Precious metal-loaded indium-based catalyst and preparation method thereof, and method for preparing methanol by hydrogenating carbon dioxide

Abstract

The present invention relates to the field of catalysts and discloses a noble metal-loaded indium-based catalyst, a preparation method thereof, and a method for preparing methanol by hydrogenating carbon dioxide, comprising the following steps: (1) providing a mixed aqueous solution containing an In salt and a carbon source; (2) reacting the mixed aqueous solution under conditions where water is in a supercritical state to obtain an indium-based catalyst; (3) mixing the indium-based catalyst, an organic solvent, and a noble metal salt to obtain an organic mixed solution, and then reacting the organic solution under a supercritical state of the organic solvent; and (4) heat-treating the product obtained from the reaction in step (3). The catalyst prepared by the simple and efficient supercritical fluid deposition technology of the present invention has excellent catalytic performance, high reaction activity, high target product selectivity, good reaction stability, and a low catalyst deactivation rate.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and in particular to a noble metal-loaded indium-based catalyst and a preparation method thereof, and a method for preparing methanol by hydrogenating carbon dioxide. Background Art

[0002] Methanol is an important raw material for chemicals and a substitute for fossil fuels. The production of methanol by reacting CO2 with H2 from renewable energy is not only an effective way to solve greenhouse gas control but also an effective way to replace fossil fuels.

[0003] Among the numerous catalysts used in the hydrogenation of CO₂ to produce methanol, modified copper-based catalysts have long been studied and applied. Cu-based catalysts for conventional syngas-to-methanol conversion have been extensively studied in CO₂-to-methanol conversion. However, their high activity in side reactions (reverse water-gas shift, RWGS), H₂O-induced sintering of the active phase, and poor stability have limited their further application. In other catalytic systems, the high cost of noble metals and the low activity and migration of ZnO have also limited their further application in this field. In₂O₃ has attracted widespread attention due to its moderate CO₂ and CO adsorption capacity, significantly superior methanol selectivity to Cu, Co, and noble metal catalysts, and higher catalytic activity than ZnO catalysts. Furthermore, In₂O₃ is easily supported and surface-modified, which can further promote the activation of CO₂ and H₂ and stabilize key intermediates to achieve high activity, selectivity, and stability, offering significant potential for the design and preparation of efficient methanol catalysts. However, in the existing technology, the reaction activity of indium-based catalysts is not high enough, the CO2 conversion rate is low, and the methanol selectivity is poor. The design and development of more effective indium oxide catalysts are of great significance for the industrial application of CO2 hydrogenation to methanol, but how to improve their catalytic performance still faces huge challenges. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems of complex preparation process, poor reproducibility, low catalyst activity and poor reaction stability of CO2 hydrogenation catalysts in the prior art, and to provide a noble metal-loaded indium-based catalyst and a preparation method thereof, and a method for preparing methanol by hydrogenating carbon dioxide. The noble metal-loaded indium-based catalyst has excellent catalytic performance, high reaction activity, high selectivity for the target product, good reaction stability and a very low catalyst deactivation rate.

[0005] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a noble metal-supported indium-based catalyst, comprising the following steps:

[0006] (1) providing a mixed aqueous solution containing an In salt and a carbon source;

[0007] (2) reacting the mixed aqueous solution under the condition that water is in a supercritical state to obtain an indium-based catalyst;

[0008] (3) mixing the indium-based catalyst, the organic solvent, and the noble metal salt to obtain an organic mixed solution, and then reacting the organic solvent under a supercritical state;

[0009] (4) heat-treating the product obtained by the reaction in step (3).

[0010] The second aspect of the present invention provides a noble metal-supported indium-based catalyst prepared by the preparation method described in the first aspect.

[0011] A third aspect of the present invention provides a method for preparing methanol by hydrogenating carbon dioxide, the method comprising:

[0012] Under conditions of producing methanol by hydrogenation of carbon dioxide, carbon dioxide and hydrogen are contacted in the presence of a catalyst; the catalyst is the noble metal-supported indium-based catalyst described in the second aspect above;

[0013] Preferably, the conditions for the carbon dioxide hydrogenation reaction to produce methanol include: reaction pressure of 0.5MPa-6MPa, reaction temperature of 200℃-450℃, volume space velocity of 2000h -1 -40000h -1 , the H2 / CO2 molar ratio is 2-7.

