A heterogenous catalyst for co2 hydrogenation and a process for the preparation thereof

Abstract

The present invention relates to a heterogeneous catalyst system comprising bimetallic composition supported onto a specific mixed metal oxides base support to achieve enhanced selectivity in hydrogenation of CO2. The present invention also relates to a process for the preparation of said heterogeneous catalyst system and application in CO2 hydrogenation thereof.

Description

[0001] A HETEROGENOUS CATALYST FOR CO2 HYDROGENATION AND A PROCESS FOR THE PREPARATION THEREOF

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a heterogeneous catalyst for CO2 hydrogenation. Particularly, the present invention relates to a process for the preparation of the heterogeneous catalyst. More particularly, the present invention relates to the heterogeneous catalyst comprising bimetallic composition supported onto a specific mixed metal oxides base support to achieve enhanced selectivity in hydrogenation of CO2.

[0004] BACKGROUND OF THE INVENTION

[0005] Increasing emissions of CO2 are showing catastrophic effects in the atmosphere in the form of climate and weather pattern changes. Industries, automobiles, and other man-made sources play a significant role in increasing the concentration of CO2 in the environment. Since CO2 is highly oxidized, having a 4+ formal oxidation state in carbon, they are thermally stable, and its activation is considered a chemically and thermodynamically challenging. The inherent stability of the CO2 molecule means any process requires high energy to activate the molecule or the development of smart catalysts for bringing down the energy barriers. The thermodynamic barrier for C-C coupling from CO2 is higher, making high energy density C2+ products more challenging.

[0006] Over the last few decades, the scientific communities and industrial personnel have made a concerted effort to mitigate CO2 concentration in the environment using various methodologies. Among them, CO2 reduction through reverse water gas shift (RWGS) reaction is one of the most attractive and effective ways to mitigate atmospheric CO2 concentration. Through the CO2 hydrogenation route, different value-added industrially useful products such as methanol [J. A. Rodriguez et al., ACS Catal. 5 (2015), pages 6696-6706], formic acid[K. Mori et al., J Am Chem Soc. 140 (2018), pages 8902- 8909], Olefins [Z. Ma et al., ACS Catal. 9 (2019), pages 2639-2656], Methane [F. Wang et al., J Am Chem Soc. 138 (2016), pages 6298-6305] and higher hydrocarbons [K. Zhang et al., Energy & Fuels. 15 (2001), pages 395-402], are reported. Through RWGS reaction, CO2 hydrogenation to CO or syngas (mixture of CO & H2) formation is an attractive and commercially viable process because CO or Syngas is a direct feedstock for Fischer-Tropsch (FT) process for obtaining liquid fuels. Reverse water gas shift reaction (RWGS) is endothermic and thermodynamically favourable. In contrast, the water gas shift reaction (WGS) is exothermic.

[0007] CO2+ H2CO+H2O AH = +41 kJmol1

[0008] CO2+ 4H2<->CH4+ 2H2O AHe= -165 kJ mol- 1 The above equation shows that the RWGS reaction is favoured at high temperatures, while the methanation reaction is exothermic at low temperatures.

[0009] Transition metal (Ni, Cu, Co, and Fe)supported over SiOi, AI2O3, and other active supports is well known for CO2 reduction reaction but suffers deactivation at higher temperatures due to aggregation of particles. On other side, noble-metal based monometallic catalysts are also reported for same reaction having high catalytic activity, selectivity, stability, and excellent resistance to coke deposition, but are not cost-effective from industrial point of view.

[0010] As discussed above, conventional Cu, Co, Fe and Ni-based catalysts are extensively used for hydrogenation of molecules like CO and CO2 but face stability issues when reactions are done for a extended period and at a higher temperature.

[0011] Therefore, there is a clear need for catalyst system with enhanced selectivity and conversion of CO2 hydrogenation reaction via RWGS reaction at lower temperatures (600°C or below) into value added products which can avoid issues related to sintering observed at higher temperatures. The inventors of present invention found a technical solution to said problems by providing heterogeneous catalyst system covering bimetals supported over ceria- zirconia (CZ) solid support for CO2 hydrogenation at atmospheric pressure and lower temperatures upto 500 °C. For this, the present invention provides a M1-M2 bimetallic composition with different metal loading from 2wt.% to 6wt.% on CZ support and demonstrated synergistic effects in catalyzing selective CO2 reduction to CO and other value added products with high space-time yields (STY). For RWGS reaction, the STY in case of alone Ml / CZ was 8.21 (umol / S) while for M2 / CZ it was 6.45(umol / S), and remarkable enhancement was observed in bimetallic catalyst due to synergism, where STY was 14.3f (umol / S) or M1M2 / CZ catalyst as substantiated below.

[0012] OBJECTS OF THE INVENTION

[0013] Main object of the present invention is to provide a heterogeneous catalyst comprising bimetallic composition supported on the mixed metal oxides base support for CO2 hydrogenation into value added products.

[0014] Another object of the present invention is to provide a process for the preparation of said heterogeneous catalyst containing bimetallic composition supported onto a mixed metal oxides base support.

[0015] Yet another object of the present invention is to provide a heterogeneous catalyst containing bimetallic composition supported onto specific mixed metal oxides base support, for enhancing the selectivity, stability and conversion of CO2 hydrogenation into CO and other value added products at ambient pressure and lower temperatures. SUMMARY OF THE INVENTION

[0016] Accordingly, in order to accomplish an objectives, the present invention provides a heterogeneous catalyst system comprising bimetallic composition supported on the mixed metal oxides base support for CO2 hydrogenation into value added products.

[0017] The present invention provides a heterogeneous catalyst of Formula I comprising:

[0018] (i) l-6wt % of at least two metal composition (M1M2);

[0019] (ii) 94-99wt % of mixed metal oxide support; wherein the metal composition (M1M2) is supported onto the mixed metal oxides support; the mixed metal oxides support is ceria oxide-zirconium oxide (CcCh-ZrCh); and the mixed metal oxides support has a particle size is in the range of 4 nm to 15 nm.

[0020] In an embodiment of the present invention, the said at least two metals composition (M1M2) comprises metal Mi and metal M2, wherein the metal Mi is selected from the group consisting of copper, nickel, aluminium and zinc, and the M2 metal is selected from the group consisting of cobalt, indium and iron.

[0021] In another embodiment of the present invention, the amount of said Mi metal in said bimetallic composition is in the range of 75 to 98% of total weight of the mixed bimetallic composition; wherein an amount of said M2 metal in said bimetallic composition is in the range of 2 to 25% of total weight of the mixed bimetallic composition; and a ratio of ceria oxide and zirconium oxide in said mixed metal oxides support is in the range of 3: 1 to 1:3.

[0022] In yet another embodiment, the present invention provides a process for the preparation of the heterogeneous catalyst comprising the steps of: a) dissolving ammonium ceric nitrate and zirconyl nitrate hydrate in a solvent followed by drop wise addition of urea under continuous stirring at a temperature in the range of 90- 110 °C for a time period in the range of 2-4 hrs to obtain a precipitate; b) stirring the precipitate obtained in step a) continuously for a time period in the range of 8- 10 hrs at a temperature in the range of 90-110°C to form a gel; c) washing the gel obtained in step b) with boiling distilled water, drying at a temperature in the range of 70-95 °C for time period of 3-5 hrs under 2-10 millibar pressure and then calcining at temperature in the range of 400 to 500 °C for 3 to 5 hrs with 2 °C min1ramping rate to obtain mixed metal oxides support; d) adding Mi-metal precursor salt followed by adding Mi-metal precursor salt in the mixed metal oxides support obtained in step c), mixing in the presence of a precipitating agent at pH in the range of 9-11 to form a crude heterogeneous mixture; e) stirring the crude heterogeneous mixture as obtained in step d) for time period in the range of 0.5 to 2 hrs at a temperature in the range of 28°C to 35°C with pH maintained throughout in the range of 9-11 followed by centrifugation, washing, drying and then calcining at temperature in the range of 300 to 500°C for 3 to 5 hrs with 2 °C min1ramping rate to obtain the heterogeneous catalyst.

