CONVERSION OF CO2 IN THE PRESENCE OF A NICKEL AND COBALT CATALYST

Abstract

The present invention relates to a process for the hydrogenation of CO2 by reverse water gas reaction (RWGS) by bringing a feedstock of a gas mixture comprising CO2 and hydrogen into contact with a catalyst comprising an active phase based on nickel and cobalt and a silica or silica-alumina support, said active phase being in the form of bimetallic nanoparticles corresponding to the formula NixCoy with x = 1 and y between 1 and 4, said nanoparticles having a number average diameter of less than 10 nm with a standard deviation relative to the size of said nanoparticles of less than or equal to 50% of said number average diameter.

Description

Title of the invention: CONVERSION OF CO2 IN THE PRESENCE OF A NICKEL AND COBALT CATALYST Technical field

[0001] The present invention relates to a process for reverse water gas shift (RWGS) in the presence of a bimetallic catalyst based on nickel and cobalt supported on silica or silica-alumina. State of the art

[0002] Current solutions for reducing greenhouse gas emissions and combating global warming are varied and are the subject of much research in the academic and industrial worlds. Improving the energy efficiency of current processes, developing renewable energies, and capturing, storing, and using carbon dioxide (CO2) are examples.

[0003] CO2 is a thermodynamically stable compound and its use in chemical products remains complex although some examples exist. At the industrial level, we can cite the synthesis of urea for the production of fertilizers or plastics, and at an advanced stage of research, the production of polycarbonates.

[0004] The hydrogenation of CO2 is an interesting recovery route which allows the production, depending on the operating conditions of the methanol, of carbon monoxide, which can themselves react and give access to a wide variety of compounds.

[0005] The reverse water gas shift reaction (also called here RWGS or Reverse Water Gas Shift according to the English terminology), makes it possible to transform CO2 into carbon monoxide (CO) in the presence of hydrogen. The main by-product of the hydrogenation of CO2 into CO is methane, the selectivity of which is favored at low temperature and in the presence of an excess of hydrogen. Oxide materials alone or mixed (spinels, CeO2, CuO / ZnO / Al2O3 composites), noble (Pt, Pd) or non-noble (Cu, Ni, Fe, Co) mono or bimetallic metals supported on generally reducible oxides (TiO2, ZrO2, CeO2) are known to selectively catalyze the RWGS reaction (Chen et al. Frontiers in Chemistry, 8,709, 2020).

[0006] The RWGS reaction is reversible and endothermic. It is therefore thermodynamically favored at high temperature, generally above 600°C. However, operability at high temperature is expensive and significant deactivation of the catalysts is observed.

[0007] There is a need to develop active, selective and stable catalysts for CO2 conversion.

[0008] Nickel is an active metal for CO2 conversion, however the strong adsorption of CO on metal nanoparticles directs the reaction towards the selective production of methane and not carbon monoxide. In addition, supported nickel catalysts deactivate during CO2 hydrogenation at high temperature due to coke formation. These catalysts have therefore been the subject of research to improve their catalytic performance. To improve CO selectivity, Hou et al. decreased the size of nickel particles by observing that isolated nickel atoms supported on carbon nanotubes can selectively convert CO2 into CO by aqueous phase electrocatalysis at room temperature (Hou et al. Applied Catalysis B: Environmental, 271, 2020, 118929). Another way to improve selectivity is to prepare bimetallic catalysts by combining nickel with another metal.Examples include the addition of copper, cobalt, or alkali metals. For example, Price et al. prepared NiCo@SiO2 core / shell materials that achieve 80% CO2 conversion at high temperature (850°C) with 90% selectivity to CO (H2 / CO2 mixture with a molar ratio of 4:1). Liu et al. prepared NiCox / lamellar double hydroxides aluminum magnesium catalysts (denoted LDH with a molar ratio of Ni:Co = 2:1, 1:1, 1:2) by coprecipitation of magnesium, cobalt, nickel, and aluminum nitrates for CO2 conversion (Liu et al. RRL Solar, 55, 8, 2100185, 2021). After reduction at 850°C, the catalysts are active for CO2 photoreduction in the presence of methane. Finally, Chen et al, prepared by mechanosynthesis NiCo bimetallic catalysts supported on a reducible CeO2 oxide with a metal content lower than 2 wt% for plasma-assisted CO2 conversion (Chen. ACS Eng. Au 2023,3,7-16).

[0009] Surprisingly, the Applicant has discovered that the use of a bimetallic catalyst supported on a specific support based on silica or silica-alumina and whose active phase is based on nickel and cobalt, according to a specific Ni / Co ratio, and a size of bimetallic nanoparticles of very small diameter, with a very narrow particle size distribution, obtained according to a very specific preparation process by colloidal route, makes it possible to significantly improve the selectivity of hydrogenation of CO2 into CO by RWGS. Objects of the invention

[0010] The subject of the present invention is a process for the hydrogenation of CO2 by reverse water gas reaction (RWGS) by bringing a charge of a gas mixture comprising CO2 and hydrogen into contact with a catalyst comprising an active phase based on nickel and cobalt and a silica or silica-alumina support, said active phase being in the form of bimetallic nanoparticles corresponding to the formula NixCoy with x = 1 and y between 1 and 4, said nanoparticles having a number average diameter less than 10 nm, measured by transmission electron microscopy, with a standard deviation relative to the size of said nanoparticles less than or equal to 50% of said average diameter, which process being carried out at a temperature between 0°C and 600°C, at a pressure between 0.1 MPa and 5 MPa, at a hydrogen / CO2 molar ratio between 0.1 and 10 and at an hourly volumetric velocity between 100 h 1 and 40,000 h1.

[0011] According to one or more embodiments according to the invention, the active phase of said catalyst is in the form of bimetallic nanoparticles corresponding to the formula NixCoy with x = 1 and y = 1.

[0012] According to one or more embodiments according to the invention, the active phase of said catalyst is in the form of bimetallic nanoparticles corresponding to the formula NixCoy with x = 1 and y = 4.

[0013] According to one or more embodiments according to the invention, the catalyst comprises a nickel content of between 0.1 and 15% by weight of nickel element relative to the total weight of the catalyst.

[0014] According to one or more embodiments according to the invention, the catalyst comprises a cobalt content of between 0.1 and 15% by weight of cobalt element relative to the total weight of the catalyst.

[0015] According to one or more embodiments according to the invention, the number-average diameter of the nickel- and cobalt-based bimetallic nanoparticles, measured by transmission electron microscopy, is less than less than 7 nm, and the standard deviation relative to the size of said nanoparticles is between 20% and 50% of said average diameter.

[0016] According to one or more embodiments according to the invention, the bimetallic nanoparticles of said catalyst are in the reduced state.