[0014] Through the above technical solution, the beneficial effects obtained by the present invention are as follows:

[0015] (1) The present invention adopts a simple and efficient supercritical fluid deposition technology. By adjusting the temperature and pressure, the In precursor is instantly supersaturated in the supercritical solution, forming a large number of crystal nuclei, and further growing C-InO particles with adjustable particle size and morphology for the reaction. x .

[0016] (2) The active components formed by the supercritical fluid deposition technology of the present invention have a fast nucleation speed, uniform dispersion, high nucleation rate and low energy consumption.

[0017] (3) The present invention conducts a methanol production reaction by hydrogenating carbon dioxide in a fixed bed reactor, with high methanol selectivity. The noble metal-supported indium-based catalyst has excellent catalytic performance, high reaction activity, high target product selectivity, good reaction stability, and low catalyst deactivation rate. DETAILED DESCRIPTION

[0018] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0019] The first aspect of the present invention provides a method for preparing a noble metal-supported indium-based catalyst, comprising the following steps:

[0020] (1) providing a mixed aqueous solution containing an In salt and a carbon source;

[0021] (2) reacting the mixed aqueous solution under the condition that water is in a supercritical state to obtain an indium-based catalyst;

[0022] (3) mixing the indium-based catalyst, the organic solvent, and the noble metal salt to obtain an organic mixed solution, and then reacting the organic solvent under a supercritical state;

[0023] (4) heat-treating the product obtained by the reaction in step (3).

[0024] According to the present invention, supercritical water has strong reactivity and wide solubility. The supercritical state of the organic solvent helps to accelerate mass transfer and increase the reaction rate. The solubility of metal oxides in the supercritical water environment is low, so the nucleation rate is high, which is conducive to the synthesis of nanoparticles. The reaction is carried out in a supercritical state, so that the In precursor reaches an instantaneous supersaturation state in the supercritical solution, forming a large number of crystal nuclei, and further growing C-InO particles with adjustable particle size and morphology for the reaction. x .

[0025] According to the present invention, by introducing a noble metal component into the indium-based catalyst, the dissociation of hydrogen is facilitated, thereby improving the CO2 conversion rate.

[0026] According to a preferred embodiment of the present invention, in the mixed solution, the mass ratio of In salt to carbon source is 1-1.8:1, preferably 1-1.4:1. Controlling the mass ratio of In salt to carbon source within the above preferred range is beneficial to enhancing the active sites of the catalyst.

[0027] According to a preferred embodiment of the present invention, the concentration of the In salt in the mixed aqueous solution is 0.1-3 mol / L, more preferably 0.2-0.5 mol / L. Under the above preferred conditions, the reaction performance of the catalyst is improved.

[0028] According to a preferred embodiment of the present invention, the water in the mixed aqueous solution is deionized water.

[0029] In the present invention, the selection range of the specific type of In salt is relatively wide, preferably a soluble salt of In, more preferably at least one of In chloride, nitrate, acetate, sulfate and metal alkoxide, and most preferably indium nitrate.

[0030] According to the present invention, there is no specific limitation on the type of the carbon source, as long as carbon can be provided. Preferably, the carbon source is selected from at least one of sucrose, starch, glucose, maltose, cellulose, citric acid, maleic acid, fumaric acid, succinic acid, tartaric acid, malic acid, gluconic acid, terephthalic acid, ethylenediaminetetraacetic acid, dipicolinic acid and trimesic acid, more preferably at least one of starch, sucrose, succinic acid, dipicolinic acid and malic acid.

[0031] According to a preferred embodiment of the present invention, the mixed solution further contains an oxidant, preferably H2O2, and preferably provided in the form of a solution. By introducing the oxidant, the oxidizing property of supercritical water can be improved.

[0032] According to a preferred embodiment of the present invention, based on the total mass of the mixed aqueous solution, the amount of the oxidant is 0.1-1% by mass, more preferably 0.1-0.7% by mass.

