Preparation method and application of aluminum modified copper-based catalyst

Abstract

The invention discloses a preparation method and application of an aluminum modified copper-based catalyst, and belongs to the technical field of heterogeneous electrochemical catalysis carbon dioxide reduction. The aluminum-modified copper-based catalyst is prepared through a hydrothermal method, the prepared aluminum-modified copper-based catalyst is used for electrochemical catalysis of a carbon dioxide reduction reaction, controllable adjustment of a hydrogen bond network in a methane and ethylene reaction path can be achieved, and therefore free switching of methane and ethylene products is achieved. According to the method disclosed by the invention, a reaction path for preparing methane and ethylene products by electrochemical catalysis of carbon dioxide reduction is effectively changed through dynamic regulation and control on a catalyst interface hydrogen bond network, so that the selectivity of the methane or ethylene products is further improved, and finally, the selectivity of the methane or ethylene products is greater than 55% under the high current density of 500mA / cm < 2 >; meanwhile, the reaction can be stably carried out for more than 50 hours.

Description

Technical Field

[0001] The present invention belongs to the technical field of heterogeneous electrochemical catalytic carbon dioxide reduction and relates to a preparation method and application of an aluminum-modified copper-based catalyst. Background Art

[0002] Carbon dioxide (CO2) is a greenhouse gas produced by humans in their daily lives. With the ongoing industrialization process, atmospheric CO2 concentrations continue to rise, leading to a series of environmental problems such as global warming and frequent extreme weather events, posing a serious threat to the sustainable development of ecosystems and human society. Therefore, it is of great significance to develop CO2 resource utilization and promote the development of related industries.

[0003] Currently, the catalytic reduction of CO2 to produce high-value-added products is an important approach for CO2 resource utilization. Common CO2 reduction methods include thermal, electrocatalytic, photocatalytic, and biocatalytic conversions. Thermal CO2 reduction often requires high temperatures and pressures. While achieving high selectivity for CO2 reduction products, thermal catalytic conversion consumes a high amount of energy, severely limiting its economic viability. Photocatalytic conversion often suffers from low CO2 conversion efficiency due to the short lifetime of photogenerated electrons in the catalyst. Biocatalytic CO2 reduction proceeds more slowly and has low conversion efficiency. However, the electrochemical CO2 reduction reaction (CO2RR) not only utilizes renewable electricity as a driving force but also boasts fast reaction rates, high efficiency, and mild reaction conditions. Therefore, utilizing renewable electricity to electrocatalyze the reduction of CO2 to high-value-added chemicals could be an effective approach for CO2 resource utilization, potentially helping to mitigate global environmental degradation caused by excessive carbon emissions and contributing to the goal of carbon neutrality by 2060.

[0004] At the same time, in the electrocatalytic CO2RR process, maintaining a high current density can activate and convert more CO2 molecules into products per unit time. Therefore, the use of a higher current density is not only conducive to improving the CO2RR conversion efficiency, but also the core driving force for promoting the industrial application of electrocatalytic CO2 reduction. However, the catalysts currently used in electrocatalytic CO2RR have low selectivity for single products, weak current tolerance, and poor stability. Especially under high current density conditions, due to the influence of competitive hydrogen evolution reaction, they often cannot fully exert their catalytic effect, which seriously violates the original intention of catalyst design and shackles the progress of electrocatalytic CO2RR towards industrial application. In addition, because the deep reduction process of electrocatalytic CO2RR is extremely complex, there are often multiple competitive multi-electron / proton coupling steps, and it involves the participation of multiple common intermediates (such as *CO and *CHO, etc.), which leads to great difficulties in the selective control of single products in the electrocatalytic CO2RR process. Especially under high current density conditions, due to the influence of competitive hydrogen evolution reaction, the selectivity of single products is generally low.

