Pd-supported magnesium-aluminum doped indium oxide catalyst, its preparation method and application

Abstract

The present invention relates to the technical field of catalysts, and discloses a Pd-loaded magnesium-aluminum-doped indium oxide catalyst, a preparation method thereof, and an application thereof. The catalyst comprises Pd, an active component, and a carrier. The active component is indium oxide, and the carrier comprises magnesium oxide and aluminum oxide. Based on the total amount of the active component and the carrier, the content of the active component is 50-85% by weight, and the content of the carrier is 15-50% by weight. Based on the total amount of the catalyst, the content of Pd is 0.01-1.5% by weight. The Pd-loaded magnesium-aluminum-doped indium oxide catalyst has a better catalytic effect and can effectively improve the carbon dioxide conversion rate on the basis of improving the methanol selectivity.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly relates to a Pd-loaded magnesium-aluminum doped indium oxide catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] As an important raw material for chemicals and a substitute for fossil fuels, methanol can not only solve the problem of greenhouse gas control but also be an effective way to replace fossil fuels by reacting CO 2 with H from renewable energy 2 Therefore, the catalytic conversion of carbon dioxide into methanol products has received more attention.

[0003] Due to the stable chemical properties and difficult activation of CO 2 , the conversion rate of this reaction is generally low. And the formation of methanol is an exothermic reaction. Thermodynamically, low temperature is beneficial to methanol production but not conducive to the activation of carbon dioxide. Therefore, it is necessary to select an appropriate reaction temperature and design an efficient catalyst.

[0004] Currently, the catalysts widely studied for methanol synthesis include modified copper-based catalysts, noble metal catalysts, and zinc oxide catalysts. However, in the modified statistical catalytic system, the high activity of the side reaction reverse water gas shift (RWGS) and the characteristics such as H 2 O-induced sintering of the active phase and poor stability limit its further application. In the noble metal catalytic system and the zinc oxide catalytic system, the high cost of noble metals and the characteristics such as low active sites and easy migration of zinc oxide also limit the further application of such catalysts in the field of carbon dioxide hydrogenation to some extent. In 2 O 3 has moderate CO 2 and CO adsorption capacities, shows significantly better methanol selectivity than Cu, Co, and noble metal catalysts, and higher catalytic activity than ZnO catalysts, thus attracting wide attention of scientific researchers. However, the catalytic effect of In 2 O 3 catalysts in the prior art still needs to be further improved. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem that the catalytic effect of In 2 O 3 catalysts in the prior art needs to be further improved, and provide a Pd-loaded magnesium-aluminum doped indium oxide catalyst, a preparation method thereof, and an application thereof. The Pd-loaded magnesium-aluminum doped indium oxide catalyst has a better catalytic effect and can effectively improve the carbon dioxide conversion rate on the basis of improving the methanol selectivity.

[0006] To achieve the above object, on the one hand, the present invention provides a Pd-loaded magnesium-aluminum doped indium oxide catalyst, which catalyst comprises Pd, an active component and a support, wherein the active component is indium oxide, and the support comprises magnesium oxide and aluminum oxide. Based on the total amount of the active component and the support, the content of the active component is 50-85% by weight, and the content of the support is 15-50% by weight. Based on the total amount of the catalyst, the content of Pd is 0.01-1.5% by weight.

[0007] Preferably, magnesium oxide accounts for 0.75-15% of the total mass of the active component and the support, and more preferably 5-10%.

[0008] Preferably, aluminum oxide accounts for 10.5-47.5% of the total mass of the active component and the support, and more preferably 22-33%.

[0009] Preferably, as determined by XRD, the indium oxide has a hexagonal structure.

[0010] Preferably, the support has an ordered mesoporous structure.

[0011] On the second aspect, the present invention provides a method for preparing a Pd-loaded magnesium-aluminum doped indium oxide catalyst, which method comprises:

[0012] (1) Mixing a support containing aluminum oxide and magnesium oxide with indium oxide, and then optionally pulverizing;

[0013] (2) Calcining the product obtained in step (1) to obtain a catalyst semi-finished product;

[0014] (3) Contacting a solution containing a metal palladium salt with the catalyst semi-finished product, and then drying and calcining;

[0015] Based on the total amount of the support and indium oxide, the content of indium oxide is 50-85% by weight, and the content of the support is 15-50% by weight;

[0016] The amounts of the metal palladium salt and the catalyst semi-finished product are such that in the prepared catalyst, based on the total amount of the catalyst, the content of Pd is 0.01-1.5% by weight.

[0017] Preferably, magnesium oxide in the support accounts for 0.75-15% of the total mass of indium oxide and the support, and aluminum oxide in the support accounts for 10.5-47.5% of the total mass of indium oxide and the support.

[0018] More preferably, magnesium oxide in the support accounts for 5-10% of the total mass of indium oxide and the support, and aluminum oxide in the support accounts for 22-33% of the total mass of indium oxide and the support.

[0019] Preferably, the method for preparing the carrier containing alumina and magnesia includes: mixing an acid, an aluminum precursor, and a magnesium precursor in the presence of a surfactant and in the presence of a solvent, and then drying and calcining.

[0020] The third aspect of the present invention provides an application of a Pd-loaded magnesium-aluminum doped indium oxide catalyst in the reaction of hydrogenating carbon dioxide to prepare methanol, wherein the Pd-loaded magnesium-aluminum doped indium oxide catalyst is the Pd-loaded magnesium-aluminum doped indium oxide catalyst described in the first aspect above or the Pd-loaded magnesium-aluminum doped indium oxide catalyst prepared by the preparation method described in the second aspect above.

[0021] The Pd-loaded magnesium-aluminum doped indium oxide catalyst of the present invention uses indium oxide as an active component and combines magnesia and alumina as carriers, and at the same time loads Pd, which can effectively improve the occurrence of the catalytic hydrogenation reaction of carbon dioxide and the selectivity during the reaction process. It can be seen from the example part that the Pd-loaded magnesium-aluminum doped indium oxide catalyst of the present invention has high catalytic activity and selectivity, and can improve the conversion rate of carbon dioxide and the content of methanol in the product. For example, under the conditions of 5 MPa and 6750 h -1 the selectivity of this catalyst for catalytic preparation of methanol can reach 92%. Moreover, this catalyst can still meet a high carbon dioxide conversion rate and methanol selectivity during the long-term operation of the reaction.

