Modified copper-zinc-aluminum catalyst for synthesizing green methanol and preparation method of modified copper-zinc-aluminum catalyst

Abstract

The invention relates to the technical field of industrial catalysis, in particular to a modified copper-zinc-aluminum catalyst for synthesizing green methanol and a preparation method. The invention relates to a modified copper-zinc-aluminum catalyst for synthesizing green methanol. The modified copper-zinc-aluminum catalyst consists of an active component, a structural additive and a modifier, the active component is CuO and ZnO, the structural auxiliary agent is Al2O3, and the modifier is ZrO2 and Ga2O3; the catalyst comprises the following components in percentage by mass: 50%-70% of CuO, 20%-30% of ZnO, 5%-15% of Al2O3, 1%-5% of ZrO2 and 0.5%-3% of Ga2O3, wherein the total mass of the catalyst is 100%. The invention relates to a preparation method of a modified copper-zinc-aluminum catalyst for synthesizing green methanol. The preparation method comprises the following steps: (1) coprecipitation; and (2) introducing a modifier. And (3) washing and filtering. And (4) drying and roasting. The comprehensive catalytic performance, especially the long-term stability, of the catalyst is fundamentally improved. The catalyst provided by the invention is specially designed for a CO2 hydrogenation reaction system, and the high performance of the catalyst plays a positive role in promoting the synthesis technology of green methanol.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of industrial catalysis technology, in particular to a modified copper-zinc-aluminum catalyst for synthesizing green methanol and a preparation method thereof, more particularly to a modified copper-zinc-aluminum catalyst for synthesizing green methanol from carbon dioxide hydrogenation, and a preparation method and application of the catalyst. BACKGROUND

[0002] Methanol, as a vital basic chemical raw material and potential clean fuel, occupies an extremely important position in modern chemical industry. Its traditional production route relies heavily on fossil resources and is mainly prepared by catalytic reaction of synthesis gas. In recent years, with the urgent pursuit of global carbon neutralization target, the technology path of using renewable energy electrolytic water to obtain "green hydrogen" and catalytically synthesizing "green methanol" from CO2 captured from industrial waste gas or atmosphere is regarded as the strategic direction to realize the recycling of carbon resources and reduce greenhouse gas emissions. The core challenge of this process lies in the development of a catalyst system that can efficiently and stably catalyze the hydrogenation of CO2 to generate methanol.

[0003] Among the numerous catalytic systems, Cu-Zn-Al catalysts with Cu, Zn, Al oxides as the main components are widely studied and applied due to their excellent catalytic performance and relatively low cost in the traditional synthesis gas methanol production process. The active center of this type of catalyst is usually considered to be highly dispersed Cu, ZnO plays a role in dispersing and stabilizing Cu particles and adsorbing and activating reactants, while Al2O3 mainly acts as a structural promoter, providing abundant specific surface area and pore structure to prevent sintering and aggregation of active components during the reaction.

[0004] However, the direct application of traditional Cu-Zn-Al catalysts in the CO2 hydrogenation reaction to produce methanol often results in unsatisfactory overall performance. This is mainly due to the characteristics of the reaction system itself and the more stringent requirements it poses on the catalyst. First, CO2 molecules have extremely high chemical stability, and their activation requires a catalyst to provide stronger reaction driving force. Second, the CO2 hydrogenation process has a complex reaction network, in addition to the main reaction of generating target product methanol, the reverse water gas shift reaction easily occurs, producing a large amount of CO, which not only reduces the atom economy of raw materials, but also increases the energy consumption and complexity of subsequent product separation. Furthermore, H2O is one of the main by-products of the reaction, and the high-temperature environment of H2O vapor under reaction conditions will accelerate the Ostwald ripening process of Cu grains, leading to rapid loss of active surface area of the catalyst, i.e. the stability of the catalyst is severely challenged.

[0005] To improve the performance of Cu-Zn-Al catalysts in the CO2 hydrogenation reaction, various strategies have been attempted by those skilled in the art. One common approach is to optimize the stoichiometric ratio of the three main elements, Cu, Zn, and Al, in the catalyst in order to achieve better metal dispersion and synergistic effects. Another widely explored strategy is to introduce a fourth component, i.e., an additive, to modify the catalyst. For example, there have been reports of adding metal oxides such as Zr, Mg, Mn, Ce, etc. to the Cu-Zn-Al system. These additives may improve certain performance indicators of the catalyst, such as initial activity or methanol selectivity, to some extent, through electronic modification, structure promotion, or increasing the number of basic sites on the surface.