[0017] According to one or more embodiments according to the invention, said catalyst is obtained by a preparation process comprising the following steps:

[0018] i) a catalytic system in the form of a colloidal suspension comprising a plurality of bimetallic nanoparticles based on nickel and cobalt, said nanoparticles having a number average diameter of less than 10 nm, measured by transmission electron microscopy, with a standard deviation relative to the size of said nanoparticles of less than or equal to 50% of said average diameter, is brought into contact with a support chosen from silica or silica-alumina to obtain a catalyst precursor;

[0019] ii) the catalyst precursor obtained at the end of step i) is dried at a temperature below 250°C, preferably at a pressure below 0.001 MPa, to obtain a catalyst;

[0020] iii) optionally, the catalyst obtained in step ii) is calcined at a temperature between 250°C and 500°C to obtain a calcined catalyst;

[0021] iv) optionally, the calcined catalyst obtained at the end of step iii) is reduced by contacting with a reducing gas to obtain a reduced catalyst.

[0022] According to one or more embodiments according to the invention, said catalytic system of step i) is obtained by a preparation process comprising the following steps:

[0023] a) at least one nickel-based organometallic precursor and at least one cobalt-based organometallic precursor are supplied separately;

[0024] b) said organometallic precursors supplied at the end of step a) are brought into contact in the presence of a solvent, at least one first stabilizing agent and at least one second stabilizing agent to obtain a colloidal suspension, said step b) comprising the following sub-steps:

[0025] bl) said organometallic precursors supplied at the end of step a) are brought into contact in the presence of the solvent to obtain a first solution;

[0026] b2) the first solution obtained at the end of step b1) is brought into contact with at least minus a first stabilizing agent to obtain a second solution;

[0027] b3) the second solution obtained at the end of step b2) is brought into contact with at at least one second stabilizing agent, different from the first stabilizing agent, to obtain the colloidal suspension;

[0028] c) said colloidal suspension obtained at the end of step b) is heated to a temperature of between 25°C and 180°C under a hydrogen pressure of between 0.01 and 1 MPa to obtain said catalytic system.

[0029] According to one or more embodiments according to the invention, said nickel-based organometallic precursor is chosen from nickel(II) bis-(hexamethyldisilazane) [Ni( / zm6?5)2]; nickel(II) bis-[N,N'-di(isopropyl)methylcarbodiimide] [Ni[' PrNC(CH3)NiPr]2]; nickel(II) bis-[N,N'-di(isopropyl)n-butylcarbodiimide], [Ni[' PrNC(CH2CH2CH2CH3)NiPr]2]; nickel(II) bis-[N,N'-di(cyclohexyl)methylcarbodiimide], [Ni[CyNC(CH3)NCy]2]; bis-(1,5-cyclooctadiene)nickel(0), Ni(q4-C8Hi2)2.

[0030] According to one or more embodiments according to the invention, said cobalt-based organometallic precursor is chosen from bis-(hexamethyldisilazane)tetrahydrofuran cobalt(II) [Co( / zm6?5)2(thf)]; cobalt(II) bis-[N,N'-di(isopropyl)methylcarbodiimide], [Co[iPrNC(CH3)NiPr]2]; cobalt(II) bis-[N,N'-di(isopropyl)n-butylcarbodiimide], [Co[iPrNC(CH2CH2CH2CH3)Ni Pr]2]; cobalt(II) bis-[N,N'-di(cyclohexyl)methylcarbodiimide], [Co[CyNC(CH3 )NCy]2]; (1,5-cyclooctadiene)(cyclooctadienyl) cobalt (I), Co(q3-C8Hi3)(q4-C8Hi2).

[0031] According to one or more embodiments according to the invention, said first stabilizing agent and / or said second stabilizing agent are chosen from carboxylic acids, carboxylate anions, primary, secondary or tertiary amines, cations primary, secondary, tertiary or quaternary ammonium, amides, esters, alcohols, alcoholates, thiols, thiolates, saturated or unsaturated, having between 1 and 30 carbon atoms.

[0032] According to one or more embodiments according to the invention, the first stabilizing agent is palmitic acid and the second stabilizing agent is hexadecylamine. Detailed description of the invention Definitions

[0033] In the following, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, 81st edition, 2000-2001). For example, group VIII (or VIIIB) according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUP AC classification.

[0034] In the present description, according to the IUP AC convention, micropores are understood to mean pores whose diameter is less than 2 nm, i.e. 0.002 pm; mesopores are understood to mean pores whose diameter is greater than or equal to 2 nm, i.e. 0.002 pm and less than or equal to 50 nm, i.e. 0.05 pm and macropores are understood to mean pores whose diameter is greater than 50 nm, i.e. 0.05 pm.

[0035] The total pore volume is measured by mercury porosimetry according to ASTM D4284-92 with a wetting angle of 140°, for example using an Autopore III™ model device from Microméritics™.

[0036] The BET specific surface area is measured by nitrogen physisorption according to ASTM D3663-03, a method described in the book Rouquerol F.; Rouquerol J.; Singh K. “Adsorption by Powders & Porous Solids: Principle, methodology and applications”, Academie Press, 1999.

[0037] The average diameter of the bimetallic nickel and cobalt nanoparticles is determined by transmission electron microscopy (TEM or Transmission Electron Microscopy according to the Anglo-Saxon terminology).

[0038] The metal content is measured by X-ray fluorescence or by induction plasma spectroscopy coupled to an atomic emission spectrometer (ICP-AES or Inductively coupled plasma atomic emission spectroscopy according to the English terminology).

[0039] In the present description, the term "comprise" is synonymous with (means the same as) "include" and "contain", and is inclusive or open and does not exclude other elements not recited. It is understood that the term "comprise" includes the exclusive and closed term "consist". Furthermore, in the present description, the term "substantially" corresponds to an approximation of ± 10%, preferably ± 5%, very preferably ± 2%, of a reference value such as a distance, a speed, a flow rate, a compound content, a temperature, a pressure, etc. 1. CO2 hydrogenation process by RWGS

[0040] The subject of the present invention is a process for the hydrogenation of CO2 by implementing the reverse water gas shift (RWGS) process by bringing a feedstock of a gas mixture comprising CO2 and hydrogen into contact with a catalyst comprising an active phase based on nickel and cobalt and a silica or silica-alumina support, said active phase being in the form of bimetallic nanoparticles corresponding to the formula NixCoy with x = 1 and y between 1 and 4, said nanoparticles having a number average diameter of less than 10 nm, measured by transmission electron microscopy, with a standard deviation relative to the size of said nanoparticles less than or equal to 50% of said average diameter, which process being carried out at a temperature of between 0°C and 600°C, at a pressure of between 0.1 MPa and 5 MPa, at a hydrogen / CO2 molar ratio included between 0.1 and 10 and at an hourly volumetric velocity between 100 h 1 and 40000 h1.

[0041] In the process according to the invention, CO2 is selectively hydrogenated to carbon monoxide by RWGS reaction in the presence of a specific catalyst as described below. The effluents contain CO, water, and optionally unconverted hydrogen and CO2. By-products of the reaction, such as methane, methanol or other alcohols, alkenes, ethers and / or alkanes may also be present in the effluent from the RWGS reaction. The charge

[0042] The CO2 contained in the gas mixture feed can come from various sources. The necessary CO2 can be provided by a unit for separating a stream comprising CO2 (e.g. combustion fumes) or a CO2 capture unit (e.g. CO2 present in the air).

