Preparation method and application of catalyst for preparing methanol through low-temperature carbon dioxide hydrogenation

Abstract

The invention provides a preparation method of a catalyst for preparing methanol through low-temperature carbon dioxide hydrogenation, which comprises the following steps: (1) adding a metal solution and a molybdenum source into water, stirring, evaporating to dryness, grinding into powder, and roasting in a muffle furnace after grinding to obtain an oxide precursor; (2) roasting the oxide precursor in CH4 / H2 gas for carburizing treatment to obtain a metal-loaded catalyst; and (3) carrying out passivating treatment on the metal-loaded catalyst in oxidizing gas. The catalyst provided by the invention can be used for a reaction for preparing methanol through hydrogenation of carbon dioxide, and a result shows that the catalyst prepared by the invention can control phase change by using metal, generates defective stable metal atoms in the phase change process, regulates and controls the valence state of the metal, greatly increases the selectivity of methanol, and realizes the feasibility of preparing methanol at a low temperature. The method provided by the invention creates a promising way for preparing methanol through high-selectivity low-temperature carbon dioxide hydrogenation.

Description

Technical Field

[0001] The invention relates to the field of catalytic technology, in particular to the preparation of a rhodium-based catalyst for low-temperature reaction and its application in the reaction of hydrogenating carbon dioxide to produce methanol. Background Art

[0002] With the increasing global attention to the sustainable use of non-petroleum carbon resources, carbon dioxide (CO2) as a major greenhouse gas, its accumulation in the atmosphere will lead to global warming and climate change. Therefore, the conversion of CO2 into high value-added products has become a hot topic of concern. Methanol is an important raw material in the chemical industry and is widely used in the production of a series of chemicals, such as formaldehyde, acetic acid and olefins. Methanol itself can also be used as an alternative fuel for internal combustion engines or to produce more complex fuels. In addition, methanol can also be used to produce hydrogen, which is then used in fuel cells, making it an important player in the future energy system. The rise of renewable energy has provided new opportunities for CO2 hydrogenation to methanol. For example, hydrogen produced by renewable energy (such as wind power, solar energy, etc.) can be combined with CO2 captured from the air or industrial emissions to achieve methanol production, thereby reducing greenhouse gas emissions and achieving energy storage and efficient utilization. At present, the catalyst system for CO2 hydrogenation to methanol mainly includes Cu-based catalysts, metal oxide catalysts and precious metal catalysts (Menghao Ren, Yanmin Zhang, XuanWang and Hengshan Qiu, Catalytic hydrogenation of CO2 to methanol: A review[j]. Catalysts, 2022, 12, 1–33; Biao Gao, Zhang Wen, Yifu Wang and Donghang Chen et al., Recent advances in alloy catalysts for CO2 hydrogenation to methanol[j]. ChemCatChem, 2024, 16, 1–16.); Among them, Cu-based catalysts have low cost and are suitable for large-scale production, but are prone to reverse water gas reaction to produce more CO, and Cu is prone to agglomeration and sintering after long-term reaction; while metal oxide catalysts with semiconductor properties, such as indium oxide (In2O3), show good selectivity and activity in CO2 hydrogenation, but are relatively expensive; although precious metal catalysts have high CO2 activation ability and can react at low temperatures, they are expensive and have poor stability.