[0005] Therefore, it is necessary to design an aluminum-modified copper-based catalyst for the efficient electrocatalytic reduction of CO2 to high-value-added methane and ethylene chemicals, while maintaining excellent current tolerance and reaction stability at higher current densities. This helps the catalyst fully exert its catalytic effect at higher current densities to improve the electrocatalytic CO2 conversion efficiency. In summary, the prepared catalyst can be used in the production of electrocatalytic CO2RR to achieve precise control of the selectivity of methane and ethylene products by dynamically regulating the hydrogen bond network at the catalyst reaction interface, thereby improving the selectivity of a single target product. Summary of the Invention

[0006] In order to overcome the problems in the background technology, the present invention modifies the copper-based catalyst by using metallic aluminum to obtain a catalyst with excellent catalytic activity, reaction stability and high current tolerance. The catalyst obtained by using the present invention to prepare at a higher current density can still overcome the influence of the competitive hydrogen evolution reaction and give full play to the catalytic effect, maintaining a high methane or ethylene product selectivity. In addition, the change in the form of aluminum on the surface of the copper-based catalyst can be achieved by systematically regulating the amount of metallic aluminum introduced, thereby affecting the strength of the hydrogen bond network at the catalyst reaction interface during the electrocatalytic CO2RR process to achieve free switching of the methane and ethylene product selectivity, which helps to further improve the selectivity of the single product of methane or ethylene.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0008] In one aspect, the present invention provides a method for preparing an aluminum-modified copper-based catalyst, the preparation method comprising the following steps:

[0009] (1) adding copper nitrate hydrate and aluminum nitrate hydrate into water and stirring until the mixture is completely dissolved to obtain a metal solution;

[0010] (2) adding anhydrous sodium citrate solution to the metal solution obtained in step (1) to obtain a mixed solution;

[0011] (3) titrating the pH of the mixed solution obtained in step (2) using a mixture of sodium carbonate and sodium hydroxide, adjusting the pH of the mixed solution to 9-12, and stirring the mixed solution while maintaining the pH after titration;

[0012] (4) using the mixed solution after stirring in step (3) as a raw material to perform a hydrothermal reaction, and obtaining a reaction product after the reaction is completed;

[0013] (5) centrifuging the reaction product obtained in step (4), and then centrifugally washing and drying the solid product obtained by centrifugation to obtain a dry solid product;

[0014] (6) The dried solid product obtained in step (5) is calcined and then ground to obtain an aluminum-modified copper-based catalyst.

[0015] Preferably, in step (1), the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate is copper nitrate hydrate:aluminum nitrate hydrate=1:(0.07-2).

[0016] Preferably, in step (2), the molar concentration of the anhydrous sodium citrate solution is 0.3-0.7 mmol / L, and the amount of the anhydrous sodium citrate solution added is 0.05-0.15 times the volume of the metal solution.

[0017] Preferably, the molar concentration of sodium carbonate in the aqueous mixture in step (3) is 1.0-1.4 mol / L, and the molar ratio of sodium carbonate to sodium hydroxide in the aqueous mixture is sodium carbonate:sodium hydroxide=2:1. Since the aqueous mixture is prepared by adding sodium carbonate and sodium hydroxide separately to the same water, the molar concentrations of the two relative to the same volume of water are known. Once the molar concentrations and the molar ratio of sodium carbonate to sodium hydroxide are known, the amounts of sodium carbonate and sodium hydroxide to be added to the water can be determined.

[0018] Preferably, in step (3), the mixed solution with a stable pH after titration is kept at room temperature and pressure and stirred for at least 2 hours.

[0019] Preferably, in step (4), the hydrothermal reaction temperature is 50-80° C., and the reaction time is 6-10 hours.

[0020] Preferably, in step (5), the solid product is washed alternately by centrifugation using deionized water and ethanol.

[0021] Preferably, in step (6), the calcination temperature is 400-600° C., and the calcination time is 1-3 hours.

[0022] Another aspect of the present invention provides an aluminum-modified copper-based catalyst, which is prepared by the above-mentioned preparation method.