[0006] However, the existing modified catalyst systems still have obvious limitations. Many improvement schemes often only focus on improving one aspect of performance, making it difficult to simultaneously optimize activity, selectivity, and stability. For example, the introduction of a certain additive may improve the selectivity of methanol to some extent, but at the cost of part of the catalytic activity; or although the activity is improved in the short term, the migration and sintering of the active components during long-term reaction are not effectively inhibited, resulting in a shortened catalyst life. In addition, some modification methods are complex in process or use expensive raw materials, which is not conducive to large-scale industrial application.

[0007] Therefore, developing a new catalyst that can simultaneously have high CO2 conversion rate, high methanol selectivity, and excellent long-term running stability is of great significance for promoting the practical industrial application of CO2 hydrogenation to green methanol technology. This requires more in-depth and innovative consideration of the composition design and preparation process of the catalyst. SUMMARY

[0008] Biomass gasification direct combustion coupled with green hydrogen to produce methanol is an important technical path to realize carbon recycling. However, the core of this process, the carbon dioxide hydrogenation to methanol reaction, still faces significant technical bottlenecks. When traditional copper-zinc-aluminum catalysts are applied to this reaction system, the following problems are prominent: First, the carbon dioxide molecule has high chemical inertness and requires a highly active catalyst to effectively activate it. Second, the reaction network is complex and prone to side reactions such as reverse water-gas shift, resulting in low selectivity of the target product, methanol. Third, the water vapor generated by the reaction and the high-temperature reaction environment can easily cause sintering and aggregation of the active components of the catalyst, resulting in poor catalyst stability and short catalyst life. In addition, existing modified catalysts often only improve one aspect of performance, making it difficult to simultaneously achieve high activity, high selectivity, and high stability. Therefore, developing a new catalyst that can comprehensively solve the above problems is of great significance for promoting the industrial application of green methanol synthesis technology.

[0009] Technical solutions of the present application: To solve the above technical problems, the application provides a modified copper-zinc-aluminum catalyst for synthesizing green methanol. The catalyst is composed of an active component, a structure aid and a modifier. The active component is copper oxide (CuO) and zinc oxide (ZnO), the structure aid is aluminum oxide (Al2O3), and the modifier is zirconium oxide (ZrO2) and gallium oxide (Ga2O3). The composition is 50-70% of CuO, 20-30% of ZnO, 5-15% of Al2O3, 1-5% of ZrO2 and 0.5-3% of Ga2O3 in terms of mass percentage, with the total mass of the catalyst being 100%.

[0010] Further, the mass percentage of CuO is 55-65%, and the mass percentage of ZnO is 22-28%. The ratio is conducive to forming a more suitable copper-zinc synergistic effect and optimizing the distribution of active sites.

[0011] Further, the mass percentage of Al2O3 is 8-12%. The aluminum oxide in the content range can provide sufficient and stable specific surface area and pore structure, effectively preventing sintering of the active component.

[0012] Further, the mass percentage of ZrO2 is 2-4%, and the mass percentage of Ga2O3 is 1-2.5%. The composite modifier of the ratio can produce the best synergistic modification effect on the surface of the catalyst.

[0013] The application also provides a preparation method of the above catalyst, which comprises the following steps: (1) Co-precipitation: a soluble metal salt solution for forming the active component and the structure aid is provided, i.e., a mixed metal salt solution A containing a copper salt for providing CuO, a zinc salt for providing ZnO and an aluminum salt for providing Al2O3; a precipitant solution B is provided; under the condition of a temperature of 60-80°C, in an environment with a constant pH value of 7.5-8.5, solution A and solution B are added into a reactor containing deionized water in parallel flow to perform a co-precipitation reaction, and slurry C is obtained; the constant pH value is monitored by a pH meter and the addition rate of the precipitant is adjusted in real time by an automatic titrator; (2) Modifier introduction: a soluble metal salt solution for forming the modifier is provided, i.e., a mixed solution containing a zirconium salt for providing ZrO2 and a gallium salt for providing Ga2O3, which is slowly added to the slurry C obtained in step (1) under continuous stirring, and is aged at 60-80°C for 2-4 hours to obtain modified slurry D; the stepwise introduction is the key to ensuring the effective loading of the modifier; (3) Washing and filtering: the modified slurry D is cooled to room temperature, and the filtering operation is performed, and the filter cake is repeatedly washed with sufficient deionized water until the concentration of nitrate ions in the filtrate is less than 50 ppm by ion chromatography or specific chemical detection method, so as to completely remove impurity ions; (4) Drying and calcination: the filter cake obtained in step (3) is placed in a drying box and dried at 100-120℃ for 8-12 hours to obtain a catalyst precursor; the catalyst precursor is calcined in a program-controlled muffle furnace at 350-450℃ in an air atmosphere for 3-5 hours, and the modified copper-zinc-aluminum catalyst product is obtained after natural cooling.