[0022] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation part. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is the XRD pattern of the hexagonal indium oxide prepared in Example 1 of the present invention;

[0024] Figure 2 is the XRD pattern of the ordered mesoporous doped carrier prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the values between the endpoint values of each range, between the endpoint values of each range and a single point value, and between single point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0026] As described above, the first aspect of the present invention provides a Pd-loaded magnesium-aluminum doped indium oxide catalyst, which catalyst comprises Pd, an active component and a support. The active component is indium oxide, and the support comprises magnesium oxide and aluminum oxide. Based on the total amount of the active component and the support, the content of the active component is 50-85% by weight, and the content of the support is 15-50% by weight. Based on the total amount of the catalyst, the content of Pd is 0.01-1.5% by weight.

[0027] The content of each component in the catalyst of the present invention can be obtained by testing with X-ray fluorescence spectrometry (XRF).

[0028] Preferably, the support has an ordered mesoporous structure, and preferably, the indium oxide has a hexagonal structure.

[0029] During the research process, the inventors of the present invention found that when the above-mentioned Pd-loaded magnesium-aluminum doped indium oxide catalyst is applied to the reaction of catalytic hydrogenation of carbon dioxide to prepare methanol, it can effectively improve the catalytic efficiency and selectivity of the catalyst, increase the conversion rate of carbon dioxide and the selectivity of methanol in the catalytic reaction, promote the formation of methanol, and increase the proportion of methanol in the products. Moreover, the catalyst deactivation rate is relatively low and the reaction stability is good.

[0030] In order to further exert the synergistic effect among the active component, the support and Pd and increase the conversion rate of carbon dioxide, preferably, based on the total amount of the active component and the support, the content of the active component is 60-70% by weight, and the content of the support is 30-40% by weight.

[0031] Preferably, based on the total amount of the catalyst, the content of Pd is 0.75-1.5% by weight. Research shows that under this condition, the catalyst has better catalytic effect and higher conversion rate of carbon dioxide.

[0032] Preferably, the mass ratio of the active component to the support is 1-6:1. Under this ratio condition, the synergistic effect among the active component, the support and Pd can be further exerted, thereby increasing the conversion rate of carbon dioxide and the selectivity of methanol. Further preferably, the mass ratio of the active component to the support is 1-3:1.

[0033] In the support of the present invention, magnesium oxide and aluminum oxide can be mixed in any ratio. Preferably, magnesium oxide accounts for 0.75-15% of the total mass of the active component and the support, and further preferably 5-10%. Adopting this preferred embodiment can further exert the synergistic effect among the support, the active component and Pd, thereby further increasing the conversion rate of carbon dioxide.

[0034] Preferably, alumina accounts for 10.5-47.5% of the active component and the carrier, and more preferably 22-33%. Under this condition, the synergistic effect between the carrier, the active component and Pd can be further exerted, thereby further improving the conversion rate of carbon dioxide.

[0035] The carrier mainly needs to meet the above limitations to achieve the object of the present invention. In order to further improve the catalytic performance of the catalyst. Preferably, the carrier has an ordered mesoporous structure.

[0036] The ordered mesoporous structure of the carrier can be determined by small-angle XRD testing.

[0037] In the present invention, preferably, as determined by XRD, the indium oxide has a hexagonal structure. The indium oxide with this hexagonal structure has better catalytic effect and can effectively improve the conversion rate of carbon dioxide and the selectivity of methanol.

[0038] As described above, the second aspect of the present invention provides a method for preparing a Pd-loaded magnesium-aluminum-doped indium oxide catalyst, and this method includes:

[0039] (1) Mix a carrier containing alumina and magnesia with indium oxide, and then optionally pulverize;

[0040] (2) Bake the product obtained in step (1) to obtain a catalyst semi-finished product;

[0041] (3) Contact a solution containing a metal palladium salt with the catalyst semi-finished product, and then carry out drying and baking;

[0042] Based on the total amount of the carrier and indium oxide, the content of indium oxide is 50-85% by weight, and the content of the carrier is 15-50% by weight;

[0043] The dosages of the metal palladium salt and the catalyst semi-finished product are such that in the prepared catalyst, based on the total amount of the catalyst, the content of Pd is 0.01-1.5% by weight.

[0044] In the preparation method of the present invention, the above mixing can be stirring mixing, ultrasonic mixing or other feasible mixing methods. Stirring mixing can be magnetic stirring, mechanical stirring or manual stirring, etc. The conditions of ultrasonic mixing and stirring conditions can be determined by those skilled in the art according to the actual situation. After mixing the carrier containing alumina and magnesia with indium oxide, it can be selected to pulverize the obtained product after mixing, or it can not be pulverized. The pulverizing method can use a pulverizer to pulverize, or use a grinding method to pulverize. Preferably, after mixing the carrier containing alumina and magnesia with indium oxide, it is placed in a ball mill for grinding. Preferably, the rotation speed of the ball mill is set to 200-800 rpm, and the ball milling time is 5-30 h.

[0045] In order to further exert the synergistic effect among indium oxide, the carrier and Pd and improve the conversion rate of carbon dioxide, preferably, based on the total amount of the carrier and indium oxide, the content of indium oxide is 60-70% by weight, and the content of the carrier is 30-40% by weight.

[0046] In order to further exert the synergistic effect among indium oxide, the carrier and Pd and improve the conversion rate of carbon dioxide, preferably, the amounts of metal palladium salt and the catalyst semi-finished product are such that in the prepared catalyst, based on the total amount of the catalyst, the content of Pd is 0.75-15% by weight.

[0047] Preferably, the mass ratio of the indium oxide to the carrier is 1-6:1. Under this ratio condition, the synergistic effect among indium oxide, the carrier and Pd can be further exerted, thereby improving the conversion rate of carbon dioxide and the methanol selectivity. Further preferably, the mass ratio of the indium oxide to the carrier is 1-3:1.

[0048] In the carrier of the present invention, magnesium oxide and aluminum oxide can be mixed in any proportion. Preferably, based on the total amount of the carrier and indium oxide, the content of magnesium oxide is 0.75-15% by weight; the content of aluminum oxide is 10.5-47.5% by weight. The synergistic effect among the carrier, indium oxide and Pd can be further exerted, thereby further improving the conversion rate of carbon dioxide.

[0049] In order to further exert the synergistic effect among the carrier, indium oxide and Pd, preferably, based on the total amount of the carrier and indium oxide, magnesium oxide in the carrier accounts for 5-10% of the total mass of indium oxide and the carrier, and aluminum oxide in the carrier accounts for 22-33% of the total mass of indium oxide and the carrier.

