Catalyst for preparing methanol through carbon dioxide hydrogenation and preparation method thereof

Abstract

The invention relates to a catalyst for preparing methanol through hydrogenation of carbon dioxide. The catalyst is an N-doped In2O3 catalyst; wherein the main catalyst In2O3 is faint yellow powder, and N atoms are uniformly dispersed on the surface of In2O3 and in a bulk phase and form an N-O-In chemical bond with In; the mass fraction of N in the catalyst is 0.08%-0.3%. The preparation method of the catalyst specifically comprises the following steps: dissolving indium-containing metal salt and a precipitator in a mixed solution of an organic solvent and water, stirring and dissolving, then carrying out solvothermal reaction, and reserving a solid product, namely a precursor; calcining the precursor at a high temperature to obtain an In2O3 main catalyst; mixing the In2O3 main catalyst and a nitrogen-containing organic matter, then carrying out high-energy ball milling to obtain a nitrogen-doped precursor, and calcining the nitrogen-doped precursor to obtain the catalyst N-In2O3 for preparing methanol through carbon dioxide hydrogenation. According to the invention, through the synergistic effect of physical mixing and thermal diffusion of high-energy ball milling, uniform dispersion of nitrogen atoms on the surface of In2O3 and in crystal lattices is realized, and the catalytic activity is improved.

Description

Technical field:

[0001] The present invention belongs to the technical field of catalyst preparation, and in particular relates to a catalyst for producing methanol by hydrogenating carbon dioxide and a preparation method thereof. Background technology:

[0002] With the rapid development of human society and economy, excessive greenhouse gas emissions, primarily CO2, have generated the greenhouse effect and contributed to increasing global warming. Methanol is not only an important chemical raw material but also an excellent energy carrier. Therefore, coupling CO2 with green hydrogen to produce methanol can not only address CO2 emissions but also partially meet human demand for fuels and chemicals, truly achieving green carbon utilization and sustainable recycling.

[0003] Among them, indium oxide (In2O3) has become one of the core catalysts due to its excellent low-temperature activity. However, under low-temperature reaction conditions (<250°C), the CO2 single-pass conversion rate is generally low; when the temperature is raised to above 300°C to increase the CO2 conversion rate, the methanol selectivity will drop rapidly.

[0004] Existing technologies mainly improve performance through metal doping (such as cobalt single atoms, CN118416894A) or structural regulation (such as solvent thermal synthesis, CN118754187A), but there are still some limitations. For example, the cost of metal doping is high and impurities are easily introduced. The doping of precious metals such as cobalt requires a complex coordination process and may form metal agglomeration sites, resulting in fluctuations in product selectivity. The traditional non-metallic doping has insufficient uniformity: conventional chemical precipitation or impregnation methods make it difficult to achieve uniform distribution of non-metallic elements (such as nitrogen) in the In2O3 lattice. Due to excessively high local concentrations, active sites are masked, thereby reducing catalytic activity. In the existing technology, the annealing temperature for catalyst synthesis usually needs to be higher than 600°C, which consumes a lot of energy and high temperatures can easily cause In2O3 to sinter, reducing the specific surface area of the catalyst and reducing active sites.

[0005] Therefore, there is an urgent need to develop a catalyst preparation method to solve the problem of the difficult balance between the preparation cost and activity-selectivity of In2O3 catalysts. Summary of the invention:

[0006] To address the above problems, the present invention proposes a ball milling-assisted N doping technology, which achieves uniform dispersion of nitrogen atoms on the In2O3 surface and in the lattice through the synergistic effect of physical mixing and thermal diffusion during high-energy ball milling.