[0023] In yet another embodiment of the present invention, said solvent used in step a) is selected from the group consisting of water, millipore water and deionized water.

[0024] In yet another embodiment of the present invention, said metal precursors / salts of Mi and M2 used in step b) are selected from the group consisting of metal sulfates, metal halides, metal nitrates, metal acetates, metal nitrites, metal oxides, metal carbonates, metal hydroxides, metal oxalates, metal pyrazolyl borates, metal azides, metal fluoroborates, metal carboxylates, metal halogencarboxylates, metal hydroxycarboxylates, metal aminocarboxylates, metal aromatic and nitro and / or fluoro substituted aromatic carboxylates, metal aromatic and nitro and / or fluoro substituted aromatic carboxylates, metal beta diketonates, metal sulfonates, and metal acetylacetonate.

[0025] In yet another embodiment of the present invention, said precipitating agent is selected from the group consisting of sodium hydroxide, potassium hydroxide and ammonium hydroxide.

[0026] A process for the hydrogenation of CO2 using the heterogeneous catalyst comprising the steps of: i. adding the heterogeneous catalyst in a reactor; ii. pre-treating said heterogeneous catalyst under H2 gas flow at a rate of 10-40 mL / min, at temperature in the range of 300 to 500 °C for time period in the range of 1.5 to 3 hrs to obtain reduced heterogeneous catalyst; and iii. adding and contacting CO2 stream and H2 stream in the reactor containing said reduced heterogeneous catalyst under specific reaction conditions to obtain CO, Ci-based products and / or value-added products.

[0027] In yet another embodiment of the present invention, the reactor is fixed-bed flow reactor.

[0028] In yet another embodiment of the present invention, the process of CO2 hydrogenation is done via batch mode or continuous mode wherein CO2 and H2 streams are continuously passed through out the reaction time period in a continuous mode.

[0029] In yet another embodiment of the present invention, an amount of bimetallic composition in the heterogeneous catalyst used is in the range of 1 wt.% to 6 wt.%; and In yet another embodiment of the present invention, the specific reaction conditions of step iii) are selected from one or more of:

[0030] I. total gas flow of CO2 and H2 in the reactor is in the range of 20 to 80 mL / min,

[0031] II. a ratio of CO2:H2 is in range of 1:0.5 to 1:4,

[0032] III. a gaseous hourly space velocity (GHSV) is in range of 30000 to 1400000 mLg“ V,

[0033] IV. a temperature for conversion of CO2 is kept in the range of 200 to 600 °C and / or,

[0034] V. an outlet pipeline of the reactor is kept at a temperature in the range of 90-110 °C.

[0035] In yet another embodiment of the present invention, said Ci based products are selected from the group consisting of carbon monoxide, methane, methanol and acetic acid; the value added products are selected from C2-C5+ olefins; and the heterogeneous catalyst is a stable for at least 72 hours, and is a recyclable.

[0036] ABBREVIATIONS USED

[0037] CZ or CeO2-ZrO2 = combination of cerium oxide (CeO2) and zirconium oxide (ZrO2).

[0038] CZ (1: 1) = combination of cerium oxide and zirconium oxide with weight ratio of 1: 1.

[0039] CZ (1:3) = combination of cerium oxide and zirconium oxide with weight ratio of 1:3.

[0040] CZ (3: 1) = combination of cerium oxide and zirconium oxide with weight ratio of 3: 1. 2CU95CO5 / CZ= 2 wt. % of CuCo mixed bimetallic catalysts supported onto CZ support wherein wt.

[0041] % of Cu is 95%, and wt. % of Co is 5% of total metal loading i.e. 2 wt.%.

[0042] BRIEF DESCRIPTION OF DRAWINGS

[0043] Fig. 1 (a) illustrates the TEM graph, and (b) & (c) illustrates the HRTEM graphs of the heterogeneous catalyst 2CU95C05 / CZ.

[0044] Fig. 2 illustrates the PXRD pattern of the different calcined samples including the heterogeneous catalyst 2CU95C05 / CZ.

[0045] Fig. 3 (a) to (e) illustrates elemental analysis of the heterogeneous catalyst 2CU95C05 / CZ.

[0046] FIG. 4 illustrates CO2 conversion and CO selectivity: A) over different supportssuch as CeO2, ZrO2, CZ (1: 1); and B) over different ratios of CZ (3: 1), CZ (1:3) and CZ (1:1). Reaction conditions - catalyst amount: 50 mg, CO2:H2: 6:24 (mE / min), GHSV: 36000 (mF g-1h-1) and temperature: 200- 500 °C. Fig. 5 shows CO2 conversion and CO selectivity for 2Cu95Cos / CeO2 and 2Cu95Cos / ZrO2, and 2CU95C05 / CZ (1: 1) catalysts with same loading amount.

[0047] FIG. 6 ILLUSTRATES CO2CONVERSION AND CO SELECTIVITY OVER THE BIMETALLIC HETEROGENEOUS CATALYST 2CU95CO5 / CZ CATALYST AT: A) DIFFERENT TEMPERATURES - REACTION CONDITIONS - A) CATALYST AMOUNT: 50 MG, CO2: H2: 1:4, CO2FLOW RATE: 6 ML / MIN, H2FLOW RATE: 24 ML / MIN, GHSV: 36000 (ML G ' H1), AND TEMP,: 200°C TO 600°C, AND B) DIFFERENT CO2AND H2FLOW RATE RATIOS AT TEMPERATURE OF 500 °C AND 600 °C = REACTION CONDITIONS- CATALYST AMOUNT: 50 MG, TEMP.: 500°C AND 600°C.THE GAS HOURLY SPACE VELOCITY(GHSV) WAS KEPT 360001FOR ALL THE CATALYSTS WITH CO2 / H2RATIO AT 1:4 AND GHSV WAS 38400 MLG^H1, 43200 MLG^H1, 57600 MLG ' H 'AND 86400 G-1H-1 WHEN CO2 / H2 RATIO WAS 1:3,1:2,1: 1AND 1:0.5 RESPECTIVELY.

[0048] DETAILED DESCRIPTION OF THE INVENTION

[0049] Unless the context requires otherwise, throughout the specification which follow, the expression “nano sized particles” and variations thereof, such as, “nano particles” and “nano shaped particles” relate mainly to the “nanoparticles”.

[0050] The terms “Bimetallic”, “bimetals” and “bimetallic catalysts” used herein refer to contain stoichiometric amounts of two metal elements (such as alkali metal, alkaline earth metal, noble metal, transition metal, lanthanide, actinide, and metalloid).

[0051] Here, the term “system” used throughout the specification, which relate to catalyst material containing multiple components i.e., metals and support. Hence, the terms “heterogeneous catalyst system” or “heterogeneous catalyst” as material are used herein interchangeably with the same meaning.

