Copper-zinc-gallium catalysts, their preparation methods and applications

Abstract

This invention employs a co-precipitation method to prepare a copper-zinc-gallium catalyst. Specifically, copper nitrate trihydrate, zinc nitrate hexahydrate, and gallium nitrate hydrate are prepared into a metal salt solution, which is then added dropwise to a reaction vessel containing a base solution along with a precipitating alkaline solution. The co-precipitation reaction is carried out under heating, stirring, and pH control. The target catalyst is then obtained through aging, solid-liquid separation, and calcination. This invention overcomes the shortcomings of existing copper-zinc-based catalysts, such as low activity and easy sintering and deactivation, and improves the long-range stability of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of copper-zinc-gallium catalyst technology, specifically to a copper-zinc-gallium catalyst, its preparation method, and its application. Background Technology

[0002] Currently, copper-zinc (Cu-ZnO) based catalysts are the main catalysts used in the industrial production of methanol from carbon dioxide. However, traditional copper-zinc catalysts still face many challenges in practical applications: First, insufficient dispersion of active sites. The interface between Cu and ZnO is considered crucial for catalytic activity, but in traditional preparation processes, copper species are prone to agglomeration, leading to a reduction in the effective Cu-ZnO interface and limiting the conversion efficiency of carbon dioxide. Second, poor structural stability. Under high temperature and high pressure reaction conditions, copper nanoparticles are prone to sintering and growth, resulting in rapid catalyst deactivation and shortened lifespan. Third, the preparation process significantly affects performance. Conventional co-precipitation methods often struggle to precisely control the microenvironment during precipitation, such as pH fluctuations, leading to complex and unevenly distributed precipitates, making it difficult to obtain ideal high specific surface area and uniform pore structure. While existing technologies have attempted to improve catalyst performance by introducing additives such as aluminum and zirconium, or by using stepwise precipitation methods to control component distribution, these often suffer from cumbersome preparation processes and insufficient interaction between components, making it difficult to simultaneously achieve high carbon dioxide conversion and high methanol selectivity.

[0003] Therefore, overcoming the shortcomings of existing copper-zinc based catalysts, such as low activity and easy sintering and deactivation, remains a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0004] This invention provides a copper-zinc-gallium catalyst, its preparation method, and its application, which improves the dispersion uniformity of components in copper-zinc-based catalysts and enhances the interaction between components, thereby solving the problems of insufficient active sites, easy sintering and deactivation leading to low carbon dioxide conversion rate, methanol selectivity, and poor long-range stability in existing copper-zinc catalysts.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a copper-zinc-gallium catalyst, the method comprising the following steps: S1, copper nitrate trihydrate, zinc nitrate hexahydrate and gallium nitrate hydrate are mixed and prepared into a metal salt solution; S2, dissolve sodium carbonate and sodium hydroxide in water to prepare a precipitated alkaline solution; S3, the metal salt solution and the precipitated alkaline solution are simultaneously added dropwise to a reaction vessel containing the bottom liquid, and a co-precipitation reaction is carried out under heating and stirring conditions, and the pH value of the reaction system is maintained by controlling the dropping rate; S4, after the addition is complete, continue aging under heating and stirring to obtain a mixed solution; S5, the mixed solution is subjected to solid-liquid separation, and the resulting solid is washed, dried and calcined to obtain the copper-zinc-gallium catalyst.

[0006] To achieve the above objectives, the present invention also provides the following technical solutions: A copper-zinc-gallium catalyst prepared by the above method, The copper-zinc-gallium catalyst comprises copper, zinc oxide, and gallium oxide; The copper oxide particles in the copper-zinc-gallium catalyst have a particle size of 5–15 nm. The specific surface area of ​​the copper-zinc-gallium catalyst is 40–120 m². 2 / g.

[0007] To achieve the above objectives, the present invention also provides the following technical solutions: The copper-zinc-gallium catalyst prepared by the above method or its application in the process of producing methanol by carbon dioxide hydrogenation.