[0033] In the present invention, there is no particular limitation on the mixing method and order of the mixed aqueous solution. The In salt and the carbon source can be dissolved in water first, and then the oxidant is introduced. Alternatively, the In salt and the oxidant can be dissolved in water first, and then the carbon source is added. The solvent water can be introduced in any of the above processes, as long as the total amount of water in the mixed aqueous solution can meet the concentration requirements of each component therein. For example, the solvent water in the mixed aqueous solution can be introduced separately as a solvent for the In salt and the oxidant, or can be added all at once. Preferably, the method for providing the mixed solution includes dissolving the In salt in water, adding the carbon source, and then adding the oxidant and water.

[0034] According to a preferred embodiment of the present invention, the mixed aqueous solution further contains a Zn salt. In the above preferred embodiment, the coordination effect of Zn is beneficial to the adsorption and desorption of H2, promoting the conversion of CO2, thereby improving the reaction performance.

[0035] According to a preferred embodiment of the present invention, in the mixed aqueous solution, the molar ratio of the In salt to the Zn salt, calculated as elements, is 1-6:1, more preferably 2-4:1. In the above preferred embodiment, the CO2 conversion rate is improved.

[0036] According to a preferred embodiment of the present invention, the reaction conditions in step (2) include: temperature of 400-650°C; reaction pressure of 23-40 MPa; reaction time of 1-120 min; further preferably, temperature of 400-550°C; reaction pressure of 25-35 MPa; reaction time of 20-80 min.

[0037] According to a preferred embodiment of the present invention, the method further comprises separating the reaction product in step (2) to obtain an indium-based catalyst; specifically, the separation process comprises: reducing the pressure and cooling the reaction system, filtering it, and achieving gas-solid-liquid separation, and the separated solid is the indium-based catalyst.

[0038] According to a preferred embodiment of the present invention, the precious metal in the precious metal salt is selected from at least one of gold, silver, ruthenium, rhodium, palladium, osmium, iridium, and platinum, more preferably at least one of platinum, palladium, ruthenium, and rhodium, and most preferably palladium. The use of a palladium-supported indium-based catalyst facilitates hydrogen dissociation, thereby improving CO conversion.

[0039] In the present invention, the noble metal salt can be selected from a wide range of noble metal salts. Preferably, the noble metal salt can be selected from at least one of noble metal nitrates, sulfates, and chlorides. For example, when the noble metal is palladium, the palladium salt can be selected from at least one of palladium nitrate, palladium dichloride, palladium sulfate, potassium tetrachloropalladate, sodium tetrachloropalladate, potassium hexachloropalladate, and sodium hexachloropalladate.

[0040] According to a preferred embodiment of the present invention, the amounts of indium-based catalyst and precious metal salt are such that the molar ratio of In to precious metal in the resulting catalyst is 1:0.001-0.2, preferably 1:0.005-0.2. This preferred embodiment facilitates H2 activation and improves CO2 conversion.

[0041] According to a preferred embodiment of the present invention, the organic solvent is selected from alcohols, preferably methanol and / or ethanol.

[0042] According to a preferred embodiment of the present invention, the amount of the organic solvent used is such that the concentration of the noble metal element in the organic solution is 0.001-0.1 mol / L, preferably 0.002-0.06 mol / L.

[0043] According to a preferred embodiment of the present invention, the reaction process of the indium-based catalyst, organic solvent and noble metal salt in step (3) further comprises: cooling the reaction system in step (2) and then introducing the organic solvent and noble metal salt.

[0044] According to a preferred embodiment of the present invention, the reaction conditions in step (3) include: temperature of 245-300°C; reaction pressure of 8.5-20 MPa; reaction time of 10-150 min; preferably, temperature of 250-290°C; reaction pressure of 9-18 MPa; reaction time of 30-100 min.

[0045] According to a preferred embodiment of the present invention, the method further comprises washing and drying the sample obtained in step (3) to obtain catalyst powder. In the present invention, the washing and drying method is not specifically limited and can be carried out by any conventional method and conditions.