[0052] The present invention provides a heterogeneous catalyst system comprising bimetallic composition supported on the mixed metal oxides base support for CO2 hydrogenation into CO, Ci-based products and / or value-added products.

[0053] The heterogeneous catalyst system includes the bimetallic catalysts and mixed metal oxides based support material comprising a surface, wherein the bimetallic catalysts are deposited on the surface of the support.

[0054] The bimetallic composition are based on combination of two metals, wherein first metal and second metal are different. The bimetallic composition are nanoparticular compounds that contain stoichiometric amounts of two metal (alkali metal, alkaline earth metal, transition metal, lanthanide, actinide, and metalloid) elements.

[0055] The metal precursors are selected from but not limited to metal halides (such as metal chlorides or metal bromides), metal nitrates, metal acetates, metal nitrites, metal oxides, metal carbonates, metal hydroxides, metal oxalates, metal pyrazolyl borates, metal azides, metal fluoroborates, metal carboxylates, metal halogen carboxylates, metal hydroxycarboxylates, metal aminocarboxylates, metal aromatic and nitro and / or fluoro substituted aromatic carboxylates, metal aromatic and nitro and / or fluoro substituted aromatic carboxylates, metal beta diketonates, metal sulfonates, metal acetylacetonate and the like.

[0056] The support material is desirably in the nanometer size range. For example, the support has an average particle size or diameter of about 1 to about 1000 nm, such as from about 50 to about 500 nm, or about 100 to about 200 nm, or about 1 to about 100 nm. Most preferably 4 nm - 15 nm.

[0057] Ci based products are methane, carbon monoxide, formic acid, methanol and the like and value added products are selected from but not limited to methane, methanol, light olefins(C2 to C5+), formic acid, acetic acid, etc. and the like.

[0058] The present invention provides a heterogeneous catalyst system comprising bimetallic composition (M1M2) supported on the specific mixed metal oxides base support, with 100% selectivity for said hydrogenation of CO2; wherein the mixed metal oxides base support is a combination of ceria oxidezirconium oxide (CeO2-ZrO2).

[0059] The weight ratio of combination of ceria oxide-zirconium oxide in said mixed metal oxides base support is in range of 3: 1 to 1:3 preferably 3: 1, 1: 1 or 1:3; more specifically 1: 1.

[0060] In said ceria-zirconia combination, due to the insertion of Zr4+ions (ionic radius 0.84A) with the replacement of Ce4+ ions (ionic radius 0.97 A) from the fluorite-type lattice structure of CeCh, some structural defects are created. This defective fluorite structure improves the physical and chemical properties of the ceria. Zr4+ions play an important role in increasing redox property (Ce4+to Ce3+), high thermal stability, and oxygen storage capacity of ceria.

[0061] The metals in said bimetallic catalysts are selected from but not limited to copper, aluminum, magnesium, manganese, zinc, chromium, lead, cadmium, cobalt, nickel, indium, iron, tungsten, molybdenum, bismuth, mixtures thereof, and salts or alloys thereof preferably copper and cobalt. The Mi metal is selected from copper, nickel, aluminum, zinc, or mixtures thereof and salts or alloys thereof preferably copper

[0062] The M2 metal is selected from cobalt, indium, iron, or mixtures thereof and salts or alloys thereof preferably cobalt.

[0063] The amount of Mi metal is in range of 75 to 98% of total weight of the mixed bimetallic composition and the amount of M2 metal is in range of 2 to 25% of total weight of the mixed bimetallic composition.

[0064] The present invention provides a process of preparation of the heterogeneous catalyst comprising the steps of: a) dissolving ammonium ceric nitrate and zirconyl nitrate hydrate in a solvent followed by dropwise addition of urea under continuous stirring at a temperature in the range of 90-110 °C for a time period in the range of 2-4 hrs to obtain a precipitate; b) stirring the precipitate obtained at step a) continuously for a time period in the range of 8-10 hrs at a temperature in the range of 90-110°C to form a gel; c) washing the gel obtained at step b) with boiling distilled water, drying at a temperature in the range of 70-95°C for time period in the range of 3-5 hrs under 2-10 millibar pressure and then calcining at temperature in the range of 400 to 500 °C for 3 to 5 hrs with 2°C min-1 ramping to obtain mixed metal oxides base support in powder form; d) adding and mixing the mixed metal oxides base support obtained at step c) with Mi -M2 bimetals by mixing Mi -metal salt with M2-metal salt in the presence of precipitating agent, at pH in the range of 9-11 to form crude heterogeneous mixture; and e) stirring the crude heterogeneous mixture of step d) for time period in the range of 0.5 to 2 hrs at a temperature in the range of 28°C to 35°C with pH maintained throughout in the range of 9-11 followed by centrifugation, washing, drying and then calcining at temperature in the range of 300 to 500 °C for 3 to 5 hrs with 2 °C min1ramping to afford the heterogeneous catalyst.

[0065] The amount of ammonium ceric nitrate used in step a) is in range of 33 to 66 wt.%.

[0066] The amount of zirconyl nitrate hydrate used in step a) is in range of 33 to 66 wt. %.

[0067] The solvent used in step a) is selected from water, millipore water and deionized water.

[0068] The stirring of step a) is done at 500 RPM using suitable stirrer known in the art.

[0069] The precipitate formed in step a) is boiled at temperature in the range of 90-110 °C for time period in the range of 7-9 hrs to obtain a gel. The gel as obtained upon boiling of precipitate in step b), is then washed at least twice times with water or distilled water to remove the excess urea.

[0070] The drying of step e) is done in vacuum oven at temperature in the range of 70-95 °C for time period of 3-5 hrs under 2-10 millibar pressure.

[0071] The calcination of step e) is done at temperature in the range of 400 to 500 °C for 3 to 5 hrs with 2 °C min1ramping to obtain mixed metal oxides based support in powder form.

[0072] The Mi metal salts and M2 metal salts used in step b) are selected from but not limited to metal sulfates, metal halides (such as metal chlorides or metal bromides), metal nitrates, metal acetates, metal nitrites, metal oxides, metal carbonates, metal hydroxides, metal oxalates, metal pyrazolyl borates, metal azides, metal fluoroborates, metal carboxylates, metal halogencarboxylates, metal hydroxycarboxylates, metal aminocarboxylates, metal aromatic and nitro and / or fluoro substituted aromatic carboxylates, metal aromatic and nitro and / or fluoro substituted aromatic carboxylates, metal beta diketonates, metal sulfonates, metal acetylacetonate and the like.

[0073] Specifically, the Mi-metal salt / precursor is Mi-metal nitrate, and the Mi-metal salt / precursor is M2- metal nitrate.

[0074] The amount of Mi-metal salt used in step d) is in range of Mi was 1.2 to 2 wt. %.

[0075] The amount of M2-metal salt used in step d) is in range of M2 was 0.02 to 2 wt. %.

[0076] The precipitating agent is selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide and so on.

[0077] The concentration of precipitating agent solution used in step d) is 0.4 to 0.6M.

[0078] The centrifugation of step e) is done at speed of 8000-12000 RPM using machine Eppendorf centrifuge machine.

[0079] The washing of step e) is done using mixture of distilled water for 3-4 times and then washed with pure ethanol or water with methanol or ethanol with ratio of solvents as pure ethanol was used for last washing.

[0080] The drying of step e) is done in vacuum oven at temperature in the range of 60-100 °C for time period of 8-12 hr under 2-10 mbar of pressure.