[0003] Single-atom catalysts (SACs) have been one of the research hotspots in the field of catalysis in recent years due to their high utilization efficiency of metal atoms, mainly because they can significantly reduce the metal dosage of the catalyst, thereby reducing the consumption of precious metals and reducing costs. The active sites of single atoms in SACs greatly increase the contact area between the reactants and the catalyst, thereby improving the activity of the catalytic reaction. Thanks to their unique structure and properties, SACs are suitable for various catalytic reactions, including oxidation, reduction, C–H activation, and CO2 hydrogenation, showing great potential (Manoj B. Gawande, Katsuhiko Ariga, and Yusuke Yamauchi, Single-atom catalysts [j]. Small, 2021, 17, 1–4.). However, SACs still face a series of challenges and problems in practical applications; for example: during the reaction, single-atom metals are prone to migration or changes in binding with the support, which may cause changes in the catalytic active sites and reduce the catalytic effect or even deactivation. In addition, the active sites in SACs may be highly sensitive to certain reactants or by-products, and the water or oxygen atoms produced in the reaction may also affect the single-atom metal, resulting in catalyst deactivation (Xiao Zhang, Mengtao Zhang, Yuchen Deng and Mingquan Xu et al., A stable low-temperature H2-production catalyst by crowding Pt on α-MoC[j]. Nature, 2021, 589, 396–401.). The performance of SACs also strongly depends on the support material. As the basis for the dispersion of single-atom metals, the support must ensure that the metal atoms can be evenly dispersed on its surface to avoid aggregation caused by uneven dispersion, which leads to reduced catalytic performance. Transition metal carbides (TMCs) as commonly used catalyst support materials not only have excellent chemical stability, but also have good electrical and thermal conductivity.As one of the important family members of TMC, molybdenum carbide (MoC) has shown excellent development potential in the field of catalysis. Studies have shown that there is a strong metal-support interaction (SMSI) between MoC and supported metals (Jinhu Dong, Qiang Fu, Zheng Jiang and Bingbao Mei et al., Carbide-supported Au catalysts for water-gas shift reactions: A new territory for the strong metal-support interaction effect [j]. J. Am. Chem. Soc. 2018, 140, 13808–13816.). However, the synthesis of carbides usually requires high temperature and high pressure. For example, the common synthesis method of α-MoC currently requires high-temperature calcination in an NH3 atmosphere to undergo topological changes, and then react with a carbon source at high temperature; such harsh and dangerous reaction conditions increase the cost of the process and the insecurity of the technology, and also bring challenges to the research of MoC. In summary, the realization of CO2 hydrogenation to methanol at low temperature still faces many challenges, and how to obtain a catalyst with high selectivity and high stability still requires design planning. In view of this, this patent application is hereby filed. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a rhodium-based catalyst for low-temperature reaction, and to use the catalyst treated by the method for hydrogenating carbon dioxide to produce methanol, thereby solving the current problems of generally high reaction temperature, obvious water-gas reverse reaction and unstable catalyst.

[0005] To achieve the above-mentioned object of the invention, the solution of the present invention is:

[0006] A method for preparing a catalyst for preparing methanol by low-temperature carbon dioxide hydrogenation comprises the following steps:

[0007] (1) adding a metal rhodium salt solution and a molybdenum source into water, stirring and evaporating the mixture to dryness, grinding the dried solid into powder, and calcining the obtained powder to obtain a catalyst oxide precursor;

[0008] (2) subjecting the catalyst oxide precursor obtained in step (1) to carburization treatment in CH4 / H2 gas to obtain a metal rhodium-loaded catalyst;

[0009] (3) The metal rhodium-loaded catalyst prepared in step (2) is passivated in an oxidizing gas.

[0010] Preferably, the metal rhodium salt described in step (1) is one of rhodium acetate, rhodium nitrate or rhodium chloride.

[0011] Preferably, the molybdenum source in step (1) is one of ammonium molybdate, molybdenum trioxide or molybdenum chloride.

[0012] Preferably, the calcination temperature in step (1) is 400-600° C., and the calcination time is 3-5 hours.

[0013] Preferably, the carburizing treatment conditions described in step (2) are: CH4 / H2 mixed gas is selected as the carburizing gas, the carburizing treatment temperature is 600-800°C, the carburizing treatment time is 2-3h, and the flow rate of the carburizing gas is 50-250mL / min.

[0014] Preferably, the passivation treatment conditions described in step (3) are: using an O2 / N2 mixed gas containing low concentration of oxygen as the passivation gas, the passivation treatment time is 6 to 8 hours, and the flow rate of the passivation gas is 30 to 60 mL / min.

