A catalyst for the hydrogenation of carbon dioxide to methanol and its preparation method

Abstract

This invention relates to a catalyst for the hydrogenation of carbon dioxide to methanol and its preparation method. The catalyst consists of a modified ZnAl spinel phase support and a highly dispersed copper particle active phase supported on the modified ZnAl spinel phase support. The chemical formula of the modified ZnAl spinel phase support is ZnAl₂O₄-M, where M is a doped metal selected from one or more of Mn, Fe, and Ce. Compared with the prior art, this invention can solve the problems of poor Cu particle dispersion, easy sintering, insufficient stability, and low CO₂ conversion and methanol selectivity in copper-based catalysts for hydrogenation to methanol.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology and relates to a catalyst for the hydrogenation of carbon dioxide to methanol and its preparation method. Background Technology

[0002] Currently, the core catalytic materials for CO2 hydrogenation to methanol are mainly copper (Cu)-based catalysts. Existing technologies of this type mainly include the following categories: Traditional co-precipitation CuZnAl catalysts are the most widely used system in industry. This involves mixing copper, zinc, and aluminum salts in a specific ratio, adding a precipitant (such as sodium carbonate or ammonia) to generate a co-precipitate, and then drying and calcining it to obtain the catalyst. Its core structure consists of Cu particles dispersed on the surface of a ZnO-Al2O3 composite support, relying on the interaction between Cu-Zn-Al to provide catalytic activity. Hydrothermal CuZnAl catalysts are a commonly used improved method in laboratories. A metal salt solution is placed in a hydrothermal reactor and reacted under high temperature and high pressure (typically 100-200℃, 1-10MPa) to generate a precursor, which is then calcined to obtain the catalyst. The catalyst prepared by this method exhibits better Cu particle dispersion than the traditional co-precipitation method. Chinese patent application CN117463361A discloses a noble metal-doped modified Cu-based catalyst, using platinum group metals (such as Pt and Pd) doped Cu-ZnO. The active component is prepared by dissolving copper nitrate, zinc nitrate and 2,5-dihydroxyterephthalic acid in ethanol and reacting them hydrothermally to prepare CuZn-MOF-74 precursor, calcining it in air to obtain CuO-ZnO precursor, and then impregnating it with platinum group metals by hydrothermal method and reducing it to obtain the catalyst. The hydrophobically modified doped Cu-based catalyst disclosed in Chinese patent application CN120618483A uses manganese-doped CuZnAlMn catalyst as a base and obtains it by hydrophobic modification. The preparation steps include the precipitation method to synthesize CuZnAlMn catalyst, the hydrophobic nanoporous polyvinylbenzene prepared by dissolving divinylbenzene and epoxy resin in DMF by hydrothermal reaction, and the two are mixed, ground and pressed into tablets to obtain the final catalyst.

[0003] The catalysts provided by the aforementioned prior art have the following drawbacks: Traditional co-precipitation CuZnAl catalysts suffer from low CO2 conversion (typically below 10%), poor methanol selectivity (below 50%), and short lifespan. The core reason is the poor dispersibility of Cu particles, which easily agglomerate and sinter during the reaction, reducing active sites. Simultaneously, the ZnO-Al2O3 support structure lacks stability, and the pores are prone to collapse, further reducing catalytic performance. While hydrothermal CuZnAl catalysts improve Cu dispersibility and lifespan, they suffer from high cost and difficulty in industrial application. Hydrothermal reactions require specialized high-temperature and high-pressure equipment, resulting in high energy consumption and equipment investment, and low production efficiency, failing to meet the economic requirements for large-scale industrial production. Noble metal-doped Cu-based catalysts (CN117463361A) improve stability and activity, but their preparation process is complex and extremely costly. On the one hand, platinum group metals are expensive, significantly increasing catalyst costs; on the other hand, MOFs... The multi-step process of precursor preparation and precious metal impregnation prolongs the production process and increases the difficulty of operation; the hydrophobically modified Cu-based catalyst (CN120618483A) has the problem of complicated preparation process and is not conducive to industrial promotion. It requires the separate synthesis of catalyst substrate and hydrophobic polymer, followed by multiple steps such as mixing, grinding and tableting. The process is complicated, the production cycle is long, and it is difficult to adapt to continuous industrial production. Summary of the Invention

[0004] The purpose of this invention is to provide a catalyst for the hydrogenation of carbon dioxide to methanol and its preparation method, so as to solve at least one of the problems of poor Cu particle dispersion, easy sintering, insufficient stability, and low catalytic performance (CO2 conversion rate, methanol selectivity) of copper-based catalysts for hydrogenation to methanol.

[0005] The objective of this invention can be achieved through the following technical solutions: In a first aspect, the present invention provides a catalyst for the hydrogenation of carbon dioxide to methanol, comprising a modified ZnAl spinel phase support and a highly dispersed copper particle active phase supported on the modified ZnAl spinel phase support, wherein the chemical formula of the modified ZnAl spinel phase support is ZnAl2O4-M, wherein M is a doped metal selected from one or more of Mn, Fe, and Ce.

