drive the thermodynamic equilibrium to high conversion and methane yield. The resulting gases were then fed into an FTIR-gas cell installed in a Bruker Alpha spectrometer where the composition was analyzed, where liquids were condensed prior to the IR cell by cooling with 17°C cooling water. The temperature of the reaction was then lowered with a step rate of 100°C per hour, and the exhaust was measured continuously by IR cell.

[0147] X-ray powder diffraction

[0148] X-ray powder diffraction patterns were acquired on a PANalytical X’Pert PRO diffractometer with Cu Ka radiation with Ni filter. The reflections of a main phase were indexed with an orthorhombic cell in the space group Cmcm (No. 64). The structural model was taken from the single-crystal X-ray diffraction refinement. Refined parameters were as follows: scale factor, zero shift, lattice parameters, metal atomic mass, and peak shapes as a Pseudo-Voigt* Axial divergence asymmetry function. [3]

[0149] Scanning Transmission Electron Microscopy and Elemental Analysis

[0150] Scanning electron microscopy and elemental analysis were carried out on a Tescan SEM Vega3 fitted with a Bruker XFIash 6-10 detector with an accelerating voltage of 20 kV. For energy-dispersive X-ray (EDX) analysis, the powder was pressed into a pellet, affixed in epoxy, and polished to 1 pm using diamond lapping films. Bulk chemistry was taken of five different areas that were 200 pm by 100 pm in size. The average and standard deviation were then calculated. Highresolution EDX mapping was obtained on a Zeiss Gemini 460 with an Ultirn max EDS detector and an accelerating voltage of 15 kV. An FEI Titan Themis operated at 300 kV was used for high-angle annular dark-field scanning transmission electron microscopy (HAADFSTEM) and energy-dispersive X-ray spectroscopy (EDS) mapping. For HAADF- STEM, a probe semiconvergence angle of 24 mrad was set in combination with an annular semidetection range of 66-200 mrad for the annular dark-field detector.

[0151] To further understand the different performances of the synthesized materials, each samples were characterized by SEM to observe any differences in morphology from the different synthesis methods. Additionally each sample was characterized before and after reaction by X-ray powder diffraction and nitrogen adsorption / desorption as shown in Figure 3. The 7-cation LDHs from precipitation and from hydrothermal synthesis have nearly the same cation composition but different catalytic activities, thus showing that synthesis protocols can play an important role and must be considered when applying HEOs to catalyst applications. Chemical composition alone is not the only parameter that affects catalytic activity; in addition particle and surface morphology, porosity, crystal structure overall, crystal structure at the exposed surface, and any other aspect affecting the surfaces influence catalytic activity. The morphology varies markedly among the studied catalysts: The scanning electron microscopy micrographs before reaction are shown in Figure 3 (Top), and for each sample, the morphology is highly sensitive to the synthesis method. Plate morphology is observed for hydrothermally synthesized samples 3-cation LDH and 7-cation LDH, while the precipitated 7-cation LDH and 7-cation hydroxycarbonate appear to have small agglomerated crystallites without a distinctive plate morphology. The solvothermal synthesized 5-cation glycerolate-derived oxide appears to be spherical in morphology. In all cases, despite equimolar amounts of cations (between similar valences cations) in the syntheses, the final compositions vary slightly from equimolarity, which is likely driven by the fact that different cations have different solubility at different pHs and will continue to present issues in general for the precipitation of multiple cations simultaneously.

[0152] The X-ray powder diffraction patterns for the precursor, calcined, and after reaction is shown in Figure 3 (Middle), and XRD was used to confirm the precursor and track any changes in the crystalline phase before and after reaction. In the precursor state, for the 3-cation low-entropy LDH, the hydrothermally synthesized 7-cation LDH, and the precipitated 7-cation LDH all have the characteristic reflection of layered double hydroxide, hydrotalcite structure. After calcination, the mixed metal oxide (MMO) structure common for LDH derived oxides is observed. Both HE-LDH derived oxides samples exhibit lower intensity in the peak reflections as well as peak broadening compared to the 3-cation counterpart.