[0007] A catalyst for producing methanol from carbon dioxide hydrogenation is a nitrogen-doped In2O3 catalyst; wherein the main catalyst In2O3 is a light yellow powder, and nitrogen atoms are uniformly dispersed on the surface and in the bulk of the In2O3, forming NO-In chemical bonds with indium atoms; the mass fraction of nitrogen in the catalyst is 0.08% to 0.3%;

[0008] The preparation method of the catalyst is a solvent thermal-ball milling synergistic method, which specifically comprises: dissolving an indium-containing metal salt and a precipitant in a mixed solution of an organic solvent and water, stirring and dissolving, and then performing a solvent thermal reaction. The solid product retained is a precursor; the precursor is calcined at high temperature to obtain an In2O3 main catalyst; the In2O3 main catalyst and a nitrogen-containing organic matter are mixed and then subjected to high-energy ball milling to obtain a nitrogen-doped precursor, and the nitrogen-doped precursor is calcined to obtain the carbon dioxide hydrogenation to methanol catalyst N-In2O3. Preferably, the mass ratio of the precipitant to the indium-containing metal salt is 0.5 to 2:1, the volume ratio of the organic solvent to water is 2 to 5:1, and the mass ratio of the nitrogen-containing organic matter to the In2O3 main catalyst is 0.08 to 0.3:1.

[0009] A preparation method for a catalyst for producing methanol by hydrogenating carbon dioxide comprises the following steps: dissolving an indium-containing metal salt and a precipitant in a mixed solution of an organic solvent and water, stirring and dissolving the mixture, and then performing a solvothermal reaction to obtain a solid product, which is a precursor; calcining the precursor at high temperature to obtain an In2O3 main catalyst; mixing the In2O3 main catalyst and a nitrogen-containing organic matter, and then performing high-energy ball milling to obtain a nitrogen-doped precursor; and calcining the nitrogen-doped precursor to obtain the carbon dioxide hydrogenation to methanol catalyst N-In2O3.

[0010] Preferably, the indium-containing metal salt is one of indium nitrate, indium chloride or indium acetylacetonate; the precipitant is urea; the organic solvent is at least one of ethanol, isopropanol, acetone, and N,N-dimethylformamide; the nitrogen-containing organic matter is at least one of urea, imidazole compounds, and polyamine compounds; generally, imidazole compounds include 2-methylimidazole, phenylimidazole, etc., and polyamine compounds include hexamethylenediamine, m-phenylenediamine, o-phenylenediamine, etc.

[0011] Preferably, the indium-containing metal salt is indium nitrate; the organic solvent is ethanol; and the nitrogen-containing organic compound is urea.

[0012] Preferably, the temperature of the solvent thermal reaction is 100°C to 150°C, and the solvent thermal time is 12h to 36h; the temperature of the high-temperature calcination of the precursor is 400°C to 500°C, the heating rate is 1 to 8°C / min, and the calcination time is 2h to 6h; the high-energy ball milling speed is 200-500rpm, and the ball milling time is 30min to 150min; the calcination temperature of the nitrogen-doped precursor is 300°C to 500°C, the heating rate is 1 to 8°C / min, and the calcination time is 2h to 6h.

[0013] Preferably, the precursor and the nitrogen-doped precursor are calcined at high temperature in a muffle furnace respectively.

[0014] Preferably, the mass ratio of the precipitant to the indium-containing metal salt is 1:1, the volume ratio of the organic solvent to water is 2:1, and the mass ratio of the nitrogen-containing organic matter to the In2O3 main catalyst is 0.15:1.

[0015] Preferably, the temperature of the solvent thermal reaction is 120°C, and the solvent thermal time is 17h; the temperature of the high-temperature calcination of the precursor is 450°C, the heating rate is 5°C / min, and the calcination time is 3h; the high-energy ball milling speed is 300rpm, and the ball milling time is 60min; the calcination temperature of the nitrogen-doped precursor is 400°C, the heating rate is 5°C / min, and the calcination time is 3h.

[0016] In the reaction of carbon dioxide hydrogenation to methanol, the amount of the carbon dioxide hydrogenation to methanol catalyst N-In2O3 is 0.1g; the reaction gas used is a mixture of CO2 and H2, the volume ratio of CO2 / H2 is 1:3, the reaction pressure is 3MPa, and the mass space velocity is 15000mL·h -1 ·g cat -1 ; The reaction temperature is 220℃~400℃.