[0006] The modified spinel phase (ZnAl2O4-M) of this invention can strongly restrict the migration and aggregation of copper particles through the "anchoring effect" of the spinel structure, thereby improving its anti-sintering ability. The doping of metal M (Mn, Fe, Ce) can optimize the electronic structure and surface acidity of the support, enhance the interaction between copper and the support, and regulate the CO2 adsorption activation efficiency.

[0007] Furthermore, the highly dispersed copper particle active phase, based on the mass of CuO, accounts for 10-70% of the total mass of the catalyst. In addition, the particle size of the main (generally above 70%) copper particle active phase is 20-50 nm.

[0008] Highly dispersed copper particles (20-50nm) have the largest specific surface area and active site density within this size range, which can significantly improve the catalytic activity of CO2 hydrogenation reaction; the copper content is controlled between 1% and 70%, which can be adapted to different reaction conditions. Low copper content reduces costs, while high copper content increases the reaction rate, ensuring the practicality and flexibility of the catalyst.

[0009] Furthermore, in the modified ZnAl spinel phase support, the doping amount of M is 1~10% relative to the total mass of the catalyst (based on the mass of M oxide).

[0010] In a second aspect, the present invention provides a method for preparing a catalyst for the hydrogenation of carbon dioxide to methanol, which is prepared by using Zn salt, Al salt, doped metal M salt, Cu salt and template agent as raw materials and employing a template-deposition precipitation method.

[0011] Furthermore, the template-deposition precipitation method includes the following steps: S1. Prepare a mixed solution of Zn salt, Al salt, doped metal M salt and template agent, add precipitant, react, filter to obtain precipitate, dry and calcine in two stages to obtain modified ZnAl spinel phase support; S2. Prepare a suspension containing modified ZnAl spinel phase support, Cu salt and template agent, add precipitant, react, filter to obtain precipitate, continue drying and calcining to obtain catalyst.

[0012] Furthermore, in the above preparation method, the template agent is selected from at least one of polyethylene glycol (PEG), polypropylene glycol (PPG), and polyvinyl alcohol (PVA), and its concentration in the mixed solution of S1 or the suspension of S2 is 1~50 g / L. The role of the template agent is to construct a hierarchical porous structure during the formation of the carrier, increase the specific surface area of ​​the carrier, and provide spatial sites for the highly dispersed loading of copper particles.

[0013] Furthermore, the precipitant is selected from ammonia, ammonium carbonate, ammonium bicarbonate, and sodium carbonate, and its addition amount is sufficient to adjust the pH of the reaction system S1 or S2 to 6-8, ensuring sufficient precipitation of metal ions and a uniform precipitate structure. Additionally, a pH deviation from the 6.0-8.0 range will affect the precipitation efficiency and product structure.

[0014] Furthermore, in the above preparation method, the two-stage calcination process in S1 is as follows: first, calcination at 200-300℃ for 1-3 hours to remove impurities such as template agents and residual solvents from the precipitate; then, calcination at 400-800℃ for 2-5 hours to form a stable ZnAl2O4-M spinel phase and convert the copper precursor into a highly active CuO species. Here, the order of the two calcination stages is not interchangeable. Impurities must be removed first in the low-temperature stage, followed by high-temperature calcination to form the target phase. Direct high-temperature calcination would cause rapid decomposition of impurities, damaging the support structure.

[0015] Furthermore, the Zn salt is zinc nitrate or zinc acetate, the Al salt is aluminum nitrate or aluminum sulfate, the doped metal M salt is a nitrate, acetate or chloride of Mn, Fe or Ce, and the Cu salt is at least one of copper nitrate, copper chloride or copper sulfate.

[0016] Furthermore, the calcination process in S2 is as follows: first, calcination is carried out at 200~300℃ for 1~3h to gently remove PEG used as a dispersant and pore-forming agent in the loading system, avoiding rapid carbonization and carbon deposition of organic matter covering the active sites; then, calcination is carried out at 400~800℃ for 2~5h to form a highly dispersed CuO active phase, which strengthens the strong interaction between the metal and the support.

[0017] Compared with the prior art, the present invention has the following advantages: (1) The copper-based spinel catalyst provided in this application has high copper nanoparticle dispersion. The introduced doped metal further enhances the spinel anchoring effect, which can greatly limit the sintering deactivation of copper particles, improve the catalyst lifespan, and enhance the interaction between copper and the support, improve the adsorption strength of intermediate species CO, and suppress side reactions. This invention innovatively introduces a template agent in the spinel preparation and copper loading process, realizing precise control of its microstructure. In the precipitation stage, the steric hindrance effect of the polymer template agent effectively inhibits the early aggregation of the metal precursor, ensures the highly uniform dispersion of the active component, and provides more sites for the controllable nucleation of metal ions, thereby avoiding particle unevenness caused by local rapid nucleation; in the calcination stage, the template agent coated by the precursor decomposes at high temperature, forming a multi-level mesoporous structure inside the spinel, providing more sufficient loading space and channels for the mass transfer of copper active phase and reactants; in the reaction stage, this unique structure significantly enhances the dispersion of copper active phase and the number of metal-support interface sites. Furthermore, this catalyst structure exhibits stronger resistance to sintering, and the pore collapse and particle agglomeration phenomena in the post-reaction sample are significantly less pronounced than in the unmodified catalyst. Compared to existing methanol catalysts, the present invention demonstrates substantial improvements in CO2 conversion, methanol selectivity, methanol space-time yield, and stability.