[0081] The calcination of step e) is done at temperature in the range of 300 to 500 °C for 3 to 5 hrs with 2 °C min-1 ramping to obtain mixed bimetallic catalysts in powder form (M1M2 / CZ).

[0082] The first metal (Mi) is provided as non-ionic copper that can be obtained from copper salt / precursor selected from but not limited to copper nitrate.

[0083] The second metal (M2) is provided as non-ionic cobalt that can be obtained from cobalt salt / precursor selected from but not limited to cobalt nitrate. The average crystallite size was calculated using the Scherer equation (eqn.l) for catalysts synthesized CeCh-, CZ and 2-CU95C05 / CZ was 6 nm, 4 nm and 4.5 nm, respectively

[0084] The present invention provides a process for the hydrogenation of CO2 using said heterogeneous catalyst system, comprising the steps of: i. adding the heterogeneous catalyst system in a reactor; ii. pre-treating said heterogeneous catalyst system under H2 gas flow to reduce the catalyst prior to the reaction; and iii. adding and contacting CO2 stream and H2 stream through the reactor under specific reaction conditions to form CO or Ci based products and / or value added products.

[0085] The reactor used in CO2 hydrogenation process is fixed-bed flow reactor.

[0086] The process of CO2 hydrogenation is done via batch mode or continuous mode wherein in continuous mode CO2 and H2 continuously pass throughout the reaction time period.

[0087] The amount of the heterogeneous catalyst system used in said CO2 hydrogenation process is in the range of 3 mg to 50 mg and metal loading is in the range of 1 wt. % to 6 wt. %.

[0088] The reaction conditions are selected from one or more of:

[0089] I. Total gas flow of CO2 and H2 in the reactor is in the range of 20 to 80 mL / min,

[0090] II. The ratio of CC fL is in range of 1:0.5 to 1:4,

[0091] III. The gaseous hourly space velocity (GHSV) is in range of 30000 to 1400000 mLg_1h_1, and / or

[0092] IV. The outlet pipeline of the reactor is kept at a temperature in the range of 90-110 °C.

[0093] The Ci based products or value added products are selected from but limited to carbon monoxide, methane, methanol, acetic acid, and C2-C5+ olefins , and so on.

[0094] The CO, Ci based products and / or value added products are determined using Thermal conductivity detector (TCD), and Flame Ionization Detector (FID).

[0095] The pre-treatment of step b) is done by treating the catalyst with H2 gas at temperature in the range of 300 to 500 °C for time period of 1.5 to 3 hrs to obtain pre-treated / reduced catalyst.

[0096] The flow rate of H2 gas in pre-treatment step is in range of 10-40 mL / min.

[0097] The heterogeneous catalyst system as mentioned above shows selectivity for CO, Ci and value added products by 75-100%, specifically, 75%, 80%, 85%, 90%, 95%, 99%, 99.9%, or higher. Preferably 100% selectivity at lower temperatures of 200 to 600°C.

[0098] The ratio of pressures between hydrogen gas and carbon dioxide, e.g. can also effect selectivity and yield of the process. Preferred reaction parameters for RWGS reaction is: i) CO2:H2 ratio ranging from 1:0.5 to 1:4 for a total flow rate ranging from 20 mL / min to 80 mL / min, preferably in the ratio of 1:4 with 72 mL / min total flow rate;ii) temperature is in range of 200 ° C - 8000C and preferably 200°C - 400 °C or 400 to 600 °C, under ambient pressure conditions, and / or; iii) GHSV of 30000 - 1400000 mL h1gcat’1, preferably 36000 to 1400000 mLh’1gcat or 36000 mL h’1gcat’1.

[0099] The hydrogenation of CCh is carried out at atmospheric pressure. The CO2 hydrogenation to methanol can also be carried out at pressures ranging from about 1 bar to 50 bar.

[0100] The reactor can be a stand-alone system for chemical synthesis, or incorporated into a renewable chemical synthesis scheme, or incorporated into a gas purification scheme. In either case, the hydrogenation of carbon dioxide with hydrogen gas, is accomplished using the catalytic process described herein.

[0101] The heterogeneous catalyst system disclosed herein may be used in any manner known to a person skilled in the art.

[0102] The total metal loading of M1+M2 in the catalyst is 0.8 to 6.8 wt.% with respect to the support (ceriazirconia).

[0103] The Mi metal in said catalyst is copper, then it recites active oxidation states selected from Cu°, Cu1+and Cu2+or mixture thereof, and in that, Cu1+is more active and has more selectivity than Cu2+for CO formation from CO2, wherein the Cu1+is prevalently present when the amount of copper is at or above 90-100 wt.% of total weight of the mixed bimetallic composition, and the Cu2+is prevalently present in between 75-90% of total weight of the mixed bimetallic composition.

[0104] The Cu wt % loading is 1.9%, and Co is present in 0.1 wt. % with respect to wt. % of the support in best catalyst.

[0105] The Cu in said catalyst is present in the form of CU2O which was confirmed by XPS and Auger spectroscopy methods.

[0106] Thenanoparticle size of CZ support in said catalyst is in the range of 3-6 nm.

[0107] The catalyst covers the Zr4+metal ions entry into the CcCh lattice to form a solid solution structure and increase in the Ce3+species, which ultimately enhanced the electron density, which also explains the increase of oxygen vacancies in CZ solid solution compared to bare CeC .

[0108] Theaverage crystallite size of the catalyst 2CU95C05 / CZ is 4.5 nm.

[0109] The catalyst and / or support comprises one or more of: i) a tetragonal metastable Z1O2 phase, ii) fluorite-type structure of ceria, iii) incorporating Zr4+ions into the ceria lattice, forming a solid solution, iv) the oxygen vacancies created by lattice oxygen displacement in the CeCh lattice, v) presence of Cu+1, Cu° and surface oxygen, vi) the reduction of surface oxygen species over Ce-Co, CZ reduction and the reduction of Co+2species, respectively, vii) The surface area of CZ (1: 1) is higher than CeO2, viii) the incorporation of Zr4+ions into the ceria lattice results in the arrested growth of CeO2 particles, ix) Metal deposition at high pH (above 7) over CZ (1: 1) support produced catalyst with overall improved surface area due to the deposition of small and highly dispersed particles, x) CLDO and CoO are in close contact providing an excellent interface for catalysis, xi) Cu and Co bimetals are well dispersed over CZ support, xii) The increase in the number of Ce3+metal ions is due to the insertion of Zr4+metal ions into the lattice of the CeOi, and / or xiii) Normally, the Zr species are in +4 oxidation state.

[0110] To check and confirm the stability of catalyst , time on stream study has been performed and the same did not show deactivation over 72 hrs study.

[0111] The present invention provides a nanostructured ceria-zirconia (CZ) supported heterogeneous catalyst with Co and Cu metal nanoparticles, showing synergistic catalysis giving unprecedented conversion compared to bare Cu nanoparticles with 100% CO selectivity. Cu+species help to achieve 100 % CO selectivity, whereas synergism between Cu and Co enhances CO2 conversion, the catalyst shows excellent CO2 conversion even under hydrogen lean conditions where H2 to CO2 ratio is 0.5: 1, with a rate of 206023 mmol / gmetai / h which is highest reported value. Also, a detailed XPS study confirms that said combined CeO2-ZrO2 solid solution support has more oxygen vacancies than individual CcCh or Z1O2. These oxygen vacancies are activation sites for CO2 which, in close proximity to Cu-Co facilitates very efficient hydrogenation.