[0017] The present invention designs a carbon dioxide hydrogenation to methanol catalyst prepared by a solvothermal-ball milling synergistic method. A small, uniformly sized In2O3 precursor is constructed through the solvothermal method. The high-energy shear force of ball milling disperses urea at the nanoscale and induces lattice strain, exposing highly active crystal planes that provide anchoring sites for nitrogen doping. The electronegativity of nitrogen atoms differs from that of oxygen atoms in the In2O3 lattice, and doping changes the electron cloud distribution of In2O3. The outer electron structure of nitrogen atoms makes them electron donors, providing additional electrons to the In2O3 lattice. This process disrupts the original charge balance of In2O3, and to maintain the electrical neutrality of the system, oxygen vacancies are generated in the lattice. Oxygen vacancies are key active sites for the adsorption and activation of CO2 molecules. They can enhance the adsorption of CO2 on the catalyst surface, making it easier to convert it into intermediates such as formate, thereby promoting the CO2 hydrogenation to methanol reaction. At the same time, nitrogen doping forms new active centers on the surface and within the In2O3 lattice. N atoms and In atoms form an N-In chemical bonding environment, and the N1s orbital hybridizes with the In 3d orbital, making the electronic structure and geometry of the active sites more favorable for the adsorption and conversion of reactant molecules. These modified active sites more effectively adsorb hydrogen molecules, promoting their dissociation and transfer to adsorbed CO2 molecules, accelerating the hydrogenation reaction rate and improving the efficiency of methanol production. During ball milling, the high-energy collisions and shearing effects of the milling media continuously refine the In2O3 particles. Smaller particles have a larger surface area, exposing more active sites and providing more reaction sites. Furthermore, ball milling enables the uniform dispersion of N dopants (such as nitrogen-containing precursors like urea) on the surface of the In2O3 particles at the nanometer level. This uniform dispersion avoids the localized overconcentration and agglomeration that can occur with traditional doping methods, ensuring a uniform distribution of catalyst active sites throughout the system, thereby improving the overall activity and stability of the catalyst. The mechanical energy generated by ball milling can cause some damage to the In2O3 crystal lattice, introducing lattice defects such as dislocations and vacancies. These lattice defects increase the atomic activity of the catalyst surface, making it easier for reactant molecules to adsorb and react at the defect sites. In addition, lattice defects can also promote the transmission of electrons within the catalyst, improve the efficiency of electron transfer, and provide a more favorable electronic environment for the CO2 hydrogenation reaction, thereby improving the performance of the thermal catalytic reaction. The N-In2O3 catalyst prepared by the present invention can further improve the reaction activity of CO2 hydrogenation to methanol, especially the methanol selectivity. When the reaction temperature is 340°C, the CO2 conversion rate is 10.1% and the methanol selectivity is as high as 67.8%, which is significantly higher than that of the undoped In2O3 catalyst (CO2 conversion rate 8.8%, methanol selectivity 64.1%). Description of the drawings:

[0018] Attachment Figure 1This is an EDS scan of the N-In2O3-1 catalyst prepared in Example 1 of the present invention.

[0019] Attachment Figure 2 It is the XPS spectrum of the N-In2O3-1 catalyst prepared in Example 1 of the present invention and the In2O3 catalyst prepared in Comparative Example 1.

[0020] Attachment Figure 3 2 is a curve showing the change of CO2 conversion rate of the N-In2O3-1 catalyst prepared in Example 1 of the present invention and the In2O3 catalyst prepared in Comparative Example 1 as a function of reaction temperature.

[0021] Attachment Figure 4 3 is a curve showing the change of methanol selectivity of the N-In2O3-1 catalyst prepared in Example 1 and the In2O3 catalyst prepared in Comparative Example 1 as a function of reaction temperature. Specific implementation method:

[0022] In order to make the technical solution of the present invention easier to understand, a catalyst for producing methanol by hydrogenation of carbon dioxide and a preparation method thereof disclosed in the present invention are now clearly and completely described in combination with embodiments and drawings.