[0023] The present invention also proposes the application of the above-mentioned aluminum-modified copper-based catalyst, which is used for electrochemical catalytic reduction of carbon dioxide to produce methane and ethylene products. When the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate is 1:0.07≤copper nitrate hydrate:aluminum nitrate hydrate<1:0.7, the selectivity of ethylene product is higher than the selectivity of methane product; when the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate is 1:0.7<copper nitrate hydrate:aluminum nitrate hydrate≤1:2, the selectivity of methane product is higher than the selectivity of ethylene product. The free switching of the selectivity of methane or ethylene products is achieved by dynamically regulating the hydrogen bond network of the catalyst reaction interface. When the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate is copper nitrate hydrate:aluminum nitrate hydrate=1:2, at 500mA / cm 2 The best methane product selectivity of 57.4% can be obtained at a high current density of 500mA / cm, at which time the selectivity of ethylene is almost zero; when the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate is copper nitrate hydrate: aluminum nitrate hydrate = 1:0.07, at 500mA / cm 2 The best ethylene product selectivity of 56.1% can be obtained at a high current density of 1.5, while the methane product selectivity is less than 1%.

[0024] When the content of aluminum introduced during the preparation process of the aluminum-modified copper-based catalyst of the present invention is different, the existence form of aluminum in the aluminum-modified copper-based catalyst prepared will be significantly different. When the content of aluminum introduced is less, aluminum will be present in the copper-based catalyst lattice in the form of atomic doping, and the interaction between atomically dispersed Al and Cu will be utilized to effectively improve the electronic environment of the Cu center, so that it can more efficiently promote the adsorption of water molecules (*H2O) and protonate with *CO to produce *CHO intermediates. At the same time, the atomically dispersed Al sites also reduce the energy barrier for CC coupling with *CO on adjacent copper sites, thereby achieving highly selective generation of ethylene products. If the aluminum introduced is excessive, aluminum will be present on the copper-based catalyst surface in the form of aluminum oxide, thereby reducing the dissociation energy barrier of water molecules at its reaction interface to produce more protons (*H), which significantly reduces the energy barrier for hydrogenation of *CO and *H on the copper site, and ultimately achieving highly selective generation of methane products.

[0025] Beneficial effects of the present invention:

[0026] 1. The present invention prepares an aluminum-modified copper-based catalyst, utilizes aluminum to optimize the electronic structure of the copper active center to reduce the adsorption and activation reaction energy barriers of CO2, and simultaneously utilizes the electronic properties of aluminum to effectively improve the properties of the hydrogen bond network within the catalyst reaction interface, thereby achieving the selective generation of protons in the *CO protonation process in the electrocatalytic CO2RR, thereby improving the selective production of methane or ethylene as a single product.

[0027] 2. The present invention can regulate the form of aluminum on the surface of the copper-based catalyst by regulating the amount of aluminum introduced, that is, at low aluminum content, aluminum exists in the form of atomic doping, and at high aluminum content, aluminum exists in the form of aluminum oxide, thereby maximizing the highly selective production of methane or ethylene products.

[0028] 3. The aluminum-modified copper-based catalyst prepared by the present invention has excellent single catalytic activity for methane or ethylene products, high current tolerance and reaction stability. 2 Under higher current density conditions, it can be stable for more than 50 hours. At the same time, under higher current density conditions, it can significantly inhibit the competitive hydrogen evolution reaction so that it can still play an excellent catalytic role, and ultimately achieve highly selective production of methane or ethylene products.

[0029] 4. The aluminum-modified copper-based catalyst used in the present invention has a simple preparation method, a simple method for selectively controlling different products, and is suitable for industrial promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 1 and 2 are SEM images of the aluminum-modified copper-based catalysts prepared in Example 1 and Example 2 of the present invention, wherein Figure (a) is a SEM image of the aluminum-modified copper-based catalyst of Example 1, and Figure (b) is a SEM image of the aluminum-modified copper-based catalyst of Example 2;

[0031] Figure 2 is the XRD pattern of the aluminum-modified copper-based catalyst prepared in Examples 1-5 of the present invention;

[0032] Figure 3 This is a performance comparison chart of electrocatalytic carbon dioxide reduction using aluminum-modified copper-based catalysts at different feed rates;

[0033] Figure 4 Graph showing the performance of the aluminum-modified copper-based catalysts prepared in Examples 1 and 2 of the present invention for electrocatalytic carbon dioxide reduction to produce methane and ethylene products at different current densities;

[0034] Figure 5 It is a gas chromatogram of methane or ethylene products prepared by electrocatalytic reduction of carbon dioxide using the aluminum-modified copper-based catalyst of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0036] In the examples and comparative examples of the present invention, chemical reagents not otherwise specified were all commercially available analytically pure for use in the experiments.

