Method for regulating and controlling grain sizes of copper and zinc components in copper-based catalyst through cobalt modification and application

Abstract

The invention relates to a method for regulating and controlling grain sizes of copper and zinc components in a copper-based catalyst through cobalt modification and application of the method, and belongs to the technical field of methanol synthesis through CO2 hydrogenation. Based on the characteristic that oxalic acid forms a complex with metal ions in an ethanol system, the cobalt-modified copper-based catalyst is prepared by adopting an oxalic acid precipitation method. By changing preparation conditions such as cobalt addition amount, precipitation temperature, reaction time and the like, effective control on the specific surface area of the catalyst, grain sizes of copper and zinc components and a copper-zinc synergistic effect is realized, the performance of the catalyst in a reaction for synthesizing methanol through CO2 hydrogenation is remarkably optimized, the CO2 conversion rate and methanol selectivity are improved, and the production cost is reduced. The regulation and control of product selectivity and methanol space-time yield are realized. The catalyst is simple in preparation process, does not introduce impurities, and has a wide application prospect in the field of industrial CO2 resource utilization.

Description

Technical Field

[0001] The present invention relates to a method for regulating the grain sizes of copper and zinc components in a copper-based catalyst by cobalt modification and its application, belonging to the technical field of CO2 hydrogenation to methanol synthesis. Background Art

[0002] The technology of synthesizing methanol from CO2 hydrogenation can effectively reduce CO2 emissions and mitigate the greenhouse effect. It can also produce clean, inexpensive, and carbon-neutral energy and chemicals, realizing the resource utilization of CO2. However, the reaction process of synthesizing methanol from CO2 hydrogenation presents significant challenges. CO2 is a non-polar, linearly symmetrical molecule. Its unique structure and chemical properties make it a weak electron donor and a strong electron acceptor, resulting in extremely stable thermodynamic properties. To activate the CO2 molecule, additional energy must be supplied. Under certain conditions, the reaction process and the final product can be manipulated to ultimately convert it into valuable chemicals, such as methanol.

[0003] Cu-ZnO-Al2O3 catalysts have been used industrially for nearly 60 years for methanol synthesis from syngas. Their high catalytic activity and stability have made them the mainstream catalyst in this field. Research has shown that the active components of these copper-based catalysts are copper and zinc. Drawing on the success of industrial methanol synthesis, copper-based catalysts are also commonly used in CO2 hydrogenation to methanol. Considering that alumina supports can increase the specific surface area of the catalyst, they also face challenges such as poor water resistance and susceptibility to deactivation. Furthermore, the reaction mechanism of copper-based catalysts remains controversial. Therefore, in-depth research on copper-zinc catalysts provides theoretical support and technical reserves for innovation in methanol synthesis technology, which is of great research value and practical significance. However, while zinc oxide supports can increase the contact area of the Cu-ZnO interface, the low specific surface area of ZnO has always limited the catalytic activity of copper-zinc catalysts. Furthermore, these industrial copper-based catalysts often suffer from poor methanol selectivity and high carbon monoxide selectivity, which is unfavorable for the production of the target product, methanol. Cobalt has a strong ability to dissociate hydrogen, making it a common metal in hydrogenation reactions. For example, it is often used as an active metal in Fischer-Tropsch catalysts. When the reactant gas is carbon dioxide-rich, cobalt is highly active in the methanation of carbon dioxide. However, when cobalt is the primary active metal in a catalyst, the products may shift toward methane and higher alcohols.

[0004] In summary, the following problems are common in the preparation and application of copper-based catalysts for the hydrogenation of carbon dioxide to methanol: (1) When copper-based catalysts are used to synthesize methanol from carbon dioxide hydrogenation, the selectivity for the product carbon monoxide is too high, which seriously restricts the methanol yield. Although modification of copper-zinc catalysts has become a key means to improve catalytic performance, existing reports have focused on the use of additives, but there are few reports on the effective control of product selectivity. In addition, the high cost of some modification additives breaks the low-cost advantage of copper-based catalysts and greatly limits their large-scale industrial application.