[0018] (2) In terms of preparation process, none of the three preparation methods require complex equipment (such as high temperature and high pressure hydrothermal reactor). The core process is solution mixing, precipitation, drying and calcination, which can be adapted to continuous industrial production and is simple to operate. No precious metal doping is required. The raw materials are conventional metal salts and template agents, which are inexpensive. The preparation process has no additional energy consumption and complex steps, which reduces the total production cost and makes the cost controllable. No toxic or harmful substances are generated in the reaction process. The wastewater generated by filtration and washing can meet the discharge standards after conventional treatment, which is green and environmentally friendly.

[0019] (3) In terms of social and economic effects, this invention helps reduce CO2 emissions and utilize hydrogen energy storage and transportation, alleviates the greenhouse effect, and promotes the realization of the "dual carbon" goal. Methanol, as a high energy density fuel and chemical raw material, has a wide range of downstream applications and can drive the development of related industries, which has significant social value. The catalyst preparation cost is reduced by more than 30% (compared to the precious metal doping scheme), and the methanol yield is increased by 15%~50%, which greatly reduces the unit cost of methanol synthesis, improves the economy and competitiveness of industrial production, and has outstanding economic effects. Attached Figure Description

[0020] Figure 1 The X-ray diffraction patterns of the catalysts obtained in the embodiments and comparative examples of this application are shown below. Figure 2 The above are the H2-TPR spectra of the catalysts obtained in the examples and comparative examples of this application. Figure 3 The images show SEM images of the catalysts obtained in the embodiments and comparative examples of this application. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0023] As used herein, the terms "and / or," "or / and," and "and / or" encompass any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that, in this application, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR."

[0024] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0025] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0026] This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0027] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument, such as ±5°C, ±4°C, ±3°C, ±2°C, or ±1°C.

[0028] In this document, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0029] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0030] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0031] In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0032] Unless otherwise specified, all preparations and tests described herein took place at 25°C.

[0033] The terms “comprising,” “including,” “containing,” “having,” “comprising,” or other variations thereof are intended to cover non-closed inclusion, and no distinction is made between these terms. The term “comprising” means that other steps and ingredients may be added without affecting the final result. The compositions and methods / processes of the present invention comprise, consist of, and substantially consist of the essential elements and limitations described herein, as well as any additional or optional ingredients, components, steps, or limitations described herein. No distinction is made between the terms “efficacy,” “performance,” “effect,” and “potency” herein.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but sequentially is preferred.

[0036] The specific preparation process for obtaining the carbon dioxide hydrogenation to methanol catalyst required by this invention is as follows: Firstly, the preparation of the spinel carrier: First, reagents and equipment are prepared. Reagents include Zn(NO3)2·6H2O, Al(NO3)3·9H2O, Cu(NO3)2·3H2O, PEG, (NH4)2CO3 and deionized water; equipment includes beakers, stirrers, constant-rate dropping devices, vacuum filtration devices, ovens, muffle furnaces, electronic balances and ultrasonic instruments.

[0037] The specific steps are as follows: First, prepare the mixed solution. Take deionized water and add Zn(NO3)2・6H2O, Al(NO3)3・9H2O, and the doped metal salt in sequence. Stir until completely dissolved to obtain a metal salt mixed solution. Then, take 40 ml of deionized water, add the template agent, and stir until completely dissolved to obtain a template agent solution. Mix the metal salt mixed solution and the template agent solution thoroughly and stir for 30 minutes to obtain template agent-mixed salt solution A. In addition, take 100 ml of deionized water, add (NH4)2CO3, and stir until completely dissolved to obtain an alkaline precipitant solution B.

[0038] The second step is the precipitation reaction. The template agent-mixed salt solution A is placed on a stirrer and continuously stirred (300 r / min). The precipitant solution B is added dropwise to solution A at a rate of 1.5 ml / min using a constant-rate dropping device. The pH value of the system is monitored in real time during the dropping process. When the pH reaches 8.0, the dropping is stopped, resulting in suspension C. Suspension C is allowed to stand at room temperature for 18 hours (the aging time can be adjusted within the range of 6 to 24 hours; for example, 18 hours can be selected to ensure sufficient precipitation). Then, it is filtered through a vacuum filtration device, and the filter cake is washed with deionized water.

[0039] The third step is drying and calcination. The washed filter cake is placed in an oven and dried at 60℃ for 12 hours to obtain a dry solid. The dry solid is then ground into powder and placed in a muffle furnace for two-stage calcination: the first stage temperature is 250℃ and held for 2 hours (to remove PEG and residual moisture); the second stage temperature is 450℃ and held for 4 hours (to form a stable ZnAl2O4 spinel phase). After calcination, the mixture is naturally cooled to room temperature to obtain the finished catalyst.