[0046] According to a preferred embodiment of the present invention, the heat treatment conditions in step (4) include: under an inert atmosphere, a temperature of 300-500°C, and a time of 1-5h; preferably, a temperature of 350-450°C, and a time of 1-3h.

[0047] According to a preferred embodiment of the present invention, the inert atmosphere is a nitrogen atmosphere and / or an argon atmosphere.

[0048] A second aspect of the present invention provides a noble metal-supported indium-based catalyst prepared by the preparation method described in the first aspect. The noble metal-supported indium-based catalyst has a simple preparation process and exhibits excellent catalytic performance, high reaction activity, high target product selectivity, good reaction stability, and a low catalyst deactivation rate.

[0049] A third aspect of the present invention provides a method for preparing methanol by hydrogenating carbon dioxide, the method comprising:

[0050] Under the conditions of producing methanol by hydrogenation of carbon dioxide, carbon dioxide and hydrogen are contacted in the presence of a catalyst; the catalyst is the noble metal-supported indium-based catalyst described in the second aspect. Preferably, the conditions of the reaction of producing methanol by hydrogenation of carbon dioxide include: a reaction pressure of 0.5 MPa-6 MPa, a reaction temperature of 200°C-450°C, a volume space velocity of 2000 h / min, and a reaction pressure of 0.5 MPa-6 MPa. -1 -40000h -1 , the H2 / CO2 molar ratio is 2-7; further preferably, the reaction pressure is 1MPa-5MPa, the reaction temperature is 200℃-400℃, and the volume space velocity is 8000h -1 -20000h -1 , the H2 / CO2 molar ratio is 4-6. Adopting the above preferred embodiment is beneficial to improving the CO2 conversion rate and methanol selectivity.

[0051] According to a preferred embodiment of the present invention, the carbon dioxide hydrogenation reaction is carried out in a fixed bed reactor.

[0052] The present invention will be described in detail below through examples.

[0053] In the following examples, the raw materials used were all purchased from commercial sources.

[0054] Example 1

[0055] (1) 15.4 g of In(NO3)3·4H2O was added to 100 mL of deionized water, and 15 g of sucrose was added, and the mixture was stirred to prepare a mixed solution; the mixed solution was added to an autoclave, and then 5 g of a 30% H2O2 solution and 100 ml of deionized water were added, and then the temperature was raised to 400°C and the pressure was increased to 25 MPa to react for 30 min; after the reaction was completed, the pressure was released and cooled to achieve gas-solid-liquid separation, and the solid remaining in the autoclave was the indium-based catalyst;

[0056] (2) After the autoclave in step (1) is cooled to 250°C, 80 ml of methanol and 0.06 g of palladium nitrate are introduced and reacted at 14 MPa for 45 min; finally, the pressure and gas are released to terminate the reaction, and the autoclave is cooled to 80°C, the autoclave is disassembled, and the sample is washed and dried to obtain a catalyst powder; the catalyst powder is placed in a tubular furnace and heated at 350°C in a N2 atmosphere and calcined for 3 h to obtain a palladium-loaded indium-based catalyst.

[0057] (3) The reaction of carbon dioxide hydrogenation to methanol was carried out in a stainless steel reactor with an inner diameter of 8 mm. The reaction conditions were as follows: 3.0 MPa, 220 °C, 10,000 h -1 , n(H2) / n(CO2)=4, the liquid product was collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 1.

[0058] Comparative Example 1

[0059] (1) Add 15.44 g of In(NO3)3·4H2O to a mixture of 80 mL of anhydrous ethanol and 48 mL of deionized water. Add 16 g of urea to a mixture of 80 mL of anhydrous ethanol and 20 mL of deionized water. Add the precipitant solution to the metal indium salt solution at 25°C to obtain a mother solution, which is stirred thoroughly for 5 h. Then, the mother solution is added to a 100 mL polytetrafluoroethylene-lined hydrothermal synthesis reactor and placed in a forced air drying oven for aging at 120°C for 20 h. After the hydrothermal reactor is cooled to room temperature, the mother solution is centrifuged with deionized water to a pH of 7, dried at 60°C for 20 h, and calcined at 350°C for 3 h to obtain an indium oxide catalyst.