[0023] Example 1:

[0024] Weigh 4g of In(NO3)3·xH2O and 4g of urea and dissolve them in a mixed solution of 20mL of deionized water and 40mL of anhydrous ethanol, and stir rapidly until the solution is clear and transparent. Transfer the mixed solution to a 100mL polytetrafluoroethylene-lined reactor, seal it, and place it in a 120℃ oven for a 17-hour solvent thermal reaction. After naturally cooling to room temperature, wash it alternately with deionized water and anhydrous ethanol through a filtration system until the filtrate is neutral (pH≈7). The retained solid product is the precursor; the precursor is dried in a 100℃ forced air drying oven for 24 hours, and the dried precursor is placed in a muffle furnace and heated at 5℃min -1 The heating rate was increased to 450 °C in air atmosphere and calcined for 3 h to obtain a light yellow In2O3 main catalyst;

[0025] Weigh 0.3g of urea and 2g of In2O3 main catalyst and put them into high-energy ball mill for ball milling. The ball milling speed is 300rpm and the ball milling time is 60min. After the ball milling is completed, put the sample into the muffle furnace and heat it at 5℃min. -1 The heating rate was increased to 400° C. in an air atmosphere and calcined for 3 h to obtain an N-doped indium oxide catalyst, which was recorded as N-In2O3-1 catalyst.

[0026] like Figure 1 As shown, the nitrogen element is evenly distributed in the catalyst, which indicates that the nitrogen element is successfully incorporated into the indium oxide catalyst.

[0027] like Figure 2 As shown in the figure, the peak of N-doped In3d5 / 2 shifts toward higher binding energy, indicating the existence of chemical interaction between NO and In. This induces local electron redistribution, increases the electron density of In, and improves the performance of the active center.

[0028] Example 2:

[0029] Weigh 4g of In(NO3)3·xH2O and 2g of urea and dissolve them in a mixed solution of 20mL of deionized water and 60mL of anhydrous ethanol, and stir rapidly until the solution is clear and transparent. Transfer the mixed solution to a 100mL polytetrafluoroethylene-lined reactor, seal it, and place it in a 100℃ oven for a 36-hour solvent thermal reaction. After naturally cooling to room temperature, wash it alternately with deionized water and anhydrous ethanol through a filtration system until the filtrate is neutral (pH≈7). The retained solid product is the precursor; the precursor is dried in a 100℃ forced air drying oven for 24 hours, and the dried precursor is placed in a muffle furnace and heated at 1℃min -1 The heating rate was increased to 400 °C in air atmosphere and calcined for 2 h to obtain a light yellow In2O3 main catalyst;

[0030] Weigh 0.16g of urea and 2g of In2O3 main catalyst and put them into a high-energy ball mill for ball milling. The ball milling speed is 200rpm and the ball milling time is 30min. After the ball milling is completed, put the sample into a muffle furnace and heat it at 1℃min. -1 The heating rate was increased to 400° C. in an air atmosphere and calcined for 3 h to obtain an N-doped indium oxide catalyst, which was recorded as N-In2O3-2 catalyst.

[0031] Example 3:

[0032] Weigh 4g of In(NO3)3·xH2O and 8g of urea and dissolve them in a mixed solution of 20mL of deionized water and 100mL of anhydrous ethanol, and stir rapidly until the solution is clear and transparent. Transfer the mixed solution to a 150mL polytetrafluoroethylene-lined reactor, seal it, and place it in a 150℃ oven for a 36-hour solvent thermal reaction. After naturally cooling to room temperature, wash it alternately with deionized water and anhydrous ethanol through a filtration system until the filtrate is neutral (pH≈7). The retained solid product is the precursor; the precursor is dried in a 100℃ forced air drying oven for 24 hours, and the dried precursor is placed in a muffle furnace and heated at 8℃min -1 The heating rate was increased to 500 °C in air atmosphere and calcined for 6 h to obtain a light yellow In2O3 main catalyst;

[0033] Weigh 0.6g of urea and 2g of In2O3 main catalyst and put them into a high-energy ball mill for ball milling. The ball milling speed is 500rpm and the ball milling time is 150min. After the ball milling is completed, put the sample into a muffle furnace and heat it at 8℃min. -1 The heating rate was increased to 400° C. in an air atmosphere and calcined for 6 h to obtain an N-doped indium oxide catalyst, which was recorded as N-In2O3-3 catalyst.