[0037] Example 1

[0038] In this embodiment, an aluminum-modified copper-based catalyst was prepared by the following method:

[0039] (1) 9 mmol (2174.4 mg) of copper nitrate trihydrate and 0.6 mmol (225.1 mg) of aluminum nitrate nonahydrate (the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate is 1:0.07) were added to a beaker containing 100 mL of deionized water and stirred until completely dissolved to obtain a metal solution.

[0040] (2) 5 mmol (1290.4 mg) of anhydrous sodium citrate was dissolved in 10 mL of deionized water to obtain a 0.5 mol / L anhydrous sodium citrate solution, which was then added to the above metal solution to obtain a mixed solution.

[0041] (3) The pH of the mixed solution was titrated using an aqueous solution of a mixture of sodium carbonate and sodium hydroxide, and the pH of the solution was adjusted to 10. The mixed solution was then stirred at room temperature and pressure for 2 hours. The concentration of sodium carbonate in the aqueous solution was 1.2 mol / L, and the concentration of sodium hydroxide was 0.6 mol / L, i.e., the molar ratio of sodium carbonate to sodium hydroxide was sodium carbonate:sodium hydroxide = 2:1.

[0042] (4) The stirred mixed solution was transferred to a hydrothermal kettle and placed in a constant temperature drying oven at 60° C. to react for 8 hours, and a reaction product was obtained after the reaction was completed.

[0043] (5) The solid product after centrifugation was washed alternately with deionized water and anhydrous ethanol for a total of 4 times, and then the solid product was dried.

[0044] (6) The dried solid product was placed in a muffle furnace at 500° C. and calcined for 2 hours. After the calcination, the solid material obtained was collected and ground to obtain a low aluminum content modified copper-based catalyst.

[0045] The aluminum-modified copper-based catalyst prepared in this embodiment and a 5% Nafion solution were ultrasonically dispersed in an isopropanol solvent to obtain a catalyst ink, which was then evenly sprayed on the surface of the gas diffusion layer to obtain a working electrode. The obtained working electrode was then fully dried and loaded into the cathode side of the flow electrolytic cell. The anode side was a titanium felt coated with iridium dioxide. After that, a 1 mol / L potassium hydroxide electrolyte was passed through the anode and cathode respectively, and then a carbon dioxide gas with a volume concentration of 99.999% was passed into the gas chamber of the flow electrolytic cell. Finally, a constant current electrolysis (current density of 500 mA / cm2) was performed using an electrochemical workstation. 2 ), the best ethylene selectivity of 57.4% was obtained, with almost no methane produced.

[0046] Example 2

[0047] In this example, the aluminum-modified copper-based catalyst was prepared by the same method as in Example 1, except that: the copper nitrate trihydrate used in this example was 9 mmol (2174.4 mg), the aluminum nitrate nonahydrate was 18 mmol (6752.3 mg), and the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate was copper nitrate hydrate: aluminum nitrate hydrate = 1:2.

[0048] The high aluminum content modified copper-based catalyst prepared in this example was subjected to the preparation method of the working electrode and the electrocatalytic CO2 reduction reaction test process in Example 1. 2 The best methane selectivity was 56.1%, and the ethylene selectivity was almost zero.

[0049] The copper-based catalysts prepared in Example 1 and Example 2 were subjected to SEM experiments. Figure 1 As shown. A comparison of the catalysts obtained in Examples 1 and 2 shows that the introduction of different aluminum contents does not change the overall structure of the copper-based catalyst. However, as the amount of aluminum introduced increases, an alumina skeleton gradually appears on the surface of the copper-based catalyst. Specifically, as the aluminum doping level gradually increases, the alumina species gradually become clearer, and the EDS spectrum clearly indicates an increase in aluminum content.

