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

Abstract

A method for preparing a hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol includes the following steps: (1) mixing appropriate amounts of copper, zinc, and zirconium precursors evenly to obtain precursor materials; (2) placing the precursor obtained in step (1) in a grinding jar, adding an appropriate amount of solvent, and simultaneously placing grinding balls into the grinding jar for grinding, obtaining ground material after grinding; (3) drying and calcining the ground material obtained in step (2) to prepare a sample; (4) subjecting the sample obtained in step (3) to laser irradiation treatment to obtain a hydrophobic Cu / ZnO / ZrO2 catalyst. The catalyst prepared by this method has good activity and hydrothermal resistance.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology for green methanol production, specifically to a hydrophobic catalyst for methanol production by carbon dioxide hydrogenation and its preparation method. Background Technology

[0002] The combustion of fossil fuels (such as coal, oil, and natural gas) is primarily used for power generation, transportation, and industrial production—all aspects closely related to human life and production. However, it also produces large amounts of carbon dioxide gas. As a major greenhouse gas, carbon dioxide poses a serious threat to the balance of ecosystems, making the search for a green and efficient carbon dioxide conversion method urgent. George A. Olah, the 1994 Nobel laureate in Chemistry, pointed out that a circular model for synthesizing methanol through hydrogenation from carbon dioxide offers a new solution to the problem of scarce fossil resources.

[0003] The process of producing methanol by CO2 hydrogenation not only reduces the greenhouse gas CO2, but also allows the high-value-added product methanol to be widely used in human production. Therefore, the reaction system for CO2 catalytic hydrogenation to methanol has significant research value and broad application prospects. However, the CO2 hydrogenation to methanol process suffers from a low feedstock conversion rate. Research has found that the selectivity of the product and the performance of the catalyst are key factors restricting the efficient production of methanol. Compared to the traditional synthesis of methanol from syngas (CO / H2), CO2 hydrogenation to methanol produces less heat; however, water, as a byproduct, easily accelerates the sintering of copper nanocrystals and the pulverization of formed catalyst particles, leading to catalyst deactivation and a short lifespan. Therefore, this process requires higher hydrothermal resistance of the catalyst. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol and its preparation method. The catalyst obtained by this method exhibits excellent hydrothermal resistance, extends the catalyst's service life, and also demonstrates good activity and selectivity.

[0005] The present invention solves the above-mentioned technical problems through the following technical solution:

[0006] A method for preparing a hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol includes the following steps:

[0007] (1) Mix an appropriate amount of copper, zinc and zirconium precursors evenly to obtain precursor materials;

[0008] (2) Place the precursor obtained in step (1) into a grinding jar, add an appropriate amount of solvent, and put grinding balls into the grinding jar for grinding. After grinding, the ground material is obtained.

[0009] (3) The ground material obtained in step (2) is dried and calcined to prepare a sample;

[0010] (4) The sample obtained in step (3) is subjected to laser irradiation to obtain a hydrophobic Cu / ZnO / ZrO2 catalyst.

[0011] Furthermore, the molar ratio of the metal elements Cu:Zn:Zr in the precursors of copper, zinc, and zirconium is 6:2-4:1-5; the precursors of copper, zinc, and zirconium are copper acetate, zinc acetate, and zirconium acetylacetone, respectively.

[0012] Furthermore, the precursor material in step (1) also includes modified silicon dioxide. The specific method for preparing modified silicon dioxide is as follows: silicon dioxide and phenyltriethoxysilane are dissolved in benzene solvent, stirred evenly, and then stirred and reacted at 30-60°C for 1-4 hours; then triethylamine is added dropwise, and then the modification treatment is completed after filtration and drying.

[0013] Preferably, the phenyltriethoxysilane is 10-20% of the mass of silicon oxide, and the triethylamine concentration is 1 mol / L;

[0014] Preferably, the modified silica accounts for 2% of the total mass of the precursor material.

[0015] Furthermore, the solvent obtained in step (2) is one or both of ethanol and isopropanol, and polyethylene glycol is also added to the solvent.

[0016] Furthermore, in step (2), the volume ratio of the precursor material to the solvent is 1:0.5-3;

[0017] Preferably, the volume ratio of the precursor material to the solvent is 1:1.5.

[0018] Furthermore, during ball milling, the diameters of the grinding balls are 20 mm, 10 mm, and 5 mm, respectively;

[0019] The ball milling process involves a rotation speed of 100–600 r / min and a total milling time of 6–12 h.