[0153] The higher performing 7-cation LDHs retains the MMO structure before and after reaction; however, a peak appears at approximately 51.4° after reaction. This peak is likely from the metallic sites that are formed during the activation in the reducing hydrogen environment, which is needed to form the catalytically active sites.

[0154] For the hydrothermally synthesized 7-cation LDH, the peak at 51.4° is broad and just above the detection limit while the precipitated 7-cation LDH has a sharper peak. Since the sharpness of the diffraction peak can often be correlated to the domain size, the larger domain size of metallic particles in the precipitated 7-cation LDH could result in the different performances of the two HE-LDHs. No peak that resembles a metallic phase is observed for the 3-cation LDH.

[0155] As shown in Table 2, the BET surface area numbers decrease for both the precipitated 7- cation LDH and hydrothermal 7-cation LDH with a reduction of 143 m2 / g to 98 m2 / g and 140 m2 / g to 88 m2 / g, respectively. This likely due to the changes caused from the formation of metallic species during reduction.

[0156] The 7-cation hydroxycarbonate as precursor sample has the distinctive peaks of ammonium dawsonite- type structures. After reaction, a severe reduction of BET surface area number from 220 m2 / g to 105 m2 / g is observed, but little change is observed in the X-ray powder diffraction and any crystalline metallic phases are below the detection limit.

[0157] The chemistry for the 7-cation hydroxycarbonate differs from the LDH in that it favors M3+ cations rather than M2+ cations, with a ratio of ~ 2 for M3+ / M2+, rather than the LDH M2+ / M3+ ratio which is ~2, meaning ultimately that the amount of nickel and cobalt is approximately ! compared to the LDHs, and this could result in the lower activity for methanation. Additionally, the poor incorporation of magnesium reduces its configuration entropy to that of a 6-cation structure.

[0158] The 5-cation spherical glycerolate-derived oxide has the characteristic diffraction pattern after calcination for spinel type structures. However, it appears that the structure is not stable under reaction conditions, and several additional diffraction peaks appearing after reaction in XRD patter in Figure 3. There also is a severe decrease of BET surface area number from 42.7 m2 / g to 3.6 m2 / g, as shown in Table 2. A portion of the transition metals leave the HEO structure to form metallic species, as indicated by the sharp reflection at 51°; however, the spherical shape is maintained after reaction. With only 5 cations in the glycerolate-derived oxide, any removal of cations into another phase would reduce the configuration entropy to medium or even low-entropy, therefore losing any potential benefits brought on by high-entropy forms.

[0159] Example 4: Elemental Analysis

[0160] In order to identify whether and which cation species are active, the highest performing 7- cation LDH derived oxides was analyzed in X-ray absorption spectroscopy and HAADF / elemental mapping after reaction, as shown in Figure 4.

[0161] Homogenous distribution of cation with no major segregation of the cations was observed by elemental mapping. The K-edge XANES spectra for Cr, Fe, Co, Ni and Zn are also shown in Figure 4. The XANES spectra for K-edges of Cr, Fe, and Zn in the 7-cation LDH derived oxide have similar edge positions to the C^Ch, Fe2Oa, and ZnO references' edge positions, and they remain in the oxide form after reaction. Meanwhile, nickel and cobalt are partially reduced to NiO and CoO. Linear combination fittings (LCF) of the Co and Ni K-edge XANES spectra were conducted using the metal foil and M2+ oxide as references. Conversely, the low-entropy 3- cation LDH was also investigated by X-ray absorption spectroscopy, and no shift appears in the XANES spectra from Ni2+ to NiO. This indicates that HEOs have a different reducibility than low-entropy oxides, allowing different temperature regimes to be accessed. Furthermore, with respect to high-entropy classification, the exsolution of approximately 50% of the cobalt and nickel leads to higher configurational entropy in the remaining oxides with molar equivalences closer to parity (Mgo.i5Coo.i2Nio.i2Zno.i5)(Alo.ioCro.i7Feo.i7) Ox, meaning that the formation of the active sites actually leads to the oxide having increased configurational entropy than its starting oxide form.