[0014] Further, the copper salt in step (1) is preferably copper nitrate, the zinc salt is preferably zinc nitrate, and the aluminum salt is preferably aluminum nitrate; the precipitating agent is preferably sodium carbonate. These raw materials are easy to obtain and economical.

[0015] Further, the zirconium salt in step (2) is preferably zirconium oxychloride, and the gallium salt is preferably gallium nitrate. These salts have good solubility, which is beneficial to the uniform dispersion of the modifier.

[0016] Further, the constant pH value in step (1) is preferably controlled at 8.0. This pH condition is most conducive to the formation of a precursor precipitate with a suitable structure.

[0017] Further, the calcination temperature in step (4) is preferably 380-420℃, and the calcination time is preferably 3.5-4.5 hours. This heat treatment condition can ensure that the precursor is fully converted into an oxide, while avoiding sintering of the active components.

[0018] The application also provides a method for synthesizing green methanol, which uses the modified copper-zinc-aluminum catalyst described above or the modified copper-zinc-aluminum catalyst prepared by the method described above. The reaction is carried out in a fixed bed, fluidized bed or slurry bed reactor, and the preferred reaction conditions are: system pressure 4.0-8.0 MPa, reaction temperature 220-250℃, raw gas CO2 and H2, and H2 / CO2 volume ratio controlled at 3:1. This method is particularly suitable for processing carbon dioxide captured from biomass gasification or industry and hydrogen produced by electrolysis of water with renewable energy.

[0019] Compared with the prior art, the technical solution provided by the application has the following advantages: 1. Comprehensive improvement of catalytic performance: through the composite modification of ZrO2 and Ga2O3, the catalyst exhibits a synergistic effect in the CO2 hydrogenation reaction, realizing the unity of high CO2 conversion, high methanol selectivity and excellent stability.

[0020] 2、Structure stability enhancement: The preparation method adopted by the application, especially the step-by-step precipitation introduction of the modifier technology, makes the modifier more effectively distributed in the active site, significantly inhibits the migration and growth of copper grains during the reaction process, and prolongs the service life of the catalyst.

[0021] 3、Strong process feasibility: The selected raw materials are common and easy to obtain, the preparation process parameters are clear, the repeatability is good, and the production is easy to enlarge, which lays a solid foundation for industrial application.

[0022] 4、Green environmental protection benefit is remarkable: The catalyst is designed for CO2 hydrogenation, and its high efficiency promotes the recycling of carbon resources, which meets the green chemistry and sustainable development direction.

[0023] Advantages of the application 1、The application realizes the functional complementation and synergistic effect between different auxiliary components by using ZrO2 and Ga2O3 as composite modifiers. ZrO2 has good oxygen storage capacity and structural stability, which can effectively anchor copper species and inhibit its migration and grain growth during the reaction and calcination process. Ga2O3 can adjust the acid-base properties of the catalyst surface, moderately weaken the surface acid sites, thereby effectively inhibit the occurrence of reverse water gas shift side reaction and reduce the generation of CO. The synergistic effect of the two modifiers makes the finally obtained catalyst maintain high CO2 hydrogenation activity while the methanol selectivity is significantly improved, overcoming the defect that single modifier can only improve certain performance while other performance may be damaged.

[0024] 2、The step-by-step precipitation preparation method adopted by the application has unique advantages. The method first forms the main structure of Cu-Zn-Al catalyst through co-precipitation, ensuring the high uniformity of dispersion and close interaction between active components and structural additives. Then Zr and Ga modification components are introduced, so that these modification agents can be preferentially loaded on the surface of the hydroxide precursor formed in the early stage, especially around the active site Cu. This sequential preparation process avoids the problem that the modification agent may be embedded and cannot effectively expose to the catalyst surface to play a role when all metal elements are co-precipitated at one time, so that the utilization rate of the modification agent is maximized, and the modification effect is more direct and efficient.