[0005] (2) Copper-zinc synergy is the key driving force for methanol synthesis, but traditional copper-zinc-aluminum catalysts have the disadvantages of poor water resistance and easy deactivation. Although zinc oxide as a carrier can enhance the copper-zinc interface contact, the physical properties of zinc oxide itself limit the specific surface area of the catalyst. While zirconium oxide as a carrier can improve the water resistance of the catalyst, the carbon monoxide selectivity in the catalytic reaction is still significantly higher than the methanol selectivity, making it difficult to meet the requirements of efficient methanol synthesis.

[0006] (3) The smaller the copper particle size in the copper-based catalyst, the higher the activity. However, small particle size tends to promote reverse water-gas shift reaction, causing the product to tend to generate carbon monoxide. How to improve methanol selectivity while maintaining a small particle size has become a key problem in current research. Summary of the Invention

[0007] To address the current challenges of using copper-based catalysts for CO2 hydrogenation to methanol, this paper proposes a method for cobalt-modified copper-based catalysts to regulate the grain size of the copper and zinc components, as well as their application. Based on the properties of oxalic acid forming complexes with metal ions in an ethanol system, the cobalt-modified copper-based catalyst is prepared using an oxalic acid precipitation method. By varying preparation conditions such as the cobalt addition amount, precipitation temperature, and reaction time, the catalyst's specific surface area, the grain size of the copper and zinc components, and the copper-zinc synergistic effect are effectively controlled. This significantly optimizes the catalyst's performance in the CO2 hydrogenation to methanol reaction, improving CO2 conversion and methanol selectivity, and enabling regulation of both product selectivity and methanol space-time yield.

[0008] A method for regulating the grain size of copper and zinc components in a copper-based catalyst by cobalt modification, characterized in that the specific steps are as follows: (1) dissolving copper nitrate, zinc nitrate and cobalt nitrate in anhydrous ethanol solution to obtain a mixed solution; (2) Add the oxalic acid-ethanol solution dropwise to the mixed solution at a uniform rate, stir and react for 2-4 hours at a water bath temperature of 20-40°C, let it stand at room temperature, separate the solid and liquid, and dry the solid to obtain the precursor; (3) The precursor is heated to 350-450°C at a constant speed and calcined at a constant temperature for 3-5 hours to obtain a cobalt-modified copper-based catalyst.

[0009] Preferably, in step (1), the molar ratio of copper nitrate, zinc nitrate and cobalt nitrate is 1:1:0.02-0.14.

[0010] Preferably, the molar ratio of the total metal ion amount of copper, zinc and cobalt in the mixed solution of step (2) to oxalic acid is 1:1.05~3.0, the oxalic acid concentration in the oxalic acid-ethanol solution is 3~5 mol / L, and the droplet acceleration rate of the oxalic acid-ethanol solution is 5~10 mL / min.

[0011] Preferably, the standing time in step (2) is 1 to 3 hours.

[0012] Preferably, the uniform heating rate in step (3) is 2-3°C / min.

[0013] The cobalt-modified regulated copper-based catalyst is used as a catalyst in the CO2 hydrogenation to methanol reaction. Before the catalytic reaction, the cobalt-modified copper-based catalyst is placed at a temperature of 280-300°C and subjected to a pre-reduction treatment in an H2 atmosphere for 2-3 hours.

[0014] After reduction, the copper-based catalyst modified by cobalt has a copper grain size of 10.0-21.8 nm, a zinc oxide grain size of 9.8-15.2 nm, and a specific surface area of 28.22-82.10 m 2 / g.

[0015] The optimal catalytic temperature of the cobalt-modified copper-based catalyst in the CO2 hydrogenation to methanol reaction is 260°C.

[0016] The present invention discloses a mechanism for regulating the grain size of copper and zinc components in a copper-based catalyst through cobalt modification: cobalt doping hinders contact between copper and zinc. An appropriate amount of cobalt additive maintains a high copper-zinc contact area while introducing a second metal, cobalt, to promote copper dispersion and restrict copper growth, thereby regulating the copper and zinc particle sizes and increasing the specific surface area of the catalyst.

[0017] The mechanism by which the cobalt-modified copper-based catalyst improves methanol selectivity is as follows: by introducing a secondary metal, cobalt, into the copper-based catalyst, its ability to dissociate H₂ is significantly enhanced, promoting the conversion of reaction products to hydrocarbons. Furthermore, the addition of an appropriate amount of cobalt as a promoter effectively inhibits the growth of copper and zinc oxide grains, ensuring high CO₂ conversion while maintaining high methanol selectivity.