[0020] Furthermore, during the grinding process, the volume ratio of grinding balls to precursor materials and solvent is 3-5:1.

[0021] Furthermore, the calcination conditions in step (3) are as follows: the tube furnace is in an air atmosphere with a gas flow rate of 100-300 mL / min and a heating rate of 1-10 °C / min, and is calcined at 300-600 °C for 4-8 hours.

[0022] Furthermore, the laser irradiation conditions in step (4) are as follows: performed at room temperature, with a wavelength of 248 nm and a laser pulse energy density of 500 mJ / cm².2 The laser repetition frequency is 10Hz, the pulse width is 30ns, the number of pulses is 1000-2000, and the sample is annealed under vacuum conditions for 0.5-2 hours after laser irradiation.

[0023] A hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol is obtained according to the preparation method described above.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. The hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol provided by the present invention can improve the interaction between different metal salt components by reasonably matching the content of metal components and adding solvent components during ball milling, and at the same time help to improve the dispersion of different components, thereby improving the activity and stability of the catalyst.

[0026] 2. The hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol provided by this invention, through laser irradiation and modification of silicon oxide, causes changes in the surface geometry and chemical properties of the material due to special photothermal effects, as well as the dual effect of modification treatment, thereby enabling the catalyst to form a superhydrophobic surface. In the reaction process of CO2 hydrogenation to methanol, it can exhibit good hydrothermal resistance and extend the service life of the catalyst.

[0027] 3. The hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol provided by this invention has a simple, scalable, low-cost, and environmentally friendly ball milling process. Attached Figure Description

[0028] Figure 1 This is a TEM image of the catalyst prepared in Example 1 of the present invention;

[0029] Figure 2 This is a TEM image of the catalyst prepared in Example 3 of the present invention;

[0030] Figure 3 Schematic diagram of an evaluation device for a catalyst used in the preparation of methanol from CO2 via hydrogenation.

[0031] In the diagram, 1 is the hydrogen gas flow; 2 is the carbon dioxide gas flow; 3 is the nitrogen gas flow; 4 is the methanol reactor; 5 is the water cooler; 6 is the circulating cooling water inlet pipe; 7 is the circulating cooling water outlet pipe; 8 is the gas-liquid separator; 9 is the gas chromatograph; and 10 is the crude methanol collection pipe. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] (1) Dissolve silicon oxide and phenyltriethoxysilane in benzene solvent, stir evenly, and stir the reaction at 50°C for 3 hours; then add 1 mol / L triethylamine dropwise until precipitation is complete, and then filter and dry to complete the modification treatment to obtain modified silicon oxide;

[0035] Cu(CH3COO)2·H2O, Zn(CH3COO)2, and zirconium acetylacetonate were mixed evenly with the metal elements Cu, Zn, and Zr in a molar ratio of 6:3:1. Modified silica was added while stirring to obtain the precursor material. The mass percentage of modified silica in the precursor material was 2%.

[0036] (2) Place the precursor material obtained in step (1) into a 125 ml corundum grinding jar (planetary ball mill PM100, Retsch), add isopropanol, the volume ratio of isopropanol to precursor material is 1.5:1, 20% (volume ratio) of polyethylene glycol is added to the isopropanol, and at the same time, put 5, 50 and 300 grinding balls with diameters of 20 mm, 10 mm and 5 mm respectively into the grinding jar, the ball-to-material ratio is 4:1, the ball milling speed is 500 r / min, and the ball milling time is 8 h.

[0037] After the ball milling is completed, the grinding balls are removed, and the grinding material in the grinding jar is obtained.

[0038] (3) The ground material obtained in step (2) was dried in an oven at 105°C for 12 hours. Then, it was calcined in a tube furnace at 450°C for 6 hours under air atmosphere conditions, with a gas flow rate of 300 mL / min and a heating rate of 5°C / min to obtain the sample.

[0039] (4) The sample obtained in step (3) was subjected to laser irradiation. The laser irradiation was performed at room temperature using a Lambda Physik LPX305iF excimer laser from Germany, with a wavelength of 248 nm and a laser pulse energy density of 500 mJ / cm². 2 The laser repetition frequency was 10 Hz, the pulse width was 30 ns, and the number of pulses was 1000. After laser irradiation, the sample was placed in a vacuum (10 - 5The catalyst was obtained by annealing at 300 degrees Celsius for 1 hour (mbar) to obtain a hydrophobic catalyst.

[0040] Figure 1 The image shows a transmission electron microscope (TEM) image of the catalyst from Example 1. Analysis of the TEM image reveals that the catalyst nanocrystals prepared by ball milling followed by laser irradiation are small, generally distributed in the range of 5-10 nm.