[0025] 3、The composition and preparation method of the catalyst of the application make the prepared catalyst have excellent microstructure performance. It has a smaller CuO grain size, usually between 5nm to 9nm, and a higher specific surface area, which can reach 80m 2 / g to 120m 2Smaller crystalline size means more active sites per unit mass of catalyst can be exposed, providing abundant sites for the activation and reaction of CO2 and H2. Larger specific surface area is beneficial for the diffusion and adsorption of reactants, and further promotes the high dispersion of active components. This optimized microstructure is an important material basis for the high catalytic activity of the catalyst of the present application.

[0026] 4、The comprehensive catalytic performance, especially the long-term stability, of the catalyst of the present application has been fundamentally improved. Under the reaction conditions of CO2 hydrogenation to methanol, the catalyst not only exhibits high initial conversion of CO2 and initial selectivity of methanol, but more importantly, it can maintain the stability of activity and selectivity in continuous operation for hundreds of hours, with extremely low decay rate. This is mainly because the structural stabilization of O2 effectively inhibits the sintering and aggregation of Cu crystalline grains, and the enhancement of the overall mechanical strength and thermal stability of the catalyst. Excellent stability is crucial for reducing the frequency of catalyst replacement and operating costs in industrial production.

[0027] 5、The preparation method of the present application has clear process parameters and clear operation flow, with good repeatability and potential for industrialization. The raw materials used are conventional and readily available metal salts and precipitants, with controllable cost. The entire preparation process does not require special equipment or harsh conditions, such as co-precipitation temperature and aging temperature between 60°C and 80°C, and calcination temperature in the conventional range of 350°C to 450°C. The end point of washing has a clear index of NO3 - ion concentration less than 50 ppm, which is easy to monitor and control the production quality. This method provides a reliable and economical solution for large-scale production of high-performance CO2 hydrogenation to methanol catalyst.

[0028] 6、The catalyst provided by the present application is specifically designed for CO2 hydrogenation reaction system, and its high performance plays a positive role in promoting the synthesis technology of green methanol. High activity and high selectivity mean lower reaction energy consumption and higher raw material utilization rate, while excellent stability ensures the continuity and economy of the production process. The successful application of the catalyst will open up a new way for the effective use of CO2, a greenhouse gas, to produce high-value chemicals, in line with the development direction of green chemistry and sustainable development, with significant environmental benefits and potential economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 A flowchart of a preparation process for a modified copper-zinc-aluminum catalyst for synthesizing green methanol. The block diagram shows the preparation process of the modified copper-zinc-aluminum catalyst described in the present application, including co-precipitation, introduction of modifier, washing and filtration, drying and calcination of the four main steps. It is used to help understand the overall flow of the preparation method described in the specification.

[0030] Figure 2The stability test comparison chart of Comparative Example 1 and the catalyst of Example 1. The broken line chart shows the trend of CO2 conversion rate with reaction time (0-260 hours) in the reaction of CO2 hydrogenation to methanol of the traditional Cu-Zn-Al catalyst (Comparative Example 1) and the modified catalyst (Example 1) of the application. The significant advantage of the catalyst of the application in long-term stability is intuitively displayed. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0032] The application will be further described in detail through examples and comparative examples, but the protection scope of the application is not limited thereto. The reagents described in the examples are all from commercial channels unless otherwise specified.

[0033] Example 1 Preparation was carried out according to the mass percentage of target components in the catalyst: CuO: 60%, ZnO: 25%, Al2O3: 10%, ZrO2: 3%, Ga2O3: 2%.

[0034] Copper nitrate (Cu (NO3) 2·3H2O) 151.2 g, zinc nitrate (Zn (NO3) 2·6H2O) 89.3 g, aluminum nitrate (Al (NO3) 3·9H2O) 75.0 g were weighed and dissolved in 500 mL of deionized water to prepare a mixed metal salt solution A. Sodium carbonate (Na2CO3) 143.0 g was weighed and dissolved in 500 mL of deionized water to prepare a precipitant solution B.

[0035] In a 2L reactor with stirring, a thermometer and a pH electrode, 300 mL of deionized water was added as bottom water, heated to 70°C and stirring was started. Solution A and solution B were added to the reactor through a double drop system, and NaOH dilute solution was added through an automatic pH controller to maintain the pH value of the system at 8.0. After the addition was completed, the stirring was continued for 0.5 hours to obtain Cu-Zn-Al slurry C.