[0050] In the present invention, preferably, the indium oxide is prepared by a precipitation method. The indium oxide prepared by the precipitation method has a hexagonal structure, and the indium oxide with this structure has a better catalytic effect and can effectively improve the conversion rate of carbon dioxide and the methanol selectivity.

[0051] Further preferably, the preparation of the indium oxide comprises the following steps:

[0052] (1-1) Mix a solution containing a metal indium precursor with a precipitant solution to obtain a precipitation mother liquor;

[0053] (1-2) Age the precipitation mother liquor to form a precipitate;

[0054] (1-3) Carry out solid-liquid separation on the product obtained in step (1-2), and then carry out drying and calcination.

[0055] According to the present invention, the metal indium precursor may be a soluble metal indium salt containing indium ions, such as In(NO 3 ) 3 , InCl 3 and In 2 (SO 4 ) 3 and at least one of them, preferably at least one of In(NO 3 ) 3 and InCl 3 . The precipitant is a substance in the prior art that can slowly precipitate the metal indium precursor. Preferably, the precipitant is urea.

[0056] The mixing in step (1-1) can be carried out by any feasible method disclosed in the prior art. Preferably, in step (1-1), the method of mixing the solution containing the metal indium precursor with the precipitant solution is: dropping the precipitant solution drop by drop into the solution containing the metal indium precursor, and continuously stirring during the dropping process and after the dropping is completed. Preferably, the conditions of the stirring at least satisfy: the time is 1-10 h. This preferred embodiment can enable the metal indium precursor and the precipitant to fully contact, thereby improving the precipitation effect.

[0057] The method of solid-liquid separation can be the filtration separation method commonly used in the art, such as filtration or centrifugal separation. Centrifugal separation is preferably used, and the conditions of centrifugation include: the rotation speed is 5000-8000 rpm, and the time is 5-10 min.

[0058] The aging reaction in step (1-2) is a hydrothermal reaction, and preferably the aging reaction is carried out under closed conditions. As a specific embodiment of the present invention, in step (1-2), the precipitation mother liquor is placed in a hydrothermal reaction kettle, and the hydrothermal reaction kettle is placed in an oven to age the precipitation mother liquor. Preferably, the aging conditions include: the temperature is 80-180 °C, and the time is 12-22 h. Further preferably, the aging conditions include: the temperature is 120-160 °C, and the time is 18-20 h. Aging under this temperature condition can further improve the catalytic effect of the obtained indium oxide.

[0059] According to the present invention, the solvents in the solution containing the metal indium precursor and the precipitant solution are independently organic solvents and / or water, preferably organic solvents and water. The mixing ratio of the organic solvent and water can be determined by those skilled in the art according to the actual situation so as to form a solution containing the metal indium precursor and a precipitant solution.

[0060] The organic solvent is preferably selected from at least one of ethanol, methanol, isopropanol, ethylene glycol, triethylene glycol, and N,N-dimethylacetamide.

[0061] The concentration of the metal indium precursor solution and the concentration of the precipitant solution can be determined by those skilled in the art according to actual conditions. Under preferred conditions, the concentration of the solution containing the metal indium precursor is 0.1-1 mol / L. Further preferably, the concentration of the precipitant solution is 1-3 mol / L.

[0062] Preferably, the method further comprises washing the product obtained in step (1-2), preferably washing until the pH value of the product obtained in step (1-2) is between 6 and 8. This can improve the purity of the obtained product.

[0063] According to the present invention, the calcination conditions in step (1-3) include: a temperature of 300-500°C and a time of 3-6 hours. The calcination under this temperature condition can further improve the catalytic effect of the obtained indium oxide. The drying conditions can meet: a temperature of 60-90°C and a time of 12-24 hours.

[0064] In order to further improve the loading effect of the carrier on indium oxide and Pd, thereby further exerting the synergistic effect between indium oxide, Pd and the carrier, preferably, the carrier is prepared by a solvent evaporation induced self-assembly method. The carrier prepared by the solvent evaporation induced self-assembly method has an ordered mesoporous structure, which can further improve the loading effect on indium oxide and Pd, thereby improving the catalytic performance of the obtained catalyst.

[0065] Further preferably, the method for preparing the carrier comprises: mixing an acid, an aluminum precursor and a magnesium precursor in the presence of a surfactant and a solvent, and then drying and calcining.

[0066] According to the present invention, preferably, the surfactant is selected from at least one of P123, cetyltrimethylammonium bromide (CTAB), malic acid, sodium 2-ethylhexane sulfosuccinate and nonylphenol polyoxyethylene ether.

[0067] According to the present invention, preferably, the solvent is selected from at least one of methanol, ethanol, isopropanol, ethylene glycol, triethylene glycol and N,N-dimethylacetamide.

[0068] According to the present invention, preferably, the acid is at least one of nitric acid, hydrochloric acid and phosphoric acid.

[0069] According to the present invention, preferably, the aluminum precursor is at least one of aluminum isopropoxide, aluminum nitrate, aluminum chloride and aluminum sulfate.

[0070] According to the present invention, preferably, the magnesium precursor is selected from at least one of magnesium nitrate, magnesium chloride and magnesium sulfate.

[0071] Preferably, the molar ratio of the organic solvent, the surfactant, the acid and the aluminum precursor is 10 - 80:0.01 - 0.05:1 - 6:1. More preferably, it is 20 - 50:0.01 - 0.03:1.5 - 3:1. Research has shown that under the above conditions, the carrier has a higher loading rate of indium oxide and Pd, thereby effectively improving the catalytic effect of the catalyst.

[0072] According to the present invention, preferably, the mixing time of the acid, the aluminum precursor and the magnesium precursor is 3 - 9 h, which can make them have a better mixing effect. Preferably, the mixing is carried out under stirring conditions. The drying conditions can be: the temperature is 60 - 90 °C and the time is 36 - 60 h.

[0073] Preferably, the calcination conditions include: the temperature is 600 - 1200 °C and the time is 3 - 6 h. Research has shown that the carrier obtained under these calcination conditions has a better loading effect.

[0074] In order to further improve the catalytic effect of the catalyst, preferably, the calcination conditions in step (2) include: the temperature is 300 - 500 °C and the time is 1 - 5 h.

[0075] In order to further improve the loading effect of Pd on the carrier and thus improve the catalytic effect of the catalyst, preferably, the metal palladium salt in step (3) is selected from at least one of palladium nitrate, palladium chloride, palladium acetate, ammonium tetrachloropalladate, ammonium hexachloropalladate, dichlorodiamminepalladium and dichlorotetraamminepalladium.