[0041] Example 2

[0042] The technical difference from Example 1 is that the molar ratio of Cu:Zn:Zr is 6:3:3.

[0043] Example 3

[0044] The technical differences from Example 1 are that the number of pulses is 2000, and the sample is in a vacuum (10) after laser irradiation. -5 Annealing at 300 degrees Celsius for 2 hours (mbar).

[0045] Figure 2 The image shown is a transmission electron microscope (TEM) image of the catalyst from Example 3. Analysis of the TEM image reveals that the catalyst nanocrystals are generally smaller than 10 nm and are uniformly distributed.

[0046] Comparative Example 1

[0047] The molar ratio of Cu:Zn:Zr is 6:1:0.5, and the other preparation processes are the same as in Example 1.

[0048] Comparative Example 2

[0049] The laser treatment in step (4) is not used; the rest of the preparation method is the same as in Example 1.

[0050] Comparative Example 3

[0051] In step (2), polyethylene glycol is not added, and the preparation method is the same as in Example 1.

[0052] Comparative Example 4

[0053] The silica in the precursor material was not modified, and the other preparation methods were the same as in Example 1.

[0054] Methods for detecting catalyst activity and selectivity need to be provided.

[0055] The performance of the catalysts for the hydrogenation of carbon dioxide to methanol of Examples 1-3 and Comparative Examples 1-4 was systematically evaluated in a self-built evaluation apparatus. A schematic diagram of the evaluation apparatus is shown below. Figure 3As shown, hydrogen gas stream 1, carbon dioxide gas stream 2, and nitrogen gas stream enter methanol reactor 4 for catalytic reaction. The catalyst is packed in methanol reactor 4. After the reaction is completed, the material is cooled by water cooler 5 and then enters gas-liquid separator 8 for gas-liquid separation. The gas flows out from the top of gas-liquid separator 8 and is analyzed by gas chromatograph 9 to detect the gas components and their corresponding contents. The liquid flows out from the bottom of gas-liquid separator 8 and enters crude methanol collection pipe 10 to discharge crude methanol.

[0056] 1. Catalytic evaluation reaction: The ratio of H2:CO2:N2 in the reaction mixture was 72:24:4; the catalyst particle size was 20-40 mesh; the volume was 1 mL; the pressure was 50 bar; the temperature was 250℃; and the space velocity was 5000 h⁻¹. -1 Before the reaction begins, the catalyst is first reduced in an H2 atmosphere (5% H2 + 95% N2) at a reduction space velocity of 5000 h⁻¹. -1 Pressure 10 bar, temperature 300 degrees, 1 hour, heating rate 5 degrees / minute.

[0057] During the reaction, the liquid phase product was sampled every 3 hours, weighed and the yield was calculated. After three samplings, the heat resistance program was started, the temperature was raised to 380℃ and held for 5 hours. After the heat resistance was completed, the temperature was lowered to 250℃ and the evaluation was continued for 6 hours. The heat resistance retention rate was the ratio of the liquid phase yield of the catalyst before and after the heat resistance.

[0058] 2. Analytical methods: Quantitative detection was performed using gas chromatography with automatic injection. The carrier gas was H2, and the driving gas for the pneumatic valve was N2. The chromatographic column was TDX-01. For liquid product analysis, the chromatographic column was Porapak Q, and the TCD detector was used. The injection port temperature was 120℃, the column temperature was 90℃, and the detector temperature was 150℃.

[0059] The main products of the reaction are methanol and carbon monoxide. The catalytic performance of the catalyst in the hydrogenation of carbon dioxide to methanol is shown in Table 1.

[0060] The results in Table 1 show that the catalyst prepared by ball milling and laser irradiation has excellent catalytic performance in the process of hydrogenating carbon dioxide to methanol, such as the CO2 conversion rate. This is mainly due to the small particle size of the catalyst prepared by ball milling. At the same time, the catalyst has a good heat retention rate, mainly due to the fact that laser irradiation improves the hydrophobicity of the catalyst, thereby improving the hydrothermal resistance and service life of the catalyst.

[0061] The comparison between the results of the examples and Comparative Example 1 shows that when the molar ratio of Cu, Zn, and Zr is within the range of the claims, the catalyst has better catalytic performance, especially CO2 conversion.

[0062] Comparison of Example 2 and Example 1 shows that the introduction of the laser irradiation step greatly improves the heat retention rate of the catalyst, mainly due to the improved hydrophobicity of the catalyst.