[0018] The zinc component in the catalyst of the present invention plays the role of dispersing the copper component and forming different copper-zinc interfaces. The precipitation reaction process using ethanol as a solvent effectively promotes efficient dispersion between the copper and zinc components and the formation of the copper-zinc interface, thereby greatly improving the reaction performance of the catalyst.

[0019] The cobalt component in the cobalt-modified copper-based catalyst of this invention disperses the copper component, limiting copper grain growth and increasing the catalyst's specific surface area. Furthermore, compared with undoped copper-zinc catalysts, the appropriate amount of cobalt doping effectively improves the catalyst's selectivity for methanol and space-time yield. The methanol selectivity of the cobalt-modified catalyst ranges from 34.51% to 67.32%.

[0020] After reduction, the copper-based catalyst modified by cobalt in the present invention has a copper grain size of 10-21.8 nm, a zinc oxide grain size of 9.8-15.2 nm, and a specific surface area of 28.22-82.10 m 2 Compared with the copper-zinc catalyst without cobalt doping, cobalt doping promotes the interaction between copper and zinc.

[0021] The beneficial effects of the present invention are: (1) The cobalt-modified copper-based catalyst of the present invention has a significant effect on improving the methanol selectivity of the carbon dioxide hydrogenation to methanol reaction even at a very low content of the modifier cobalt element; by changing the content of the modifier cobalt, the copper and zinc particle sizes of the catalyst are regulated, and the copper-zinc interaction and product selectivity are regulated; (2) The present invention uses oxalic acid as a precipitant without introducing other impurities, which is green and environmentally friendly; (3) The cobalt-modified copper-based catalyst of the present invention exhibits higher CO2 conversion rate, methanol selectivity and methanol yield in the CO2 hydrogenation to methanol reaction. Compared with the blank control group, the reaction product has higher chemical added value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The XRD patterns of the copper-based catalysts of Examples 1 to 5 and Comparative Example 1 after reduction treatment; Figure 2 Graph showing the relationship between the cobalt content in the catalysts of Examples 1 to 5 and Comparative Example 1 and the methanol selectivity and space-time yield. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below in conjunction with specific implementation methods, but the scope of protection of the present invention is not limited to the specific implementation methods described below. It should also be pointed out that the following examples only describe the preparation process of the catalyst within a certain specific range. Without departing from the technical premise of the present invention, other researchers can make multiple modifications to the present invention, and these modifications also fall within the scope of protection of the present invention.

[0024] Example 1: A method for regulating the grain size of copper and zinc components in a copper-based catalyst by cobalt modification, the specific steps are as follows: (1) dissolving copper nitrate, zinc nitrate and cobalt nitrate in an anhydrous ethanol solution to obtain a mixed solution; the molar ratio of the copper nitrate, zinc nitrate and cobalt nitrate is 1:1:0.02; (2) adding oxalic acid-ethanol solution (the oxalic acid concentration in the oxalic acid-ethanol solution is 3 mol / L) to the mixed solution at a rate of 10 mL / min, stirring the mixture for 3 h at a water bath temperature of 30°C, aging the mixture at room temperature for 1.5 h, washing the solid with anhydrous ethanol by centrifugation, and drying the solid at a temperature of 80°C for 12 h to obtain a precursor; the molar ratio of the total metal ions of copper, zinc and cobalt in the mixed solution to that of oxalic acid is 1:1.05; (3) The precursor was heated at a rate of 2°C / min to 350°C and calcined at this temperature for 3 h to obtain a cobalt-modified copper-based catalyst; The cobalt-modified copper-based catalyst was placed at a temperature of 280° C. and subjected to a pre-reduction treatment in a H 2 atmosphere for 2 h to obtain a pre-reduced cobalt-modified copper-based catalyst; The copper-based catalyst modified by cobalt in this embodiment has a Cu grain size of about 13.3 nm and a ZnO grain size of about 11.3 nm after the pre-reduction treatment. The specific surface area of the copper-based catalyst modified by cobalt is about 48.31 m 2 / g; Application of cobalt-modified copper-based catalyst in CO2 hydrogenation to methanol: The pre-reduced cobalt-modified copper-based catalyst was placed in the reaction zone of the fixed bed, and the raw gas H2 and CO2 (H2 to CO2 molar ratio of 3:1) were introduced at a temperature of 260°C, a pressure of 3 MPa, and a mass space velocity of 11000 mL / g. cat The methanol synthesis reaction was carried out by hydrogenation of CO2 at ·h. The relationship between methanol selectivity and time-space yield in this embodiment is shown in FIG. Figure 2 The reaction results are shown in Table 1.