[0008] Compared with the prior art, the present invention has achieved the following beneficial effects: The copper-zinc-gallium catalyst obtained by this invention has better catalytic activity, selectivity and long-range stability. This is because by introducing metallic gallium as a promoter into the copper-zinc system and combining it with the above-mentioned specific co-precipitation preparation process, the specific surface area of ​​the catalyst is effectively increased, which is conducive to exposing more active sites. Compared with traditional copper-zinc catalysts, the copper-zinc-gallium catalyst prepared by this invention significantly improves the conversion rate of carbon dioxide, the selectivity of methanol and the long-range stability.

[0009] The microstructure of the copper-zinc-gallium catalyst obtained in this invention has been optimized. Specifically, a co-precipitation process with simultaneous dropwise addition and pH control is adopted to ensure that the three components of copper, zinc, and gallium can be uniformly precipitated to form a uniform nanoparticle structure. This preparation method can effectively improve the dispersion of active species in the copper-zinc-gallium catalyst, improve the contact between copper and zinc species, enhance the interaction between copper and zinc, and thus promote the synthesis reaction of methanol. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other solutions can be obtained based on these drawings without creative effort.

[0011] Figure 1 A flowchart illustrating a method for preparing a copper-zinc-gallium catalyst according to an embodiment of the present invention. Figure 2 This is a graph showing the long-range stability test results of the copper-zinc-gallium catalyst provided in Example 2 of the present invention in the reaction of carbon dioxide hydrogenation to methanol; Figure 3 The X-ray diffraction pattern of the catalyst obtained in the comparative examples and embodiments of the present invention is shown. The size data of the copper oxide grains in the obtained catalyst can be calculated from the diffraction peak at 35.5° in the X-ray diffraction pattern. Detailed Implementation

[0012] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be understood that the specific embodiments described herein are only for illustration and explanation of the present invention and are not intended to limit the present invention.

[0013] Any specific numerical values ​​disclosed herein (including the endpoints of numerical ranges) are not limited to their exact values, but should be understood to also include values ​​close to the exact value, such as all possible values ​​within ±5% of the exact value. Furthermore, with respect to the disclosed numerical ranges, one or more new numerical ranges can be obtained by arbitrarily combining the endpoint values ​​of the range, the endpoint values ​​with specific point values ​​within the range, and the specific point values ​​themselves; these new numerical ranges should also be considered as specifically disclosed herein.

[0014] The terminology used in this invention is for the purpose of describing specific exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” as used herein are intended to include the plural forms as well. The terms “comprising,” “including,” “containing,” and “having” are inclusive and thus describe the presence of said features, elements, compositions, steps, integers, operations, and / or components, but do not exclude the presence or inclusion of one or more other features, integers, steps, operations, elements, components, and / or sets thereof. Although the open-ended term “comprising” should be understood as a non-limiting term used to describe and claim the various embodiments described in this invention, in some aspects it may instead be understood as a more restrictive and limiting term, such as “consisting of” or “essentially composed of.” Thus, for any given embodiment describing a composition, material, component, element, feature, integer, operation, and / or process step, the invention also particularly includes embodiments consisting of or substantially consisting of such compositions, materials, components, elements, features, integers, operations, and / or process steps. In the case of “consisting of…”, the alternative embodiments exclude any additional compositions, materials, components, elements, features, integers, operations and / or process steps. In the case of “essentially composed of…”, any additional compositions, materials, components, elements, features, integers, operations and / or process steps that substantially affect the essential and novel characteristics are excluded from such embodiments. However, any compositions, materials, components, elements, features, integers, operations and / or process steps that do not substantially affect the essential and novel characteristics may be included in the embodiments.

[0015] Any method steps, processes, and operations described in this invention should not be construed as necessarily requiring them to be performed in the specific order discussed or shown, unless explicitly specified. It should also be understood that, unless otherwise stated, additional or alternative steps may be used.

[0016] In this invention, except where expressly stated, any matters or issues not mentioned are directly applicable to those known in the art without any modification. Furthermore, any embodiment described in this invention can be freely combined with one or more other embodiments described in this invention, and the resulting technical solutions or concepts are considered part of the original disclosure or original record of this invention, and should not be regarded as new content not disclosed or anticipated by this invention, unless those skilled in the art consider the combination to be clearly unreasonable.