[0060] (2) The activity of the prepared indium oxide catalyst was evaluated in a fixed bed reactor. The reaction conditions were the same as in Example 1. The test results are shown in Table 1.

[0061] Comparative Example 2

[0062] (1) The preparation of indium oxide catalyst is the same as that of comparative example 1.

[0063] (2) Weigh 0.06 g of palladium nitrate and dissolve it in deionized water to obtain a palladium salt solution. Then weigh 2 g of indium oxide catalyst and add it to the palladium salt solution. Stir at 25° C. for 1 h, then dry it by rotary evaporation at 45° C., 20 ppm, and 0.1 MPa, and finally calcine it at 350° C. for 4 h to obtain a Pd-supported indium-based catalyst. The catalyst is pressed into a 40-60 mesh size tablet and sieved.

[0064] (3) The activity of the prepared palladium-supported indium oxide catalyst was evaluated in a fixed-bed reactor. The reaction conditions were the same as in Example 1. The test results are shown in Table 1.

[0065] Example 2

[0066] (1) 35.4 g of In(NO3)3·4H2O was added to 100 mL of deionized water, and 35 g of starch was added, followed by mixing and stirring to prepare a mixed solution; the mixed solution was added to an autoclave, and then 5 g of a 30% H2O2 solution and 100 ml of deionized water were added, followed by heating to 400°C and pressurizing to 25 MPa for reaction for 45 min; after the reaction was completed, the pressure was released and cooled to achieve gas-solid-liquid separation, and the solid remaining in the autoclave was the indium-based catalyst;

[0067] (2) After the autoclave in step (1) is cooled to 285°C, 100 ml of ethanol and 0.17 g of palladium nitrate are introduced and reacted at 9 MPa for 65 min; finally, the pressure is released to terminate the reaction, and after the autoclave is cooled to 75°C, the autoclave is disassembled, and the sample is washed and dried to obtain a catalyst powder; the catalyst powder is placed in a tubular furnace and heated at 380°C in a N2 atmosphere and calcined for 2 h to obtain a palladium-supported indium-based catalyst.

[0068] (3) The reaction of carbon dioxide hydrogenation to methanol was carried out in a stainless steel reactor with an inner diameter of 8 mm. The reaction conditions were as follows: 5.0 MPa, 200 °C, 8000 h -1 , n(H2) / n(CO2)=6, the liquid product was collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 1.

[0069] Example 3

[0070] (1) 63.4 g of In(NO3)3·4H2O was added to 300 mL of deionized water, and 50 g of succinic acid was added, and the mixture was stirred to prepare a mixed solution; the mixed solution was added to an autoclave, and 9 g of a 30% H2O2 solution and 330 ml of deionized water were added, and then the temperature was raised to 520°C and the pressure was increased to 23 MPa to carry out the reaction for 50 min; after the reaction was completed, the pressure was released and the mixture was cooled to achieve gas-solid-liquid separation, and the solid remaining in the autoclave was the indium-based catalyst;

[0071] (2) After the autoclave in step (1) is cooled to 253°C, 100 ml of ethanol and 0.30 g of palladium nitrate are introduced and reacted at 17 MPa for 75 min; finally, the pressure is released to terminate the reaction, and after the autoclave is cooled to 75°C, the autoclave is disassembled, the sample is washed and dried to obtain a catalyst powder; the catalyst powder is placed in a tubular furnace and heated at 400°C in a N2 atmosphere and calcined for 2 h to obtain a palladium-supported indium-based catalyst.

[0072] (3) The reaction of carbon dioxide hydrogenation to methanol was carried out in a stainless steel reactor with an inner diameter of 8 mm. The reaction conditions were as follows: 5.0 MPa, 340 °C, 15000 h -1 , n(H2) / n(CO2)=4, the liquid product was collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 1.