[0036] Zirconium oxychloride (ZrOCl2·8H2O) 5.23 g and gallium nitrate (Ga (NO3) 3·xH2O, about 2.74 g of Ga2O3) were weighed and dissolved in 50 mL of deionized water. Under stirring, the mixed solution was slowly added to the slurry C. After the addition was completed, the aging was continued at 70°C for 3 hours to obtain the modified slurry D.

[0037] Cooling slurry D to room temperature, filtration, washing the filter cake with deionized water until no chloride ion is detected in the filtrate by silver nitrate solution and no NO3 - less than 50 ppm. The filter cake was dried in an oven at 110°C for 10 hours. The dried solid was calcined in a muffle furnace at 400°C for 4 hours, broken and sieved after natural cooling, and the 40-60 mesh fraction was collected to obtain catalyst Cat-1. The specific surface area of the catalyst was 108 m 2 / g, and the CuO crystallite size was 6.5 nm as calculated from the XRD pattern by the Scherrer equation.

[0038] Example 2 The catalyst was prepared according to the following mass percentage of the target components in the catalyst: CuO: 55%, ZnO: 28%, Al2O3: 12%, ZrO2: 4%, Ga2O3: 1%.

[0039] Copper nitrate 138.6 g, zinc nitrate 100.0 g, and aluminum nitrate 90.0 g were weighed and prepared into a mixed metal salt solution A. Sodium carbonate 143.0 g was weighed and prepared into solution B.

[0040] The preparation process was the same as in Example 1, and the co-precipitation temperature was controlled at 65°C and the pH value was controlled at 8.2. The modifier solution was prepared from zirconium oxychloride 6.97 g and gallium nitrate (about 1.37 g of Ga2O3). The aging temperature was 65°C and the aging time was 3.5 hours. The drying and calcination conditions were the same as in Example 1. The obtained catalyst was recorded as Cat-2, and the specific surface area was 98 m 2 / g, and the CuO crystallite size was 7.2 nm.

[0041] Example 3 The catalyst was prepared according to the following mass percentage of the target components in the catalyst: CuO: 65%, ZnO: 22%, Al2O3: 8%, ZrO2: 2.5%, Ga2O3: 2.5%.

[0042] Copper nitrate 163.8 g, zinc nitrate 78.6 g, and aluminum nitrate 60.0 g were weighed and prepared into a mixed metal salt solution A. Sodium carbonate 143.0 g was weighed and prepared into solution B.

[0043] The preparation process was the same as in Example 1, and the co-precipitation temperature was controlled at 75°C and the pH value was controlled at 7.8. The modifier solution was prepared from zirconium oxychloride 4.36 g and gallium nitrate (about 3.42 g of Ga2O3). The aging temperature was 75°C and the aging time was 2.5 hours. The drying and calcination conditions were the same as in Example 1. The obtained catalyst was recorded as Cat-3, and the specific surface area was 115 m 2 / g, and the CuO crystallite size was 5.9 nm.

[0044] Example 4 Prepared according to the target composition in the catalyst as follows: CuO: 58%, ZnO: 27%, AI2O3: 9%, ZrO2: 5%, Ga2O3: 1%.

[0045] Copper nitrate 146.2 g, zinc nitrate 96.4 g, and aluminum nitrate 67.5 g were weighed and prepared into a mixed metal salt solution A. The precipitant solution B was the same as in Example 1.

[0046] The preparation process was the same as in Example 1, and the coprecipitation pH value was controlled at 8.5. The modifier solution was prepared from zirconium oxychloride 8.71 g and gallium nitrate (about 1.37 g as Ga2O3). The aging time was 4 hours. The drying and calcination conditions were the same as in Example 1. The obtained catalyst was recorded as Cat-4, and its specific surface area was 92 m 2 / g, and the CuO grain size was 7.8 nm.

[0047] Example 5 Prepared according to the target composition in the catalyst as follows: CuO: 62%, ZnO: 23%, AI2O3: 11%, ZrO2: 1%, Ga2O3: 3%.

[0048] Copper nitrate 156.2 g, zinc nitrate 82.5 g, and aluminum nitrate 82.5 g were weighed and prepared into a mixed metal salt solution A. The precipitant solution B was the same as in Example 1.