[0112] EXAMPLES

[0113] The following examples are given as a way of illustration only and should not be construed to limit the scope of the present invention.

[0114] Materials used: All chemicals were used without purification. Metal precursors cobalt(iii)nitrate hexahydrate, copper(ii)nitrate trihydrate & zirconium(iv)oxynitrate hydrate (zirconyl nitrate) were purchased from Himedia. NaOH flakes were purchased from Merck. Ammonium ceric nitrate and urea were purchased from Loba Chemie. Carbon dioxide (99.999% pure) and hydrogen gas cylinders were purchased from Vadilal Chemical Ltd.

[0115] Example 1: Synthesis Of Ceria-Zirconia (CZ) Support

[0116] 3g of ammonium ceric nitrate and 2.4g of zirconyl nitrate hydrate was dissolved in 30 ml millipore water. Urea was added to this continuously, stirring with heating at a temperature of 100 °C, until a clear solution formed. This solution was transferred to a pre-heated oil bath and heated to 100°C with stirring until the precipitation. Once the precipitate was formed, stirring was stopped and boiled for 8h at a temperature of 100°C to remove excess urea. The gel obtained was washed with boiled distilled water twice, dried in a vacuum oven at 80°C and 5 m bar pressure, and then calcined at 450°C for 4 h with 2 °C min1ramping. The yellow-coloured powder was used as a support for catalyst synthesis.

[0117] Example 2: Synthesis of the hetereogeneous catalyst (Cu-Co as Ml and M2)

[0118] The bimetallic catalyst was synthesized via the deposition precipitation method. For the synthesis, copper nitrate and cobalt nitrate are used as metal precursors and added in the support synthesised in example 1 and 0.5M NaOH is used as a precipitating agent at a pH in a range of 9 - 11. After the synthesis sample was centrifuged, washed with distilled water and ethanol, and dried overnight [10 hrs] in the oven. All the catalysts were calcined at 400°C for 4h with 2°C min1ramping.

[0119] The catalyst which labelled as 2CU95C05 / CZ indicates total metal loading is 2 wt. % and Cu and Co ratio is 95:5. For example 100 mg catalyst contains 98 mg support and 2 mg active metals i.e. Cu and Co. The series of catalysts prepared are shown in below table: wherein X is wt. % of (Cu+Co).

[0120] Comparative Example 1: Monometalic supported on CZ catalyst (Cu or Co onto CZ)

[0121] The synthesis procedure for the monometalic supported on CZ catalyst is same as covered in example

[0122] 2 with exception of using only one metal precursor i.e., either copper nitrate or cobalt nitrate. Rest process is same.

[0123] Characterization of prepared CZ support

[0124] Various analytical and spectroscopic techniques characterized calcined samples. UV-visible spectroscopy was done on Shimadzu 2700 spectrometer using BaSC as a reference. Powder XRD (PXRD) was done on Rigaku mini flex XRD instrument using Cu Ka as an X-rays source. Samples were scanned at a 4° min1scan rate from 10° - 80° 29 value. The average crystallite size was calculated by the Scherer equation. BET surface area analysis was performed on a Quantachrome instrument (Automated Surface area & Pore Size Analyzer) using the nitrogen physisorption method at liquid N2 temperature. The specific surface area was derived using the Brunaur-Emmett-Teller (BET) method, and pore size distribution spectra were plotted using the Barrett- Joyner-Halenda (BJH) method. Raman analysis was done for the CeCh, Z1O2 and CZ (1: 1) to determine the oxygen vacancies and CZ solid solution formation using a Renishaw InVia microscope instrument with a 532 nm Ar laser and CCD synapse detector. H2 temperature-programmed reduction (H2-TPR) was carried out using the Micromeritics 2920 instrument attached to a TCD detector. Transmission electron microscopy (TEM), HRTEM, and HAADF-STM were done with FEI TECHNI T20 and JEOL JEM F200, using an acceleration voltage of 20kV and 200kV, respectively. X-ray photoemission spectroscopy (XPS) measurements were carried out using a Thermo Scientific Kalpha+ spectrometer using micro-focused and monochromatic Al Ka radiation with an energy of 1486.6 eV. The pass energy for the spectral acquisition was kept at 50 eV for individual core levels. The electron flood gun was utilized for providing charge compensation during data acquisition. The peak fitting of individual core levels was done using Advantage software with a smart-type background. The in-situ DRIFT study was conducted with NICOLET iS50 FTIR instrument equipped with liquid nitrogen cooled MCT / B detector, Praying mantis accessory, and KBr windows dome and in-situ reaction cell. In the UV-visible spectra analysis, one intense broad absorption band in the 700 nm- 800 nm range is observed, corresponding to the CoO phase. The absence of a counter absorption band in the lower wavelength region of 350-400, which corresponds to the Co3+ion, proves that only CoO particles are present in the catalyst. The broad absorption in the region of 700 nm-800 nm is present due to the d- d transition in high spin Co2+ion (CoO). In the case of 2Cu / CZ, 2CU95C05 / CZ, and 4CU95C05 / CZ, a feeble or no absorption band was observed for CuO in the visible region (400 to 440) characteristic of d-d transition. This clearly confirms that Cu is present in the form of Cu20which was also confirmed by XPS and Auger spectroscopy. Moreover, in the bimetallic catalyst, the absorption band corresponding to CoO is not visible because of less amount of Co as CU2O is the major component. A broad absorption band with peaks close to 240 nm, 280 nm, and 340 nm wavelength and corresponds to the LMCT in the ceria-zirconia (O’2to Ce4+and Zr4+).

[0125] Powder XRD spectra for calcined samples, CeO2, ZrO2, CeO2 -ZrO2 (CZ), and metal deposited CZ, are shown in FIG. 2. X-ray diffraction peak for the CZ obtained neither reflected pure CeO2 nor ZrO2 diffraction peak indicating the formation of a Ceria-Zirconia composite. The line broadening of the diffraction peaks pointed to the smaller crystallite size. The peak shifting and broadening from the pure CeCh was due to the insertion of Zr4+ions into the ceria lattice. The average crystallite size was calculated using the Scherer equation (eqn.l) for CcOi-. CZ and 2-CU95C05 / CZ was 6 nm, 4 nm and 4.5 nm, respectively and summarized in the Table 1.

[0126] D = - (1)

[0127] Pcosev

[0128] Where D is crystallite size, X is the wavelength of X-ray radiation (for Cu Ka, it is 1.54nm), 9 is the diffraction angle and, P represents the full width at half maxima.

[0129] Table 1: Crystalline size & BET surface area determined by XRD and N2 porosimeter analysis.

[0130] No separate diffraction peaks were observed for CuO and CoO in 2-CU95C05 / CZ, which confirms that Cu and Co metals were highly dispersed on the support. The XRD pattern confirms that CZ synthesized by the urea-gelation method is present in the solid solution form with a small crystallite size. The ICP analysis was done for all catalysts where the overall weight loading is 2 wt.%. After this study, actual loading was in the range of 1.6-1.8 wt. % to theoretical loading, particularly 2CU95C05 catalyst shows 1.8 wt.% loading.