[0017] Unless otherwise stated, the terms used herein have the same meaning as commonly understood by those skilled in the art, and if a term is defined herein and its definition differs from the common understanding in the art, the definition herein shall prevail.

[0018] It is worth noting that the term "species" or "species" mentioned in this invention refers to a "chemical entity" having a distinguishable valence state, coordination environment, adsorption configuration, electronic structure, or local chemical environment, or a class of "chemical species" in a specific chemical environment or structural state; the above concept is commonly found in the fields of catalysts, surface science, coordination chemistry, and solid-state chemistry.

[0019] Existing copper-zinc (Cu-ZnO) based catalysts generally suffer from insufficient dispersion of active sites and the tendency of copper nanoparticles to agglomerate and sinter under high-temperature and high-pressure reaction conditions, leading to rapid catalyst deactivation and shortened lifespan. In view of this, the present invention provides the following technical solution to address the aforementioned technical problems.

[0020] First aspect See Figure 1 This invention provides a method for preparing a copper-zinc-gallium catalyst, comprising the following steps: S1, mixing copper nitrate trihydrate, zinc nitrate hexahydrate, and gallium nitrate hydrate to prepare a metal salt solution; S2, dissolving sodium carbonate and sodium hydroxide in water to prepare a precipitating alkaline solution; S3, simultaneously adding the metal salt solution and the precipitating alkaline solution dropwise into a reaction vessel containing a base liquid, and carrying out a co-precipitation reaction under heating and stirring conditions, maintaining the pH value of the reaction system by controlling the dropping rate; S4, after the dropping is completed, aging is continued under heating and stirring to obtain a mixed solution; S5, the mixed solution is subjected to solid-liquid separation, and the obtained solid is washed, dried, and calcined to obtain the copper-zinc-gallium catalyst. This invention, by employing a co-precipitation method and introducing a gallium (Ga) source as a third component, utilizes the differences in solubility products of the components and the synergistic precipitation mechanism to enable the three metal ions of copper, zinc, and gallium to achieve atomic-level uniform mixing and precipitation in a homogeneous liquid phase environment. This preparation method not only effectively inhibits the migration and aggregation of copper species during subsequent heat treatment and reaction processes, significantly improving the dispersion of active components, but also enhances the interaction between copper and zinc components through the structural aid effect of gallium species. This overcomes the defects of low activity and easy sintering and deactivation of existing copper-zinc based catalysts, and prepares a catalyst with both high activity and high stability.

[0021] In some embodiments of the present invention, in step S1, the total concentration of metal ions in the metal salt solution is 0.8–1.2 mol / L. It should be noted that controlling the total concentration of metal ions within the range of 0.8–1.2 mol / L ensures that the reaction system has a suitable degree of supersaturation; if the concentration is too low, the yield is insufficient and energy consumption increases; if the concentration is too high, excessive instantaneous nucleation can easily lead to agglomeration or encapsulation. This concentration range helps to form a precipitate precursor with uniform particle size distribution and good crystallinity, laying the foundation for finally obtaining copper oxide particles with a particle size of 5–15 nm, thereby solving the problem of balancing the nucleation rate and crystal growth rate during precipitation.

[0022] In some embodiments of the present invention, in step S1, the molar ratio of copper nitrate trihydrate, zinc nitrate hexahydrate, and gallium nitrate hydrate in the metal salt solution is (4-8):(2-4):(0.3-5). Controlling the molar ratio of copper, zinc, and gallium within this specific range, particularly by introducing an appropriate amount of gallium, maximizes the dual role of gallium as an electronic and structural aid. This avoids both insufficient improvement in anti-sintering ability due to excessively low gallium content and the covering of active copper sites due to excessively high gallium content. Under this ratio, the specific surface area of ​​the catalyst and the exposure of active sites achieve an optimal balance, significantly improving carbon dioxide conversion, methanol selectivity, and long-range stability.