[0040] Secondly, copper loading involves a process similar to the steps described above, including solution preparation, precipitation reaction, drying, and two-stage calcination.

[0041] Regarding the steps and their connections, in the preferred embodiment of this invention, the mixing order of the metal salt and template agent in step 1 should preferably not be reversed. It is preferable to dissolve the metal salt first and then add the template agent to ensure that the template agent is uniformly dispersed in the metal salt solution, avoiding excessively high local concentrations that could lead to uneven pore structure. Simultaneously, the dropping rate and pH value in step 2 are also key parameters. An excessively fast dropping rate can lead to rapid local precipitation and particle agglomeration. A pH deviation from the 6.0-8.0 range can affect precipitation efficiency and product structure, all of which can negatively impact catalyst performance. The two-stage calcination sequence in step 3 cannot be interchanged. Impurities must be removed first in the low-temperature stage, followed by high-temperature calcination to form the target phase. Direct high-temperature calcination will cause rapid decomposition of impurities, damaging the support structure. The connection relationship of the components in the catalyst is that highly dispersed CuO particles are uniformly loaded onto the pore surface and outer surface of the ZnAl2O4-M spinel support, forming a stable "support-active phase" structure through the anchoring effect of the spinel phase. Figure 1 The XRD pattern clearly shows the uniform dispersion of Cu particles, and the SEM image in Figure 3 clearly shows the porous structure of the support.

[0042] The present invention will now be described in more detail with reference to specific embodiments and experimental data.

[0043] Example 1 (1) Dissolve 2.677g Zn(NO3)2·6H2O, 6.751g Al(NO3)3·9H2O, 0.465ml 50 wt% Mn(NO3)2 solution and 2g PEG-6000 in 40ml deionized water to obtain metal salt solution A.

[0044] (2) Dissolve 9.6g of (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution B. Under continuous stirring, add alkaline solution B dropwise to the salt solution A obtained in step (1) at a rate of 1.5ml / min until the pH of the system is 8 to obtain suspension C.

[0045] (3) After the suspension C obtained in step (2) was left to stand at room temperature for 18 hours, it was filtered and washed until no residual salt was found. The obtained sample was dried in an oven at 60°C for 12 hours. Then the ground solid powder was placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 600°C for 4 hours to obtain ZnAl2O4-Mn support.

[0046] (4) Weigh 0.9100g Cu(NO3)2·3H2O and 2g PEG-6000 and dissolve them in 50mL of deionized water. After they are fully dissolved, mix them together and add 1.0g of the above carrier. Stir well for 2h to obtain suspension D.

[0047] (5) Dissolve 0.96g (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution E. Under continuous stirring, add alkaline solution E dropwise to suspension D obtained in step (4) at a rate of 1.5ml / min until the pH of the system is 7.5 to obtain suspension E.

[0048] (6) After the suspension E obtained in step (5) was allowed to stand at room temperature for 18 hours, it was filtered and washed until no PEG and residual salt were found. The obtained sample was dried in an oven at 60°C for 12 hours. Then the ground solid powder was placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 450°C for 4 hours to obtain the catalyst.

[0049] Example 2 (1) Dissolve 2.677g Zn(NO3)2·6H2O, 6.751g Al(NO3)3·9H2O, 0.808g Fe(NO3)3·9H2O and 2g PEG-6000 in 40ml of deionized water to obtain metal salt solution A.

[0050] (2) Dissolve 9.6g of (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution B. Under continuous stirring, add alkaline solution B dropwise to the salt solution A obtained in step (1) at a rate of 1.5ml / min until the pH of the system is 8 to obtain suspension C.

[0051] (3) After the suspension C obtained in step (2) was left to stand at room temperature for 18 hours, it was filtered and washed until no residual salt was found. The obtained sample was dried in an oven at 60°C for 12 hours. Then the ground solid powder was placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 600°C for 4 hours to obtain ZnAl2O4-Fe support.

[0052] (4) Weigh 0.9100g Cu(NO3)2·3H2O and 2g PEG-6000 and dissolve them in 50mL of deionized water. After they are fully dissolved, mix them together and add 1.0g of the above carrier. Stir well for 2h to obtain suspension D.

[0053] (5) Dissolve 0.96g (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution E. Under continuous stirring, add alkaline solution E dropwise to suspension D obtained in step (4) at a rate of 1.5ml / min until the pH of the system is 7.5 to obtain suspension E.

[0054] (6) After the suspension E obtained in step (5) was left to stand at room temperature for 18 hours, it was filtered and washed until no PEG and residual salt were found. The obtained sample was dried in an oven at 60°C for 12 hours. Then the ground solid powder was placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 450°C for 4 hours to obtain the catalyst.

[0055] Example 3 (1) Dissolve 2.677g Zn(NO3)2·6H2O, 6.751g Al(NO3)3·9H2O, 0.868g Ce(NO3)3·6H2O and 2g PEG-6000 in 40ml of deionized water to obtain metal salt solution A.