[0131] Raman spectra recorded for Ceria, Zirconia and CZ, wherein three peaks were observed for CZ at 310 cm1, 470 cm1and, 630 cm1as compared to Zirconia and Ceria alone. These three peaks are attributed to the tetragonal metastable ZrC phase. The peak at 470 cm1is the characteristic F2gpeak and Raman active mode for the fluorite-type structure of ceria. The peak at 310 cm1and 630 cm1corresponds to the oxygen vacancies created by lattice oxygen displacement in the CeCh lattice or from t-ZrO2(space group P42 / nmc).The oxygen vacancy, linked to the longitudinal optical mode, arises due to symmetry rule relaxation. Here, the F2gpeak is shifted towards higher wave number in CZ because of incorporating Zr4+ions into ceria lattice, forming solid solution. After metal deposition on CZ support, FWHM of F2gpeak was found to be increased, and peaks at 310 and 630 cm4shifted towards lower wave number (295 & 620 cm4), likely due to metal ions incorporation into CZ lattice. Despite these changes, position of F2gpeak was intact, showing overall structural integrity of solid solution.

[0132] The H2-TPR experiments were used to understand the redox property of the catalyst. According to previous reports, ceria shows two reduction peaks approximately at 500°C and 800°C, which are assigned to the surface and bulk reduction of Ce4+to Ce3+’ respectively. In the case of ceria- zirconia solid solution of present invention, the first reduction peak was observed in the region of 350°C to 500°C and the second peak at around 700°C which can be attributed to surface and bulk reduction of Ce4+to Ce+3, respectively. Here in the case of ceria-zirconia (CZ with ratio of 1: 1), the first reduction peak was observed at around 400°C and the second peak at around 600°C, which are assigned to the surface and bulk reduction of Ce4+, respectively. After metal (2 wt.% Cu) deposition, these peaks shifted towards the lower temperature at around 315°C and 570°C due to strong metal-support interaction. The reduction peak at 145°C with a small shoulder at 124°C is attributed to the reduction of highly dispersed Cu+1to Cu° and surface oxygen, respectively. Similar trend in reduction was observed for bimetallic 2wt.% CU95C05 / CZ catalyst where 149°C and 129°C peaks and broad reduction peak in the range of 370°C to 680°C. The broad reduction peak with four peaks with very less intensity at 290°C, 393°C, 490°C and 650°C, corresponds to reduction of surface oxygen species over Ce-Co, CZ reduction and reduction of Co+2species, respectively.

[0133] The solid solution formation, heat treatment, and metal loading were reflected on the BET surface area. The BET surface area of CeC , CZ (with ratio of 1:1), and 2CU95C05 / CZ are compared, and it was found that CZ(1:1) has the highest surface area compared to CcOi alone. The surface area of CZ(1: 1) is higher than CcCh; incorporation of Zr4+ions into the ceria lattice results in the arrested growth of CeOi particles. As a result, CZ particles have a small crystallite size and larger surface area. Metal deposition at high pH over CZ(1: 1) support produced a catalyst with overall improved surface area due to the deposition of small and highly dispersed particles. The results from BET and XRD are presented in Table 1.

[0134] To identify the morphology and atomic interfaces present in the catalyst, TEM and HRTEM were used (Figure 1). From the TEM image (Figure.la), inventors confirmed that the catalyst particles were very small and in the 3 to 6 nm range, corroborating well with the XRD data. HRTEM images (Figure, lb & c) show CZ-supported Cu-Co, which their lattice fringes could distinguish. In Figure, lb, 0.31 nm lattice fringes are attributed to the

[0111] facets of CeCh-ZrCh (CZ) solid solution. While in Figure.lc, 0.24nm d-spacing is attributed to the CuiO

[0111] , and 0.26 nm and 0.15 nm attributed to the CoO

[0002] and

[0220] facets, respectively. The HRTEM is supportive that the CU2O and CoO are in close contact providing an excellent interface for catalysis. To prove the presence of respective elements in the catalyst, STEM-EDS elemental mapping (Figure 3, a-e) was carried out along with line profile analysis. From this EDS, inventors confirmed that Cu and Co bimetals are well dispersed over CZ support.

[0135] In heterogeneous catalysis, gas-solid interaction occurs on the catalyst’s surface; thus, surface characterization plays an important role. To unravel the electronic structure of the catalyst, X-ray photoelectron spectroscopy (XPS) was carried out and analyzed. In XPS analysis, the Ce 3d XPS spectra of CeCh, CZ (1: 1), CZ (1:3) and CZ (3: 1) supports are analyzed to find out Ce3+concentration. The Ce 3d core level XPS spectra could be deconvoluted into 10 components fitted in 5 doublets corresponding to 3ds / 2(labeled as u) and 3ds / 2 (labeled as u) components. The five main 3ds / 2 features are denoted as components v°( 881.6 eV), v (882.8 eV), v' ( 885.6 eV), v" (889.0 eV), v"' (897.6) and five3ds / 2, u° (899.1 eV), u (901.2 eV), u' (903.0 eV), u" (907. eV7), and U"' (916.8 eV) respectively. The relation used for the determination of surface Ce3+concentration is given as

[0136] Ce3+= Ce3+ / (Ce3++ Ce4+)

[0137] Where, Ce4+= v + v" + v"’ + u + u" +u"’ and Ce3+= v° + v’ + u° + u’ .

[0138] This Ce3+species improves redox property and CO2 adsorption capacity of CZ solid solution. An increase in the number of Ce3+is due to the insertion of Zr4+ions into the lattice of the CeCh.in CZ (1: 1) sample has highest amount of Ce3+species which summarized in table 2.

[0139] Table 2: Relative concentration of Ce3+% species determined by XPS analysis

[0140] The concentration of Ce3+in different CZ ratios and bare ceria follows the order of CZ (1: 1) > CZ (3: 1) > CZ (1:3) > CeCh. The u’” peak is relatively well separated from the rest of the spectrum and is characteristic of the presence of tetravalent Ce (Ce4+) in all compounds.