[0050] Example 3

[0051] In this example, an aluminum-modified copper-based catalyst was prepared using the same method as in Example 1, except that: 9 mmol (2174.4 mg) of copper nitrate trihydrate and 6 mmol (2250.8 mg) of aluminum nitrate nonahydrate were used in this example, and the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate was 1:0.7.

[0052] The high aluminum content modified copper-based catalyst prepared in this example was subjected to the preparation method of the working electrode and the electrocatalytic CO2 reduction reaction test process in Example 1. 2 The methane selectivity was 28.1% and the ethylene selectivity was 24.3%. The methane and ethylene selectivities were essentially equal.

[0053] Example 4

[0054] In this example, the aluminum-modified copper-based catalyst was prepared using the same method as in Example 1, except that: the copper nitrate trihydrate used in this example was 9 mmol (2174.4 mg), the aluminum nitrate nonahydrate was 3 mmol (1125.4 mg), and the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate was copper nitrate hydrate: aluminum nitrate hydrate = 1:0.3.

[0055] The aluminum-modified copper-based catalyst prepared in this example was subjected to the preparation method of the working electrode and the electrocatalytic CO2 reduction reaction test process in Example 1. 2 A methane selectivity of 15.8% and an ethylene product selectivity of 35.7% were obtained.

[0056] Example 5

[0057] In this example, an aluminum-modified copper-based catalyst was prepared using the same method as in Example 1, except that: 9 mmol (2174.4 mg) of copper nitrate trihydrate and 12 mmol (4501.6 mg) of aluminum nitrate nonahydrate were used in this example, and the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate was 1:1.3.

[0058] The aluminum-modified copper-based catalyst prepared in this example was subjected to the preparation method of the working electrode and the electrocatalytic CO2 reduction reaction test process in Example 1. 2 A methane selectivity of 42.5% and an ethylene product selectivity of 12.4% were obtained.

[0059] The copper-based catalysts prepared in Examples 1-5 were subjected to XRD experiments, and the results were as follows: Figure 2 As shown. Figure 2It can be seen that after the present invention introduces aluminum atoms on the surface of the copper-based catalyst, it has a diffraction peak distribution similar to that of the copper oxide catalyst that has not been modified with aluminum, indicating that the introduction of a low aluminum content will not change the overall structure of the catalyst. Specifically, copper oxide phases are present in the copper-based catalyst modified with low aluminum content, wherein the diffraction peaks located near 35.7°, 39.1° and 48.8° correspond to the (111), (11-1) and (20-2) crystal planes of copper oxide, respectively. In addition, the prepared copper-based catalyst modified with high aluminum content exhibits a similar copper oxide pattern, and at the same time, the copper-based catalyst modified with high aluminum content also exhibits diffraction peaks related to aluminum oxide, wherein the key diffraction peaks located at 30.4° and 41.8° are related to the (111) and (020) crystal planes of aluminum oxide.

[0060] The copper-based catalysts prepared in Examples 1-5 were tested for their electrochemical catalytic carbon dioxide reduction performance. The experimental results are as follows: Figure 3 As shown, the copper-based catalyst modified with low aluminum content prepared in Example 1 exhibits higher ethylene selectivity, and the copper-based catalyst modified with high aluminum content prepared in Example 2 exhibits higher methane selectivity. The aluminum-modified copper-based catalyst prepared in Example 3 exhibits a critical value for selective conversion of ethylene and methane. By comparing the product selectivities of Examples 1-5, it can be seen that as the aluminum content increases, the selectivity of the catalyst for ethylene gradually decreases. And as the aluminum content further increases, the selectivity of the catalyst for methane gradually increases. In particular, the copper-based catalyst modified with low aluminum content in Example 1 and the copper-based catalyst modified with high aluminum content in Example 2 were subjected to electrochemical carbon dioxide reduction reactions at different current densities, as shown in FIG. Figure 4 As shown, at 500mA / cm 2 At a current density of 1.5 wt %, the catalyst obtained in Example 1 exhibited an ethylene selectivity of 56.1%, and the catalyst obtained in Example 2 exhibited a methane selectivity of 57.4%.