[0023] In some embodiments of the present invention, the concentration of the precipitating alkaline solution in step S2 is 0.8–1.2 mol / L. Maintaining the concentration of the precipitating alkaline solution at a similar order of magnitude to the concentration of the metal salt solution facilitates rapid matching of the stoichiometric ratio during parallel-flow addition, reduces impurities such as simple hydroxides or heterogeneous basic salts caused by localized excess or deficiency of alkali, and ensures the uniformity of the precipitate composition. This avoids the problem of localized concentration gradients when the precipitant and metal salt solution are mixed.

[0024] In some embodiments of the present invention, in step S2, the molar ratio of sodium carbonate to sodium hydroxide in the precipitating alkaline solution is 2:1. This ratio helps to guide the formation of precursors with specific layered structures, such as hydrotalcite or basic carbonates, like chalcopyrite or similar structures. These precursors can generate more porous structures during subsequent decomposition, thereby obtaining a larger specific surface area, thus solving the technical problem of precursor phase structure control. Furthermore, the composite alkaline solution composed of sodium carbonate and sodium hydroxide, especially when their molar ratio is 2:1, provides a better pH buffering capacity compared to a single alkaline source when used as a precipitant.

[0025] In some embodiments of the present invention, in step S3, the base liquid is water or an aqueous base liquid. Using water as the base liquid can avoid the introduction of organic impurities and provide sufficient heat capacity buffer for the initial stage of co-current dripping, preventing uneven precipitation properties caused by localized exothermic reactions or concentration fluctuations in the early stages of the reaction. In some embodiments, an aqueous base liquid can be selected as the base liquid in step S3 according to the actual application scenario or production requirements to achieve purposes such as adjusting the reaction rate.

[0026] In some embodiments of the present invention, in step S3, the pH value is maintained at 6.0–7.0. It is worth noting that if the pH is too low, copper precipitation will be incomplete, while if the pH is too high, zinc and gallium will dissolve and be lost in the form of zincates or gallates. This pH range control ensures that all metal components enter the precipitate in stoichiometric proportions, guaranteeing the accuracy of the final catalyst composition. Furthermore, the aforementioned pH range solves the technical problems of incomplete co-precipitation of multi-component metal ions and the redissolution of zinc and gallium amphoteric metal ions. This is because the precipitation pH ranges for copper, zinc, and gallium are different, and precisely maintaining the pH value of the reaction system within the weakly acidic to neutral range of 6.0–7.0 is a crucial window for achieving co-precipitation of the three.

[0027] In some embodiments of the present invention, in step S3, the heating temperature is controlled at 55–65°C, and the stirring speed is 550–650 rpm. It should be noted that the temperature range of 55–65°C is conducive to the formation of precursors with better crystal structure, avoiding the formation of amorphous colloids that are difficult to filter and wash; while the high-speed stirring at 550–650 rpm enhances the micro-mixing state, rapidly dispersing the dripping droplets, preventing particle agglomeration caused by localized over-concentration, and promoting the formation of small and narrowly distributed precipitated particles, thus solving the problems of precipitated particle morphology control and mass transfer efficiency.

[0028] In some embodiments of the present invention, the aging time in step S4 is 4 to 5 hours. It is understood that the 4 to 5 hour aging process allows tiny, unstable crystal nuclei to dissolve and redeposit on the surface of larger crystal grains, eliminating lattice defects and making the crystal structure of the precipitate more complete and ordered. This process is crucial for forming a stable pore structure and directly affects the final specific surface area of ​​the catalyst.

[0029] In some embodiments of the present invention, step S5 involves centrifugal washing at a speed of 4000–5000 rpm for 3–5 minutes per cycle. Residual sodium ions are a serious poison for copper-based catalysts, accelerating sintering at high temperatures. Using high-speed centrifugation, such as 4000–5000 rpm, and multiple short-duration centrifugal washes, compared to traditional filtration, can more thoroughly separate sodium ions adsorbed on the colloidal surface from the precipitate, while avoiding the loss of ultrafine nanoparticles through filtration. This ensures the high purity and high activity of the catalyst, thereby efficiently removing impurity ions, including sodium ions, while reducing the loss of active components.