[0015] The catalyst prepared by the above-mentioned method for preparing a catalyst for preparing methanol by hydrogenation of low-temperature carbon dioxide is characterized in that the catalyst uses precious metal rhodium as an active component and molybdenum carbide as a catalyst carrier, and its general formula can be expressed as Rh x -Mo n C; wherein the catalyst carrier is one of β-phase dimolybdenum carbide or α-phase monomolybdenum carbide; the content of the metal rhodium is 0.01% to 5%, and the balance is the carrier.

[0016] The specific steps of using the above catalyst in preparing methanol from carbon dioxide are as follows: in a continuous flow fixed bed reactor, the reaction mixture is brought into contact with the catalyst to react.

[0017] Preferably, the reaction mixture is a mixture of CO2, H2 and N2, the gas flow rate of the reaction mixture is 10 to 50 mL / min, the reaction temperature is 30 to 230°C, and the reaction pressure is 2 to 5 MPa.

[0018] The design principle of the present invention is as follows:

[0019] The preparation method of the catalyst provided by the present invention mainly utilizes the carbonization process to load the metal Rh on the molybdenum carbide carrier, and the presence of the metal Rh realizes the in-situ conversion of molybdenum oxide into molybdenum carbide directly in the atmosphere of CH4 / H2 as a carbon source; at the same time, during the in-situ change process, Rh enters the lattice of the Mo-C matrix, which also ensures that Rh can be evenly and stably dispersed on the molybdenum carbide carrier. The atomically dispersed Rh forms an asymmetric local environment with the surrounding Mo, realizing the conversion of CO2 hydrogenation. Specifically, the atomic-level Rh-Mo asymmetric structure in the catalyst prepared by the present invention causes the deformation of the C-O double bond in the adsorbed CO2, because Rh is more inclined to bond with C, while Mo with oxygen-philic properties tends to combine with O, and such adsorption causes the molecular structure of CO2 to bend, thereby helping to break the C-O double bond. Therefore, using a catalyst with such a structure can obtain higher methanol selectivity and higher atomic utilization at low temperatures. Secondly, the carrier MoC used in the preparation method of the catalyst for preparing methanol by hydrogenation of low-temperature carbon dioxide provided by the present invention is to directly complete the structural transformation in the CH4 / H2 carbon source atmosphere by adding a trace amount of rhodium: the carbon produced by the dissociation of CH4 at a higher temperature will enter the Mo-O lattice, and in this in-situ change process, Rh will also enter the Mo-O lattice at the same time, so that atomic-level dispersed Rh can be obtained. As mentioned above, because Rh occupies the position of Mo in the carrier, it causes lattice defects and structural distortion of the MoC matrix, thus forming an asymmetric Rh-Mo local environment with the surrounding Mo, and the carbon affinity of Rh and the oxygen affinity of Mo cause the molecular structure of the adsorbed CO2 to bend and deform, which is conducive to the breaking of the C-O double bond, and the formed *CO intermediate can be hydrogenated to form methanol. It is worth mentioning that only a small amount of CH4 and CO will be produced in this reaction process, thereby reducing the methanation reaction and the reverse water gas reaction, which is conducive to improving the selectivity of methanol and the utilization rate of atoms. In addition, there are dynamic changes in carbon during the reaction process of preparing the catalyst: carbon migrates to the surrounding of Rh to form an appropriate carbon layer distributed on its surface, which can not only stabilize the interaction between Rh and MoC and reduce the surface oxidation of Rh, but also further stabilize the Rh single atom.

[0020] Compared with the existing catalyst for the reaction of hydrogenating carbon dioxide to produce methanol and its preparation method, the method provided by the present invention has the following beneficial effects:

[0021] (1) The preparation method provided by the present invention can omit the topological change process of molybdenum oxide undergoing a high-temperature reaction in an NH3 atmosphere, making the operation of forming a MoC structure safer and saving energy consumption.

[0022] (2) The catalyst preparation method provided by the present invention has the advantages of simple operation method and mild operation conditions, and the preparation process is also safer, more reliable, energy-saving and environmentally friendly.