[0049] The preparation process was the same as in Example 1, and the coprecipitation pH value was controlled at 7.5. The modifier solution was prepared from zirconium oxychloride 1.74 g and gallium nitrate (about 4.11 g as Ga2O3). The aging time was 2 hours. The drying and calcination conditions were the same as in Example 1. The obtained catalyst was recorded as Cat-5, and its specific surface area was 102 m 2 / g, and the CuO grain size was 6.9 nm.

[0050] Example 6 Prepared according to the target composition in the catalyst as follows: CuO: 52%, ZnO: 30%, AI2O3: 13%, ZrO2: 3.5%, Ga2O3: 1.5%.

[0051] Copper nitrate (Cu(NO3)2·3H2O) 131.0 g, zinc nitrate (Zn(NO3)2·6H2O) 107.2 g, and aluminum nitrate (Al(NO3)3·9H2O) 97.5 g were weighed and dissolved in 500 mL of deionized water to prepare a mixed metal salt solution A. Sodium carbonate (Na2CO3) 143.0 g was weighed and dissolved in 500 mL of deionized water to prepare a precipitant solution B.

[0052] The preparation procedure is the same as Example 1, but the co-precipitation temperature is controlled at 68°C and the pH value is controlled at 8.1. The modifier solution is prepared from zirconium oxychloride (ZrOCl2*8H2O) 6.09 g and gallium nitrate (Ga(NO3)3*xH2O, about 2.05 g as Ga2O3). The aging temperature is 68°C and the aging time is 3.2 hours. The drying and calcination conditions are the same as Example 1. The obtained catalyst is denoted as Cat-6, which has a specific surface area of 95 m 2 / g and a CuO crystallite size of 7.5 nm.

[0053] Example 7 The preparation is carried out according to the same procedure as Example 1, but the target components and mass percentages in the catalyst are: CuO: 68%, ZnO: 20%, Al2O3: 7%, ZrO2: 4.5%, Ga2O3: 0.5%.

[0054] Copper nitrate 171.4 g, zinc nitrate 71.4 g and aluminum nitrate 52.5 g are weighed out and dissolved in 500 mL of deionized water to prepare a mixed metal salt solution A. The precipitant solution B is the same as Example 1.

[0055] The preparation procedure is the same as Example 1, but the co-precipitation temperature is controlled at 72°C and the pH value is controlled at 7.9. The modifier solution is prepared from zirconium oxychloride (ZrOCl2*8H2O) 7.83 g and gallium nitrate (Ga(NO3)3*xH2O, about 0.68 g as Ga2O3). The aging temperature is 72°C and the aging time is 2.8 hours. The drying and calcination conditions are the same as Example 1. The obtained catalyst is denoted as Cat-7, which has a specific surface area of 110 m 2 / g and a CuO crystallite size of 6.2 nm.

[0056] Comparative Example 1 The preparation is carried out according to the same procedure as Example 1, but the target components and mass percentages in the catalyst are: CuO: 60%, ZnO: 30%, Al2O3: 10%.

[0057] Copper nitrate 151.2 g, zinc nitrate 107.2 g and aluminum nitrate 75.0 g are weighed out to prepare a mixed metal salt solution A. The precipitant solution B is the same as Example 1.

[0058] The co-precipitation procedure is the same as Example 1, but no subsequent modifier introduction step is carried out. The slurry obtained from co-precipitation is directly subjected to cooling, filtration, washing, drying and calcination. The obtained catalyst is denoted as Ref-Cat-1, which has a specific surface area of 75 m 2 / g and a CuO crystallite size of 12.1 nm.

[0059] Comparative Example 2 The preparation is carried out according to the same procedure as Example 1, but the target components and mass percentages in the catalyst are: CuO: 68%, ZnO: 20%, Al2O3: 7%, ZrO2: 4.5%, Ga2O3: 0.5%.

[0060] Copper nitrate 151.2 g, zinc nitrate 89.3 g, aluminum nitrate 75.0 g, zirconium oxychloride 5.23 g and gallium nitrate (about 2.74 g as Ga2O3) were weighed out and dissolved in 550 mL of deionized water to prepare a mixed metal salt solution A. Precipitant solution B was the same as in Example 1.

[0061] The subsequent steps of co-precipitation, aging, washing, drying and calcination were the same as in Example 1. The obtained catalyst was labeled as Ref-Cat-2, which had a specific surface area of 88 m 2 / g and CuO grain size of 9.8 nm.

[0062] Comparative Example 3 Preparation was carried out according to the target composition of CuO: 60%, ZnO: 25%, Al2O3: 10%, ZrO2: 5% by mass in the catalyst.