[0030] In some embodiments of the present invention, in step S5, the drying temperature is 100–120°C and the drying time is 10–15 hours. It is understood that a gentle and prolonged drying process can prevent capillary tension caused by rapid water evaporation from damaging the porous framework of the precursor, thus preserving the pore structure formed during aging and achieving stable removal of physically adsorbed water and preventing the collapse of the catalyst precursor structure.

[0031] In some embodiments of the present invention, in step S5, the calcination temperature is 330–370°C, and the calcination time is 4–6 hours. The temperature range of 330–370°C is sufficient to completely decompose precursors such as basic carbonates into their corresponding oxides, such as CuO, ZnO, and Ga2O3, forming an active phase. Simultaneously, this temperature avoids the problem of decreased active specific surface area caused by high temperatures. The calcination time of 4–6 hours ensures that the decomposition reaction is thorough, thereby obtaining a stable crystal phase structure.

[0032] Second aspect This invention provides a copper-zinc-gallium catalyst prepared by the method described in the first aspect, wherein the copper-zinc-gallium catalyst comprises copper, zinc oxide, and gallium oxide; the copper oxide in the copper-zinc-gallium catalyst has a particle size of 5–15 nm; and the specific surface area of ​​the copper-zinc-gallium catalyst is 40–120 m². 2 / g. It should be noted that existing catalysts, due to their large copper oxide particle size, are prone to agglomeration, which severely affects the catalyst's stability. In view of this, the present invention incorporates an appropriate amount of gallium into the catalyst, thereby reducing the copper oxide particle size and resulting in a catalyst with better stability. Furthermore, gallium doping promotes the uniform distribution of the active components, thereby increasing the catalyst's specific surface area.

[0033] For example, the specific surface area of ​​the aforementioned copper-zinc-gallium catalyst can specifically be 45 m². 2 / g、50 m 2 / g、55 m 2 / g、60 m 2 / g、65 m 2 / g、70 m2 / g、75 m 2 / g、80 m 2 / g、90 m 2 / g、100 m 2 / g、110 m 2 Any value in / g, or a range of values ​​consisting of any two of the above values ​​and any value within that range.

[0034] Third aspect This invention provides the use of a copper-zinc-gallium catalyst prepared by the method described in the first aspect, or a copper-zinc-gallium catalyst as described in the second aspect, in the process of producing methanol from carbon dioxide via hydrogenation. It should be noted that existing carbon dioxide hydrogenation processes for methanol suffer from technical challenges such as low single-pass conversion, numerous byproducts, poor methanol selectivity, and poor long-range stability. Applying the copper-zinc-gallium catalyst of this invention to this process, thanks to the optimized electronic and geometric structure of the gallium promoter, the catalyst exhibits superior catalytic performance. Experimental results show that, under the same reaction conditions, this catalyst can achieve a carbon dioxide conversion rate of over 20% and a methanol selectivity of over 60%. This not only significantly improves the methanol yield, reduces the feedstock recycling ratio and energy consumption, but also reduces the generation of byproducts and significantly lowers the cost of subsequent separation and purification, demonstrating extremely high industrial application value.

[0035] Example The following is information about some of the reagents described in the embodiments of this invention, including their chemical formulas, specifications, and manufacturers: Copper nitrate trihydrate, Cu(NO3)2·3H2O, analytical grade, Sinopharm Chemical Reagent Co., Ltd. Zinc nitrate hexahydrate, Zn(NO3)2·6H2O, analytical grade, Sinopharm Chemical Reagent Co., Ltd. Gallium nitrate hydrate, Ga(NO3)3·xH2O, analytical grade, Sinopharm Chemical Reagent Co., Ltd. Sodium hydroxide, NaOH, analytical grade, Shanghai Maclean Biochemical Technology Co., Ltd. Sodium carbonate, Na2CO3, analytical grade, Beijing Bailingwei Technology Co., Ltd.

[0036] It is worth noting that the particle size in this invention refers to the size of copper oxide crystallites in the catalyst calculated using the Scherrer equation based on the peak at around 35.5° in the XRD pattern.