[0073] Example 4

[0074] (1) 26.3 g of In(NO3)3·4H2O was added to 100 mL of deionized water, and 20 g of pyridinedicarboxylic acid was added, and the mixture was stirred to prepare a mixed solution; the mixed solution was added to an autoclave, and 2 g of a 30% H2O2 solution and 100 mL of deionized water were added, and then the temperature was raised to 460°C and the pressure was increased to 32 MPa to react for 25 min; after the reaction was completed, the pressure was released and cooled to achieve gas-solid-liquid separation, and the solid remaining in the autoclave was the indium-based catalyst;

[0075] (2) After the autoclave in step (1) is cooled to 265°C, 100 ml of ethanol and 0.26 g of palladium nitrate are introduced and reacted at 8 MPa for 40 min; finally, the pressure is released to terminate the reaction, and the autoclave is cooled to 75°C. The autoclave is disassembled, and the sample is washed and dried to obtain a catalyst powder; the catalyst powder is placed in a tubular furnace and heated at 420°C in a N2 atmosphere and calcined for 1.5 h to obtain a palladium-supported indium-based catalyst.

[0076] (3) The reaction of carbon dioxide hydrogenation to methanol was carried out in a stainless steel reactor with an inner diameter of 8 mm. The reaction conditions were as follows: 1.0 MPa, 400 °C, 10,000 h -1, n(H2) / n(CO2)=5, the liquid product was collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 1.

[0077] Example 5

[0078] (1) 105.3 g of In(NO3)3·4H2O was added to 300 mL of deionized water, and 80 g of malic acid was added, followed by mixing and stirring to prepare a mixed solution; the mixed solution was added to an autoclave, and then 5 g of a 30% H2O2 solution and 310 ml of deionized water were added, followed by heating to 460°C and pressurizing to 32 MPa for reaction for 75 min; after the reaction was completed, the pressure was released and cooled to achieve gas-solid-liquid separation, and the solid remaining in the autoclave was the indium-based catalyst;

[0079] (2) After the autoclave in step (1) is cooled to 275°C, 100 ml of methanol and 1.45 g of palladium nitrate are introduced and reacted at 10 MPa for 85 min; finally, the pressure is released to terminate the reaction, and after the autoclave is cooled to 75°C, the autoclave is disassembled, and the sample is washed and dried to obtain a catalyst powder; the catalyst powder is placed in a tubular furnace and heated at 360°C in a N2 atmosphere and calcined for 3 h to obtain a palladium-loaded indium-based catalyst.

[0080] (3) The reaction of carbon dioxide hydrogenation to methanol was carried out in a stainless steel reactor with an inner diameter of 8 mm. The reaction conditions were as follows: 4.0 MPa, 250°C, 20,000 h -1 , n(H2) / n(CO2)=6, the liquid product was collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 1.

[0081] Example 6

[0082] The method of Example 5 was followed, except that 35.2 g of zinc nitrate was added at the same time as the In salt.

[0083] Example 7

[0084] The method of Example 5 was followed, except that 22.5 g of zinc nitrate was added at the same time as the In salt.

[0085] Table 1

[0086]

[0087]

[0088] The results in Table 1 indicate that the noble metal-supported indium-based catalysts prepared according to the present invention exhibit excellent catalytic performance, high reaction activity, high target product selectivity, good reaction stability, and low catalyst deactivation rate. Examples 6-7 indicate that the further prepared In / Zn-based catalysts exhibit even better catalytic performance and improved CO2 conversion.

[0089] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing a noble metal-supported indium-based catalyst, comprising the following steps: (1) providing a mixed aqueous solution containing an In salt, a Zn salt, and a carbon source; the molar ratio of the In salt to the Zn salt is 1-6:1; and the mass ratio of the In salt to the carbon source is 1-1.8:1; (2) reacting the mixed aqueous solution under the condition that water is in a supercritical state to obtain an indium-based catalyst; (3) mixing the indium-based catalyst, the organic solvent, and the noble metal salt to obtain an organic mixed solution, and then reacting the organic solvent under a supercritical state; (4) heat-treating the product obtained by the reaction in step (3).

2. The preparation method according to claim 1, wherein The mass ratio of In salt to carbon source is 1-1.4:

1.

3. The preparation method according to claim 1, wherein In the mixed aqueous solution, the concentration of In salt is 0.1-3 mol / L.