[0162] Example 5: Materials and Methods

[0163] Materials

[0164] All chemicals were purchased from Sigma-Aldrich at highest available purity grades, and they were used without further purification.

[0165] Wet Impregnation

[0166] Ni(NO3)2'6H2O (Sigma Aldrich) in different loadings (0.5 at%, 5 at%, and 40 at%) was added to AI2O3 (Sigma Aldrich, 199443) and dissolved in deionized water. The samples were sonicated in a water bath (RT) for 20 minutes and afterwards dried in an oven at 100 °C overnight. Calcination of the samples was performed in a tubular oven at 400 °C with an air flux of 1 L min-1 for 4 hours.

[0167] Example 6: Calculation for CO2 methanation

[0168] Conversion of CO2 was calculated based on an equation: where:

[0169] [CO2] - concentration of carbon dioxide

[0170] [CO]- concentration of carbon oxide

[0171] [CH4] - concentration of methane

[0172] Selectivity of methane was calculated based on an equation:

[0173] [CH4]

[0174] ScH4 =[CO] + [CH4] '100%where:

[0175] [CH4] - concentration of methane

[0176] [CO] - concentration of carbon oxide Example 7 Preparation of high-entropy oxides for CO? conversion to methanol

[0177] The high-entropy glycerolates were obtained by using solvothermal synthesis procedure that have been previous described in literature for low-entropy metal-glycerolates. [6, 7] Total amount of 0.002 moles of metal cations were dissolved into 25 ml of isopropanol, and the solution was stirred approximately 1 hour. 7 ml of glycerol was added then added to the same solution, and it was stirred for an additional 30 minutes. The solution was poured into 50 ml PTFE-lined stainless steel autoclave which was placed in the oven at 170°C for 6 hours. Next, the autoclave was cooled down, precipitates were collected and washed three times by ethanol. The precipitant was then redispersed in 32 ml of distilled water and poure again into the autoclave and heated at 150°C for 3 hours. After cooling down, the product was separated by centrifugation and washed by distilled water. The collected solid fraction was dried in air in the oven at 80°C overnight. In the end, material was calcined at 450°C in air for 2 hours with a heating rate 2°C / min.

[0178] The amount of each nitrates depended on the final number of cations in the formulation. Specifically cations with M3+charge were equimolar with each other, and the Co2+was kept at a consistent amount for all formulations. The amounts of each nitrate added for the synthesis containing 5, 6, and 7 cations are shown below.

[0179] Mass of Reagent [g]

[0180] The first generation of CO2 to methanol catalysts was built off the methanation catalysts. Specifically, the synthesis of mesoporous spherical high-entropy glycerolates precursors which could then be calcined into oxides was investigated, focusing on M3+cations - specifically Al, Cr, Fe, Co, In, Ga, and Ce. The best selectivity of methanol was observed for the highest number of cations in the structure (7 -cation composed of Al, Cr, Fe, Co, In, Ga, and Ce).

[0181] The second generation CO2 to methanol catalyst was developed by utilizing high-throughput synthesis (via precipitation of hydroxycarbonate precursors), high-through catalyst testing with Al-feedback to conduct 4 rounds of optimization of the chemistry for improved methanol yield (external synthesis). The cations considered were Al, Cr, Fe, Ga, In, Ho, Y, Er, Ce, Mg, Co, Ni, Zn, Mn, Cu, Ca, and Sr, and formulations needed to have 5-10 cations.

[0182] Table 4 shows the highest performing high-entropy oxides that led to methanol flow rates of above 0.005 mol / (h*gCat).