[0037] Furthermore, the specific surface area of ​​the catalysts obtained in the examples and comparative examples in this specification was measured using a Micromeritics ASAP 2020 instrument and the BET test method known in the art.

[0038] Comparative Example 1 This comparative example provides a method for preparing a copper-zinc binary catalyst, comprising the following steps: (1) Preparation of metal salt solution: Weigh 0.06 mol copper nitrate trihydrate and 0.03 mol zinc nitrate hexahydrate, dissolve them in 90 mL of deionized water, and stir until homogeneous to obtain metal salt solution A.

[0039] (2) Preparation of precipitating alkaline solution: Weigh 0.128 mol sodium carbonate and 0.064 mol sodium hydroxide, dissolve them in 192 mL of deionized water, and stir evenly to obtain precipitating alkaline solution B.

[0040] (3) Co-precipitation: The metal salt solution A and the precipitating alkali solution B are placed in two constant pressure dropping funnels respectively, and simultaneously dropped into the bottom liquid of a beaker containing 200 mL of deionized water and preheated to 60 °C; during the dropping process, the stirring speed is maintained at 600 rpm to ensure thorough stirring, the dropping rate of the metal salt solution A is kept constant, and the pH value of the reaction system is maintained at 6.5 ± 0.2 by adjusting the dropping rate of the precipitating alkali solution B.

[0041] (4) Aging: After the metal salt solution A has been added, keep the heating temperature and stirring conditions unchanged and continue aging for 4 hours to obtain mixed solution D.

[0042] (5) Post-processing: The mixed solution D was centrifuged and the precipitate was washed with water until no sodium ion residue was detected; the obtained solid was dried in an oven for 12 hours, and then calcined in a muffle furnace at 350°C for 5 hours; finally, it was ground and sieved, and particles of 40-60 mesh were selected to obtain the catalyst of Comparative Example 1.

[0043] In Comparative Example 1, the copper oxide crystal size in the catalyst was 13.27 nm, and the specific surface area of ​​the catalyst was 41.9372 m². 2 / g.

[0044] Example 1 This embodiment provides a method for preparing a copper-zinc-gallium catalyst, including the following steps: (1) Preparation of metal salt solution: Weigh 0.06 mol copper nitrate trihydrate, 0.03 mol zinc nitrate hexahydrate and 0.003 mol gallium nitrate hydrate, dissolve them in 93 mL of deionized water, and stir well to obtain metal salt solution A.

[0045] (2) Preparation of precipitating alkaline solution: Weigh 0.128 mol sodium carbonate and 0.064 mol sodium hydroxide, dissolve them in 192 mL of deionized water, and stir evenly to obtain precipitating alkaline solution B.

[0046] (3) Co-precipitation: The metal salt solution A and the precipitating alkali solution B are placed in two constant pressure dropping funnels respectively, and simultaneously dropped into the bottom liquid of a beaker containing 200 mL of deionized water and preheated to 60 °C; during the dropping process, the stirring speed is maintained at 600 rpm to ensure thorough stirring, the dropping rate of the metal salt solution A is kept constant, and the pH value of the reaction system is maintained at 6.5 ± 0.2 by adjusting the dropping rate of the precipitating alkali solution B.

[0047] (4) Aging: After the metal salt solution A has been added, keep the heating temperature and stirring conditions unchanged and continue aging for 4 hours to obtain mixed solution D.

[0048] (5) Post-processing: The mixed solution D was centrifuged and the precipitate was washed with water until no sodium ion residue was detected; the obtained solid was dried in an oven for 12 hours, and then calcined in a muffle furnace at 350°C for 5 hours; finally, it was ground and sieved, and particles of 40-60 mesh were selected to obtain the catalyst of Example 1.

[0049] In this example, the copper oxide crystal size in the catalyst is 12.91 nm, and the specific surface area of ​​the catalyst is 44.7649 m². 2 / g.

[0050] Example 2 This embodiment provides a method for preparing a copper-zinc-gallium catalyst. Except for changing the amount of gallium nitrate hydrate in step (1) to 0.005 mol and the amount of deionized water used for dissolution to 95 mL, the remaining preparation steps and parameters are the same as in Example 1. The catalyst of Example 2 is finally obtained.