[0076] Preferably, the contact conditions in step (3) include: carried out under stirring conditions, the temperature is 20 - 35 °C and the time is 0.5 - 2 h. Under these conditions, there can be a good loading effect and it will not affect the catalytic effects of the components in the catalyst.

[0077] Preferably, the concentration of the solution containing the metal palladium salt is 0.001 - 0.02% by weight.

[0078] In order to improve the drying effect and thus improve the catalytic effect of the catalyst, preferably, the drying is rotary evaporation drying. More preferably, the conditions of the rotary evaporation drying include: the temperature is 45 - 72 °C, the rotation speed is 10 - 30 rpm, the vacuum degree is 0.05 - 0.1 MPa, and the rotary evaporation time is 1 - 3 h.

[0079] Preferably, the calcination conditions in step (3) include: the temperature is 300 - 500 °C and the time is 1 - 5 h. At this calcination temperature, the catalyst has a good catalytic effect.

[0080] As described above, the third aspect of the present invention provides the application of the Pd-loaded magnesium-aluminum doped indium oxide catalyst described in the first aspect or the Pd-loaded magnesium-aluminum doped indium oxide catalyst prepared by the preparation method of the second aspect in the reaction of hydrogenating carbon dioxide to prepare methanol. Applying the catalyst provided by the present invention to the reaction of hydrogenating carbon dioxide to prepare methanol can significantly improve the selectivity of methanol and the conversion rate of carbon dioxide.

[0081] Preferably, in order to further improve the conversion rate of carbon dioxide and the selectivity of methanol, preferably, the conditions for the reaction of hydrogenating carbon dioxide to prepare methanol include: the reaction pressure is between 1.0 - 5.0 MPa, the reaction temperature is between 200 - 400 °C, the volumetric space velocity of the raw materials is between 4500 - 18000 h -1 -1 2 , and the H 2 2 -1 / CO 2 2 2 molar ratio is between 1 - 6. More preferably, the conditions for hydrogenating carbon dioxide include: the reaction pressure is between 3.0 - 5.0 MPa, the reaction temperature is between 240 - 280 °C, the volumetric space velocity of the raw materials is between 8000 - 12000 h

[0082] According to a particularly preferred embodiment of the present invention, a method for preparing a Pd-loaded magnesium-aluminum doped indium oxide catalyst is provided, and the method includes the following steps:

[0083] (1) Mix the carrier containing alumina and magnesia with indium oxide, place it in a ball mill for grinding, set the rotation speed of the ball mill to 200 - 800 rpm, and the ball milling time to 5 - 30 h;

[0084] Among them, the preparation method of indium oxide includes the following steps:

[0085] (a) Dropwise add the precipitant solution to the solution containing the metal indium precursor, and continuously stir during the dropping process and after the dropping is completed (the total stirring time is 1 - 10 h) to obtain a precipitation mother liquor; the metal indium precursor is at least one of In(NO 3 ) 3 3 3 and InCl

[0086] 3 , the precipitant is urea, the concentration of the solution containing the metal indium precursor is 0.1 - 1 mol / L, the concentration of the precipitant solution is 1 - 3 mol / L, the solvents in the solution containing the metal indium precursor and the precipitant solution are organic solvents and water, and the organic solvent is selected from at least one of methanol, ethanol, isopropanol, ethylene glycol, triethylene glycol, and N,N-dimethylacetamide;(b) Aging the precipitation mother liquor (at a temperature of 80 - 160 °C for 12 - 22 h) to form a precipitate;

[0087] (c) Separating the solid and liquid of the product obtained in step (b), and then drying (at a temperature of 60 - 90 °C for 12 - 24 h) and calcining (at a temperature of 300 - 500 °C for 3 - 6 h);

[0088] The preparation method of the carrier includes the following steps:

[0089] In the presence of a surfactant and in the presence of a solvent, mixing an acid, an aluminum precursor, and a magnesium precursor, and then drying (at a temperature of 60 - 90 °C for 36 - 60 h) and calcining (at a temperature of 600 - 1200 °C for 3 - 6 h); the surfactant is selected from at least one of P123, CTAB, malic acid, sodium 2 - ethylhexane sulfosuccinate, and nonylphenol polyoxyethylene ether; the solvent is selected from at least one of ethanol, methanol, isopropanol, ethylene glycol, triethylene glycol, and N,N - dimethylacetamide; the acid is nitric acid and / or hydrochloric acid; the aluminum source is at least one of aluminum isopropoxide, aluminum nitrate, aluminum chloride, and aluminum sulfate; the magnesium precursor is selected from at least one of magnesium nitrate, magnesium chloride, and magnesium sulfate, and the molar ratio of the organic solvent, the surfactant, the acid, and the aluminum precursor is 20 - 50:0.01 - 0.03:1.5 - 3:1;

[0090] (2) Calcining the product obtained in step (1) (at 300 - 500 °C for 1 - 5 h); obtaining a catalyst semi - product;

[0091] (3) Contacting a solution containing a metal palladium salt (0.005 - 0.02 wt%) with the catalyst semi - product at 20 - 35 °C for 0.5 - 2 h, then rotary evaporation drying at a temperature of 45 - 72 °C, a rotation speed of 10 - 30 rpm, and a vacuum degree of 0.05 - 0.1 MPa for 1 - 3 h, and finally calcining at 300 - 500 °C for 1 - 5 h;

[0092] Based on the total amount of the carrier and indium oxide, the content of indium oxide is 60 - 70 wt%, the content of magnesium oxide is 5 - 10 wt%, the content of aluminum oxide is 22 - 33 wt%, the mass ratio of indium oxide to the carrier is 1 - 3:1, and the amounts of the metal palladium salt and the catalyst semi - product are such that in the prepared catalyst, based on the total amount of the catalyst, the content of Pd is 0.75 - 15 wt%.

[0093] The present invention will be described in detail below through examples.

[0094] In the following examples, the gas chromatograph was purchased from Agilent Technologies (China) Co., Ltd.; P123 is poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), a commercially available product with the company number sigma-aldrich; absolute ethanol, urea, and nitric acid were purchased from Sinopharm Group.