[0183] Material characterisation

[0184] X-ray powder diffraction patterns were acquired for a 20 range of 5°-80° using a PANalytical X’Pert PRO diffractometer with Cu Ka radiation. High-resolution images were obtained on Zeiss Gemini 460 with an accelerating voltage of 5.0kV. For energy-dispersive X-ray (EDX) analysis, the powder was pressed into a pellet and bulk chemistry was taken of five different areas that were 100 pm by 100 pm in size. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) in combination with energy dispersive X-ray spectroscopy (EDX) was carried out on a probe-corrected FEI Titan Themis microscope operated at 300 kV using a SuperX EDX detector and employing a beam current of about 0.5 nA.

[0185] Prior to nitrogen adsorption measurements, the samples were degassed under vacuum at 200°C overnight, and N2 isotherms were measured on a Microtrac Belsorp Mini X. Surface areas were determined by the Brunauer-Emmet-Teller method (BET), and the pore size distribution was determined by the Barret, Joyner, Halenda method (BJH).

[0186] Room temperature x-ray photoemission spectra were measured using the Physical Electronics (PHI) Quantum 2000 X-ray photoelectron spectrometer equipped with a monochromatic Al-Karadiation source generated from an electron beam operated at 15 kV and 32.3 W. The spectra was recorded at 1 x10-6Pa chamber pressure with an electron take-off angle of 45°, a pass energy of 46.50 eV and the charge neutraliser was set to automatic.

[0187] Cited prior art documents:

[0188] [1] A. J. Knorpp, A. Zawisza, S. Huangfu, A. Borzi, A. H. Clark, D. Kata, T. Graule, M. Stuer, RSC Adv. 2022, 12, 26362-26371.

[0189] [2] M. Kim, I. Oh, H. Choi, W. Jang, J. Song, C. S. Kim, J.-W. Yoo, S. Cho, Cell Reports Phys. Sci. 2021 , 100702.

[0190] [3] A. J. Knorpp, P. Allegri, S. Huangfu, A. Vogel, M. Stuer, Inorg. Chem. 2023, 62, 4999-5007.

[0191] [4] J. M. Gongalves, A. Ghorbani, T. G. Ritter, I. S. Lima, M. Tamadoni Saray, A. H. Phakatkar, V. D. Silva, R. S. Pereira, A. L. Yarin, L. Angnes, R. Shahbazian-Yassar, J. Colloid Interface Sci. 2023, 641 , 643-652.

[0192] [5] M. Nikolic, F. Longo, E. Billeter, A. Cesarini, P. Trtik, A. Borgschulte, Phys. Chem. Chem. Phys. 2022, 24, 27394-27405.

[0193] [6] A. Baiker, M. Kilo, M. Macicjewshi, S. Menzi and A. Wokaun, in Proceedings of the 10th International Congress on Catalyst, Elsevier, Budapest, 1993, p. 1257.

[0194] [7] M. Behrens, F. Studt, I. Kasatkin, S. Kuhl, M. Havecker, F. Abild-pedersen, S. Zander, F. Girgsdies, P. Kurr, B. Kniep, M. Tovar, R. W. Fischer, J. K. Norskov and R. Schldgl, Science, 2012, 336, 893-898

[0195] [8] Dippo OF, Vecchio KS. A universal configurational entropy metric for high-entropy materials. Scripta Mater 2021 ;201: 113974

[0196] All scientific publications and patent documents cited in the present specification are incorporated by reference herein.

[0197] Table 1

[0198] Table 2

[0199] Table 3 Table 4

[0200] Table 5

[0201] Table 6

[0202] Table 7

[0203] Table 8

Claims

1. Claims1 . A multi cationic oxide catalyst comprising at least 5 metal cations.

2. The multi cationic oxide catalyst according to claim 1 , comprising at least 7 metal cations.

3. The multi cationic oxide catalyst according to claim 1 , comprising 5 to 16 metal cations, particularly comprising 5 to 14 metal cations, more particularly 5 to 12 metal cations, more particularly 5 to 10 metal cations.

4. The multi cationic oxide catalyst according to claim 2, comprising 7 to 16 metal cations, particularly comprising 7 to 14 metal cations, more particularly 7 to 12 metal cations, more particularly 7 to 10 metal cations.