4. The preparation method according to claim 1, wherein The In salt is a soluble salt of In.

5. The preparation method according to claim 4, wherein The In salt is at least one of In chloride, nitrate, acetate, sulfate and metal alkoxide.

6. The preparation method according to claim 1, wherein The carbon source is selected from at least one of sucrose, starch, glucose, maltose, cellulose, citric acid, maleic acid, fumaric acid, succinic acid, tartaric acid, malic acid, gluconic acid, terephthalic acid, ethylenediaminetetraacetic acid, pyridinedicarboxylic acid and trimesic acid.

7. The preparation method according to claim 6, wherein The carbon source is selected from at least one of starch, sucrose, succinic acid, dipicolinic acid, and malic acid.

8. The preparation method according to claim 1, wherein The mixed aqueous solution also contains an oxidant.

9. The preparation method according to claim 8, wherein The oxidant is H2O2.

10. The preparation method according to claim 9, wherein The oxidizing agent is provided in the form of a solution.

11. The preparation method according to claim 8, wherein Based on the total mass of the mixed aqueous solution, the amount of the oxidant is 0.1-1 mass %.

12. The preparation method according to any one of claims 1 to 11, wherein The reaction conditions of step (2) include: temperature of 400-650° C.; reaction pressure of 23-40 MPa; and reaction time of 1-120 min.

13. The preparation method according to claim 12, wherein The reaction conditions of step (2) include: temperature of 400-550° C.; reaction pressure of 25-35 MPa; and reaction time of 20-80 min.

14. The preparation method according to any one of claims 1 to 11, wherein The noble metal in the noble metal salt is selected from at least one of platinum, palladium, ruthenium and rhodium.

15. The preparation method according to claim 14, wherein The noble metal in the noble metal salt is palladium.

16. The preparation method according to claim 15, wherein The noble metal salt is selected from at least one of palladium nitrate, palladium dichloride, palladium sulfate, potassium tetrachloropalladate, sodium tetrachloropalladate, potassium hexachloropalladate and sodium hexachloropalladate.

17. The preparation method according to any one of claims 1 to 11, wherein: The amounts of the indium-based catalyst and the noble metal salt are such that the molar ratio of In to the noble metal element in the prepared catalyst is 1:0.001-0.

2.

18. The preparation method according to any one of claims 1 to 11, wherein: The organic solvent is selected from alcohols.

19. The preparation method according to claim 18, wherein The organic solvent is selected from methanol and / or ethanol.

20. The preparation method according to any one of claims 1 to 11, wherein: The amount of the organic solvent used is such that the concentration of the noble metal element in the organic mixed solution is 0.001-0.1 mol / L.

21. The preparation method according to any one of claims 1 to 11, wherein The reaction conditions of step (3) include: temperature of 245-300° C.; reaction pressure of 8.5-20 MPa; and reaction time of 10-150 min.

22. The preparation method according to claim 21, wherein The reaction conditions of step (3) include: temperature of 250-290° C.; reaction pressure of 9-18 MPa; and reaction time of 30-100 min.

23. The preparation method according to any one of claims 1 to 11, wherein: The heat treatment conditions in step (4) include: in an inert atmosphere, a temperature of 300-500° C., and a time of 1-5 h.

24. The preparation method according to claim 23, wherein The heat treatment conditions in step (4) include: in an inert atmosphere, a temperature of 350-450° C., and a time of 1-3 h.

25. A noble metal-supported indium-based catalyst prepared by the preparation method according to any one of claims 1 to 24.

26. A method for preparing methanol by hydrogenating carbon dioxide, the method comprising: Under conditions of producing methanol by hydrogenation of carbon dioxide, carbon dioxide and hydrogen are contacted in the presence of a catalyst; The catalyst is the noble metal-supported indium-based catalyst according to claim 25.

27. The method according to claim 26, wherein The conditions for the carbon dioxide hydrogenation reaction to produce methanol include: reaction pressure of 0.5MPa-6MPa, reaction temperature of 200℃-450℃, volume space velocity of 2000h -1 -40000h -1 , the H2 / CO2 molar ratio is 2-7.

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