[0025] Comparative Example 1: This comparative example differs from Example 1 in that: no cobalt nitrate is added in step (1), and a copper-based catalyst free of cobalt is prepared; The copper-based catalyst is placed at a temperature of 280° C. and subjected to a pre-reduction treatment in a H 2 atmosphere for 2 hours to obtain a pre-reduced copper-based catalyst; The Cu crystal size of the pre-reduced copper-based catalyst after the pre-reduction treatment is about 21.1 nm, the ZnO crystal size is about 15.2 nm, and the specific surface area of the pre-reduced copper-based catalyst is about 28.22 m 2 / g; Application of copper-based catalyst in CO2 hydrogenation to methanol: The pre-reduced copper-based catalyst was placed in the fixed bed reaction zone, and the raw gas H2 and CO2 (H2 to CO2 molar ratio of 3:1) were introduced at a temperature of 260 ° C, a pressure of 3 MPa, and a mass space velocity of 11000 mL / g. cat The methanol synthesis reaction was carried out by CO2 hydrogenation under ·h. The relationship between methanol selectivity and time-space yield of this comparative example is shown in the figure. Figure 2 The reaction results are shown in Table 1.

[0026] Example 2: A method for regulating the grain size of copper and zinc components in a copper-based catalyst by cobalt modification, the specific steps are as follows: (1) dissolving copper nitrate, zinc nitrate and cobalt nitrate in an anhydrous ethanol solution to obtain a mixed solution; the molar ratio of the copper nitrate, zinc nitrate and cobalt nitrate is 1:1:0.05; (2) An oxalic acid-ethanol solution (the oxalic acid concentration in the oxalic acid-ethanol solution is 4 mol / L) is uniformly added dropwise to the mixed solution at a rate of 10 mL / min, and the mixture is stirred at a water bath temperature of 30°C for 3 h. The mixture is allowed to stand for aging for 1.5 h at room temperature, and anhydrous ethanol is used as a detergent. The solid is washed by centrifugation and dried at a temperature of 80°C for 12 h to obtain a precursor. The molar ratio of the total metal ions of copper, zinc and cobalt in the mixed solution to oxalic acid is 1:1.5. (3) The precursor was heated at a constant temperature of 3°C / min to 400°C and calcined at this temperature for 4 h to obtain a cobalt-modified copper-based catalyst; The cobalt-modified copper-based catalyst was placed at a temperature of 280° C. and subjected to a pre-reduction treatment in a H 2 atmosphere for 2 h to obtain a pre-reduced cobalt-modified copper-based catalyst; The copper-based catalyst modified by cobalt in this embodiment has a Cu grain size of about 13.7 nm and a ZnO grain size of about 11.1 nm after the pre-reduction treatment. The specific surface area of the copper-based catalyst modified by cobalt is about 50.48 m 2 / g; Application of cobalt-modified copper-based catalyst in CO2 hydrogenation to methanol: The pre-reduced cobalt-modified copper-based catalyst was placed in the reaction zone of the fixed bed, and the raw gas H2 and CO2 (H2 to CO2 molar ratio of 3:1) were introduced at a temperature of 260°C, a pressure of 3 MPa, and a mass space velocity of 11000 mL / g. cat The methanol synthesis reaction was carried out by hydrogenation of CO2 at ·h. The relationship between methanol selectivity and time-space yield in this embodiment is shown in FIG. Figure 2 The reaction results are shown in Table 1.