[0141] The Zr3d spectra shows the peaks at 181.8 eV -182.3 eV, denote the Zr 3ds / 2, whereas the signals at 184.4 - 184.9 eV correspond to the Zr 3ds / 2 levels, which could be attributed to the Zr species in +4 oxidation state. It can be seen that the peak corresponds to Z1O2 3ds / 2 (181.7 eV) shift to higher binding energies (181.8 eV) for CZ (1:3), 182.3 for CZ (1: 1) and CZ (3: 1), which indicates the strong interaction between Ce and Zr by electron transfer. Additionally, the Ce4+enters the Z1O2 lattice to form a solid solution structure and increase the Ce3+species, ultimately enhancement in electron density, which also explains the increase of oxygen vacancies in CZ solid solution compared to bare CeO2, which also correlates with Ce 3d XPS. Ols XPS shows: i) lattice oxygen (OL), ii) oxygen vacancies (Ov), and weakly bound oxygen (Ow) at the binding energies of 529.3, 531.3 and 533 eV respectively. Ov / (OL + Ov + Ow) ratio can be implied to calculate the relative concentration of oxygen vacancies. CZ (1:1) support has the highest oxygen vacancies among all supports. From Raman analysis and Ce 3d, Zr 3d, and O Is spectra, CZ (1: 1) has high oxygen vacancies, so it is best support for CO2 hydrogenation reaction as oxygen vacancies play an important role in such reactions. In the case of the 2CU95C05 / CZ catalyst, the Ce 3d XPS spectra deconvoluted into 10 components and it has 31 % Ce3+concentration. The Zr 3d XPS spectra for 2CU95C05 / CZ show two prominent peaks at 182.3 eV and 184.9 eV, attributed to Zr4+3ds / 2 and Zr4+3ds / 2 specie. In Cu 2p XPS, two major peaks were observed at 932.7eV and 953.09eV, along with peaks at 936.3 eV and 955.4 eV which corresponded to Cu 2p3 / 2 and Cu2pi / 2, respectively. A weak shake-up satellite peak at 941.2 eV and 944.2 eV, this weak satellite peak reveals that copper is present in the form of Cu2° or Cu+state. To discern between Cu° and Cu+as a minimal difference in peak position, the Auger L3VV lines are further investigated. The peaks in the Auger kinetic spectra 915.4 and 917.5 eV correspond to Cu+and Cu2+species, respectively. By contrast, the peak of Cu° in the Cu L3VV spectrum is generally at 918.7 eV; no peak at 918.7 suggests no existence of Cu°, also confirming the presence of Cu+. As the TEM analysis, the d-spacing study showed the presence of the CU2O phase, the peak at 932.8 eV represents a Cu+ mixture. In 2CU95C05 / CZ, 2CU98C02 / CZ and 2Cu / CZ catalysts copper is present in a 1+ oxidation state. Whereas, in the case of 2Cu75Co2s / CZ and 2CU88C012 / CZ, catalyst Cu is present in a 2+ oxidation state, because in the case of CuO or Cu2+, intense satellite peaks at 965 eV were observed. In all catalysts, along with the main peak, another peak at 936.2 eV is also present, corresponding to Cu (OH)2 due to NaOH as precipitating agent is used in the synthesis process. While O ls XPS spectra show OL, OV and Ow-type oxygen species present in all catalysts. 2CU95C05 / CZ catalyst has the highest amount of oxygen vacancies (37.19 %).

[0142] In Co 2p spectrum of the fresh 2Co / CZ catalyst, three peaks at 784.9 eV, 781.5 eV, and 780.0 eV were observed, and they correspond to Co2+(CO3O4), Co2+(CoO), and Co3+(CO3O4), respectively. In case of 2CU95C05 / CZ, and 2CU98C02 / CZ total Co loading is very less i.e., 0.1 and 0.04 wt.% respectively, therefore in XPS spectra, no Co were detected in both cases.

[0143] Example 3: CO2 hydrogenation: Catalytic Performance Testing of prepared CuCo bimetallic catalysts supported on CZ support and Product Analysis

[0144] All the samples / catalysts prepared according to example 2 were tested for CO2 hydrogenation reaction at atmospheric pressure in a fixed-bed flow microreactor made up of a quartz tube. The reaction was carried out over 50 mg of the catalyst, with a total gas flow in range of 10 ml / min to 80 ml / min ml min1. The ratio of CO2:H2 was 1:4 diluted with N2gas. The gaseous hourly space velocity (GHSV) was 36000 mEg^h1. The outlet pipeline of the reactor was kept above 100 °C to avoid water condensation. An online Nucon GC detected obtained products (gas chromatograph) 5765, attached with TCD and FID. In the obtained products, hydrocarbons were detected using FID, while TCD / methanizer was used to detect N2, CO, and CO2 gas. Before activity test, the supported catalyst was pre-treated in 20 ml H2 flow at 400° C for 2h.

[0145] CO2 hydrogenation reaction was carried out using Cu-Co-based catalysts with different metal ratios, supported over CZ solid- solution in the temperature range 200°C to 600°C. Inventors have optimized metal loading and the ratio of the metals to improve the catalytic activity and selectivity. When the catalytic activity is compared with bare ceria / zirconia, the ceria-zirconia solid (CZ) shows a much better catalytic activity, here Ce: Zr ratio is 1: 1. For reference, the support CZ was also studied for activity with different ratios (refer, Fig. 4 - A and B). This revealed that Ceria-Zirconia solid solution is also moderately active for CO2 hydrogenation. Among the different compositions, CZ (1: 1) was found to be better in terms of conversion and CO selectivity at low temperature. Over CZ (1:1) support, different weight % of Cu (mono-metallic) was tested for CO2 hydrogenation reaction. There was a considerable enhancement in activity with metal loading while going from 1% loading to 2 wt. % metal loading. The mono-metallic 2 wt. % Cu and 2 wt.% Co supported on CZ (1: 1) were compared with their bimetallic forms. 2Cu / CZ catalyst showed 100 % CO selectivity with 44 % CO2 conversion, whereas 2Co / CZ showed high conversion (72 %), but CO selectivity dropped to 64% with 36 % CH4 formation as Co based catalysts are known for methanation reaction at 500 °C temperature whereas bimetallic catalyst shows good conversion and 100 % CO selectivity. It can be inferred that bimetallic compositions were far more effective in catalyzing CO2 hydrogenation reactions. To optimize metal ratio, different compositions of Cu and Co with 2 wt.% metal loading were deposited over CZ (1: 1) support and CO2 hydrogenation activity was tested and summarized in Table 3.

[0146] Table 3: Catalytic evaluation results with various support at 500 °C

[0147] The 2Cu-Co in the ratio of 95:5 (2CU95C05 / CZ) showed the optimum activity catalytic activity with 62% CO2 conversion and 100% CO selectivity, when compared to 75:25 or 88: 12 ratio, whereas when decreases Co ratio to 98:2, selectivity remains the same. The catalytic activity was also tested over bare 2Cu95Cos / CeO2 and 2Cu95Cos / ZrO2, and in comparison, the 2CU95C05 / CZ catalyst (Figure 5) showed highest CO2 conversion with molecules and reducing the energy barriers as well as promoting CO desorption, thus boosting catalytic activity.

[0148] The catalytic performance of 2CU95C05 / CZ catalyst was showed in Figure 6A at 36000mLg_1h_1GHSV with CO2 / H2 ratio 1:4. Further, the effect of the CO2:H2 ratio was also studied over 2CU95C05 / CZ catalyst; high CO2:H2 ratio favors high CO2 conversion, whereas CO selectivity remains 100% with all different ratios (refer, Figure 6B), the ratio was varied from 1:4 to 1:0.5. The catalyst showed 25% and 40% conversion at 500°C and 600°C respectively when this ratio was 1:0.5 which indicates the catalyst works even when H2 concentration is less than CO2. Inventors compared the activity by STY (space-time yield) as shown in Table 4. When the CO2:H2 ratio was 1:0.5, the total STY reached 14.28 from 3.21 when temperature was increased from 300°C to 600°C, which is considerably higher than previous reports.

[0149] Table 4: Conditions and catalytic performance of RWGS reaction on different catalysts *Reaction conditions -Catalyst amount 50 mg, CO2:H2 = 48:24 (ml / min), GHSV-86400 mL g-1h-1.

[0150] The effect of GHSV on CO2 conversion and CO production rate was studied over 2CU95C05 / CZ by varying catalyst amounts 50 mg, 25 mg, 12.5,6.5 mg, and 3.2 mg, with 48 ml CO2flow and 24 ml H2 flow (CO2:H2 -1:05 ratio). When the catalyst amount is reduced from 50 mg to 3.1 mg GHSV changes from 86400 mLg_1h_1to 1380000 mLg_1h_1the 2CU95C05 / CZ catalyst by keeping the CO2:H2 ratio 1:0.5. The 2CU95C05 / CZ catalyst has a CO production rate per metal site, which is the highest reported value till date (refer, Table 5). The catalyst of present invention showed the highest STY, TOF and rate of CO production per metal site than previous reports (refer, table 5).