[0043] The hydrogen required for the conversion of CO2 can be produced by a water electrolysis unit, said water being able to come from the effluent of the RWGS reaction unit and optionally from downstream units (for example Fischer-Tropsch (FT) or alcohol synthesis units). Preferably, the use of the water electrolysis unit to treat the water produced by the RWGS reaction unit also makes it possible to minimize the environmental impact of the process. Thus, the process according to the invention does not require an external supply of hydrogen, for example produced by steam reforming of natural gas. The electrolyzer can preferably operate with low-carbon electricity, which contributes to the renewable nature of the synthesis gas and the hydrocarbons which will then be produced from this synthesis gas.Furthermore, the water used for hydrogen production can come at least in part from the recycling of water produced by the RWGS reaction, which has the advantage of limiting the external water supply.

[0044] The hydrogen / CO2 molar ratio is preferably between 0.1 and 10, preferably between 0.5 and 5, more preferably between 1 and 3, and even more preferably between 1 and 2.

[0045] The gas mixture constituting the charge may contain, in addition to CO2 and hydrogen, other gaseous elements such as water vapor, alkanes such as methane, propane and / or isobutane. Implementation

[0046] The technological implementation of the RWGS process is for example carried out by injection, in ascending or descending flow, of the feedstock, i.e. the gas mixture comprising CO2 and hydrogen, into at least one fixed-bed or fluid-bed reactor. Preferably, the reactor is a fixed-bed reactor. Said reactor may be of the isothermal type or of the adiabatic type. An adiabatic reactor is preferred.

[0047] The feedstock can advantageously be diluted by one or more reinjections of the effluent from said reactor where the selective hydrogenation reaction takes place, at various points in the reactor, located between the inlet and the outlet of the reactor, in order to limit the temperature gradient in the reactor.

[0048] In an embodiment according to the invention, the RWGS reaction is carried out with a hydrogen / CO2 molar ratio of between 0.1 and 10, preferably between 0.5 and 5, more preferably between 1 and 3, and even more preferably between 1 and 2, a temperature of between 0°C and 600°C, preferably between 25°C and 600°C, and even more preferably between 30°C and 550°C, an hourly volumetric velocity (HVV) of between 100 h 1 and 40000 h1, preferably between 2000 h 1 and 20000 h1, and a pressure of between 0.1 MPa and 5.0 MPa, preferably between 0.1 MPa and 4.0 MPa, and even more preferably between 0.1 MPa and 3.0 MPa.

[0049] Preferably, the catalyst is previously heat-treated in the reactor under a reducing atmosphere before the injection of the charge, at a temperature between 100°C and 600°C, preferably between 150°C and 500°C and for a duration between 30 minutes and 12 hours. 2. Catalytic system

[0050] The catalytic system making it possible to obtain the catalyst used in the context of the process according to the invention is in the form of a colloidal suspension comprising, preferably consisting of, a plurality of bimetallic nanoparticles based on nickel and cobalt corresponding to the formula NixCoy with x = 1 and y between 1 and 4, said nanoparticles having a number-average diameter of less than 10 nm, measured by transmission electron microscopy, preferably less than 9 nm, preferably less than 7 nm, more preferably less than 5 nm, even more preferably less than 4 nm, and even more preferably less than or equal to 3 nm, and in that the standard deviation relative to the size of said nanoparticles is less than or equal to 50% of said average diameter, preferably between 20% and 50%, more preferably between 20% and 35%, and even more preferably between 22% and 28%.

[0051] In one embodiment x = 1 and y = 1.

[0052] In another embodiment according to the invention x = 1 and y = 4.

[0053] A person skilled in the art knows the techniques suitable for determining the average particle diameter and also knows the degree of uncertainty existing in these measurements. For example, the average particle diameter of a set, the standard deviation and the size distribution can be determined by statistical studies from microscopy images, and in particular by transmission electron microscopy (TEM). The number average diameter is calculated on at least 250 nanoparticles. The standard deviation is calculated as the square root of the variance.

[0054] Advantageously, the bimetallic nanoparticles of the catalyst used in the process according to the invention are in the reduced state, that is to say in the zero valence state. 3. Process for preparing the catalytic system

[0055] The catalytic system is prepared according to a particular preparation method, comprising at least the following steps:

[0056] a) at least one nickel-based organometallic precursor and at least one cobalt-based organometallic precursor are supplied separately;

[0057] b) said organometallic precursors supplied at the end of step a) are brought into contact in the presence of a solvent, at least one first stabilizing agent and at least one second stabilizing agent to obtain a colloidal suspension, said step b) comprising the following sub-steps:

[0058] bl) said organometallic precursors supplied at the end of step a) are brought into contact in the presence of the solvent to obtain a first solution;

[0059] b2) the first solution obtained at the end of step b1) is brought into contact with at least minus a first stabilizing agent to obtain a second solution;

[0060] b3) the second solution obtained at the end of step b2) is brought into contact with at at least one second stabilizing agent, different from the first stabilizing agent, to obtain the colloidal suspension;

[0061] c) said colloidal suspension obtained at the end of step b) is heated to a temperature between 25°C and 180°C under a hydrogen pressure between 0.01 and 1 MPa to obtain said catalytic system.

[0062] Steps a) to c) are described in more detail below.

[0063] According to step a) of the process for preparing the catalytic system, at least one nickel-based organometallic precursor and at least one cobalt-based organometallic precursor are supplied separately.

[0064] More particularly, said organometallic precursors supplied in step a) are chosen from transition metal complexes of nickel and cobalt, neutral or charged, containing one or more organic or inorganic ligands.

[0065] When said organometallic precursor is selected from nickel transition metal complexes, the oxidation state of nickel in the complex is 0, 1, 2, 3 or 4. Preferably the oxidation state of nickel in the complex is 2.

[0066] When said organometallic precursor is selected from cobalt transition metal complexes, the oxidation state of cobalt in the complex is 0, 1, 2 or 3. Preferably the oxidation state of cobalt in the complex is 2.

[0067] Advantageously, the transition metal complexes may contain neutral, anionic or cationic ligands. The ligands may form single, double or triple bonds with the metal center. The ligands may be identical or different from each other, bonded or not to each other, and are preferably chosen from a hydride, fluoride, chloride, bromide, iodide group, an organic compound, preferably an alkyl, cyclic or not, having from 1 to 15 carbon atoms (C1-C15) comprising or not one or more heteroelements and / or one or more multiple bonds, and / or an organic compound, preferably a substituted or unsubstituted aryl, having between 4 and 15 carbon atoms (C4-C15) comprising or not one or more heteroelements, or a substituted or unsubstituted aryl having between 4 and 15 carbon atoms (C4-C15) comprising or not one or more heteroelements.

[0068] The donor atom, that is to say the one which forms the bonds with the metal center, can be chosen from the elements H, C, N, O, Si, P, S, F, Cl, Br, I. Preferably, the donor atom is chosen from N or O.

[0069] In a particular non-limiting case, the organometallic complex may be chosen from multinucleated coordination complexes containing 2 or more metal atoms, which may be identical or different. The multinucleated complexes may be linked together by one or more bridging ligands, and / or by the formation of metal-metal type chemical bonds.