[0051] In this Example 2, the copper oxide crystal size in the catalyst is 11.68 nm, and the specific surface area of ​​the catalyst is 64.5820 m². 2 / g.

[0052] Example 3 This embodiment provides a method for preparing a copper-zinc-gallium catalyst. Except for changing the amount of gallium nitrate hydrate in step (1) to 0.01 mol and the amount of deionized water used for dissolution to 100 mL, the other preparation steps and parameters are the same as in Example 1. The catalyst of Example 3 is finally obtained. The long-range stability test results of the copper-zinc-gallium catalyst obtained in this embodiment in the carbon dioxide hydrogenation to methanol reaction are as follows: Figure 2 As shown.

[0053] In this example, the copper oxide crystal size in the catalyst is 10.27 nm, and the specific surface area of ​​the catalyst is 73.25 × 10 m². 2 / g.

[0054] Example 4 This embodiment provides a method for preparing a copper-zinc-gallium catalyst. Except for changing the amount of gallium nitrate hydrate in step (1) to 0.03 mol and the amount of deionized water used for dissolution to 120 mL, the remaining preparation steps and parameters are the same as in Example 1. The catalyst of Example 4 is finally obtained.

[0055] In this example, the copper oxide crystal size in the catalyst is 10.48 nm, and the specific surface area of ​​the catalyst is 79.7353 m². 2 / g.

[0056] Example 5 This embodiment provides a method for preparing a copper-zinc-gallium catalyst. Except for changing the amount of gallium nitrate hydrate in step (1) to 0.05 mol and the amount of deionized water used for dissolution to 140 mL, the remaining preparation steps and parameters are the same as in Example 1. The catalyst of Example 5 is finally obtained.

[0057] In this example, the copper oxide crystal size in the catalyst is 11.97 nm, and the specific surface area of ​​the catalyst is 101.0862 m². 2 / g.

[0058] Performance Testing and Evaluation 1. Catalyst activity evaluation methods The catalytic activity of the catalysts prepared in Examples 1-5 and Comparative Example 1 was evaluated.

[0059] The specific evaluation process is as follows: Weigh 1g (40-60 mesh) of catalyst using an analytical balance and pack it into a fixed-bed reactor; first, introduce nitrogen gas and back pressure to a level 0.35-0.5 MPa higher than the reaction pressure to check the airtightness of the reaction apparatus; if the pressure remains constant within 20 minutes, it is considered to be airtight; after the airtightness check is completed, perform gradient reduction. Under normal pressure, introduce a mixture of 20 vol% hydrogen and 80 vol% nitrogen gas, with a hydrogen flow rate of 20 mL / min; raise the temperature to 180℃ at a rate of 2℃ / min for 4 hours of reduction, then continue to raise the temperature to 250℃ and reduce for another 4 hours; after the reduction is completed, cool down to 230℃, introduce a feed gas with a molar ratio of H2 / CO2 = 3:1, adjust the system pressure to 3 MPa to start the reaction, and control the space velocity at 3000 h⁻¹. - ¹.

[0060] The formula for carbon dioxide conversion rate is: .

[0061] The formula for methanol selectivity is: Furthermore, it should be noted that gaseous components (CO2, CO) were detected online using a gas chromatography system (Agilent, 7890B) equipped with an N2 internal standard, and quantitative analysis of the reactor outlet gas was performed using a calibration normalization method. Liquid products (methanol and H2O) were detected offline using a Perkinlemer-Clarus 580 gas chromatograph. TCD (CO2, CO, N2): Hayesep Q+5A molecular sieve. FID (methanol, ethanol): Elite-Wax capillary column.

[0062] 2. Test Results The catalytic performance test results of carbon dioxide hydrogenation to methanol in each embodiment and comparative example are shown in Table 1 below.

[0063] Table 1 Catalytic performance of the catalysts obtained in various embodiments and comparative examples of the present invention.