[0034] Example 4:

[0035] Weigh 4g of In(NO3)3·xH2O and 4g of urea and dissolve them in a mixed solution of 20mL of deionized water and 40mL of anhydrous ethanol, and stir rapidly until the solution is clear and transparent. Transfer the mixed solution to a 100mL polytetrafluoroethylene-lined reactor, seal it, and place it in a 120℃ oven for a 17-hour solvent thermal reaction. After naturally cooling to room temperature, wash it alternately with deionized water and anhydrous ethanol through a filtration system until the filtrate is neutral (pH≈7). The retained solid product is the precursor; the precursor is dried in a 100℃ forced air drying oven for 24 hours, and the dried precursor is placed in a muffle furnace and heated at 5℃min -1 The heating rate was increased to 450 °C in air atmosphere and calcined for 3 h to obtain a light yellow In2O3 main catalyst;

[0036] Weigh 0.3g of urea and 2g of In2O3 sample and mill them in a high-energy ball mill. The urea / In2O3 mass ratio is 0.15, the milling speed is 300 rpm, and the milling time is 60 minutes. After ball milling, the sample is calcined in a muffle furnace at 300°C for 3 hours to obtain the N-doped indium oxide catalyst, designated as N-In2O3-4 catalyst.

[0037] Example 5:

[0038] Weigh 4g of In(NO3)3·xH2O and 4g of urea and dissolve them in a mixed solution of 20mL of deionized water and 40mL of anhydrous ethanol, and stir rapidly until the solution is clear and transparent. Transfer the mixed solution to a 100mL polytetrafluoroethylene-lined reactor, seal it, and place it in a 120℃ oven for a 17-hour solvent thermal reaction. After naturally cooling to room temperature, wash it alternately with deionized water and anhydrous ethanol through a filtration system until the filtrate is neutral (pH≈7). The retained solid product is the precursor; the precursor is dried in a 100℃ forced air drying oven for 24 hours, and the dried precursor is placed in a muffle furnace and heated at 5℃min -1 The heating rate was increased to 450 °C in air atmosphere and calcined for 3 h to obtain a light yellow In2O3 main catalyst;

[0039] Weigh 0.3g of urea and 2g of In2O3 sample and mill them in a high-energy ball mill. The urea / In2O3 mass ratio is 0.15, the milling speed is 300 rpm, and the milling time is 60 minutes. After ball milling, the sample is calcined in a muffle furnace at 500°C for 3 hours to obtain the N-doped indium oxide catalyst, designated as N-In2O3-4 catalyst.

[0040] Comparative Example 1:

[0041] Weigh 4g of In(NO3)3·xH2O and 4g of urea and dissolve them in 17mL of deionized water and 40mL of anhydrous ethanol, and stir rapidly until the solution is clear and transparent. Transfer the mixed solution to a 100mL polytetrafluoroethylene-lined reactor, seal it, and place it in a 120℃ oven for a 17-hour solvent thermal reaction. After naturally cooling to room temperature, wash it alternately with deionized water and anhydrous ethanol through a filtration system until the filtrate is neutral (pH≈7). The obtained product is dried in a 100℃ forced air drying oven for 24 hours. Place the dried sample in a muffle furnace and refrigerate it at 5℃min -1 The temperature was raised to 450°C in an air atmosphere and calcined for 3 hours to obtain a light yellow indium oxide (In2O3) powder, which was designated as In2O3 catalyst.