[0061] Example 6

[0062] In this embodiment, an aluminum-modified copper-based catalyst was prepared by the following method:

[0063] (1) 9 mmol (2174.4 mg) of copper nitrate trihydrate and 0.6 mmol (225.1 mg) of aluminum nitrate nonahydrate (the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate is 1:0.07) were added to a beaker containing 100 mL of deionized water and stirred until completely dissolved to obtain a metal solution.

[0064] (2) 1.5 mmol of anhydrous sodium citrate was dissolved in 5 mL of deionized water to obtain a 0.3 mol / L anhydrous sodium citrate solution, and the solution was added to the metal solution to obtain a mixed solution.

[0065] (3) The pH of the mixed solution was titrated using an aqueous solution of a mixture of sodium carbonate and sodium hydroxide, and the pH of the solution was adjusted to 9. The mixed solution was then stirred at room temperature and pressure for 2 hours. The concentration of sodium carbonate in the aqueous solution was 1.0 mol / L, and the concentration of sodium hydroxide was 0.5 mol / L, i.e., the molar ratio of sodium carbonate to sodium hydroxide was sodium carbonate:sodium hydroxide = 2:1.

[0066] (4) The stirred mixed solution was transferred to a hydrothermal kettle and placed in a constant temperature drying oven at 50° C. to react for 10 hours, and a reaction product was obtained after the reaction was completed.

[0067] (5) The solid product after centrifugation was washed alternately with deionized water and anhydrous ethanol for a total of 4 times, and then the solid product was dried.

[0068] (6) The dried solid product was placed in a muffle furnace at 400° C. and calcined for 3 hours. After the calcination, the solid material obtained was collected and ground to obtain a low aluminum content modified copper-based catalyst.

[0069] The aluminum-modified copper-based catalyst prepared in this example was subjected to the preparation method of the working electrode and the electrocatalytic CO2 reduction reaction test process in Example 1. 2 When the ethylene selectivity was 45.8%, the methane selectivity was within 10%. The aluminum-modified copper-based catalyst prepared in this example also maintained a high selectivity for ethylene under high current density conditions.

[0070] Example 7

[0071] In this example, the aluminum-modified copper-based catalyst was prepared using the same method as in Example 6, except that the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate in this example was 1:2.

[0072] The aluminum-modified copper-based catalyst prepared in this example was subjected to the preparation method of the working electrode and the electrocatalytic CO2 reduction reaction test process in Example 1. 2 The methane selectivity was 43.2% and the ethylene selectivity was less than 7%. The aluminum-modified copper-based catalyst prepared in this example also maintained a high methane selectivity under high current density conditions.

[0073] Example 8

[0074] In this embodiment, an aluminum-modified copper-based catalyst was prepared by the following method:

[0075] (1) 9 mmol (2174.4 mg) of copper nitrate trihydrate and 0.6 mmol (225.1 mg) of aluminum nitrate nonahydrate (the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate is 1:0.07) were added to a beaker containing 100 mL of deionized water and stirred until completely dissolved to obtain a metal solution.

[0076] (2) 10.5 mmol of anhydrous sodium citrate was dissolved in 15 mL of deionized water to obtain a 0.7 mol / L anhydrous sodium citrate solution, which was then added to the metal solution to obtain a mixed solution.

[0077] (3) The pH of the mixed solution was titrated using an aqueous solution of a mixture of sodium carbonate and sodium hydroxide, and the pH of the solution was adjusted to 12. The mixed solution was then stirred at room temperature and pressure for 2 hours. The concentration of sodium carbonate in the aqueous solution was 1.4 mol / L, and the concentration of sodium hydroxide was 0.7 mol / L, i.e., the molar ratio of sodium carbonate to sodium hydroxide was sodium carbonate:sodium hydroxide = 2:1.

[0078] (4) The stirred mixed solution was transferred to a hydrothermal kettle and placed in a constant temperature drying oven at 80° C. to react for 6 hours, and a reaction product was obtained after the reaction was completed.

[0079] (5) The solid product after centrifugation was washed alternately with deionized water and anhydrous ethanol for a total of 4 times, and then the solid product was dried.

[0080] (6) The dried solid product was placed in a muffle furnace at 600° C. and calcined for 1 hour. After the calcination, the solid material obtained was collected and ground to obtain a low aluminum content modified copper-based catalyst.