[0023] (3) The catalyst provided by the present invention can not only improve the selectivity of the product methanol in the CO2 hydrogenation reaction, but also improve the utilization efficiency of metal atoms. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The XRD pattern of the catalyst prepared by the present invention;

[0025] Figure 2 The catalyst Rh prepared in Example 1 0.05 -Spherical aberration electron microscope image of MoC;

[0026] Figure 3 The catalyst Rh prepared in Example 1 0.05 -MoC stability data graph;

[0027] Figure 4 Rh 0.05 -MoC, Rh 0.5 -Raman spectra of MoC and Rh5-MoC before and after reaction. DETAILED DESCRIPTION

[0028] The present application is further described in detail below through the accompanying drawings and embodiments. Through these descriptions, the characteristics and advantages of the present application will become clearer and more specific.

[0029] The reagent ammonium molybdate ((NH4)6Mo7O 24 ·4H2O), ferric nitrate (Fe(NO3)3·9H2O), cobalt nitrate (Co(NO3)2·6H2O), copper nitrate (Cu(NO3)2·3H2O), ruthenium acetylacetonate (C 15 H 21 O6Ru), rhodium acetate (C 14 H 21 O 15 Rh3·3H2O), palladium acetate (C4H6O4Pd), silver nitrate (AgNO3), platinum acetylacetonate (C 10 H 14 O4Pt) ​​and chloroauric acid (HAuCl4) can be purchased through commercial channels. Before the experiment, rhodium acetate and chloroauric acid can be prepared into aqueous solutions, with the concentration of Rh solution being 2 mg / mL and the concentration of Au solution being 0.47 mg / mL.

[0030] Example 1

[0031] The steps for preparing the catalyst are as follows:

[0032] (1) Weigh 3 g of ammonium molybdate ((NH4)6Mo7O 24·4H2O, purity is AR grade), 0.46mL of rhodium acetate solution is mixed with 30mL of water and stirred at room temperature for 4h; then the obtained mixture is heated to 90°C and continued to be stirred until evaporated to dryness, the obtained solid is dried in an oven at 100°C for 8h, the dried solid is ground into powder and calcined in a muffle furnace at 500°C for 4h to obtain a catalyst precursor;

[0033] (2) transferring the catalyst precursor prepared in step (1) to a tubular furnace and performing carburizing treatment in a 20% CH4 / 80% H2 atmosphere, first heating to 300°C at a rate of 5°C / min and then heating to 700°C at a rate of 1°C / min and continuing heating for 2h, with a CH4 / H2 flow rate of 150mL / min, and cooling to obtain a catalyst containing a carburizing material;

[0034] (3) The catalyst containing carburizing material prepared in step (2) is passivated at room temperature for 6 hours under 1% O2 / N2 atmosphere. The obtained catalyst is denoted as Rh 0.05 -MoC; wherein the mass fraction of Rh is 0.05%. The obtained catalyst was characterized by XRD, and the specific results are as follows Figure 1 As shown in a: The results show that the Rh in the prepared catalyst will enter the MoC matrix. The obtained catalyst was photographed by spherical aberration electron microscope, and the specific results are as follows Figure 2 As shown: The results show that Rh in the prepared catalyst is dispersed at the atomic level and uniformly dispersed on MoC.

[0035] The evaluation steps of the catalyst are as follows:

[0036] 0.3 g of Rh 0.05 -MoC catalyst was mixed with 1.7g quartz sand and filled in a quartz tube and placed in a continuous flow fixed bed reactor. 15% CH4 / H2 was introduced at normal pressure, and the temperature was raised to 590°C and heated for 2h to activate the catalyst; after cooling, a mixed gas of 24% CO2 / 72% H2 / 4% N2 was introduced for reaction. The reaction pressure was 3MPa, the reaction temperature was 110°C, and the mixed gas flow rate was 20mL / min. The product was analyzed online using an Agilent 7890 gas chromatograph equipped with a flame ionization detector (FID), and the capillary column was KB-PONA. CH4, CO, CO2, and N2 were analyzed online using a GC2060 gas chromatograph equipped with a thermal conductivity detector (TCD), and the filling column was TDX-01. The catalytic results are shown in Table 1, and the stability data of the catalyst are shown in Table 1. Figure 3 Shown: From Figure 3 It can be seen that at 110 °C, the catalyst Rh 0.05 -MoC can run stably for more than 100 hours.