[0056] (2) Dissolve 9.6g of (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution B. Under continuous stirring, add alkaline solution B dropwise to the salt solution A obtained in step (1) at a rate of 1.5ml / min until the pH of the system is 8 to obtain suspension C.

[0057] (3) After the suspension C obtained in step (2) was left to stand at room temperature for 18 hours, it was filtered and washed until no residual salt was found. The obtained sample was dried in an oven at 60°C for 12 hours. Then the ground solid powder was placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 600°C for 4 hours to obtain ZnAl2O4-Ce support.

[0058] (4) Weigh 0.9100g Cu(NO3)2·3H2O and 2g PEG-6000 and dissolve them in 50mL of deionized water. After they are fully dissolved, mix them together and add 1.0g of the above carrier. Stir well for 2h to obtain suspension D.

[0059] (5) Dissolve 0.96g (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution E. Under continuous stirring, add alkaline solution E dropwise to suspension D obtained in step (4) at a rate of 1.5ml / min until the pH of the system is 7.5 to obtain suspension E.

[0060] (6) After the suspension E obtained in step (5) was left to stand at room temperature for 18 hours, it was filtered and washed until no PEG and residual salt were found. The obtained sample was dried in an oven at 60°C for 12 hours. Then the ground solid powder was placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 450°C for 4 hours to obtain the catalyst.

[0061] Comparative Example 1 The process is basically the same as in Example 1, except that the template agent PEG is omitted during spinel synthesis and copper precipitation. Specifically: (1) Dissolve 2.677g Zn(NO3)2·6H2O, 6.751g Al(NO3)3·9H2O and 0.465ml 50 wt% Mn(NO3)2 solution in 40ml deionized water to obtain metal salt solution A.

[0062] (2) Dissolve 9.6g of (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution B. Under continuous stirring, add alkaline solution B dropwise to the salt solution A obtained in step (1) at a rate of 1.5ml / min until the pH of the system is 8 to obtain suspension C.

[0063] (3) After the suspension C obtained in step (2) was left to stand at room temperature for 18 hours, it was filtered and washed until no residual salt was found. The obtained sample was dried in an oven at 60°C for 12 hours. Then the ground solid powder was placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 600°C for 4 hours to obtain ZnAl2O4-Mn support.

[0064] (4) Weigh 0.9100g Cu(NO3)2·3H2O and dissolve it in 100mL of deionized water. After it is fully dissolved, add 1.0g of the above carrier and stir thoroughly for 2h to obtain suspension D.

[0065] (5) Dissolve 0.96g (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution E. Under continuous stirring, add alkaline solution E dropwise to suspension D obtained in step (4) at a rate of 1.5ml / min until the pH of the system is 7.5 to obtain suspension E.

[0066] (6) After the suspension E obtained in step (5) is left to stand at room temperature for 18 hours, it is filtered and washed until no residual salt is found. The obtained sample is dried in an oven at 60°C for 12 hours. Then the ground solid powder is placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 450°C for 4 hours to obtain the catalyst.

[0067] Comparative Example 2 Similar to Example 2, except that the template agent was omitted during spinel synthesis and copper precipitation. Specifically: (1) Dissolve 2.677g Zn(NO3)2·6H2O, 6.751g Al(NO3)3·9H2O and 0.808g Fe(NO3)3·9H2O in 40ml of deionized water to obtain metal salt solution A.

[0068] (2) Dissolve 9.6g of (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution B. Under continuous stirring, add alkaline solution B dropwise to the salt solution A obtained in step (1) at a rate of 1.5ml / min until the pH of the system is 8 to obtain suspension C.

[0069] (3) After the suspension C obtained in step (2) was left to stand at room temperature for 18 hours, it was filtered and washed until no residual salt was found. The obtained sample was dried in an oven at 60°C for 12 hours. Then the ground solid powder was placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 600°C for 4 hours to obtain ZnAl2O4-Fe support.

[0070] (4) Weigh 0.9100g Cu(NO3)2·3H2O and dissolve it in 100mL of deionized water. After it is fully dissolved, add 1.0g of the above carrier and stir thoroughly for 2h to obtain suspension D.

[0071] (5) Dissolve 0.96g (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution E. Under continuous stirring, add alkaline solution E dropwise to suspension D obtained in step (4) at a rate of 1.5ml / min until the pH of the system is 7.5 to obtain suspension E.

[0072] (6) After the suspension E obtained in step (5) is left to stand at room temperature for 18 hours, it is filtered and washed until no residual salt is found. The obtained sample is dried in an oven at 60°C for 12 hours. Then the ground solid powder is placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 450°C for 4 hours to obtain the catalyst.

[0073] Comparative Example 3 Similar to Example 3, except that the template agent was omitted in the spinel synthesis and copper precipitation process, specifically: (1) 2.677g Zn(NO3)2·6H2O, 6.751g Al(NO3)3·9H2O and 0.868g Ce(NO3)3·6H2O solution were dissolved in 40ml deionized water to obtain metal salt solution A.