[0070] In one embodiment according to the invention, when said organometallic precursor is nickel-based, said precursor is chosen from nickel(II) bis-(hexamethyldisilazane) [Ni[iPrNC(CH3)NiPr]2]; nickel(II) bis-[N,N'-di(isopropyl)methylcarbodiimide] [Ni[iPrNC(CH2CH2CH2CH3)NiPr]2]; nickel(II) bis-[N,N'-di(isopropyl)n-butylcarbodiimide], [Ni[iPrNC(CH2CH2CH2CH3)NiPr]2]; nickel(II) bis-[N,N'-di(cyclohexyl)methylcarbodiimide], [Ni[CyNC(CH3 )NCy]2]; bis-(1,5-cyclooctadiene)nickel(0), Ni(q4-C8Hi2)2. Preferably, said Nickel-based organometallic precursor is the nickel(II) bis-[N,N'-di(isopropyl)methylcarbodümide] complex [Ni[iPrNC(CH3)NiPr]2] whose chemical structure is shown below:

[0071] [Chem.l] T AA —A' AAA /

[0072] In one embodiment according to the invention, when said organometallic precursor is cobalt-based, said precursor is chosen from bis-(hexamethyldisilazane)tetrahydrofuran cobalt(II) [Co( / zm6?5)2(thf)]; bis-[N,N'-di(isopropyl)methylcarbodiimide] of cobalt(II), [Co[iPrNC(CH3)NiPr]2]; bis-[N,N'-di(isopropyl)n-butylcarbodiimide] of cobalt(II), [Co[iPrNC(CH2CH2CH2CH3)Ni Pr]2]; bis-[N,N'-di(cyclohexyl)methylcarbodiimide] of cobalt(II), [Co[CyNC(CH3 )NCy]2]; (1,5-cyclooctadiene)(cyclooctadienyl) cobalt(I), Co(q3-C8Hi3)(q4-C8Hi2). Preferably, said cobalt-based organometallic precursor is the cobalt(II) bis-(hexamethyldisilazane)tetrahydrofuran complex [Co( / zm6?5)2(thf)] whose chemical structure is represented below:

[0073] [Chem.2]

[0074] The solvent may be chosen from organic solvents and in particular from ethers, alcohols, chlorinated solvents and saturated, unsaturated, aromatic or non-aromatic, cyclic or non-cyclic hydrocarbons. Preferably, the solvent is chosen from hexane, cyclohexane, methylcyclohexane, heptane, butane or isobutane, mono-olefins or diolefins preferably comprising 4 to 20 carbon atoms, cycloocta-1,5-diene, benzene, toluene, orthoxylene, mesitylene, ethylbenzene, dichloromethane, chlorobenzene, methanol, ethanol, pure or as a mixture, and ionic liquids. In the case where the solvent is an ionic liquid, it is advantageously chosen from the ionic liquids described in patents US 6,951,831 B2 and FR 2895406 B1.

[0075] According to step b) of the process for preparing the catalytic system, said organometallic precursors of nickel and cobalt supplied at the end of step a) are brought into contact in the presence of a solvent, at least one first stabilizing agent and at least one second stabilizing agent to obtain a colloidal suspension.

[0076] The role of the first stabilizing agent is to form a stabilizing complex before the nucleation phase but also to stabilize the suspended nanoparticles obtained after the nucleation phase.

[0077] The role of the second stabilizing agent is to initiate the nucleation phase allowing the formation of the suspended bimetallic nanoparticles while playing a stabilizing role once the suspended nanoparticles have been formed.

[0078] More particularly, step b) comprises the following sub-steps:

[0079] bl) said organometallic precursors supplied at the end of step a) are brought into contact in the presence of a solvent to obtain a first solution;

[0080] b2) the first solution obtained at the end of step b1) is brought into contact with a first stabilizing agent to obtain a second solution;

[0081] b3) the second solution obtained at the end of step b2) is brought into contact with a second stabilizing agent, different from the first stabilizing agent, to obtain the colloidal suspension.

[0082] In step b1) the solvent may be identical or different, preferably identical, from the solvent(s) optionally used in step a). The solvent may be chosen from organic solvents and in particular from ethers, alcohols, chlorinated solvents and saturated, unsaturated, aromatic or non-aromatic, cyclic or non-cyclic hydrocarbons. Preferably, the solvent is chosen from hexane, cyclohexane, methylcyclohexane, heptane, butane or isobutane, monoolefins or diolefins preferably comprising 4 to 20 carbon atoms, cycloocta-1,5-diene, benzene, toluene, orthoxylene, mesitylene, ethylbenzene, dichloromethane, chlorobenzene, methanol, ethanol, pure or as a mixture, and ionic liquids. Preferably, the solvent is mesitylene. In the case where the solvent is an ionic liquid, it is advantageously chosen from the ionic liquids described in patents US 6,951,831 B2 and FR 2895406 B1.

[0083] In step b2) the first stabilizing agent may be chosen from carboxylic acids, carboxylate anions, primary, secondary or tertiary amines, primary, secondary, tertiary or quaternary ammonium cations, amides, esters, alcohols, alcoholates, thiols, thiolates, saturated or unsaturated, having between 1 and 30 carbon atoms.

[0084] Preferably, said first stabilizing agent is palmitic acid.

[0085] In step b3), the second stabilizing agent may be chosen from carboxylic acids, carboxylate anions, primary, secondary or tertiary amines, primary, secondary, tertiary or quaternary ammonium cations, amides, esters, alcohols, alcoholates, thiols, thiolates, saturated or unsaturated, having between 1 and 30 carbon atoms.

[0086] Preferably, the second stabilizing agent is hexadecylamine.

[0087] Preferably, the molar ratio between the stabilizing agents supplied in step b) and said organometallic precursors supplied in step a) is greater than 0 and less than or equal to 10, preferably between 0.05 and 5, and even more preferably between 0.05 and 1.5.

[0088] Preferably, the molar ratio between the first stabilizing agent and said organometallic precursors supplied in step a) is less than 0.5, more preferably between 0.1 and 0.3.

[0089] Preferably, the molar ratio between the second stabilizing agent and said organometallic precursors supplied in step a) is less than 1.5, more preferably between 0.8 and 1.2. Step c)

[0090] After step b) of contacting, said colloidal suspension obtained at the end of step b) is heated to a temperature of between 25°C and 180°C, preferably between 30°C and 170°C, under a hydrogen pressure of between 0.01 MPa and 1 MPa, preferably between 0.1 MPa and 0.3 MPa, to obtain said catalytic system, preferably for a period of between 1 and 24 hours, preferably between 2 and 20 hours.

[0091] The concentration of said organometallic precursors contained in the solution obtained at the end of step c) is less than or equal to 1 mol / L, preferably between 0.001 mol / L and 0.1 mol / L, and very preferably between 0.025 mol / L and 0.75 mol / L.