[0095] Example 1

[0096] (1) Add 15.37 g of In(NO 3 ) 3 ·4H 2 O to a mixed solution of 80 mL of absolute ethanol and 48 mL of deionized water, and dissolve to obtain a solution containing a metal indium precursor. Add 16 g of urea to a mixed solution of 80 mL of absolute ethanol and 20 mL of deionized water, and dissolve to obtain a precipitant solution. At 25 °C, add the precipitant solution to the solution containing the metal indium precursor to obtain a precipitation mother liquor, stir well for 5 h, then add the precipitation mother liquor to a 100 mL hydrothermal synthesis reaction kettle with a polytetrafluoroethylene liner, place it in a blast drying oven and let it stand for aging. The aging temperature is 120 °C and the aging time is 20 h. After the hydrothermal synthesis reaction kettle naturally cools to room temperature, centrifuge the aging solution with deionized water until the pH is 7, then dry it at 60 °C for 20 h, and then calcine it at 350 °C for 3 h to obtain indium oxide. Perform XRD( Figure 1 ) characterization analysis on the obtained indium oxide. The results show that indium oxide has a hexagonal structure.

[0097] (2) Mix 4.6 g of P123 and 80 ml of absolute ethanol and dissolve them under ultrasonic waves; then add 6.4 mL of concentrated nitric acid. After clarification, add 5.2 g of aluminum isopropoxide and 3.2 g of magnesium nitrate; stir for 5 h, dry at 60 °C for 48 h, and finally calcine at 800 °C for 3 h to obtain a support. Perform XRD( Figure 2 ) characterization analysis on the obtained support. The results show that the support has an ordered mesoporous structure.

[0098] (3) Mix 2 g of indium oxide and 1 g of the support and put them into a ball mill. Set the ball mill speed to 300 rpm and the ball milling time to 5 h; then calcine the solid powder obtained after ball milling at 350 °C to obtain a catalyst semi-finished product.

[0099] (4) Weigh 0.057 g of palladium nitrate and dissolve it in 10 mL of deionized water to obtain a palladium salt solution. Weigh 2 g of the catalyst semi-finished product and put it into the palladium salt solution. Stir at 25 °C for 1 h, then rotary evaporate and dry at 45 °C, 20 ppm, and 0.1 MPa for 1.5 h. Finally, calcine at 350 °C for 4 h to obtain a catalyst. Press and sieve it into 40-60 mesh, and the composition is shown in Table 1.

[0100] (5) The reaction of hydrogenation of carbon dioxide to methanol was carried out in a stainless-steel reactor with an inner diameter of 8 mm, and the reaction conditions were as follows: 3.0 MPa, 280 °C, 10000 h -1 , n(H 2 ) / n(CO 2 ) = 4. The liquid-phase products were collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 2.

[0101] Example 2

[0102] (1) 7.21 g of In(NO 3 ) 3 ·4H 2 O was added to a mixed solution of 40 mL of absolute ethanol and 25 mL of deionized water to dissolve and obtain a solution containing a metal indium precursor. 8 g of urea was added to a mixed solution of 60 mL of absolute ethanol and 20 mL of deionized water to dissolve and obtain a precipitant solution. At 30 °C, the precipitant solution was added to the solution containing the metal indium precursor to obtain a precipitation mother liquor, which was stirred thoroughly for 6 h. Then, the precipitation mother liquor was added to a hydrothermal synthesis reactor with a 100 mL polytetrafluoroethylene inner liner and placed in a forced-air drying oven for static aging. The aging temperature was 140 °C, and the aging time was 15 h. After the hydrothermal synthesis reactor naturally cooled to room temperature, the aged solution was centrifuged with deionized water until the pH was 7.5, then dried at 60 °C for 24 h, and then calcined at 300 °C for 3 h to obtain indium oxide. The obtained indium oxide was characterized by XRD analysis, and the results showed that the indium oxide had a hexagonal structure.

[0103] (2) 3.8 g of P123 and 80 ml of absolute ethanol were mixed and dissolved under ultrasound; then 6.1 mL of concentrated nitric acid was added. After clarification, 9.5 g of aluminum isopropoxide and 1.59 g of magnesium nitrate were added; stirred for 5 h, dried at 60 °C for 48 h, and finally calcined at 800 °C for 3 h to obtain a support. The obtained support was characterized by XRD analysis, and the results showed that the support had an ordered mesoporous structure.

[0104] (3) 1 g of indium oxide and 1 g of the support were mixed and placed in a ball mill. The rotation speed of the ball mill was set at 500 rpm, and the ball milling time was 8 h; then the solid powder obtained after ball milling was calcined at 500 °C for 1 h to obtain a catalyst semi-finished product.

[0105] (4) 0.038 g of palladium nitrate was weighed and dissolved in 4 mL of deionized water to obtain a palladium salt solution. Then, 2 g of the catalyst semi-finished product was weighed and put into the palladium salt solution, stirred at 25 °C for 1 h, then rotary evaporated and dried at 45 °C, 20 ppm, and 0.1 MPa for 1 h, and finally calcined at 350 °C for 4 h to obtain a catalyst, which was pressed and sieved into 40-60 mesh, and the composition is shown in Table 1.

[0106] (5) The reaction of hydrogenating carbon dioxide to methanol was carried out in a stainless-steel reactor with an inner diameter of 8 mm, and the reaction conditions were as follows: 5.0 MPa, 200 °C, 6750 h -1 , n(H 2 ) / n(CO 2 ) = 6. The liquid-phase products were collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 2.

[0107] Example 3

[0108] (1) 8.43 g of In(NO 3 ) 3 ·4H 2 O was added to a mixed solution of 50 mL of absolute ethanol and 25 mL of deionized water to dissolve and obtain a solution containing a metal indium precursor. 8 g of urea was added to a mixed solution of 60 mL of absolute ethanol and 20 mL of deionized water to dissolve and obtain a precipitant solution. At 30 °C, the precipitant solution was added to the solution containing the metal indium precursor to obtain a precipitation mother liquor, which was stirred thoroughly for 4 h. Then, the precipitation mother liquor was added to a hydrothermal synthesis reaction kettle with a 100 mL polytetrafluoroethylene inner lining and placed in a blast drying oven for static aging. The aging temperature was 120 °C, and the aging time was 18 h. After the hydrothermal synthesis reaction kettle naturally cooled to room temperature, the aged solution was centrifuged with deionized water until the pH was 8, then dried at 60 °C for 15 h, and then calcined at 380 °C for 3 h to obtain indium oxide. The obtained indium oxide was characterized by XRD analysis, and the results showed that indium oxide had a hexagonal structure.

[0109] (2) 5.2 g of P123 and 100 ml of absolute ethanol were mixed and dissolved under ultrasound; then 7.3 mL of concentrated nitric acid was added. After clarification, 10.66 g of aluminum isopropoxide and 3.82 g of magnesium nitrate were added; stirred for 5 h, dried at 60 °C for 48 h, and finally calcined at 800 °C for 3 h to obtain a support. The obtained support was characterized by XRD analysis, and the results showed that the support had an ordered mesoporous structure.