[0063] The preparation process was the same as in Example 1, but the modifier solution only contained zirconium oxychloride (8.71 g) without adding gallium nitrate. The obtained catalyst was labeled as Ref-Cat-3.

[0064] Comparative Example 4 Preparation was carried out according to the target composition of CuO: 60%, ZnO: 25%, Al2O3: 10%, Ga2O3: 5% by mass in the catalyst.

[0065] The preparation process was the same as in Example 1, but the modifier solution only contained gallium nitrate (about 6.85 g as Ga2O3) without adding zirconium oxychloride. The obtained catalyst was labeled as Ref-Cat-4.

[0066] Comparative Example 5 Preparation was carried out according to the target composition of CuO: 58%, ZnO: 25%, Al2O3: 10%, ZrO2: 3%, Ga2O3: 4% by mass in the catalyst.

[0067] Copper nitrate 146.2 g, zinc nitrate 89.3 g, aluminum nitrate 75.0 g, zirconium oxychloride 5.23 g and gallium nitrate (about 5.48 g as Ga2O3) were weighed out to prepare a mixed metal salt solution A.

[0068] The preparation process was the same as in Example 1. The obtained catalyst was labeled as Ref-Cat-5, which had a specific surface area of 90 m 2 / g and CuO grain size of 8.5 nm.

[0069] Comparative Example 6 Preparation was carried out according to the same target composition by mass in the catalyst as in Example 1, but after the introduction of the modifier in step (2), the aging time was shortened to 0.5 hour, and other conditions remained unchanged.

[0070] The obtained catalyst is denoted as Ref-Cat-6, which has a specific surface area of 92 m 2 / g, and a CuO grain size of 9.2 nm.

[0071] Evaluation of catalytic performance of the catalysts of the present application The catalysts obtained in each of the above examples and comparative examples were pressed into tablets, crushed, and 40-60 mesh particles were sieved out. 1.0 g of each catalyst was weighed and loaded into a fixed bed reactor. The performance of the catalysts in the CO2 hydrogenation to methanol was evaluated under the conditions of a reaction pressure of 5.0 MPa, a reaction temperature of 240°C, a raw gas H2 / CO2 volume ratio of 3:1, a space velocity of 6000 mL·g -1 ·h -1 The tail gas was analyzed online by chromatography, and the CO2 conversion rate and methanol selectivity were calculated by area normalization. The data were recorded after the reaction was stable for 5 hours, and the stability was continuously observed for 260 hours. The results are shown in the following table: Table 1: Physical properties and reaction performance data of the catalysts

[0072] Table 2: Chemical composition of the catalysts (mass percentage)

[0073] Analysis of the results of the catalysts From the data in the above table, it can be seen that the catalysts (Cat-1 to Cat-5) prepared in Examples 1-5 of the present application all exhibit significantly higher CO2 conversion rate and methanol selectivity than Comparative Example 1 (traditional catalyst) in the CO2 hydrogenation to methanol reaction. In particular, in the long-term stability test of 260 hours, the activity and selectivity of the catalysts of the present application decayed very little (all less than 5%), while the activity of Comparative Example 1 decreased by more than 18%, and the selectivity decreased by nearly 7%.

[0074] Comparative Example 2 used the same components as Example 1 but was prepared by one-step co-precipitation, and its initial performance and stability were significantly inferior to those of Example 1, which proves the unique advantages and creativity of the “step-by-step precipitation method” preparation process of the present application.

[0075] Comparative Example 3 and Comparative Example 4 respectively investigate the effect of single Zr modifier and single Ga modifier. The data show that, although they are better than Comparative Example 1 without modification, they are inferior to Example 1 using both composite modification, which indicates that Zr and Ga have a clear synergistic effect in improving the comprehensive performance of the catalyst, rather than a simple additive effect. Comparative Example 5 (Ref-Cat-5) increases the Ga2O3 content to 4% (beyond the scope of the present application), and the results show that excessive Ga2O3 has a negative impact on the performance of the catalyst, and its initial activity and stability are inferior to the examples of the present application, proving that the determined modifier content range of the present application is the best range verified by a large number of experiments. Comparative Example 6 (Ref-Cat-6) shortens the key aging time, and its performance, especially the stability (activity decay more than 13%), decreases significantly, which shows that the determined aging time of 2-4 hours is a key process parameter to ensure that the modifier fully functions and obtain a stable catalyst structure, further highlighting the creativity of the preparation method of the present application.