[0092] One of the advantages of the process for preparing the catalytic system used to prepare the catalyst used in the CO2 hydrogenation process by RWGS according to the invention is that the bimetallic particles are already in the reduced state, i.e. in the zero valence state. It is therefore not necessary to carry out a step of reducing the catalyst before its use in the RWGS process. 4. Process for preparing the catalyst

[0093] The catalyst used in the context of the process according to the invention, comprising an active phase based on nickel and cobalt, and a porous support chosen from silica or silica-alumina, is obtained according to a preparation process comprising at least the following steps:

[0094] i) a catalytic system according to the invention is brought into contact with a support chosen from silica or silica-alumina to obtain a catalyst precursor;

[0095] ii) the catalyst precursor obtained at the end of step i) is dried at a temperature temperature below 250°C, preferably at a pressure below 0.001 MPa, to obtain a catalyst;

[0096] iii) optionally, the catalyst obtained in step ii) is calcined at a temperature between 250°C and 500°C to obtain a calcined catalyst;

[0097] iv) optionally, the calcined catalyst obtained at the end of step iii) is reduced by contacting it with a reducing gas to obtain a reduced catalyst.

[0098] Preferably, step i) of contacting is carried out by impregnating the support with a volume of colloidal suspension of between 0.25 and 1.5 times the pore volume of the support to be impregnated.

[0099] The catalyst precursor obtained at the end of step i) is then dried at a temperature below 250°C, preferably between 15°C and 180°C, more preferably between 30°C and 160°C, even more preferably between 50°C and 150°C, and even more preferably between 70°C and 140°C, for a duration typically between 0.5 hours and 12 hours, and more preferably for a duration between 0.5 hours and 5 hours. Longer durations are not excluded, but do not necessarily provide an improvement.

[0100] The drying step can be carried out by any technique known to those skilled in the art. It is advantageously carried out under an inert atmosphere or under an atmosphere containing oxygen or under a mixture of inert gas and oxygen. It is advantageously carried out at atmospheric pressure or at reduced pressure. Preferably, this step is carried out at a pressure of less than 0.001 MPa.

[0101] After drying, the catalyst obtained at the end of step ii) can be calcined at a temperature of between 250°C and 600°C, preferably between 350°C and 550°C, for a period typically of between 0.5 and 24 hours, preferably for a period of between 0.5 and 12 hours, and even more preferably for a period of between 0.5 and 10 hours, preferably under an inert atmosphere or under an atmosphere containing oxygen. Longer periods are not excluded, but do not necessarily provide an improvement. A calcined catalyst is obtained.

[0102] The calcined catalyst obtained at the end of step iii) (optional) can be reduced. This step is preferably carried out in the presence of a reducing gas, either in situ, i.e. in the reactor where the catalytic transformation is carried out, or ex situ. Preferably, this step is carried out at a temperature between 80°C and 450°C, even more preferably between 100°C and 400°C.

[0103] The reduction is carried out in the presence of a reducing gas comprising between 25% by volume and 100% by volume of hydrogen relative to the total volume of the reducing gas, preferably 100% by volume of hydrogen. The hydrogen is optionally supplemented by an inert gas for the reduction, preferably argon, nitrogen or methane.

[0104] The reduction generally includes a temperature increase phase followed by a plateau.

[0105] The duration of the reduction stage is generally between 1 hour and 40 hours, preferably between 2 hours and 20 hours.

[0106] The Hourly Volumetric Velocity (HVV) is generally between 150 and 3000, preferably between 300 and 1500 liters of reducing gas per hour and per liter of catalyst. 5. Catalyst

[0107] The catalyst used in the context of the process according to the invention is a bimetallic catalyst comprising, preferably consisting of, an active phase based on cobalt and nickel, and a porous support chosen from silica and silica-alumina.

[0108] The nickel content is generally between 0.1 and 15% by weight of nickel element relative to the total weight of the catalyst, preferably between 0.5 and 10% by weight, and even more preferably between 1 and 7.5% by weight.

[0109] The cobalt content is generally between 0.1 and 15% by weight of cobalt element relative to the total weight of the catalyst, preferably between 0.5 and 10% by weight, and even more preferably between 1 and 7.5% by weight.

[0110] The number-average diameter of the nickel- and cobalt-based bimetallic nanoparticles, measured by transmission electron microscopy, is generally less than 10 nm, preferably less than 9 nm, preferentially less than 7 nm, more preferentially less than 5 nm, even more preferentially less than 4 nm, and even more preferably less than or equal to 3 nm, it being understood that the standard deviation relative to the size of said nanoparticles is less than or equal to 50% of said average diameter, preferably between 20% and 50%, more preferentially between 20% and 35%, and even more preferentially between 22% and 28%.

[0111] According to the invention, said active phase of said catalyst is in the form of bimetallic nanoparticles corresponding to the formula NixCoy with x = 1 and y between 1 and 4. In one embodiment according to the invention, x = 1 and y = 1. In another embodiment according to the invention x = 1 and y = 4.

[0112] The specific surface area of ​​the catalyst is generally between 10 m2 / g and 450 m2 / g, preferably between 25 m2 / g and 400 m2 / g, more preferably between 45 m2 / g and 370 m2 / g, and even more preferably between 85 m2 / g and 350 m2 / g.

[0113] The total pore volume of the catalyst is generally between 0.1 ml / g and 1 ml / g, preferably between 0.2 ml / g and 0.9 ml / g, and particularly preferably between 0.3 ml / g and 0.8 ml / g. 6. Support

[0114] The catalyst support comprises silica or silica-alumina. Preferably the support is made of silica or silica-alumina, more preferably silica-alumina.

[0115] When the support is silica-based, it is understood that it comprises at least 95%, preferably at least 98%, and particularly preferably at least 99% by weight of silica relative to the weight of the support. The silica generally has an amorphous crystallographic structure, but may contain crystalline silica quartz, tridymite, cristobalite alone or in a mixture. The silica may be fused silica.

[0116] When the support is based on silica-alumina, the silica content is between 1 and 95% by weight, preferably between 5 and 90% and more preferably between 10 and 80% by weight relative to the total weight of the support. The alumina content is between 1 and 95% by weight, preferably between 5 and 90% by weight and more preferably between 10 and 80% by weight relative to the total weight of the support. The silica-alumina can be prepared by any method known to those skilled in the art such as the sol-powder, sol-gel, coprecipitation or cogelation method. The silica-alumina contains, depending on its method of preparation, domains of amorphous crystallographic structure and of delta, gamma or theta alumina type, alone or as a mixture.

[0117] The silica-based support may comprise impurities such as metal oxides of groups IIA, IIIB, IVB, IIB, IIIA, IVA according to the CAS classification, preferably alumina, titanium dioxide, zirconium dioxide, zinc oxide, magnesium oxide and calcium oxide, or alkali metals, preferably lithium, sodium or potassium, and / or alkaline earth metals, preferably magnesium, calcium, strontium or barium or sulfur.

[0118] The specific surface area of ​​the support is generally between 10 m2 / g and 450 m2 / g, preferably between 30 m2 / g and 400 m2 / g, more preferably between 50 m2 / g and 370 m2 / g, and even more preferably between 90 m2 / g and 350 m2 / g.

[0119] The pore volume of the support is generally between 0.1 ml / g and 1.2 ml / g, preferably between 0.3 ml / g and 1 ml / g, and very preferably between 0.5 ml / g and 0.9 ml / g.