[0110] (3) 1.8 g of indium oxide and 1.2 g of the support were mixed and placed in a ball mill. The rotation speed of the ball mill was set at 450 rpm, and the ball milling time was 6 h; then the solid powder obtained after ball milling was calcined at 400 °C for 3 h to obtain a catalyst semi-finished product.

[0111] (4) 0.038 g of palladium nitrate was weighed and dissolved in 5 mL of deionized water to obtain a palladium salt solution. Then, 1 g of the catalyst semi-finished product was weighed and put into the palladium salt solution, stirred at 25 °C for 1 h, then rotary evaporated and dried at 45 °C, 20 ppm, and 0.1 MPa for 3 h, and finally calcined at 350 °C for 4 h to obtain a catalyst, which was tableted and sieved into 40-60 mesh, and the composition is shown in Table 1.

[0112] (5) The reaction of hydrogenation of carbon dioxide to methanol was carried out in a stainless-steel reactor with an inner diameter of 8 mm, and the reaction conditions were as follows: 5.0 MPa, 340 °C, 18000 h -1 , n(H 2 ) / n(CO 2 ) = 4. The liquid-phase products were collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 1.

[0113] Example 4

[0114] (1) 10.3 g of In(NO 3 ) 3 ·4H 2 O was added to a mixed solution of 80 mL of absolute ethanol and 40 mL of deionized water to dissolve and obtain a solution containing a metal indium precursor. 9.2 g of urea was added to a mixed solution of 80 mL of absolute ethanol and 30 mL of deionized water to obtain a precipitant solution. At 30 °C, the precipitant solution was added to the solution containing the metal indium precursor to obtain a precipitation mother liquor, which was stirred thoroughly for 7 h. Then, the precipitation mother liquor was added to a hydrothermal synthesis reactor with a 100 mL polytetrafluoroethylene inner lining and placed in a forced-air drying oven for static aging. The aging temperature was 130 °C, and the aging time was 20 h. After the hydrothermal synthesis reactor naturally cooled to room temperature, the aging solution was centrifuged with deionized water until the pH was 6, then dried at 80 °C for 12 h, and then calcined at 450 °C for 3 h to obtain indium oxide. XRD characterization analysis was performed on the obtained indium oxide, and the results showed that indium oxide had a hexagonal structure.

[0115] (2) 4.7 g of P123 and 90 ml of absolute ethanol were mixed and dissolved under ultrasonic waves; then 7.6 mL of concentrated nitric acid was added. After clarification, 8.5 g of aluminum isopropoxide and 4.77 g of magnesium nitrate were added; it was stirred for 5 h, dried at 60 °C for 48 h, and finally calcined at 800 °C for 3 h to obtain a support. XRD characterization analysis was performed on the obtained support, and the results showed that the support had an ordered mesoporous structure.

[0116] (3) 2.8 g of indium oxide and 1.2 g of the support were mixed and placed in a ball mill. The rotation speed of the ball mill was set at 600 rpm, and the ball milling time was 10 h; then the solid powder obtained after ball milling was calcined at 450 °C for 3 h to obtain a catalyst semi-finished product.

[0117] (4) 0.061 g of palladium nitrate was weighed and dissolved in 10 mL of deionized water to obtain a palladium salt solution. Then, 2 g of the catalyst semi-finished product was weighed and put into the palladium salt solution, stirred at 25 °C for 1 h, then rotary evaporated and dried at 45 °C, 20 ppm, and 0.1 MPa for 2 h, and finally calcined at 350 °C for 4 h to obtain a catalyst, which was tableted and sieved into 40-60 mesh, and the composition is shown in Table 1.

[0118] (5) The reaction for hydrogenating carbon dioxide to produce methanol was carried out in a stainless-steel reactor with an inner diameter of 8 mm, and the reaction conditions were as follows: 1.0 MPa, 400 °C, 9000 h -1 、n(H 2 ) / n(CO 2 ) = 5. The liquid-phase product was collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 2.

[0119] Example 5

[0120] (1) 6.4 g of In(NO 3 ) 3 ·4H 2 O was added to a mixed solution of 40 mL of absolute ethanol and 20 mL of deionized water to dissolve and obtain a solution containing a metal indium precursor. 6 g of urea was added to a mixed solution of 50 mL of absolute ethanol and 20 mL of deionized water to obtain a precipitant solution. At 30 °C, the precipitant solution was added to the solution containing the metal indium precursor to obtain a precipitation mother liquor, which was stirred thoroughly for 6 h. Then, the precipitation mother liquor was added to a hydrothermal synthesis reactor with a 100 mL polytetrafluoroethylene inner liner and placed in a forced-air drying oven for static aging. The aging temperature was 150 °C, and the aging time was 16 h. After the hydrothermal synthesis reactor naturally cooled to room temperature, the mother solution was centrifuged with deionized water until the pH was 7.5, then dried at 80 °C for 14 h, and then calcined at 500 °C for 3 h to obtain indium oxide. XRD characterization and analysis were performed on the obtained indium oxide, and the results showed that indium oxide had a hexagonal structure.

[0121] (2) 7.3 g of P123 and 120 ml of absolute ethanol were mixed and dissolved under ultrasound; then 8.5 mL of concentrated nitric acid was added. After clarification, 4.2 g of aluminum isopropoxide and 5.73 g of magnesium nitrate were added; stirred for 5 h, dried at 60 °C for 48 h, and finally calcined at 800 °C for 3 h to obtain the carrier. SEM characterization and analysis were performed on the obtained carrier, and the results showed that the carrier had an ordered mesoporous structure.

[0122] (3) 1.6 g of indium oxide and 0.4 g of the carrier were mixed and placed in a ball mill. The rotation speed of the ball mill was set at 350 rpm, and the ball milling time was 15 h; then the solid powder obtained after ball milling was calcined at 550 °C for 3 h to obtain a catalyst semi-finished product.

[0123] (4) 0.046 g of palladium nitrate was weighed and dissolved in 8 mL of deionized water to obtain a palladium salt solution. Then, 2 g of the catalyst semi-finished product was weighed and put into the palladium salt solution, stirred at 25 °C for 1 h, then rotary evaporated and dried at 45 °C, 20 ppm, and 0.1 MPa for 3 h, and finally calcined at 350 °C for 4 h to obtain the catalyst, which was pressed and sieved into 40 - 60 mesh, and the composition is shown in Table 1.