[0037] Example 2

[0038] The preparation steps of the catalyst are as described in Example 1, except that the amount of the rhodium acetate solution in step (1) is changed to 4.6 mL, and the remaining steps are the same as those in Example 1.

[0039] The obtained catalyst was recorded as Rh 0.5 -MoC; wherein the mass fraction of Rh is 0.5%.

[0040] The catalyst evaluation procedure is similar to that of Example 1, except that the catalyst is replaced with Rh 0.5 -MoC catalyst, and the other operating conditions were the same as those in Example 1; the catalytic results are shown in Table 1.

[0041] Example 3

[0042] The preparation steps of the catalyst are the same as those of Example 1, except that the amount of rhodium acetate in step (1) is changed to 0.229 g, and the remaining steps are the same as those of Example 1.

[0043] The obtained catalyst is recorded as Rh5-MoC, wherein the mass fraction of Rh is 5%.

[0044] The catalyst evaluation steps refer to Example 1, except that the catalyst is replaced with Rh5-MoC catalyst, and the other operating conditions are the same as Example 1; the catalytic results are shown in Table 1.

[0045] The catalysts after the reaction of Examples 1-3 were subjected to Raman characterization test. The results are as follows: Figure 4 As shown in a: After the reaction is completed, a carbon layer will be deposited on the catalyst surface, which indicates that there is a dynamic change of carbon in the gas phase CO2. After the reaction, the catalyst has a Raman characteristic peak belonging to the carbon layer, a D peak representing defective carbon species, and a G peak representing graphite structure; and the peak intensity signal is: Rh5-MoC>Rh 0.5 -MoC>Rh 0.05 -MoC, which indicates that Rh acts as a capture agent during carbon deposition, capturing carbon in the gas phase around Rh atoms. Figure 4 b also shows that for the position covered by the carbon layer, the vibration peak intensity of the Mo–O Raman band is very weak. However, for the position without the carbon layer, the vibration peak intensity of the Mo–O Raman band is very strong. Therefore, the coverage of the carbon layer can prevent Rh from being oxidized.

[0046] Table 1: Catalyst activity test results

[0047]

[0048] Comparative Example 1

[0049] The steps for preparing the catalyst are as follows:

[0050] (1) Weigh 3 g of ammonium molybdate ((NH4)6Mo7O 24 4H2O, purity AR grade) was ground into powder and then transferred to a muffle furnace and calcined at 500℃ for 4h to obtain MoO3;

[0051] (2) placing 1 g of MoO3 prepared in step (1) in a tubular furnace, introducing NH3 gas, first heating to 300°C at 5°C / min and then heating to 700°C at 2°C / min and continuing heating for 2 h, with an NH3 flow rate of 100 mL / min. During this process, the topological structure of MoO3 changes, and Mo2N is obtained after cooling;

[0052] (3) Carburizing the Mo2N prepared in step (2) in a 20% CH4 / 80% H2 atmosphere, first heating to 300°C at 5°C / min and then heating to 700°C at 2°C / min and continuing heating for 2h, with a CH4 / H2 flow rate of 150mL / min, and obtaining a catalyst containing a carburizing material after cooling;

[0053] (4) The catalyst containing carburizing material prepared in step (3) is passivated for 6 hours in a 1% O2 / N2 atmosphere.

[0054] The obtained catalyst was recorded as MoC.

[0055] The evaluation steps of the catalyst refer to Example 1, except that the catalyst is replaced with MoC catalyst and the other operating conditions are the same as Example 1. The catalytic results are shown in Table 1.