[0120] The mesoporous median diameter of the support is advantageously between 3 nm and 25 nm, and preferably between 6 nm and 20 nm, and particularly preferably between 8 nm and 18 nm.

[0121] The catalyst support is generally in the form of grains advantageously having a diameter of between 0.5 mm and 10 mm. The grains may have any shape known to those skilled in the art, for example the shape of balls (preferably having a diameter of between 1 mm and 8 mm), extrudates, tablets, hollow cylinders. Preferably, the support is in the form of extrudates with a diameter of between 0.5 mm and 10 mm, preferably between 0.8 mm and 3.2 mm and very preferably between 1.0 mm and 2.5 mm and of length between 0.5 mm and 20 mm. The term "diameter" of the extrudates means the diameter of the circle circumscribed to the cross section of these extrudates. The support can advantageously be presented in the form of cylindrical, multi-lobed, preferably tri-lobed or quadri-lobed extrudates. The shape of the lobes can be adjusted according to all the methods known from the prior art. Examples

[0122] The invention will now be illustrated via the following examples which are in no way limiting.

[0123] Example 1 (non-compliant): NiCo catalytic system prepared by impregnation of Ni and Co metal salts (Ni / Co molar ratio=1)

[0124] An aqueous solution of nickel and cobalt precursors is prepared by dissolving nickel nitrate (NiNO3, supplier Strem Chemicals®) and cobalt nitrate (Co(NO3)2, supplier Strem Chemicals®) in a volume of 13 mL of distilled water.

[0125] This solution is prepared so as to finally obtain a Ni / Co=1 ratio on the final catalyst. The solution obtained is dry impregnated onto 10 grams of a silica-alumina support. The silica-alumina (SA) with an alumina content of 80% has a specific surface area of ​​300 m2 / g, a pore volume of 0.6 mL / g and a median mesoporous diameter of 7 nm.

[0126] The solid thus obtained is then dried in an oven overnight at 120°C, then calcined under an air flow of 1 L / h / g of catalyst at 450°C for 2 hours.

[0127] The content of metallic elements, i.e. nickel plus cobalt, is 5% by weight relative to the weight of the final catalyst.

[0128] The average diameter of bimetallic nanoparticles determined by Transmission Microscopy (TEM) on 250 measured nanoparticles is 14 nm with a standard deviation of 4.18 (60.6%).

[0129] Furthermore, the theoretically targeted ratio of Ni / Cu is 1. Out of 250 nanoparticles counted, 40 are composed only of nickel, and the molar ratio Ni / Cu measured by EDS (energy dispersive X-ray spectroscopy) allowing analysis of the composition of the measured particles varies between 1 and 14.

[0130] Example 2: Catalytic system based on nickel alone prepared by colloidal route (non-compliant)

[0131] In a glove box, a solution of 342 mg (1 mmol Ni) of the complex [Ni[' PrNC(CH3)NiPr]2] in 8 mL of mesitylene is prepared and introduced into a Fisher-Porter bottle of 120 mL capacity. Then, 51 mg (0.2 mmol) of palmitic acid dissolved in 8 mL of mesitylene are added to the medium with stirring. Finally, a solution of 241 mg (1 mmol) of 1-hexadec y lamine dissolved in 4 mL of Mesitylene is introduced into the Fisher-Porter. The bottle is then closed and removed from the glove box, pressurized to 0.2 MPa of H2, and the reaction medium is heated to 150°C for 18 hours with stirring.

[0132] At the end of the reaction, a drop of the colloidal solution is placed on a grid for analysis by Transmission Microscopy.

[0133] The average diameter of bimetallic nanoparticles determined by Transmission Microscopy (TEM) on 250 measured nanoparticles is 5.9 nm with a standard deviation of 2.1 (35.6%).

[0134] Example 3: Catalytic system based on cobalt alone prepared by colloidal route (non-compliant)

[0135] In a glove box, a solution of 452 mg (1 mmol Co) of the complex Co[N(SiMe3)2]2(THF) in 8 mL of mesitylene is prepared and introduced into a Fisher-Porter bottle of 120 mL capacity. Then, 51 mg (0.2 mmol) of palmitic acid dissolved in 8 mL of mesitylene are added to the medium with stirring. Finally, a solution of 241 mg (1 mmol) of 1-hexadec y lamine dissolved in 4 mL of mesitylene is introduced into the Fisher-Porter. The bottle is then closed and removed from the glove box, pressurized to 0.2 MPa of H2, and the reaction medium is heated to 150 °C for 18 hours with stirring.

[0136] At the end of the reaction, a drop of the colloidal solution is placed on a grid for analysis by Transmission Microscopy.

[0137] The average diameter of bimetallic nanoparticles determined by Transmission Microscopy (TEM) on 250 measured nanoparticles is 4.0 nm with a standard deviation of 2.0 (50%).

[0138] Example 4 (compliant): NiCo bimetallic catalytic system by colloidal route (Ni / Co molar ratio=1)

[0139] In the glove box, a solution of 171 mg (0.5 mmol Ni) of the complex [Ni[' PrNC(CH3)NiPr]2] in 4 mL of mesitylene and a solution of 226 mg (0.5 mmol Co) of the complex [Co( / zmtA)2(thf)] in 4 mL of mesitylene are prepared. These two solutions are introduced into a Fisher-Porter bottle of 120 mL capacity while stirring. Then, 51 mg (0.2 mmol) of palmitic acid dissolved in 8 mL of mesitylene are added to the medium while stirring. Finally, a solution of 241 mg (1 mmol) of 1-hexadecylamine dissolved in 4 mL of mesitylene is introduced into the Fisher-Porter. The bottle is then closed and removed from the glove box, pressurized to 0.2 MPa of H2, and the reaction medium is heated to 150°C for 18 hours with stirring.

[0140] At the end of the reaction, a drop of the colloidal solution is placed on a grid for analysis by Transmission Microscopy.

[0141] The average diameter of bimetallic nanoparticles determined by Microscopy in Transmission (MET) on 250 measured nanoparticles is 2.3 nm with a standard deviation of 0.8 (34.8%).

[0142] The theoretically targeted Ni / Co ratio was 1. Out of 10 particles counted, the Ni / Co ratio measured by EDS (energy dispersive X-ray spectroscopy, which allows analysis of the composition of the measured particles) fluctuates from 0.8 to 1.2.

[0143] Example 5 (compliant): Bimetallic NiCo4 catalytic system by colloidal route (molar ratio Co / Ni=4)

[0144] This synthesis is identical to that described in Example 3, except that a solution of 69 mg (0.2 mmol Ni) of the complex [Ni[iPrNC(CH3)NiPr]2] in 4 mL of mesitylene and a solution of 362 mg (0.8 mmol Co) of the complex [Co( / zmtA)2(thf)] in 4 mL of mesitylene are used instead.

[0145] The average diameter of bimetallic nanoparticles determined by Transmission Microscopy (TEM) on 250 measured nanoparticles is 2.0 nm with a standard deviation of 0.5 (25.0%).