[0151] Table 5: Comparison between various known catalysts and present invention catalyst.

[0152] *Reaction conditions -Catalyst amount 3.2 mg, (ICP metal loading 1.8 mg), Temp. - 600 °C, CO2:H2 = 1:0.5 (48 mL: 24 mL), GHSV- 1380000 mL g’1.

[0153] Correlating the CO selectivity with XPS data; Cu+is known for high CO selectivity and CO conversion. Thus, the 2CU95C05 / CZ catalytic site is superior to activating CO2 molecules and reducing the energy barriers as well as promoting CO desorption, thus boosting the catalytic activity. HRTEM image of the spent catalyst confirms that the catalyst morphology is retained, and no structure deformation occurred. Also, the XPS analysis of spent catalyst shows Cu present in 1+ oxidation state. ADVANTAGES OF THE INVENTION

[0154] The heterogeneous catalyst system provides 100% selectivity for CO and upto 75% conversion of

[0155] CO2 into CO with higher stability and recyclability of the catalyst. Reduction and resistance in coke deposition in said catalyst system provide a preferable, reliable and improved catalyst system. The heterogeneous catalyst system is highly stable upto 72hrs of reaction. The heterogeneous catalyst system is highly re-usable upto numerous cycles. CeCh-ZrCh solid solution has been used as a support for bimetallic Co-Cu catalyst for CO2 hydrogenation at atmospheric pressure. The physiochemical properties-activity correlation study suggests that the 2CU95C05 / CZ exhibits excellent structural properties, reducibility, and surface chemical characteristics, which determines the catalytic performance of CO2 hydrogenation. CO2 conversion process covers lower CO2:H2 ratio (1:0.5) i.e., hydrogen lean condition, requires lower temperature (200-600 °C), requires lower loading amount of catalyst (from 2 wt.%), and requires 1: 1 amount of CZ, to obtain CO with 100% selectivity and upto 74 % conversion. Due to low metal loading (2%) CO productivity rate per metal site is very high compared to the available literature with long term stability. The catalyst showed 25% and 40% conversion at 500°C and 600°C respectively when this ratio was 1 :0.5 which indicates the catalyst works even when H2 concentration is less than CO2.

Claims

We claim1. A heterogeneous catalyst of Formula I comprising:(i) l-6wt % of at least two metal composition (M1M2);(ii) 94-99wt % of mixed metal oxide support; wherein the metal composition (M1M2) is supported onto the mixed metal oxides support; the mixed metal oxides support is ceria oxide-zirconium oxide (CcC -ZrC ); and the mixed metal oxides support has a particle size is in the range of 4 nm to 15 nm.

2. The heterogeneous catalyst as claimed in claim 1, wherein said at least two metal composition (M1M2) comprises metal Mi and metal M2, wherein the metal Mi is selected from the group consisting of copper, nickel, aluminium and zinc, and the metal M2 is selected from the group consisting of cobalt, indium and iron.

3. The heterogeneous catalyst as claimed in claim 1 or 2, wherein an amount of said Mi metal in said composition is in the range of 75 to 98% of total weight of the mixed composition; wherein an amount of said M2 metal in said composition is in the range of 2 to 25% of total weight of the mixed composition; and a ratio of ceria oxide and zirconium oxide in said mixed metal oxide support is in the range of 3: 1 to 1:3.

4. A process for the preparation of the heterogeneous catalyst as claimed in claim 1, comprising the steps of: a) dissolving ammonium ceric nitrate and zirconyl nitrate hydrate in a solvent followed by drop wise addition of urea under continuous stirring at a temperature in the range of 90- 110 °C for a time period in the range of 2-4 hrs to obtain a precipitate; b) stirring the precipitate obtained in step a) continuously for a time period in the range of 8- 10 hrs at a temperature in the range of 90-110°C to form a gel; c) washing the gel obtained in step b) with boiling distilled water, drying at a temperature in the range of 70-95°C for time period of 3-5 hrs under 2-10 millibar pressure and then calcining at a temperature in the range of 400 to 500 °C for 3 to 5 hrs with 2 °C min1ramping rate to obtain a mixed metal oxide support; d) adding a Mi-metal precursor salt followed by adding a M2-metal precursor salt in the mixed metal oxides support obtained in step c), and mixing in the presence of a precipitating agent at pH in the range of 9-11 to form a crude heterogeneous mixture; e) stirring the crude heterogeneous mixture obtained in step d) for a time period in the range of 0.5 to 2 hrs at a temperature in the range of 28°C to 35°C with pH maintained throughout in the range of 9-11 followed by centrifugation, washing, drying and then calcining attemperature in the range of 300 to 500°C for 3 to 5 hrs with 2 °C min1ramping rate to obtain the heterogeneous catalyst.

5. The process as claimed in claim 4, wherein said solvent used in step a) is selected from the group consisting of water, millipore water and deionized water.

6. The process as claimed in claim 4, wherein said metal precursor salts of Mi and M2 used in step d) are selected from the group consisting of metal sulfates, metal halides, metal nitrates, metal acetates, metal nitrites, metal oxides, metal carbonates, metal hydroxides, metal oxalates, metal pyrazolyl borates, metal azides, metal fluoroborates, metal carboxylates, metal halogencarboxylates, metal hydroxycarboxylates, metal aminocarboxylates, metal aromatic and nitro and / or fluoro substituted aromatic carboxylates, metal aromatic and nitro and / or fluoro substituted aromatic carboxylates, metal beta diketonates, metal sulfonates, and metal acetylacetonate.

7. The process as claimed in claim 4, wherein said precipitating agent used in step d) is selected from the group consisting of sodium hydroxide, potassium hydroxide and ammonium hydroxide.

8. A process for the hydrogenation of CO2 using the heterogeneous catalyst as claimed in claim 1, comprising the steps of: i. adding the heterogeneous catalyst as claimed in claim 1 in a reactor; ii. pre-treating said heterogeneous catalyst under H2 gas flow at a rate of 10-40 mL / min, at a temperature in the range of 300 to 500 °C for a time period in the range of 1.5 to 3 hrs to obtain a reduced heterogeneous catalyst; and iii. adding and contacting CO2 stream and H2 stream in the reactor containing said reduced heterogeneous catalyst under specific reaction conditions to obtain, Ci-based products and / or value-added products.

9. The process as claimed in claim 8, wherein: a) the reactor is a fixed-bed flow reactor; b) the process of CO2 hydrogenation is done via batch mode or continuous mode wherein CO2 and H2 streams are continuously passed through out the reaction time period in a continuous mode; c) an amount of said composition in the heterogeneous catalyst used is in the range of 1 wt.% to 6 wt.%; and d) the specific reaction conditions of step iii) are selected from one or more of:I. total gas flow of CO2 and H2 in the reactor is in the range of 20 to 80 mL / min, II. a ratio of CO2:H2 is in range of 1:0.5 to 1:4,III. a gaseous hourly space velocity (GHSV) is in range of 30000 to 1400000 mLg“ V,IV. a temperature for conversion of CO2 is kept in the range of 200 to 600 °C and / or,V. an outlet pipeline of the reactor is kept at a temperature in the range of 90-110 or10. The process as claimed in claim 8, wherein said Ci based products and / or value-added products are selected from the group consisting of carbon monoxide, methane, methanol and C2-C5+ olefins; and the heterogeneous catalyst is stable for at least 72 hours, and is a recyclable.

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