5. The multi cationic oxide catalyst according to any of the preceding claims, wherein the multi cationic oxide catalyst comprises an entropic metric of >1.15.

6. The multi cationic oxide catalyst according to any of the preceding claims, wherein the metal cations are selected from the groups of rare earth metal cations, noble metal cations, base metal cations, and alkaline earth metal cations, particularly from base metal cations and alkaline earth metal cations.

7. The multi cationic oxide catalyst according to any of the preceding claims, wherein the metal cations are selected from Al, Cr, Fe, Ga, In, Ho, Y, Er, Yb, Ce, Mg, Co, Ni, Zn, Mn, Cu, Ca, Sr or Si.

8. The multi cationic oxide catalyst according to any of the preceding claims, wherein the metal cations are selected from Al, Cr, Fe, Mg, Co, Ni, Cu or Zn, particularly Al, Cr, Fe, Mg, Co, Ni or Zn.

9. The multi cationic oxide catalyst according to any of the preceding claims, wherein the metal cations are selected from Al, Ca, Co, Cr, In, Ni, Ho, Zn or Ce, Cr, Cu, Er, Fe, Ga, In, Ni, Y, Zn, particularly Al, Ca, Ce, Co, Cr, Cu, Er, Fe, Ga, In, Ni, Y or Zn.

10. The multi cationic oxide catalyst according to claim 8, wherein the metal cations are AI,Ca,Co,Cr,ln,Ni,Zn or Ce,Cr,Cu,Er,Fe,Ga,ln,Y,Zn.

11. The multi cationic oxide catalyst according to any of the preceding claims, wherein the base metal cations are selected from Al, Ce, Co, Cr, Mg, Mn, Si, Sr or Zn.

12. The multi cationic oxide catalyst according to any of the preceding claims, wherein the metal cations are selected from, Co2+, Co3+, Ni2+, Ni3+, Zn2+, Zn3+, Mn2+, Mn3+, Al2+, Al3+, Cr2+, Cr3+, Fe2+and Fe3+Ga3+, ln3+, Ho3+, Y3+, Er3+, Yb3+, Ce3+, Ce4+, Mg2+, Ca2+, Sr2+, Cu2+, Cu1+13. The multi cationic oxide catalyst according to any of the preceding claims, comprising 7 metal cations and an oxide anion.

14. A method for converting CO2 or NOX, particularly for converting CO2, using hydrogen or ammonia, in the presence of an active multi cationic oxide catalyst according to claims 1 to 13.

15. The method according to claim 14 wherein the method yields methane, methanol, CO, C2-C4 hydrocarbons or nitrogen, particularly CO, methanol or methane particularly methanol or methane, more particularly methane.

16. The method according to claims 14 to 15, wherein the metal cations are selected from a. Al, Cr, Fe, Mg, Co, Ni, Cu or Zn, particularly Al, Cr, Fe, Mg, Co, Ni or Zn for converting CO2 into methane, b. Al, Ca, Co, Cr, In, Ni, Ho, Zn or Ce, Cr, Cu, Er, Fe, Ga, In, Ni, Y, Zn, particularly Al, Ca, Ce, Co, Cr, Cu, Er, Fe, Ga, In, Ni, Y or Zn for converting CO2 into methanol, c. Al, Ce, Co, Cr, Mg, Mn, Si, Sr or Zn for converting CO2 into C2-C4 hydrocarbons, d. Al, Ca, Ce, Cr, Ho, Cu, Fe, Ga, Mg, Mn, Ni or Zn, particularly Al, Ca, Ce, Cu, Cr, Fe, Ga, Mg, Mn, Ni or Zn, more particularly Al, Ca, Ce, Cr, Fe, Ga, Mg, Mn, Ni or Zn for converting CO2 into CO, e. Al, Ce, Co, Cu, Fe, Mg, or Mn for converting CO2 into nitrogen.

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