[0146] The theoretically targeted Co / Ni ratio was 4. Out of 10 particles counted, the Co / Ni ratio measured by EDS fluctuates from 3 to 5.

[0147] Example 6 (non-compliant): Bimetallic catalytic system NLCo by colloidal route molar ratio Ni / Co=4)

[0148] This synthesis is identical to that described in Example 3, except that a solution of 276 mg (0.8 mmol Ni) of the complex [Ni[iPrNC(CH3)NiPr]2] in 4 mL of mesitylene and a solution of 90 mg (0.2 mmol Co) of the complex [Co( / zmt / 5)2(thf)] in 4 mL of mesitylene are used instead.

[0149] The average diameter of bimetallic nanoparticles determined by Transmission Microscopy (TEM) on 250 measured nanoparticles is 3.9 nm with a standard deviation of 1.0 (25.6%).

[0150] The theoretically targeted Ni / Co ratio was 4. Out of 10 particles counted, the Ni / Co ratio measured by EDS fluctuates from 3 to 5.

[0151] Example 7: Impregnation of catalytic systems on a porous support

[0152] In a Schlenk tube under argon, a solution containing the colloidal nanoparticles in mesitylene is brought into contact with a support, aiming for a theoretical mass content of active phase of 5% by weight relative to the total weight of the catalyst. In a typical experiment, a solution containing 50 mg of metal is brought into contact with 950 mg of support. The suspension is soaked in an ultrasonic bath for 20 minutes at room temperature. Then, the solvent is evaporated under vacuum at 150 °C. The solid obtained is washed twice with 5 mL of toluene and then dried under vacuum at room temperature for at least one hour.

[0153] The porous supports used are a silica-alumina SA, an alumina A and a silica S.

[0154] Alumina (A) has a specific surface area of ​​80 m2 / g, a pore volume of 0.7 mL / g and a median mesoporous diameter of 12 nm.

[0155] Silica-alumina (SA) with an alumina content of 80% has a specific surface area of ​​300 m2 / g, a pore volume of 0.6 mL / g and a median mesoporous diameter of 7 nm.

[0156] Silica (S) has a specific surface area of ​​350 m2 / g, a pore volume of 0.8 mL / g and a median mesoporous diameter of 10 nm.

[0157] Catalyst A is thus obtained as described in Example 1, the support being a silica-alumina (SA) support as described above and also in Example 1.

[0158] Catalyst B is obtained as described above after impregnation of the solution from example 2 on a silica-alumina (SA) support.

[0159] Catalyst C is also obtained as described above after impregnation of the solution from Example 3 on a silica-alumina (SA) support.

[0160] Catalyst D is obtained as described above after impregnation of the solution from Example 4 on a silica-alumina (SA) support.

[0161] Catalyst E is obtained as described above after impregnation of the solution from Example 5 on a silica-alumina (SA) support.

[0162] Catalyst F is obtained as described above after impregnation of the solution from Example 6 on a silica-alumina (SA) support.

[0163] Catalyst G is obtained as described above after impregnation of the solution from Example 4 on an alumina support (A).

[0164] Catalyst H is obtained as described above after impregnation of the solution from example 4 on a silica support (S).

[0165] The Co and Ni contents for catalysts A to F are measured by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and are listed in Table 1 below.

[0166] [Tables 1] Catalyst Composition Average diameter (nm) Ni content (% by weight) Co content (% by weight) A (non-compliant) NiCo / SA 14 1.9 2.1 B (non-compliant) Ni / SA 5.9 4.2 - C (non-compliant) Co / SA 4.0 - 4.0 D (compliant) NiCo / SA 2.3 1.9 2.1 E (compliant) NiCo4 / SA 2.0 0.7 3.1 F (non-compliant) Ni4Co / SA 3.9 3.1 0.8

[0167] Example 8: Catalytic tests, performance in hydrogenation of carbon dioxide

[0168] The catalysts described in the examples above are tested for the hydrogenation of CO2 by RWGS.

[0169] The catalysts are tested with an Avantium® unit comprising 16 parallel stainless steel reactors, with an internal diameter of 2 mm and a length of 560 mm. The reaction is carried out in the gas phase, at a pressure of 1.2 bar absolute (0.12 MPaa). The feed gases are CO2 and hydrogen with an H2 / CO2 molar ratio of 1.1. The CO2 and H2 are co-injected in a downflow and mixed upstream of the reactor head. The feed comprising the gas mixture containing CO2 and hydrogen is then heated to 300°C in the first part of the reactor. The catalyst is loaded in the form of extrudates with a diameter of 1.6 mm. The mass of catalyst loaded into each reactor is 100 mg, corresponding to a loading height of 6 cm to 15 cm depending on the catalyst.

[0170] At the unit outlet, the products are analyzed by gas chromatography.

[0171] The products observed are mainly carbon monoxide (CO), hydrogen (H2), unconverted carbon dioxide (CO2), methanol (CH3OH), methane (CH4), traces of hydrocarbon products (alkenes, alkanes) and traces of alcohols other than methanol.

[0172] Catalyst performance is defined by CO2 conversion and CO selectivity.

[0173] The CO2 conversion is defined according to the following formula:

[0174] CO2 Conversion (%) = 100 x [Q (CO2) in - Q (CO2) out] / [Q (CO2) in]

[0175] with: - Q (CO2)inlet ■ molar flow rate of CO2 inlet in NmL / min - Q (CO2)output: molar flow rate of CO2 output in NmL / min

[0176] The molar selectivity in CO (also called here SCO) is defined according to the following formula:

[0177] SCO (%) = Q (CO) output / (Q (CO2) input - Q (CO2) output)

[0178] For each test, catalysts A to E are treated at atmospheric pressure at 300°C, for 4 hours with a hydrogen flow rate of 12.5 Nml / min per reactor, i.e. a VVH of approximately 10,000 h A

[0179] The H2 / CO2 =1.1 molar mixture charge is then injected into the reactor at 300°C for 4 hours with a gas flow rate of 12.5 Nml / min per reactor, i.e. a VVH of approximately 10,000 h1.

[0180] The temperature is then increased to 500°C in temperature increments of 25°C with a ramp of 300°C between each level. For each new temperature, the analyses are triggered after 1 hour of stabilization under load. The total duration of each level is 4 hours.

[0181] The test protocol makes it possible to know the evolution of conversion with temperature and of CO selectivity with conversion.

[0182] A first series of tests is carried out on catalysts A to F. The results are shown in Table 2 below.

[0183] [Tables2] Catalyst Composition Average diameter (nm) CO2 conversion at 500°C (%) CO selectivity at 500°C (%) A (non-compliant) NiCo / SA 14 20 20 B (non-compliant) Ni / SA 5.9 30 35 C (non-compliant) Co / SA 4.0 12 85 D (compliant) NiCo / SA 2.3 36 73 E (compliant) NiCo4 / SA 2.0 35 90 F (compliant) Ni4Co / SA 3.9 35 47

[0184] Table 2: Influence of NiCo composition on the performance of catalysts supported on SA in CO2 hydrogenation.