[0027] Example 3: A method for regulating the grain size of copper and zinc components in a copper-based catalyst by cobalt modification, the specific steps are as follows: (1) dissolving copper nitrate, zinc nitrate and cobalt nitrate in an anhydrous ethanol solution to obtain a mixed solution; the molar ratio of the copper nitrate, zinc nitrate and cobalt nitrate is 1:1:0.07; (2) Oxalic acid-ethanol solution (oxalic acid concentration in oxalic acid-ethanol solution is 5 mol / L) was uniformly added dropwise to the mixed solution at a rate of 10 mL / min, stirred for reaction at a water bath temperature of 25°C for 3 h, and aged at room temperature for 2.5 h. Anhydrous ethanol was used as a detergent, and the solid was washed by centrifugation. The solid was dried at a temperature of 75°C for 14 h to obtain a precursor; the molar ratio of the total metal ions of copper, zinc and cobalt in the mixed solution to oxalic acid was 1:2.0; (3) The precursor was heated at a rate of 2.5°C / min to a temperature of 450°C and calcined at this temperature for 3 h to obtain a cobalt-modified copper-based catalyst; The cobalt-modified copper-based catalyst was placed at a temperature of 280° C. and subjected to a pre-reduction treatment in a H 2 atmosphere for 2 h to obtain a pre-reduced cobalt-modified copper-based catalyst; The Cu crystal size of the pre-reduced cobalt-modified copper-based catalyst after the pre-reduction treatment is about 10.8 nm, the ZnO crystal size is about 9.8 nm, and the specific surface area of the pre-reduced cobalt-modified copper-based catalyst is about 74.66 m 2 / g; Application of cobalt-modified copper-based catalyst in CO2 hydrogenation to methanol: The pre-reduced cobalt-modified copper-based catalyst was placed in the reaction zone of the fixed bed, and the raw gas H2 and CO2 (H2 to CO2 molar ratio of 3:1) were introduced at a temperature of 260°C, a pressure of 3 MPa, and a mass space velocity of 11000 mL / g. cat The methanol synthesis reaction was carried out by hydrogenation of CO2 at ·h. The relationship between methanol selectivity and time-space yield in this embodiment is shown in FIG. Figure 2 The reaction results are shown in Table 1.

[0028] Example 4: A method for regulating the grain size of copper and zinc components in a copper-based catalyst by cobalt modification, the specific steps are as follows: (1) dissolving copper nitrate, zinc nitrate and cobalt nitrate in an anhydrous ethanol solution to obtain a mixed solution; the molar ratio of the copper nitrate, zinc nitrate and cobalt nitrate is 1:1:0.10; (2) An oxalic acid-ethanol solution (the oxalic acid concentration in the oxalic acid-ethanol solution is 5 mol / L) is uniformly added dropwise to the mixed solution at a rate of 10 mL / min, and the mixture is stirred at a water bath temperature of 30°C for 2.5 h. The mixture is allowed to stand for aging for 2.5 h at room temperature, and anhydrous ethanol is used as a detergent. The solid is washed by centrifugation and dried at a temperature of 60°C for 18 h to obtain a precursor. The molar ratio of the total metal ions of copper, zinc and cobalt in the mixed solution to oxalic acid is 1:2.5. (3) The precursor was heated at a constant temperature of 400°C at a heating rate of 2°C / min and calcined at this temperature for 5 h to obtain a cobalt-modified copper-based catalyst; The cobalt-modified copper-based catalyst was placed at a temperature of 280° C. and subjected to a pre-reduction treatment in a H 2 atmosphere for 2 h to obtain a pre-reduced cobalt-modified copper-based catalyst; The copper-based catalyst modified by cobalt in this embodiment has a Cu grain size of about 13.4 nm and a ZnO grain size of about 12.1 nm after the pre-reduction treatment. The specific surface area of the copper-based catalyst modified by cobalt is about 43.49 m 2 / g; Application of cobalt-modified copper-based catalyst in CO2 hydrogenation to methanol: The pre-reduced cobalt-modified copper-based catalyst was placed in the reaction zone of the fixed bed, and the raw gas H2 and CO2 (H2 to CO2 molar ratio of 3:1) were introduced at a temperature of 260°C, a pressure of 3 MPa, and a mass space velocity of 11000 mL / g. cat The methanol synthesis reaction was carried out by hydrogenation of CO2 at ·h. The relationship between methanol selectivity and time-space yield in this embodiment is shown in FIG. Figure 2 The reaction results are shown in Table 1.