[0074] (2) Dissolve 9.6g of (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution B. Under continuous stirring, add alkaline solution B dropwise to the salt solution A obtained in step (1) at a rate of 1.5ml / min until the pH of the system is 8 to obtain suspension C.

[0075] (3) After the suspension C obtained in step (2) was left to stand at room temperature for 18 hours, it was filtered and washed until no residual salt was found. The obtained sample was dried in an oven at 60°C for 12 hours. Then the ground solid powder was placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 600°C for 4 hours to obtain ZnAl2O4-Ce support.

[0076] (4) Weigh 0.9100g Cu(NO3)2·3H2O and dissolve it in 100mL of deionized water. After it is fully dissolved, add 1.0g of the above carrier and stir thoroughly for 2h to obtain suspension D.

[0077] (5) Dissolve 0.96g (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution E. Under continuous stirring, add alkaline solution E dropwise to suspension D obtained in step (4) at a rate of 1.5ml / min until the pH of the system is 7.5 to obtain suspension E.

[0078] (6) After the suspension E obtained in step (5) is left to stand at room temperature for 18 hours, it is filtered and washed until no residual salt is found. The obtained sample is dried in an oven at 60°C for 12 hours. Then the ground solid powder is placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 450°C for 4 hours to obtain the catalyst.

[0079] Comparative Example 4 Similar to Example 1, the main differences are that the addition of doping metals and template agents was omitted during spinel synthesis and copper precipitation, and the amounts of Zn salt and Al salt were slightly adjusted to meet the requirements for ZnAl2O4 support preparation. Specifically: (1) Dissolve 2.974g Zn(NO3)2·6H2O and 7.5028g Al(NO3)3·9H2O in 40ml of deionized water to obtain metal salt solution A.

[0080] (2) Dissolve 9.6g of (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution B. Under continuous stirring, add alkaline solution B dropwise to the salt solution A obtained in step (1) at a rate of 1.5ml / min until the pH of the system is 8 to obtain suspension C.

[0081] (3) After the suspension C obtained in step (2) is left to stand at room temperature for 18 hours, it is filtered and washed until no residual salt is found. Then, it is calcined at 250℃ for 2 hours and 600℃ for 4 hours to obtain the ZnAl2O4 support.

[0082] (4) Weigh 0.9100g Cu(NO3)2·3H2O and dissolve it in 100mL of deionized water. After it is fully dissolved, add 1.0g of the above carrier and stir thoroughly for 2h to obtain suspension D.

[0083] (5) Dissolve 0.96g (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution E. Under continuous stirring, add alkaline solution E dropwise to suspension D obtained in step (4) at a rate of 1.5ml / min until the pH of the system is 7.5 to obtain suspension E.

[0084] (6) After the suspension E obtained in step (5) is left to stand at room temperature for 18 hours, it is filtered and washed until no residual salt is found. The obtained sample is dried in an oven at 60°C for 12 hours. Then the ground solid powder is placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 450°C for 4 hours to obtain the catalyst.

[0085] Comparative Example 5 Similar to Comparative Example 4, except that a template agent was added during the copper loading and spinel synthesis precipitation process, specifically: (1) 2.974g Zn(NO3)2·6H2O, 7.5028g Al(NO3)3·9H2O and 2g PEG-6000 were dissolved in 40ml of deionized water to obtain metal salt solution A.

[0086] (2) Dissolve 9.6g of (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution B. Under continuous stirring, add alkaline solution B dropwise to the salt solution A obtained in step (1) at a rate of 1.5ml / min until the pH of the system is 8 to obtain suspension C.

[0087] (3) After the suspension C obtained in step (2) was left to stand at room temperature for 18 hours, it was filtered and washed until no residual salt was found. The obtained sample was dried in an oven at 60°C for 12 hours. Then the ground solid powder was placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 600°C for 4 hours to obtain ZnAl2O4 support.

[0088] (4) Weigh 0.9100g Cu(NO3)2·3H2O and 2g PEG-6000 and dissolve them in 100mL of deionized water. After they are fully dissolved, add 1.0g of the above carrier and stir thoroughly for 2h to obtain suspension D.

[0089] (5) Dissolve 0.96g (NH4)2CO3 in 100ml of deionized water to obtain alkaline solution E. Under continuous stirring, add alkaline solution E dropwise to suspension D obtained in step (4) at a rate of 1.5ml / min until the pH of the system is 7.5 to obtain suspension E.

[0090] (6) After the suspension E obtained in step (5) is left to stand at room temperature for 18 hours, it is filtered and washed until no residual salt is found. The obtained sample is dried in an oven at 60°C for 12 hours. Then the ground solid powder is placed in a muffle furnace for stepwise calcination, that is, calcined at 250°C for 2 hours and calcined at 450°C for 4 hours to obtain the catalyst.