[0063] In the catalyst prepared in Comparative Example 4, the silicon oxide modifier was changed to hexamethyldisilazane, which resulted in a decrease in the heat retention rate of the catalyst.

[0064] Comparison of Example 3 and the Example shows that, during ball milling, a suitable solvent-to-material ratio helps to improve the conversion rate of the catalyst in the carbon dioxide hydrogenation process.

[0065] The performance indicators of the catalysts prepared in specific Examples 1-3 and Comparative Examples 1-4 are shown in Table 1 below.

[0066] Table 1

[0067] Conversion rate (%) Methanol selectivity (%) Heat retention rate (%) Example 1 25.3 82.2 88.9 Example 2 21.6 84.1 87.0 Example 3 24.1 81.9 92.1 Comparative Example 1 14.2 79.7 81.6 Comparative Example 2 22.8 78.0 61.4 Comparative Example 3 13.6 76.3 82.5 Comparative Example 4 23.7 77.9 74.2

[0068] As shown in Table 1 above, changing the content of heavy metal elements in the precursor of the catalyst and changing the composition of the solvent during ball milling will affect the CO2 conversion rate of the catalyst; while the modification of silica and the laser irradiation treatment have no significant effect on the CO2 conversion rate of the prepared catalyst, but their heat retention rate is significantly better.

Claims

1. A method for preparing a hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol, characterized in that, Includes the following steps: (1) Mix an appropriate amount of copper, zinc and zirconium precursors evenly to obtain precursor materials; (2) Place the precursor material obtained in step (1) into a grinding jar, add an appropriate amount of solvent, and at the same time put grinding balls into the grinding jar for grinding. After grinding, the ground material is obtained. (3) The ground material obtained in step (2) is dried and calcined to prepare a sample; (4) The sample obtained in step (3) is subjected to laser irradiation to obtain a hydrophobic Cu / ZnO / ZrO2 catalyst; The molar ratio of the metal elements Cu:Zn:Zr in the copper, zinc, and zirconium precursors is 6:2-4:1-5; The precursor material in step (1) also includes modified silicon dioxide. The specific preparation method of modified silicon dioxide is as follows: silicon dioxide and phenyltriethoxysilane are dissolved in benzene solvent, stirred evenly, and stirred for 1 to 4 hours at a temperature of 30 to 60°C; then triethylamine is added dropwise, and the modification is completed after filtration and drying. Polyethylene glycol is also added to the solvent mentioned in step (2).

2. The method for preparing the hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol according to claim 1, characterized in that, The precursors for copper, zinc, and zirconium are copper acetate, zinc acetate, and zirconium acetylacetone, respectively.

3. The method for preparing the hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol according to claim 1, characterized in that, The phenyltriethoxysilane is 10-20% of the mass of silicon oxide, and the triethylamine concentration is 1 mol / L.

4. The method for preparing the hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol according to claim 1, characterized in that, The solvent in step (2) is one or both of ethanol and isopropanol.

5. The method for preparing the hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol according to claim 1, characterized in that, The volume ratio of the precursor material to the solvent in step (2) is 1:0.5-3.

6. The method for preparing the hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol according to claim 5, characterized in that, The volume ratio of the precursor material to the solvent is 1:1.

5.

7. The method for preparing the hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol according to claim 1, characterized in that, During ball milling, the diameters of the grinding balls were 20 mm, 10 mm, and 5 mm, respectively. The ball milling process involves a rotation speed of 100–600 r / min and a total milling time of 6–12 h.

8. The method for preparing the hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol according to claim 7, characterized in that, During the grinding process, the volume ratio of grinding balls to precursor materials and solvent is 3-5:

1.

9. The method for preparing the hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol according to claim 1, characterized in that, The calcination conditions in step (3) are as follows: the tube furnace is in an air atmosphere with a gas flow rate of 100-300 mL / min and a heating rate of 1-10℃ / min, and is calcined at 300-600℃ for 4-8 hours.

10. The method for preparing the hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol according to claim 1, characterized in that, The laser irradiation conditions in step (4) are as follows: performed at room temperature, with a wavelength of 248 nm and a laser pulse energy density of 500 mJ / cm². 2 The laser repetition frequency is 10 Hz, the pulse width is 30 ns, the number of pulses is 1000-2000, and the sample is annealed under vacuum conditions for 0.5-2 hours after laser irradiation.

11. A hydrophobic catalyst for the hydrogenation of carbon dioxide to methanol, characterized in that, The preparation method according to any one of claims 1-10 is obtained.

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