[0029] Example 5: A method for regulating the grain size of copper and zinc components in a copper-based catalyst by cobalt modification, the specific steps are as follows: (1) dissolving copper nitrate, zinc nitrate and cobalt nitrate in an anhydrous ethanol solution to obtain a mixed solution; the molar ratio of the copper nitrate, zinc nitrate and cobalt nitrate is 1:1:0.14; (2) An oxalic acid-ethanol solution (the oxalic acid concentration in the oxalic acid-ethanol solution is 4.5 mol / L) is uniformly added dropwise to the mixed solution at a rate of 10 mL / min, and the mixture is stirred at a water bath temperature of 40°C for 2.8 h. The mixture is allowed to stand for aging at room temperature for 2 h. Anhydrous ethanol is used as a detergent, and the solid is washed by centrifugation. The solid is then dried at a temperature of 60°C for 18 h to obtain a precursor. The molar ratio of the total metal ions of copper, zinc and cobalt in the mixed solution to oxalic acid is 1:2.8. (3) The precursor was heated to 380°C at a rate of 3°C / min and calcined at this temperature for 5 h to obtain a cobalt-modified copper-based catalyst; The cobalt-modified copper-based catalyst was placed at a temperature of 280° C. and subjected to a pre-reduction treatment in a H 2 atmosphere for 2 h to obtain a pre-reduced cobalt-modified copper-based catalyst; The XRD patterns of the copper-based catalysts of Examples 1 to 5 and Comparative Example 1 after reduction treatment are shown in FIG. Figure 1 ,in Figure 1 (a) is the XRD spectrum of the catalyst after reduction at 280℃ for 2h, (b) is the XRD spectrum of the catalyst after reduction at 30° to 52°; Figure 1(a) It can be seen that CuO turns into Cu (PDF#85-1326) after reduction, and the diffraction peaks at 43.32°, 50.45° and 74.12° are attributed to the characteristic peaks of (111), (200) and (220) crystal planes respectively; zinc oxide is mainly ZnO (PDF#99-0111); in addition, Figure 1 (a) It can be seen that the doping of cobalt makes the diffraction peak gradually broaden. The decomposition product of cobalt oxalate in air atmosphere below 700℃ is cobalt tetroxide. It may be due to the low content that no relevant diffraction peak is found in the XRD pattern, or it may be that the cobalt component is well dispersed in the catalyst; Figure 1 (b) It can be seen that compared with the catalyst in Comparative Example 1, the catalysts doped with different cobalt contents have a phenomenon of shifting the characteristic diffraction peaks of Cu and ZnO to low diffraction angles. The above results indicate that after reduction treatment, part of the Cu enters the ZnO lattice, while the Zn (or Co) enters the Cu. The doping of cobalt promotes this process, that is, it improves the interaction between metal-metal and metal-support. In addition, all the catalysts doped with Co have a shift of Cu and ZnO diffraction peaks to low angles compared with Comparative Example 1, proving that the cobalt promoter has been successfully introduced into the Cu / ZnO catalyst. The copper-based catalyst modified by cobalt in this embodiment has a Cu grain size of about 10.1 nm and a ZnO grain size of about 10.0 nm after the pre-reduction treatment. The specific surface area of the copper-based catalyst modified by cobalt is about 82.10 m 2 / g; Application of cobalt-modified copper-based catalyst in CO2 hydrogenation to methanol: The pre-reduced cobalt-modified copper-based catalyst was placed in the reaction zone of the fixed bed, and the raw gas H2 and CO2 (H2 to CO2 molar ratio of 3:1) were introduced at a temperature of 260°C, a pressure of 3 MPa, and a mass space velocity of 11000 mL / g. cat The methanol synthesis reaction was carried out by hydrogenation of CO2 at ·h. The relationship between methanol selectivity and time-space yield in this embodiment is shown in FIG. Figure 2 The reaction results are shown in Table 1.