[0091] X-ray diffraction (XRD) characterization is used to analyze the crystal phase composition, crystallinity, and dispersion state of Cu species in samples. XRD patterns of some examples and corresponding proportions are shown below. Figure 1As shown, diffraction peaks appeared at 2θ≈31.2°, 36.8°, 50.6°, 56.7°, 61.3°, and 66.2° in all samples, attributed to ZnAl2O4 spinel. Furthermore, the peak positions showed no significant shift, indicating that the preparation process of this invention does not damage the ZnAl2O4 spinel crystal structure. The stable crystal structure of the carrier in each sample provides a stable framework for anchoring the active copper component. No doped metal was observed in the XRD spectra of Examples 1-2 and Comparative Examples 1-2 because Mn / Fe / Ce in this invention is lattice doped (replacing Al in the spinel). 3+ / Zn 2+ The doped ions enter the crystal lattice but do not form an independent metal oxide phase, thus no XRD diffraction peaks of the doped metal appear. Further comparison of the characteristic diffraction peaks of Cu in the examples and comparative examples (2θ=43.5°) reveals that, compared to the comparative example, the Cu diffraction peaks of all example samples show significantly reduced intensity and broadened peak shape. In Comparative Example 1 and Comparative Example 2, the Cu diffraction peaks are sharp and have high intensity, with Cu particle sizes calculated according to the Scherrer formula of 56.4 nm and 54.6 nm, respectively, reflecting the presence of a larger-sized Cu phase. In contrast, in Example 1 and Example 2, the Cu diffraction peak intensity is significantly reduced and the peak width is increased, with Cu particle sizes of 28.7 nm and 31.9 nm, respectively. This indicates that adding a template agent during Cu precipitation can significantly enhance Cu dispersion. Compared to the unmodified sample Comparative Example 4, the Cu grain size in Comparative Examples 1 and 2, which only underwent metal doping modification, is significantly reduced, indicating that metal doping can strengthen the interfacial interaction between Cu and the support, thereby improving Cu species dispersion. The Cu grain size in Example 1 was the lowest among all the tested samples, indicating that the coupled modification of the metal additive and the PEG template agent has the best synergistic effect in refining the grains and optimizing the Cu dispersion.

[0092] Table 1. Changes in BET specific surface area before and after the reaction in the examples and comparative examples. As shown in Table 1, compared to Comparative Example 4, which was modified with undoped metal and template agent, Comparative Example 5, modified with only PEG, still showed an improved initial specific surface area, with a decrease of only 0.4% after the reaction. This demonstrates that PEG can regulate pore structure during the preparation stage, optimize pore structure, and significantly inhibit pore collapse and particle sintering during the hydrothermal reaction. Comparative Examples 1, 2, and 3, which introduced Mn, Fe, and Ce metal additives individually, also showed higher initial specific surface areas than Comparative Example 4, confirming that metal additive doping can improve the pore structure of the carrier. The decrease in specific surface area of ​​Comparative Example 1, modified with Mn, was lower than that of the Fe and Ce modified samples, indicating that Mn additives have a better effect on improving the thermal stability of the pore structure than Fe and Ce. Compared to Comparative Example 1, which only added Mn, Example 1, modified with a combination of Mn and PEG, showed an initial specific surface area of ​​55.1 m². 2 ·g -1 Increased to 59.3 m 2 ·g -1 Furthermore, the decrease in specific surface area after the reaction further decreased from 10.0% to 5.1%, further verifying that PEG can synergistically inhibit the destruction of pore structure during the reaction process. In addition, comparing Example 1 and Comparative Example 4, the synergistic effect of Mn regulating the crystal framework of the support and PEG optimizing the pore structure can simultaneously improve the initial specific surface area of ​​the catalyst and the stability of the pore structure under hydrothermal conditions. Among all the composite modification systems, the sample modified by the synergistic combination of Mn and PEG has both the optimal pore structure and anti-sintering performance.

[0093] The microstructure of representative samples was characterized using scanning electron microscopy (SEM). Figure 3 SEM images of Examples 1, 2, Comparative Example 1, and Comparative Example 2 are shown. Example 1 exhibits a loose and porous aggregate morphology with abundant mesoporous voids between particles. The surface is rough and the pores are well-connected, demonstrating the regulatory effect of PEG as a structure-directing agent on the pore structure. Furthermore, the particle dispersion is significantly improved, with predominantly spherical nanoparticles of uniform size and no obvious large agglomerations, indicating that PEG can effectively inhibit particle growth and aggregation, promoting the uniform distribution of active species. In Comparative Example 1 without PEG, no uniform particles were observed.

[0094] H2-TPR characterization was used to investigate the reduction characteristics of the active Cu species in the catalyst and the strength of the metal-support interface interaction. Compared with Comparative Example 1, the reduction peak of Cu species in Example 1 shifted to the high-temperature range, and the peak area of ​​the reduction peak was increased. This result indicates that the addition of PEG to the modified Mn additive can further enhance the metal-support interaction between the active Cu component and the ZnAl2O4 spinel support, effectively anchoring Cu particles and inhibiting the migration and sintering of copper particles under high-temperature hydrothermal conditions.