[0124] (5) The reaction of hydrogenation of carbon dioxide to methanol was carried out in a stainless-steel reactor with an inner diameter of 8 mm, and the reaction conditions were as follows: 4.0 MPa, 240 °C, 13000 h -1 , n(H 2 ) / n(CO 2 ) = 6. The liquid-phase products were collected in an ice-water bath, and the product composition was analyzed by gas chromatography. The evaluation results are shown in Table 2.

[0125] Example 6

[0126] According to the method of Example 1, the difference is that the preparation of the support in step (2) includes:

[0127] 4.2 g of P123 and 80 ml of absolute ethanol were mixed and dissolved under ultrasound; then 6.4 mL of concentrated nitric acid was added. After clarification, 1.5 g of aluminum isopropoxide and 7.3 g of magnesium nitrate were added; stirred for 5 h, dried at 60 °C for 48 h, and finally calcined at 800 °C for 3 h to obtain the support. The obtained support was characterized by XRD analysis, and the results showed that the support had an ordered mesoporous structure.

[0128] The composition is shown in Table 1, and the evaluation results are shown in Table 2.

[0129] Example 7

[0130] According to the method of Example 1, the difference is that the preparation of the support in step (2) includes:

[0131] 4.2 g of P123 and 80 ml of absolute ethanol were mixed and dissolved under ultrasound; then 6.4 mL of concentrated nitric acid was added. After clarification, 6.7 g of aluminum isopropoxide and 1.5 g of magnesium nitrate were added; stirred for 5 h, dried at 60 °C for 48 h, and finally calcined at 800 °C for 3 h to obtain the support. The obtained support was characterized by XRD analysis, and the results showed that the support had an ordered mesoporous structure.

[0132] The composition is shown in Table 1, and the evaluation results are shown in Table 2.

[0133] Example 8

[0134] According to the method of Example 1, the difference is that the preparation method of the support is as follows: 9.6 g of aluminum nitrate and 3.2 g of magnesium nitrate were added to 500 mL of water to prepare a salt solution, and 6.5 g of sodium carbonate was added to 500 mL of deionized water to prepare a precipitant solution. The two solutions were subjected to co-current precipitation, controlling the pH at about 7.5. The mixed solution was stirred for 1 h, aged statically for 2 h, centrifugally washed 3 times with deionized water, dried at 60 °C for 48 h, and finally calcined at 800 °C for 3 h to obtain the support.

[0135] Comparative Example 1

[0136] (1) The preparation of indium oxide was the same as that in Example 1.

[0137] (2) The prepared indium oxide was evaluated for activity on a fixed-bed reactor. The reaction conditions were the same as those in Example 1, and the test results are shown in Table 2.

[0138] Comparative Example 2

[0139] (1) The indium oxide was prepared in the same manner as in Example 1.

[0140] (2) 0.057 g of palladium nitrate was weighed and dissolved in 10 mL of deionized water to obtain a palladium salt solution. Then, 2 g of indium oxide support was added to the palladium salt solution, and the mixture was stirred at 25 °C for 1 h. Then, it was rotary evaporated and dried at 45 °C, 20 ppm, and 0.1 MPa, and finally calcined at 350 °C for 4 h to obtain a catalyst, which was pressed and sieved to 40-60 mesh.

[0141] (3) The reaction conditions for the activity test were the same as those in Example 1, and the activity test results are shown in Table 2.

[0142] Comparative Example 3

[0143] (1) The indium oxide was prepared in the same manner as in Example 1.

[0144] (2) The support was prepared in the same manner as in Example 1.

[0145] (3) 2 g of indium oxide and 1 g of the support were mixed and placed in a ball mill. The rotation speed of the ball mill was set at 300 rpm, and the ball milling time was 5 h. Then, the solid powder obtained after ball milling was calcined at 350 °C to obtain a catalyst.

[0146] (4) The reaction conditions for the activity test were the same as those in Example 1, and the activity test results are shown in Table 2.

[0147] Table 1

[0148]

[0149] Note: The content of each component in Table 1 is in mass percentage

[0150] Table 2

[0151]

[0152]

[0153] It can be seen from the results in Table 2 that, compared with Comparative Examples 1-3, using the catalysts of Examples 1-7 of the present invention for catalytic hydrogenation of carbon dioxide can effectively improve the conversion rate of carbon dioxide and the selectivity of methanol, indicating that the catalysts within the protection scope of the present invention have good catalytic effects and good methanol selectivity.

[0154] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A Pd-loaded magnesium-aluminum doped indium oxide catalyst, which catalyst comprises Pd, an active component, and a support. The active component is indium oxide, and the support comprises magnesium oxide and aluminum oxide. Based on the total amount of the active component and the support, the content of the active component is 50-85% by weight, and the content of the support is 15-50% by weight. Based on the total amount of the catalyst, the content of Pd is 0.01-1.5% by weight; The mass ratio of the active component to the support is 1-6:1; Magnesium oxide accounts for 0.75-15% of the total mass of the active component and the support; Aluminum oxide accounts for 10.5-47.5% of the total mass of the active component and the support; As determined by XRD, the indium oxide has a hexagonal structure; The support has an ordered mesoporous structure; A method for preparing a Pd-loaded magnesium-aluminum doped indium oxide catalyst, which method comprises: (1) Mixing a support containing aluminum oxide and magnesium oxide with indium oxide, and then optionally pulverizing; (2) Calcining the product obtained in step (1) to obtain a catalyst semi-finished product; (3) Contacting a solution containing a metal palladium salt with the catalyst semi-finished product, and then drying and calcining.

2. The catalyst according to claim 1, wherein, Based on the total amount of the active component and the support, the content of the active component is 60-70% by weight, and the content of the support is 30-40% by weight.

3. The catalyst according to claim 1, wherein, Based on the total amount of the catalyst, the content of Pd is 0.75-1.5% by weight.

4. The catalyst according to claim 1, wherein, The mass ratio of the active component to the support is 1-3:

1.

5. The catalyst according to any one of claims 1-4, wherein, Magnesium oxide accounts for 5-10% of the total mass of the active component and the support; aluminum oxide accounts for 22-33% of the total mass of the active component and the support.

6. A method for preparing a Pd-loaded magnesium-aluminum doped indium oxide catalyst according to any one of claims 1-5, which method comprises: (1) Mixing a support containing aluminum oxide and magnesium oxide with indium oxide, and then optionally pulverizing; (2) Calcining the product obtained in step (1) to obtain a catalyst semi-finished product; (3) Contacting a solution containing a metal palladium salt with the catalyst semi-finished product, and then drying and calcining; Based on the total amount of the support and indium oxide, the content of indium oxide is 50-85% by weight, and the content of the support is 15-50% by weight; The amounts of the metal palladium salt and the catalyst semi-finished product are such that in the prepared catalyst, based on the total amount of the catalyst, the content of Pd is 0.01-1.5% by weight.