[0042] Comparative Example 2:

[0043] Weigh 4g of In(NO3)3·xH2O and 4g of urea and dissolve them in 17mL of deionized water and 40mL of anhydrous ethanol, and stir rapidly until the solution is clear and transparent. Transfer the mixed solution to a 100mL polytetrafluoroethylene-lined reactor, seal it, and place it in a 120℃ oven for a 17-hour solvent thermal reaction. After naturally cooling to room temperature, wash it alternately with deionized water and anhydrous ethanol through a filtration system until the filtrate is neutral (pH≈7). The obtained product is dried in a 100℃ forced air drying oven for 24 hours. Place the dried sample in a muffle furnace and refrigerate it at 5℃min -1 The heating rate was increased to 450°C in an air atmosphere and calcined for 3 hours to finally obtain light yellow indium oxide (In2O3) powder.

[0044] Weigh 0.8g of urea and 2g of In2O3 sample and mill them in a high-energy ball mill. The urea / In2O3 mass ratio is 0.4, the milling speed is 300 rpm, and the milling time is 60 minutes. After ball milling, the sample is calcined in a muffle furnace at 400°C for 3 hours to obtain the N-doped indium oxide catalyst, designated as N-In2O3-6 catalyst.

[0045] Comparative Example 3:

[0046] Weigh 4g of In(NO3)3·xH2O and 4g of urea and dissolve them in 17mL of deionized water and 40mL of anhydrous ethanol, and stir rapidly until the solution is clear and transparent. Transfer the mixed solution to a 100mL polytetrafluoroethylene-lined reactor, seal it, and place it in a 120℃ oven for a 17-hour solvent thermal reaction. After naturally cooling to room temperature, wash it alternately with deionized water and anhydrous ethanol through a filtration system until the filtrate is neutral (pH≈7). The obtained product is dried in a 100℃ forced air drying oven for 24 hours. Place the dried sample in a muffle furnace and refrigerate it at 5℃min -1 The heating rate was increased to 450°C in an air atmosphere and calcined for 3 hours to finally obtain light yellow indium oxide (In2O3) powder.

[0047] Weigh 0.3g of urea and 2g of In2O3 sample and mill them in a high-energy ball mill. The urea / In2O3 mass ratio is 0.15, the milling speed is 300 rpm, and the milling time is 60 minutes. After ball milling, the sample is calcined in a muffle furnace at 200°C for 3 hours to obtain the N-doped indium oxide catalyst, designated as N-In2O3-7 catalyst.

[0048] Comparative Example 4:

[0049] Weigh 4g of In(NO3)3·xH2O and 4g of urea and dissolve them in 17mL of deionized water and 40mL of anhydrous ethanol, and stir rapidly until the solution is clear and transparent. Transfer the mixed solution to a 100mL polytetrafluoroethylene-lined reactor, seal it, and place it in a 120℃ oven for a 17-hour solvent thermal reaction. After naturally cooling to room temperature, wash it alternately with deionized water and anhydrous ethanol through a filtration system until the filtrate is neutral (pH≈7). The obtained product is dried in a 100℃ forced air drying oven for 24 hours. Place the dried sample in a muffle furnace and refrigerate it at 5℃min -1 The heating rate was increased to 450°C in an air atmosphere and calcined for 3 hours to finally obtain light yellow indium oxide (In2O3) powder.

[0050] Weigh 0.3g of urea and 2g of In2O3 sample and mill them in a high-energy ball mill. The urea / In2O3 mass ratio is 0.15, the milling speed is 300 rpm, and the milling time is 60 minutes. After ball milling, the sample is calcined in a muffle furnace at 600°C for 3 hours to obtain the N-doped indium oxide catalyst, designated as N-In2O3-8 catalyst.

[0051] The above-mentioned implementation operations 1 to 5 and comparison operations 1 to 4 were used to test the reaction performance of carbon dioxide hydrogenation to produce methanol.