[0030] Example 6: A method for regulating the grain size of copper and zinc components in a copper-based catalyst by cobalt modification, the specific steps are as follows: (1) dissolving copper nitrate, zinc nitrate and cobalt nitrate in an anhydrous ethanol solution to obtain a mixed solution; the molar ratio of the copper nitrate, zinc nitrate and cobalt nitrate is 1:1:0.07; (2) Oxalic acid-ethanol solution (the oxalic acid concentration in the oxalic acid-ethanol solution is 3 mol / L) was uniformly added dropwise to the mixed solution at a rate of 5 mL / min, stirred in a water bath at 25°C for 4 h, and aged at room temperature for 2 h. Anhydrous ethanol was used as a detergent, and the solid was washed by centrifugation. The solid was dried at 75°C for 14 h to obtain a precursor; the molar ratio of the total metal ions of copper, zinc and cobalt in the mixed solution to oxalic acid was 1:2.0; (3) The precursor was heated to 400 °C at a rate of 2.5 °C / min and calcined at this temperature for 5 h to obtain a cobalt-modified copper-based catalyst. The cobalt-modified copper-based catalyst was placed at a temperature of 290° C. and subjected to a pre-reduction treatment in a H 2 atmosphere for 2.8 h to obtain a pre-reduced cobalt-modified copper-based catalyst; The Cu crystal size of the pre-reduced cobalt-modified copper-based catalyst after the pre-reduction treatment is about 15.3 nm, the ZnO crystal size is about 13.0 nm, and the specific surface area of the pre-reduced cobalt-modified copper-based catalyst is about 64.22 m 2 / g; Application of cobalt-modified copper-based catalyst in CO2 hydrogenation to methanol: The pre-reduced cobalt-modified copper-based catalyst was placed in the reaction zone of the fixed bed, and the raw gas H2 and CO2 (H2 to CO2 molar ratio of 3:1) were introduced at a temperature of 260°C, a pressure of 3 MPa, and a mass space velocity of 11000 mL / g. cat The methanol synthesis reaction was carried out by CO2 hydrogenation at 400 ℃ and 800 ℃. The reaction results are shown in Table 1.

[0031] Example 7: A method for regulating the grain size of copper and zinc components in a copper-based catalyst by cobalt modification, the specific steps are as follows: (1) dissolving copper nitrate, zinc nitrate and cobalt nitrate in an anhydrous ethanol solution to obtain a mixed solution; the molar ratio of the copper nitrate, zinc nitrate and cobalt nitrate is 1:1:0.07; (2) An oxalic acid-ethanol solution (the oxalic acid concentration in the oxalic acid-ethanol solution is 3.5 mol / L) is uniformly added dropwise to the mixed solution at a rate of 8 mL / min, and the mixture is stirred at a water bath temperature of 35°C for 2.5 h. The mixture is allowed to stand for aging at room temperature for 1.5 h. Anhydrous ethanol is used as a detergent, and the solid is washed by centrifugation. The solid is then dried at a temperature of 70°C for 10 h to obtain a precursor. The molar ratio of the total metal ions of copper, zinc and cobalt in the mixed solution to that of oxalic acid is 1:1.05. (3) The precursor was heated to 380°C at a rate of 3°C / min and calcined at this temperature for 4 h to obtain a cobalt-modified copper-based catalyst; The cobalt-modified copper-based catalyst is placed at a temperature of 300° C. and subjected to a pre-reduction treatment in a H 2 atmosphere for 2 hours to obtain a pre-reduced cobalt-modified copper-based catalyst; The Cu crystal size of the pre-reduced cobalt-modified copper-based catalyst after the pre-reduction treatment is about 16.2 nm, the ZnO crystal size is about 13.9 nm, and the specific surface area of the pre-reduced cobalt-modified copper-based catalyst is about 39.47 m 2 / g; Application of cobalt-modified copper-based catalyst in CO2 hydrogenation to methanol: The pre-reduced cobalt-modified copper-based catalyst was placed in the reaction zone of the fixed bed, and the raw gas H2 and CO2 (H2 to CO2 molar ratio of 3:1) were introduced at a temperature of 260°C, a pressure of 3 MPa, and a mass space velocity of 11000 mL / g. cat ·h, CO2 hydrogenation to methanol reaction was carried out, and the reaction results are shown in Table 1; Table 1. Results of CO2 hydrogenation to methanol over cobalt-modified copper-based catalysts catalyst XCO2(%) CO selectivity (%) CH3OH selectivity (%) CH4 selectivity (%) Methanol space-time yield (g / g·h) Comparative Example 1 19.19 69.13 30.43 0.44 0.23 Example 1 11.26 46.21 52.08 1.71 0.24 Example 2 9.46 25.73 61.86 12.41 0.27 Example 3 12.37 19.00 67.32 13.68 0.34 Example 4 11.82 15.06 59.00 25.94 0.28 Example 5 15.50 9.00 34.51 51.77 0.22 Example 6 10.61 23.58 63.32 13.10 0.27 Example 7 10.91 35.60 45.89 18.52 0.21 As can be seen from Table 1, the selectivity of the Co-doped catalyst to methanol is significantly improved compared with that of Comparative Example 1; the main product of the catalyst in Comparative Example 1 is CO. After doping with Co, the product moves towards methanol. The doping of surface Co improves the ability of the catalyst to dissociate and adsorb H2, and promotes the hydrogenation process of the catalyst; As can be seen from Table 1, Example 3 has the highest catalytic activity, the selectivity of methanol reaches 67.32%, and the methanol space-time yield is 0.335 g / g cat ·h; while the methanol selectivity of Comparative Example 1 was 30.43%, and the methanol space-time yield was 0.23 g / g cat h, it can be seen that cobalt doping has a positive effect on the catalyst in the reaction of producing methanol by hydrogenation of carbon dioxide. On the other hand, the higher methane selectivity (51.8%) of Example 5 leads to its poor performance. The generation of higher hydrocarbon products (4.72%) was detected in Example 5, which may be caused by excessive Co doping; therefore, with the increase of cobalt content, the selectivity of the catalyst for methanol and methane continues to increase until the best methanol activity is achieved in Example 3. The cobalt content directly affects the selectivity of the product for methanol and the time-space yield of methanol. With the increase of Co content, it shows a volcano-shaped trend. At 7Co, the time-space yield and selectivity of methanol both reach their maximum values, as shown in Figure 3. Figure 2 shown.