[0185] The monometallic Ni / SA catalyst (catalyst B) comprising only nickel is active for the CO2 conversion reaction at 500°C while the monometallic Co / SA catalyst (catalyst C) composed only of cobalt is not very active with a conversion of 12%. The CO selectivity of the Co / SA catalyst is 85% while that of the Ni / SA catalyst is only 35%. On the contrary, the NiCo and NiCo4 catalysts supported on SA (catalysts D and E) according to the invention are both active and selective for the CO2 conversion reaction. Furthermore, the bimetallic Ni4Co / SA catalyst is active for the CO2 conversion reaction but a significant decrease in CO selectivity is observed.

[0186] A second series of tests is carried out on catalysts obtained by impregnation of the solution obtained in Example 4 (Bimetallic NiCo catalytic system by colloidal route with a molar ratio Ni / Co=1) on three different supports as defined above: silica-alumina (SA), silica (S) and alumina (A). The results are shown in Table 3 below.

[0187] [Tables3] Catalyst Average diameter (nm) Conversion (%) CO selectivity (%) NiCo / SA Catalyst D 2.3 36 73 NiCo / A Catalyst G 2.3 36 30 NiCo / S Catalyst H 2.3 38 78

[0188] Table 3: Influence of the support on the performance of supported NiCo catalysts in selective hydrogenation of CO2.

[0189] The NiCo catalysts supported on SA, S and A are all active for CO2 conversion at 500°C. However, the CO selectivity is better for the silica-alumina and silica supported catalysts compared to that of the alumina supported catalyst.

Claims

Claims

1. A process for the hydrogenation of CO2 by reverse water gas reaction (RWGS) by contacting a feedstock of a gas mixture comprising CO2 and hydrogen with a catalyst comprising an active phase based on nickel and cobalt and a silica or silica-alumina support, said active phase being in the form of bimetallic nanoparticles corresponding to the formula NixCoy with x = 1 and y between 1 and 4, said nanoparticles having a number average diameter of less than 10 nm, measured by transmission electron microscopy, with a standard deviation relative to the size of said nanoparticles less than or equal to 50% of said number average diameter, which process being carried out at a temperature of between 0°C and 600°C, at a pressure of between 0.1 MPa and 5 MPa, at a hydrogen / CO2 molar ratio of between 0.1 and 10 and at a speed hourly volume between 100 h 1 and 40,000 h 1.

2. The method of claim 1, wherein the active phase of said catalyst is in the form of bimetallic nanoparticles corresponding to the formula NixCoy with x = 1 and y = 1.

3. The method of claim 1, wherein the active phase of said catalyst is in the form of bimetallic nanoparticles corresponding to the formula NixCoy with x = 1 and y = 4.

4. A method according to any one of claims 1 to 3, wherein the catalyst comprises a nickel content of between 0.1 and 15% by weight of element nickel relative to the total weight of the catalyst.

5. A method according to any one of claims 1 to 4, wherein the catalyst comprises a cobalt content of between 0.1 and 15% by weight of element cobalt relative to the total weight of the catalyst.

6. A method according to any one of claims 1 to 5, wherein the number average diameter of the nickel and cobalt based bimetallic nanoparticles, measured by transmission electron microscopy, is less than less than 7 nm, and in that the standard deviation relative to the size of said nanoparticles is between 20% and 50% of said average diameter.

7. A method according to any one of claims 1 to 6, wherein the bimetallic nanoparticles of said catalyst are in the reduced state.

8. A method according to any one of claims 1 to 7, wherein said catalyst is obtained by a preparation method comprising the next steps: i) a catalytic system in the form of a colloidal suspension comprising a plurality of bimetallic nanoparticles based on nickel and cobalt is brought into contact, said nanoparticles having a number average diameter of less than 10 nm, measured by transmission electron microscopy, with a standard deviation relative to the size of said nanoparticles less than or equal to 50% of said average diameter, with a support chosen from silica or silica-alumina to obtain a catalyst precursor; ii) the catalyst precursor obtained at the end of step i) is dried at a temperature below 250°C, preferably at a pressure below 0.001 MPa to obtain a catalyst; iii) optionally, the catalyst obtained in step ii) is calcined at a temperature between 250°C and 500°C to obtain a calcined catalyst; iv) optionally, the calcined catalyst obtained at the end of step iii) is reduced by contacting it with a reducing gas to obtain a reduced catalyst.

9. A method according to claim 8, wherein said catalytic system of step i) is obtained by a preparation method comprising the following steps: a) at least one nickel-based organometallic precursor and at least one cobalt-based organometallic precursor are supplied separately; b) said organometallic precursors supplied at the end of step a) are brought into contact in the presence of a solvent, at least one first stabilizing agent and at least one second stabilizing agent to obtain a colloidal suspension, said step b) comprising the following sub-steps: bl) bringing said organometallic precursors supplied at the end of step a) into contact in the presence of the solvent to obtain a first solution; b2) the first solution obtained at the end of step b1) is brought into contact with at least one first stabilizing agent to obtain a second solution; b3) the second solution obtained at the end of step b2) is brought into contact with at least one second stabilizing agent, different from the first stabilizing agent, to obtain the colloidal suspension; c) said colloidal suspension obtained at the end of step b) is heated to a temperature between 25°C and 180°C under a hydrogen pressure between 0.01 MPa and 1 MPa to obtain said catalytic system.

10. The method of claim 9, wherein said nickel-based organometallic precursor is selected from nickel(II) bis-(hexamethyldisilazane) [Ni[iPrNC(CH2CH2CH2CH3)NiPr]2]; nickel(II) bis-[N,N'-di(isopropyl)methylcarbodiimide] [Ni[iPrNC(CH3)NCy]2]; nickel(II) bis-[N,N'-di(cyclohexyl)methylcarbodiimide] [Ni[CyNC(CH3)NCy]2]; nickel(II) bis-(1,5-cyclooctadiene)nickel(0), Ni(q4-C8Hi2)2.

11. The method of any one of claims 9 and 10, wherein said cobalt-based organometallic precursor is selected from cobalt(II) bis-(hexamethyldisilazane)tetrahydrofuran [Co^mdsO^thf)]; cobalt(II) bis-[N,N'-di(isopropyl)methylcarbodiimide], [Co[' PrNC(CH3)N'Pr]2]; cobalt(II) bis-[N,N'-di(isopropyl)n-butylcarbodiimide], [CopPrNQCHzCHzCHzCH^NiPrh]; cobalt(II) bis-[N,N'-di(cyclohexyl)methylcarbodiimide], [Co[CyNC(CH3 )NCy]2]; (l,5-cyclooctadiene)(cyclooctadienyl) cobalt (I), Co(q3-C8H 13)(if-C8H12).

12. A method according to any one of claims 9 to 11, wherein said first stabilizing agent and / or said second stabilizing agent are selected from carboxylic acids, carboxylate anions, primary, secondary or tertiary amines, primary, secondary, tertiary or quaternary ammonium cations, amides, esters, alcohols, alcoholates, thiols, thiolates, saturated or unsaturated, having between 1 and 30 carbon atoms.

13. The method of claim 12, wherein the first stabilizing agent is palmitic acid and the second stabilizing agent is hexadecylamine.