[0095] Table 2. Catalyst Evaluation Results for Examples and Comparative Examples At 250°C, 3MPa, H2:CO2 = 3:1, and space velocity 20000 mL·g -1 ·h -1 Under the reaction conditions, the performance of all examples and comparative catalysts for CO2 hydrogenation to methanol was evaluated, and the results are shown in Table 2. Before the activity evaluation, all samples were subjected to CO2 hydrogenation at 300°C, 0.1 MPa, 10% H2, and a space velocity of 20000 mL·g. -1 ·h -1 Activation was performed for 1 hour under the specified conditions. Using the unmodified catalyst (Comparative Example 4) as a blank control, the introduction of individual metal promoters such as Mn, Fe, and Ce (Comparative Examples 1-3), and the addition of PEG only during Cu precipitation (Comparative Example 5), all improved CO2 conversion efficiency and methanol selectivity. Among all single-metal doped samples, the methanol yield, from highest to lowest, was: Comparative Example 1 > Comparative Example 2 > Comparative Example 3, indicating that Comparative Example 1, modified with only Mn, exhibited the best catalytic activity, with a methanol yield of 0.283 g. 甲醇 ·(g 催化剂 ·h) -1 When metal additives are coupled with PEG for modification, the catalyst's performance is further improved, demonstrating the synergistic effect of the doped metal and PEG. Example 1, with Mn / PEG composite modification, exhibits the best overall performance, with a CO2 conversion rate of 11.1%, a methanol selectivity of 63.2%, and a methanol space-time yield of 0.401 g. 甲醇 ·(g 催化剂 ·h) -1 Compared to Comparative Example 1 (Mn only) and Comparative Example 5 (PEG only), the improvement was significant. The catalytic performance of the Fe / PEG and Ce / PEG modified samples decreased sequentially, but all were superior to the corresponding single-agent modified, single-PEG modified, and unmodified samples. These results confirm that the metal component and PEG have synergistic modification advantages, and the Mn-PEG coupling system has the best optimization effect on the activity and methanol selectivity of CuZnAl catalyst.

[0096] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A catalyst for the hydrogenation of carbon dioxide to methanol, characterized in that, It consists of a modified ZnAl spinel phase support and a highly dispersed copper particle active phase supported on the modified ZnAl spinel phase support. The chemical formula of the modified ZnAl spinel phase support is ZnAl2O4-M, where M is a doped metal selected from one or more of Mn, Fe, and Ce.

2. The catalyst for the hydrogenation of carbon dioxide to methanol according to claim 1, characterized in that, The highly dispersed copper particle active phase, based on the mass of CuO, accounts for 10-70% of the total mass of the catalyst.

3. The catalyst for the hydrogenation of carbon dioxide to methanol according to claim 1, characterized in that, In the modified ZnAl spinel phase support, the doping amount of M, based on the mass of M oxide, is 1 to 10% relative to the total mass of the catalyst.

4. A method for preparing a catalyst for the hydrogenation of carbon dioxide to methanol according to any one of claims 1-3, characterized in that, The preparation method is a template-deposition precipitation method, which includes the following steps: S1. Prepare a mixed solution of Zn salt, Al salt, doped metal M salt and template agent, add precipitant, react, filter to obtain precipitate, dry and calcine in two stages to obtain modified ZnAl spinel phase support; S2. Prepare a suspension containing modified ZnAl spinel phase support, Cu salt and template agent, add precipitant, react, filter to obtain precipitate, continue drying and calcining to obtain catalyst.

5. The method for preparing a catalyst for the hydrogenation of carbon dioxide to methanol according to claim 4, characterized in that, The template agent is selected from at least one of polyethylene glycol, polypropylene glycol, and polyvinyl alcohol, and its concentration in the mixed solution in S1 or the suspension in S2 is 1~50 g / L.

6. The method for preparing a catalyst for the hydrogenation of carbon dioxide to methanol according to claim 4, characterized in that, In S1, the two-stage roasting process is as follows: first roasting at 200~300℃ for 1~3 hours, and then roasting at 400~800℃ for 2~5 hours.

7. The method for preparing a catalyst for the hydrogenation of carbon dioxide to methanol according to claim 4, characterized in that, The Zn salt is zinc nitrate or zinc acetate, the Al salt is aluminum nitrate or aluminum sulfate, and the Cu salt is at least one of copper nitrate, copper chloride, and copper sulfate.

8. The method for preparing a catalyst for the hydrogenation of carbon dioxide to methanol according to claim 4, characterized in that, The doped metal M salt is a nitrate, acetate, or chloride of Mn, Fe, or Ce.

9. The method for preparing a catalyst for the hydrogenation of carbon dioxide to methanol according to claim 4, characterized in that, The precipitant is selected from ammonia, ammonium carbonate, ammonium bicarbonate, and sodium carbonate, and its addition amount is sufficient to adjust the pH of the reaction system of S1 or S2 to 6-8.

10. The method for preparing a catalyst for the hydrogenation of carbon dioxide to methanol according to claim 4, characterized in that, The roasting process in S2 is as follows: first roast at 200~300℃ for 1~3 hours, then roast at 400~800℃ for 2~5 hours.

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