[0032] The above describes the specific embodiments of the present invention in detail, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

Claims

1. A method for regulating the grain size of copper and zinc components in a copper-based catalyst by cobalt modification, characterized in that: The specific steps are as follows: (1) dissolving copper nitrate, zinc nitrate and cobalt nitrate in anhydrous ethanol solution to obtain a mixed solution; (2) Add the oxalic acid-ethanol solution dropwise to the mixed solution at a uniform rate, stir and react for 2-4 hours at a water bath temperature of 20-40°C, let it stand at room temperature, separate the solid and liquid, and dry the solid to obtain the precursor; (3) The precursor is heated to 350-450°C at a constant speed and calcined at a constant temperature for 3-5 hours to obtain a cobalt-modified copper-based catalyst.

2. The method for controlling the grain size of copper and zinc components in a copper-based catalyst by cobalt modification according to claim 1, characterized in that: In step (1), the molar ratio of copper nitrate, zinc nitrate and cobalt nitrate is 1:1:0.02-0.

14.

3. The method for controlling the grain size of copper and zinc components in a copper-based catalyst by cobalt modification according to claim 1, characterized in that: The molar ratio of the total metal ion molar amount of copper, zinc and cobalt in the mixed solution of step (2) to oxalic acid is 1:1.05~3.0, the oxalic acid concentration in the oxalic acid-ethanol solution is 3~5 mol / L, and the droplet acceleration rate of the oxalic acid-ethanol solution is 5~10 mL / min.

4. The method for regulating the grain size of copper and zinc components in a copper-based catalyst by cobalt modification according to claim 1, characterized in that: The standing time in step (2) is 1 to 3 hours.

5. The method for controlling the grain size of copper and zinc components in a copper-based catalyst by cobalt modification according to claim 1, characterized in that: The uniform heating rate in step (3) is 2~3℃ / min.

6. Use of a cobalt-modified copper-based catalyst prepared by the method according to any one of claims 1 to 5 in the CO2 hydrogenation to methanol reaction.

7. The use according to claim 6, characterized in that: The cobalt-modified copper-based catalyst is placed at a temperature of 280-300° C. and subjected to a pre-reduction treatment in a H 2 atmosphere for 2-3 hours before the catalytic reaction.

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