[0064] As shown in Table 2, compared with Comparative Example 1 (which does not contain gallium), Examples 1-5, which introduced the metal additive gallium, all exhibited higher carbon dioxide conversion rates and methanol selectivity. Furthermore, a "volcano-like" relationship exists between the catalyst activity and gallium content, with Example 2 showing the best catalytic effect. It should be noted that the "volcano-like" relationship refers to the curve in Table 1 exhibiting a shape that is "low at both ends and high in the middle" on the horizontal axis.

[0065] 3. Catalyst stability test To further investigate the stability of the catalyst, the catalyst prepared in Example 2 was selected for the reaction. The reduction conditions were controlled in the same manner as the activity evaluation method described above, and remained unchanged. The reaction conditions were adjusted as follows: temperature 230 °C, pressure 5 MPa, feed gas molar ratio H2 / CO2 = 6:1, and space velocity 3000 h⁻¹. - ¹.

[0066] The reaction results are as follows Figure 2 As shown, during the 180 h reaction period, the carbon dioxide conversion rate remained at approximately 37.5%, and the methanol selectivity remained at approximately 80.0%. These test results demonstrate that the copper-zinc-gallium catalyst prepared in this invention exhibits good long-range stability.

[0067] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. Furthermore, specific examples have been used in the specification to illustrate the principles and implementation methods of the present invention. The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention, and the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing a copper-zinc-gallium catalyst, characterized in that, The preparation method includes the following steps: S1, copper nitrate trihydrate, zinc nitrate hexahydrate and gallium nitrate hydrate are mixed and prepared into a metal salt solution; S2, dissolve sodium carbonate and sodium hydroxide in water to prepare a precipitated alkaline solution; S3, the metal salt solution and the precipitated alkaline solution are simultaneously added dropwise to a reaction vessel containing the bottom liquid, and a co-precipitation reaction is carried out under heating and stirring conditions, and the pH value of the reaction system is maintained by controlling the dropping rate; S4, after the addition is complete, continue aging under heating and stirring to obtain a mixed solution; S5, the mixed solution is subjected to solid-liquid separation, and the resulting solid is washed, dried and calcined to obtain the copper-zinc-gallium catalyst.

2. The preparation method according to claim 1, characterized in that, In step S1, the total concentration of metal ions in the metal salt solution is 0.8–1.2 mol / L; And / or, in step S1, the molar ratio of copper nitrate trihydrate, zinc nitrate hexahydrate and gallium nitrate hydrate in the metal salt solution is (4-8):(2-4):(0.3-5).

3. The preparation method according to claim 1, characterized in that, The concentration of the precipitating alkaline solution in step S2 is 0.8–1.2 mol / L.

4. The preparation method according to claim 1, characterized in that, In step S2, the molar ratio of sodium carbonate to sodium hydroxide in the precipitated alkaline solution is 2:

1.

5. The preparation method according to claim 1, characterized in that, In step S3, the base liquid is water or an aqueous base liquid; And / or, in step S3, the pH value is maintained at 6.0 to 7.

0.

6. The preparation method according to claim 5, characterized in that, In step S3, the heating temperature is controlled at 55-65℃ and the stirring speed is 550-650rpm.

7. The preparation method according to claim 1, characterized in that, In step S4, the aging time is 4 to 5 hours.

8. The preparation method according to claim 1, characterized in that, It has at least one of the following characteristics: In step S5, centrifugal washing is used, and the centrifugation speed is 4000-5000 rpm, with a single centrifugation time of 3-5 min. In step S5, the drying temperature is 100-120℃ and the drying time is 10-15h. In step S5, the calcination temperature is 330–370°C and the calcination time is 4–6 hours.

9. A copper-zinc-gallium catalyst prepared by the method according to any one of claims 1 to 8, characterized in that, The copper-zinc-gallium catalyst comprises copper, zinc oxide, and gallium oxide; The copper oxide particles in the copper-zinc-gallium catalyst have a particle size of 5–15 nm. The specific surface area of ​​the copper-zinc-gallium catalyst is 40–120 m². 2 / g.

10. The use of the copper-zinc-gallium catalyst prepared by any one of claims 1 to 8 or the copper-zinc-gallium catalyst as described in claim 9 in the process of producing methanol by carbon dioxide hydrogenation.

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