[0052] The catalyst was tableted, crushed, and sieved (40-80 mesh). 0.1 g of catalyst was weighed and mixed with an equal mass of quartz sand and then loaded into a stainless steel reaction tube with a built-in quartz tube (inner diameter 8 mm). Before the reaction began, the catalyst was pretreated at normal pressure by passing high-purity N2 at a flow rate of 90 mL / min at 5 °C min -1 The heating rate was raised to 300 °C for pretreatment for 1 h, and then the mixed feed gas (H2 / CO2 = 3 / 1, molar ratio) was introduced into the fixed bed reactor. The reactor pressure was adjusted to 3 MPa and the gas mass space velocity was maintained at 15000 mL·h -1 ·g cat -1 The temperature range for catalyst activity evaluation was 220°C to 400°C, with a heating rate of 3°C min -1 The reaction time at each reaction temperature was maintained at 1 h. All pipelines between the reactor outlet and the six-way chromatograph valve were maintained at 150°C to prevent product condensation. Product composition and content at different reaction temperatures were monitored online using a gas chromatograph. The catalyst activity test results are shown in Table 1.

[0053] Table 1 Catalyst activity test results

[0054]

[0055] Analyzing the data in Table 1, as the mass ratio of urea to In2O3 increases from 0.08 to 0.4, the CO2 conversion rate and methanol selectivity both show a trend of first increasing and then decreasing. When the mass ratio of urea to In2O3 is 0.15, the CO2 conversion rate and methanol selectivity both reach their peak values, and the methanol production activity is the highest. Figure 3 ,4 It can be seen that for the optimal N-In2O3-1 catalyst, when the CO2 conversion rate is 10.1%, the methanol selectivity can still be maintained at 67.8%, which is much higher than that of In2O3 alone (Compared with Operation 1), which fully demonstrates that N-In2O3-1 exhibits excellent methanol production activity in the carbon dioxide hydrogenation to methanol reaction. N doping not only promotes the formation of In2O3 active sites and improves CO2 adsorption, but also enhances the electron density of oxygen vacancies near In, which is beneficial to methanol production. However, too high a N content will destroy the crystal structure of In2O3, resulting in excessively strong surface alkalinity, which is not conducive to the carbon dioxide hydrogenation to methanol reaction, and the CO2 conversion rate and methanol selectivity are significantly reduced (N-In2O3-6). Compared with In2O3 alone, adding an appropriate amount of urea (the mass ratio of urea to In2O3 is 0.08 to 0.3) can simultaneously improve the CO2 conversion rate and methanol selectivity, and the CO2 conversion rate is improved more significantly; the CO2 conversion rate is greater than 9%, and the methanol selectivity is greater than 65%. Appropriate amount of N element doping can improve the methanol production activity of In2O3.

[0056] Furthermore, during the calcination process after ball milling, when the calcination temperature was low (200°C), the CO2 conversion rate and methanol selectivity were 8.5% and 63.2%, respectively. At a higher calcination temperature of 600°C, the CO2 conversion rate and methanol selectivity were 7.8% and 63.9%, respectively, both lower than those of In2O3 alone. If the calcination temperature is too low, the nitrogen doping level is minimal, and urea cannot be completely decomposed, covering some active sites. If the calcination temperature is too high, the In2O3 particle size increases, resulting in a decrease in the active indium surface area and oxygen vacancy concentration, both of which are detrimental to methanol formation.

[0057] In summary, when the mass ratio of urea to In2O3 is within the range of 0.08-0.3 and the calcination temperature is maintained between 300 and 500°C, nitrogen doping not only effectively promotes the formation of In2O3 active sites, improving their distribution and reaction efficiency, but also enhances the electron density of oxygen vacancies near In, favoring methanol production. The N-In2O3 catalyst maintains relatively high methanol production activity during the carbon dioxide hydrogenation reaction.

[0058] It should be pointed out that for ordinary technicians in this technical field, they can make several improvements, replacements, modifications and embellishments without departing from the principles and purpose of the present invention. These improvements, replacements, modifications and embellishments should also be regarded as the scope of protection of the present invention.