[0076] In summary, the present application successfully obtains a high-performance and high-stability CO2 hydrogenation to methanol catalyst through a specific composite modifier combination (ZrO2 and Ga2O3) and its unique step-by-step introduction preparation method, the technical effect is remarkable, and the purpose of the present application is completely achieved. Figure 1 A modified copper-zinc-aluminum catalyst preparation process flowchart for synthesizing green methanol. Figure 2 A comparative graph of the stability test of Comparative Example 1 and Example 1 catalyst.

[0077] The remaining matters of the present application are known technologies.

[0078] The above examples are only to illustrate the technical concept and characteristics of the present application, the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and it cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A modified copper zinc aluminum catalyst for the synthesis of green methanol, characterized in that, The active component is CuO and ZnO, the structural aid is Al2O3, and the modifier is ZrO2 and Ga2O3; the composition is 50-70% of CuO, 20-30% of ZnO, 5-15% of Al2O3, 1-5% of ZrO2, and 0.5-3% of Ga2O3, based on the total mass of the catalyst.

2. The modified copper zinc aluminum catalyst for synthesis of green methanol as claimed in claim 1 wherein, The mass percentage of CuO is 55-65%, and the mass percentage of ZnO is 22-28%.

3. The modified copper-zinc-aluminum catalyst for synthesis of green methanol as claimed in claim 1 wherein, The mass percentage of Al2O3 is 8-12%.

4. The modified copper-zinc-aluminum catalyst for synthesis of green methanol as claimed in claim 1 wherein, The mass percentage of ZrO2 is 2-4%, and the mass percentage of Ga2O3 is 1-2.5%.

5. A process for the preparation of a modified copper-zinc-aluminum catalyst for the synthesis of green methanol as claimed in any one of claims 1 to 4, characterized in that, The method comprises the following steps: (1) Coprecipitation: a solution of soluble metal salts for forming the active component and the structural aid is provided, i.e., a mixed metal salt solution A containing a copper salt for providing CuO, a zinc salt for providing ZnO, and an aluminum salt for providing Al2O3; a precipitant solution B is provided; under the conditions of 60-80°C and constant pH value of 7.5-8.5, solution A and solution B are added into a reactor containing deionized water in parallel flow to carry out a coprecipitation reaction, and slurry C is obtained; constant pH value is achieved by real-time adjustment with a pH meter; (2) Modifier introduction: a solution of soluble metal salts for forming the modifier is provided, i.e., a mixed solution containing a zirconium salt for providing ZrO2 and a gallium salt for providing Ga2O3, which is added into the slurry C obtained in step (1) under stirring conditions, and is aged at 60-80°C for 2-4 hours to obtain modified slurry D; (3) Washing and filtration: the modified slurry D is cooled to room temperature, filtered, and the filter cake is washed with deionized water until the concentration of nitrate ions in the filtrate is less than 50 ppm; (4) Drying and calcination: the filter cake obtained in step (3) is dried at 100-120°C for 8-12 hours to obtain a catalyst precursor; the catalyst precursor is calcined at 350-450°C in an air atmosphere for 3-5 hours to obtain the modified copper-zinc-aluminum catalyst.

6. The method for preparing a modified copper-zinc-aluminum catalyst for synthesizing green methanol according to claim 5, characterized in that, In step (1), the copper salt is copper nitrate, the zinc salt is zinc nitrate, and the aluminum salt is aluminum nitrate; the precipitant is sodium carbonate.

7. The method for preparing a modified copper-zinc-aluminum catalyst for synthesizing green methanol according to claim 5, characterized in that, In step (2), the zirconium salt is zirconium oxychloride, and the gallium salt is gallium nitrate.

8. The method for preparing a modified copper-zinc-aluminum catalyst for synthesizing green methanol according to claim 5, characterized in that, In step (1), the constant pH value is 8.

0.

9. The method for preparing a modified copper-zinc-aluminum catalyst for synthesizing green methanol according to claim 5, characterized in that, In step (4), the calcination temperature is 380-420°C, and the calcination time is 3.5-4.5 hours.

10. A method of synthesizing green methanol, characterized by, The modified copper-zinc-aluminum catalyst according to any one of claims 1-4, or prepared by the method of any one of claims 5-9, is used; the reaction conditions are: pressure of 4.0-8.0 MPa, temperature of 220-250°C, and raw material gas of CO2 and H2, wherein the volume ratio of H2 / CO2 is 3:1.

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