7. The preparation method according to claim 6, wherein, Based on the total amount of the support and indium oxide, the content of indium oxide is 60-70% by weight, and the content of the support is 30-40% by weight.

8. The preparation method according to claim 6, wherein, The amounts of the metal palladium salt and the catalyst semi-finished product are such that in the prepared catalyst, based on the total amount of the catalyst, the content of Pd is 0.75-1.5% by weight.

9. The preparation method according to claim 6, wherein, The mass ratio of indium oxide to the support is 1-6:

1.

10. The preparation method according to claim 9, wherein, the mass ratio of indium oxide to the carrier is 1-3:

1.

11. The preparation method according to claim 6, wherein, magnesium oxide in the carrier accounts for 0.75-15% of the total mass of indium oxide and the carrier, and alumina in the carrier accounts for 10.5-47.5% of the total mass of indium oxide and the carrier.

12. The preparation method according to claim 11, wherein, magnesium oxide in the carrier accounts for 5-10% of the total mass of indium oxide and the carrier, and alumina in the carrier accounts for 22-33% of the total mass of indium oxide and the carrier.

13. The preparation method according to claim 6, wherein, the preparation of the indium oxide comprises the following steps: (1-1) Mixing a solution containing a metal indium precursor with a precipitant solution to obtain a precipitation mother liquor; (1-2) Aging the precipitation mother liquor to form a precipitate; (1-3) Separating the solid and liquid of the product obtained in step (1-2), and then performing drying and calcination.

14. The preparation method according to claim 13, wherein, the solvents in the solution containing the metal indium precursor and the precipitant solution are independently organic solvents and / or water.

15. The preparation method according to claim 14, wherein, the solvents in the solution containing the metal indium precursor and the precipitant solution are organic solvents and water, and the organic solvent is selected from at least one of methanol, ethanol, isopropanol, ethylene glycol, triethylene glycol, and N,N-dimethylacetamide.

16. The preparation method according to claim 13, wherein, the concentration of the solution containing the metal indium precursor is 0.1-1 mol / L.

17. The preparation method according to claim 13, wherein, the concentration of the precipitant solution is 1-3 mol / L.

18. The preparation method according to claim 13, wherein, the precipitant is urea.

19. The preparation method according to claim 13, wherein, the mixing in step (1-1) is carried out under stirring conditions.

20. The preparation method according to claim 19, wherein, the mixing in step (1-1) is carried out for 1-10 h under stirring conditions.

21. The preparation method according to claim 13, wherein, the aging conditions in step (1-2) include: temperature is 80-160 °C, and time is 12-22 h.

22. The preparation method according to claim 13, wherein, the method further comprises washing the product obtained in step (1-2).

23. The preparation method according to claim 22, wherein, washing until the pH value of the product obtained in step (1-2) is between 6-8.

24. The preparation method according to claim 13, wherein, the calcination conditions in step (1-3) include: temperature is 300-500 °C, and time is 3-6 h.

25. The preparation method according to claim 6, wherein, the preparation method of the carrier containing alumina and magnesium oxide comprises: mixing an acid, an aluminum precursor, and a magnesium precursor in the presence of a surfactant and in the presence of a solvent, and then performing drying and calcination.

26. The preparation method according to claim 25, Among them, the surfactant is selected from at least one of P123, cetyltrimethylammonium bromide, malic acid, sodium 2-ethylhexane sulfosuccinate, and nonylphenol polyoxyethylene ether; the solvent is selected from at least one of ethanol, methanol, isopropanol, ethylene glycol, triethylene glycol, and N,N-dimethylacetamide; the acid is at least one of nitric acid, hydrochloric acid, and phosphoric acid; the aluminum precursor is selected from at least one of aluminum isopropoxide, aluminum nitrate, aluminum chloride, and aluminum sulfate.

27. According to the preparation method described in claim 25, Among them, the mixing time of the acid, aluminum precursor, and magnesium precursor is 3 - 9 h.

28. According to the preparation method described in claim 27, Among them, the mixing is carried out under stirring conditions.

29. According to the preparation method described in claim 25, Among them, the conditions for roasting include: the temperature is 600 - 1200 °C, and the time is 3 - 6 h.

30. According to the preparation method described in any one of claims 6 - 29, Among them, the conditions for roasting in step (2) include: the temperature is 300 - 500 °C, and the time is 1 - 5 h.

31. According to the preparation method described in any one of claims 6 - 29, Among them, the metal palladium salt in step (3) is selected from at least one of palladium nitrate, palladium chloride, palladium acetate, ammonium tetrachloropalladate, ammonium hexachloropalladate, dichlorodiamminepalladium, and dichlorotetraamminepalladium.

32. According to the preparation method described in any one of claims 6 - 29, Among them, the conditions for contacting in step (3) include: carried out under stirring conditions, the temperature is 20 - 35 °C, and the time is 0.5 - 2 h.

33. According to the preparation method described in any one of claims 6 - 29, Among them, the concentration of the solution containing the metal palladium salt is 0.001 - 0.02 wt%.

34. According to the preparation method described in any one of claims 6 - 29, Among them, the drying is rotary evaporation drying.

35. According to the preparation method described in claim 34, Among them, the conditions for rotary evaporation drying include: the temperature is 45 - 72 °C, the rotation speed is 10 - 30 rpm, the vacuum degree is 0.05 - 0.1 MPa, and the rotary evaporation time is 1 - 3 h.

36. According to the preparation method described in any one of claims 6 - 29, Among them, the conditions for roasting in step (3) include: the temperature is 300 - 500 °C, and the time is 1 - 5 h.

37. Application of the Pd-loaded magnesium-aluminum doped indium oxide catalyst described in any one of claims 1 - 5 or the Pd-loaded magnesium-aluminum doped indium oxide catalyst prepared by the preparation method described in any one of claims 6 - 36 in the reaction of hydrogenating carbon dioxide to produce methanol.

38. According to the application described in claim 37, Among them, The conditions for the reaction of hydrogenation of carbon dioxide to methanol include: the reaction pressure is between 1.0 - 5.0 MPa, the reaction temperature is between 200 - 400 °C, the raw material volume space velocity is between 4500 - 18000 h -1 between, H 2 / CO 2 The molar ratio is between 1 - 6.

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