Claims

1. A catalyst for producing methanol by hydrogenation of carbon dioxide, characterized in that: The catalyst is an N-doped In2O3 catalyst; wherein the main catalyst In2O3 is a light yellow powder, and the N atoms are uniformly dispersed on the surface and in the bulk of the In2O3, forming NO-In chemical bonds with the In atoms; the mass fraction of N in the catalyst is 0.08% to 0.3%; The preparation method of the catalyst is a solvent thermal-ball milling synergistic method, specifically: dissolving an indium-containing metal salt and a precipitant in a mixed solution of an organic solvent and water, stirring and dissolving, and then performing a solvent thermal reaction, and retaining a solid product, which is a precursor; calcining the precursor at high temperature to obtain an In2O3 main catalyst; mixing the In2O3 main catalyst and nitrogen-containing organic matter, and then performing high-energy ball milling to obtain a nitrogen-doped precursor; calcining the nitrogen-doped precursor to obtain the carbon dioxide hydrogenation to methanol catalyst N-In2O3.

2. A method for preparing a catalyst for producing methanol by hydrogenation of carbon dioxide, characterized in that: The method specifically comprises the following steps: dissolving an indium-containing metal salt and a precipitant in a mixed solution of an organic solvent and water, stirring and dissolving the mixture, performing a solvent thermal reaction, and retaining a solid product as a precursor; calcining the precursor at high temperature to obtain an In2O3 main catalyst; mixing the In2O3 main catalyst and nitrogen-containing organic matter, and performing high-energy ball milling to obtain a nitrogen-doped precursor; and calcining the nitrogen-doped precursor to obtain the carbon dioxide hydrogenation to methanol catalyst N-In2O3.

3. The method for preparing a catalyst for producing methanol by hydrogenation of carbon dioxide according to claim 2, wherein: The mass ratio of the precipitant to the indium-containing metal salt is 0.5-2:1, the volume ratio of the organic solvent to water is 2-5:1, and the mass ratio of the nitrogen-containing organic matter to the In2O3 main catalyst is 0.08-0.3:

1.

4. The method for preparing a catalyst for producing methanol by hydrogenation of carbon dioxide according to claim 3, wherein: The indium-containing metal salt is one of indium nitrate, indium chloride or indium acetylacetonate; the precipitant is urea; the organic solvent is at least one of ethanol, isopropanol, acetone and N,N-dimethylformamide; and the nitrogen-containing organic matter is at least one of urea, imidazole compounds and polyamine compounds.

5. The method for preparing a catalyst for producing methanol by hydrogenation of carbon dioxide according to claim 4, wherein: The indium-containing metal salt is indium nitrate; the organic solvent is ethanol; and the nitrogen-containing organic matter is urea.

6. The method for preparing a catalyst for producing methanol by hydrogenation of carbon dioxide according to claim 2, wherein: The temperature of the solvent thermal reaction is 100°C to 150°C, and the solvent thermal time is 12h to 36h; the temperature of the high-temperature calcination of the precursor is 400°C to 500°C, the heating rate is 1 to 8°C / min, and the calcination time is 2h to 6h; the high-energy ball milling speed is 200-500rpm, and the ball milling time is 30min to 150min; the calcination temperature of the nitrogen-doped precursor is 300°C to 500°C, the heating rate is 1 to 8°C / min, and the calcination time is 2h to 6h.

7. The method for preparing a catalyst for producing methanol by hydrogenation of carbon dioxide according to claim 6, wherein: The precursor and the nitrogen-doped precursor are respectively calcined at high temperature in a muffle furnace.

8. The method for preparing a catalyst for producing methanol by hydrogenation of carbon dioxide according to claim 7, wherein: The mass ratio of the precipitant to the indium-containing metal salt is 1:1, the volume ratio of the organic solvent to water is 2:1, and the mass ratio of the nitrogen-containing organic matter to the In2O3 main catalyst is 0.15:

1.

9. The method for preparing a catalyst for producing methanol by hydrogenation of carbon dioxide according to claim 8, wherein: The temperature of the solvent thermal reaction is 120°C, and the solvent thermal time is 17 hours; the temperature of the high-temperature calcination of the precursor is 450°C, the heating rate is 5°C / min, and the calcination time is 3 hours; the high-energy ball milling speed is 300 rpm, and the ball milling time is 60 minutes; the calcination temperature of the nitrogen-doped precursor is 400°C, the heating rate is 5°C / min, and the calcination time is 3 hours.

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