[0056] Comparative Example 2

[0057] The steps for preparing the catalyst are as follows:

[0058] (1) Weighing 0.8 g of MoC prepared according to Comparative Example 1 and adding 0.20 mL of rhodium acetate solution to impregnate for 8 h; then transferring the mixture to a vacuum drying oven and drying at 80° C., grinding the obtained solid into powder to obtain a catalyst precursor;

[0059] (2) placing the catalyst precursor obtained in step (1) in a tube furnace, raising the temperature to 400° C. and calcining for 2 h in a 20% CH4 / 80% H2 atmosphere with a CH4 / H2 gas flow rate of 150 mL / min; cooling to obtain a metal impregnated catalyst;

[0060] (3) The metal impregnated catalyst obtained in step (2) is passivated at room temperature for 6 hours in a 1% O2 / N2 atmosphere.

[0061] The obtained catalyst was recorded as Rh0.05 / MoC; wherein the Rh loading is 0.05%. The obtained catalyst was characterized by XRD, and the specific results are as follows Figure 1 As shown in a: The results show that the XRD diffraction peak of MoC in the prepared catalyst did not shift, indicating that Rh is basically on the surface of MoC.

[0062] The catalyst evaluation procedure is similar to that of Example 1, except that the catalyst is replaced with Rh 0.05 / MoC catalyst, and the rest of the operations were the same as in Example 1. The catalytic results are shown in Table 1.

[0063] Comparative Example 3

[0064] The steps for preparing the catalyst are as follows:

[0065] (1) Weigh 1.226 g of ammonium molybdate ((NH4)6Mo7O 24 ·4H2O, AR grade purity), 0.015g of ferric nitrate (Fe(NO3)3·9H2O, AR grade purity) and 30mL of water were mixed and stirred at room temperature for 4h, then heated to 90°C and continued to stir until the mixture was evaporated to dryness, the obtained solid was dried in an oven at 100°C for 8h, the dried solid was ground into powder and calcined in a muffle furnace at 500°C for 4h to obtain a catalyst precursor;

[0066] (2) transferring the catalyst precursor prepared in step (1) to a tubular furnace and performing carburizing treatment in a 20% CH4 / 80% H2 atmosphere, first heating to 300°C at 5°C / min, then heating to 700°C at 1°C / min and continuing heating for 2h, with a CH4 / H2 flow rate of 150mL / min, and cooling to obtain a catalyst containing a carburizing material;

[0067] (3) The catalyst containing carburizing material prepared in step (2) is passivated for 6 hours in a 1% O2 / N2 atmosphere.

[0068] The obtained catalyst was recorded as Fe-MoC x The Fe loading is 0.26% to 0.28%. The XRD scanning of the prepared catalyst is shown in the following results: Figure 1 As shown in b: The presence of a small amount of Fe cannot obtain the MoC structure, and the structure after carburizing is Mo2C.

[0069] The catalyst evaluation procedure is similar to that of Example 1, except that the catalyst is replaced with Fe-MoC x The catalyst and other operating conditions are the same as those in Example 1. The catalytic results are shown in Table 1.

[0070] Comparative Example 4

[0071] The preparation steps of the catalyst refer to Comparative Example 3, except that the iron nitrate in step (1) is replaced with 0.0099 g of cobalt nitrate (Co(NO3)2·6H2O, purity is AR grade), and the remaining steps are the same as Comparative Example 3.

[0072] The obtained catalyst was recorded as Co-MoC x The loading amount of Co is 0.26% to 0.28%. The XRD scanning of the prepared catalyst is shown in the following results: Figure 1 As shown in b: The presence of a small amount of Co cannot obtain the MoC structure, and the structure after carburizing is Mo2C.

[0073] The catalyst was evaluated with reference to Example 1, except that the catalyst was replaced with Co-MoC x The catalyst and other operations are the same as those in Example 1. The catalytic results are shown in Table 1.

[0074] Comparative Example 5

[0075] The preparation steps of the catalyst refer to Comparative Example 3, except that the iron nitrate in step (1) is replaced with 0.0076 g of copper nitrate (Cu(NO3)2·3H2O, purity is AR grade), and the remaining steps are the same as Comparative Example 3.

[0076] The obtained catalyst was recorded as Cu-MoC x The Cu loading is 0.26% to 0.28%. The XRD scanning of the prepared catalyst is shown in the following results: Figure 1 As shown in b: The presence of a small amount of Cu cannot obtain the MoC structure, and the structure after carburizing is Mo2C.

[0077] The catalyst evaluation procedure is similar to that of Example 1, except that the catalyst is replaced with Cu-MoC x The catalyst and other operations are the same as those in Example 1. The catalytic results are shown in Table 1.

[0078] Comparative Example 6

[0079] The preparation steps of the catalyst refer to Comparative Example 3, except that the iron nitrate in step (1) is replaced with 0.0079 g of ruthenium acetylacetonate (C 15 H 21 O6Ru, purity is AR grade), and the remaining steps are the same as those in Comparative Example 3.

[0080] The obtained catalyst was recorded as Ru-MoC x The Ru loading is 0.26% to 0.28%. The XRD scan of the prepared catalyst shows the following results: Figure 1As shown in b: The presence of a small amount of Ru can obtain MoC, but it cannot completely transform Mo–O into MoC. What is prepared is a mixed phase of MoC and Mo2C.

[0081] The catalyst evaluation procedure is similar to that of Example 1, except that the catalyst is replaced with Ru-MoC x The catalyst and other operations are the same as those in Example 1. The catalytic results are shown in Table 1.

[0082] Comparative Example 7

[0083] The preparation steps of the catalyst refer to Comparative Example 3, except that the iron nitrate in step (1) is replaced with 0.0042 g of palladium acetate (C4H6O4Pd, purity is AR grade), and the remaining steps are the same as Comparative Example 3.

[0084] The obtained catalyst was recorded as Pd-MoC x The Pd loading is 0.26% to 0.28%. The XRD scan of the prepared catalyst is shown in the following figure. Figure 1 As shown in b: The presence of a small amount of Pd can obtain MoC, and the prepared structure is MoC.

[0085] The catalyst evaluation procedure is similar to that of Example 1, except that the catalyst is replaced with Pd-MoC x The catalyst and other operations are the same as those in Example 1. The catalytic results are shown in Table 1.

[0086] Comparative Example 8

[0087] The preparation steps of the catalyst refer to Comparative Example 3, except that the iron nitrate in step (1) is replaced with 0.0031 g of silver nitrate (AgNO3, purity is AR grade), and the remaining steps are the same as Comparative Example 3.

[0088] The obtained catalyst was recorded as Ag-MoC x The loading amount of Ag is 0.26% to 0.28%. The XRD scanning of the prepared catalyst is shown in the following results: Figure 1 As shown in b: The presence of a small amount of Ag cannot obtain the MoC structure, and the structure after carburization is Mo2C.

[0089] The catalyst evaluation procedure is similar to that of Example 1, except that the catalyst is replaced with Ag-MoC x The catalyst and other operations are the same as those in Example 1. The catalytic results are shown in Table 1.

[0090] Comparative Example 9

[0091] The preparation steps of the catalyst refer to Comparative Example 3, except that the iron nitrate in step (1) is replaced with 0.0040 g of platinum acetylacetonate (C10 H 14 O4Pt, purity is AR grade), and the remaining steps are the same as those in Comparative Example 3.

[0092] The obtained catalyst was recorded as Pt-MoC x The Pt loading is 0.26% to 0.28%. The XRD scan of the prepared catalyst is shown in the following figure. Figure 1 As shown in b: The presence of a small amount of Pt can obtain MoC, but it cannot completely transform Mo–O into MoC. What is prepared is a mixed phase of MoC and Mo2C.

[0093] The catalyst evaluation procedure is similar to that of Example 1, except that the catalyst is replaced with Pt-MoC x The catalyst and other operations are the same as those in Example 1. The catalytic results are shown in Table 1.

[0094] Comparative Example 10

[0095] The preparation steps of the catalyst refer to Comparative Example 3, except that the iron nitrate in step (1) is replaced with 4.22 mL of Au solution, and the remaining steps are the same as Comparative Example 3.

[0096] The obtained catalyst was recorded as Au-MoC x The Au loading is 0.26% to 0.28%. The XRD scan of the prepared catalyst shows the following results: Figure 1 As shown in b: The presence of a small amount of Au cannot obtain the MoC structure, and the structure after carburization is Mo2C.

[0097] The catalyst evaluation procedure is similar to that in Example 1, except that the catalyst is replaced with Au-MoC x The catalyst and other operations are the same as those in Example 1. The catalytic results are shown in Table 1.

Claims

1. A method for preparing a catalyst for low-temperature carbon dioxide hydrogenation to methanol, characterized in that: The following steps are involved: (1) adding a metal rhodium salt solution and a molybdenum source into water, stirring and evaporating the mixture to dryness, grinding the dried solid into powder, and calcining the obtained powder to obtain a catalyst oxide precursor; (2) subjecting the catalyst oxide precursor obtained in step (1) to carburization treatment in CH4 / H2 gas to obtain a metal rhodium-loaded catalyst; (3) The metal rhodium-loaded catalyst prepared in step (2) is passivated in an oxidizing gas.

2. The method for preparing a catalyst for preparing methanol by low-temperature carbon dioxide hydrogenation according to claim 1, characterized in that: The metal rhodium salt described in step (1) is one of rhodium acetate, rhodium nitrate or rhodium chloride.

3. The method for preparing a catalyst for preparing methanol by low-temperature carbon dioxide hydrogenation according to claim 1, characterized in that: The molybdenum source described in step (1) is one of ammonium molybdate, molybdenum trioxide or molybdenum chloride.

4. The method for preparing a catalyst for preparing methanol by low-temperature carbon dioxide hydrogenation according to claim 1, characterized in that: The calcination temperature in step (1) is 400-600° C., and the calcination time is 3-5 hours.

5. The method for preparing a catalyst for preparing methanol by low-temperature carbon dioxide hydrogenation according to claim 1, characterized in that: The carburizing treatment conditions described in step (2) are: using CH4 / H2 mixed gas as the carburizing gas, the carburizing treatment temperature is 600-800°C, the carburizing treatment time is 2-3h, and the carburizing gas flow rate is 50-250mL / min.

6. The method for preparing a catalyst for preparing methanol by low-temperature carbon dioxide hydrogenation according to claim 1, characterized in that: The passivation treatment conditions described in step (3) are: using an O2 / N2 mixed gas containing low-concentration oxygen as the passivation gas, the passivation treatment time is 6 to 8 hours, and the flow rate of the passivation gas is 30 to 60 mL / min.

7. The catalyst prepared by the method for preparing a catalyst for preparing methanol by low-temperature carbon dioxide hydrogenation according to claims 1-6, characterized in that: The catalyst uses precious metal rhodium as an active component and molybdenum carbide as a catalyst carrier. Its general formula can be expressed as Rh x -Mo n C; wherein the catalyst carrier is one of β-phase dimolybdenum carbide or α-phase monomolybdenum carbide; the content of the metal rhodium is 0.01% to 5%, and the balance is the carrier.

8. The preparation method according to claims 1-6 or the use of the catalyst according to claim 7 in preparing methanol from carbon dioxide, characterized in that: The specific steps are as follows: in a continuous flow fixed bed reactor, the reaction mixture gas is contacted with the catalyst to react.

9. The use of the rhodium-based catalyst according to claim 8 in preparing methanol by hydrogenation of carbon dioxide, characterized in that: The reaction mixed gas is a mixed gas composed of CO2, H2 and N2, the gas flow rate of the reaction mixed gas is 10-50 mL / min, the reaction temperature is 30-230° C., and the reaction pressure is 2-5 MPa.

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