[0081] The aluminum-modified copper-based catalyst prepared in this example was subjected to the preparation method of the working electrode and the electrocatalytic CO2 reduction reaction test process in Example 1. 2 When the ethylene selectivity was 40.7%, the methane selectivity was less than 10%. The aluminum-modified copper-based catalyst prepared in this example also maintained a high selectivity for ethylene under high current density conditions.

[0082] Example 9

[0083] This example used the same method as Example 8 to prepare an aluminum-modified copper-based catalyst, except that 9 mmol (2174.4 mg) of copper nitrate trihydrate and 18 mmol (6752.3 mg) of aluminum nitrate nonahydrate were used, and the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate was 1:2. Similarly, the pH of the mixed solution was titrated using an aqueous solution of sodium carbonate and sodium hydroxide, and the pH of the solution was adjusted to 12.

[0084] The aluminum-modified copper-based catalyst prepared in this example was subjected to the preparation method of the working electrode and the electrocatalytic CO2 reduction reaction test process in Example 1. 2 The methane selectivity was 44.5% and the ethylene selectivity was less than 10%. The aluminum-modified copper-based catalyst prepared in this example also maintained a high methane selectivity under high current density conditions.

[0085] Comparative Example 1

[0086] In this comparative example, the aluminum-modified copper-based catalyst was prepared by the same method as in Example 1, except that the pH in this comparative example was adjusted to 7.

[0087] Compared with the selectivity of the ethylene product obtained in Example 1, the selectivity of the aluminum-modified copper-based catalyst for the ethylene product obtained in this comparative example is reduced, mainly because the pH of the metal solution during the catalyst preparation process is too low, which results in significant differences in the existence form of aluminum species on the catalyst surface, thereby causing the electrochemical catalytic carbon dioxide reduction reaction to be significantly affected by the hydrogen evolution reaction.

[0088] Comparative Example 2

[0089] In this comparative example, the aluminum-modified copper-based catalyst was prepared by the same method as in Example 1, except that the pH in this comparative example was adjusted to 14.

[0090] Compared with the selectivity of the ethylene product obtained in Example 1, the aluminum-modified copper-based catalyst obtained in this comparative example showed a decrease in the selectivity of the ethylene product in the electrochemical catalytic carbon dioxide reduction reaction, while the selectivity of carbon monoxide produced was increased. Therefore, it is necessary to control the pH within the range of the present invention to obtain better selectivity for ethylene or methane.

[0091] By comparing Comparative Example 1 and Comparative Example 2 with Example 1, it can be seen that excessively high or low pH will have a certain impact on the performance of the aluminum-modified copper-based catalyst prepared by the present invention. Although the degree of impact is relatively weak, the farther away from the pH range of the present invention, the greater the impact. Therefore, limiting the pH to the range of the present invention can effectively maintain the relative stability of the performance of the aluminum-modified copper-based catalyst, and during use, the selectivity of methane or ethylene products is maintained in a high range.

[0092] In summary, the aluminum-modified copper-based catalyst prepared by the present invention can maintain excellent methane or ethylene catalytic activity and reaction stability at a higher current density, effectively improving the reaction efficiency while promoting the high selectivity of methane and ethylene. In addition, the high selectivity switching of electrochemical catalytic carbon dioxide to prepare methane or ethylene products can be achieved by simply regulating the amount of aluminum introduced, which further improves the selectivity of a single target product.

[0093] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for preparing an aluminum-modified copper-based catalyst, characterized in that: The preparation method comprises the following steps: (1) adding copper nitrate hydrate and aluminum nitrate hydrate into water and stirring until the mixture is completely dissolved to obtain a metal solution; (2) adding anhydrous sodium citrate solution to the metal solution obtained in step (1) to obtain a mixed solution; (3) titrating the pH of the mixed solution obtained in step (2) using a mixture of sodium carbonate and sodium hydroxide, adjusting the pH of the mixed solution to 9-12, and stirring the mixed solution while maintaining the pH after titration; (4) using the mixed solution after stirring in step (3) as a raw material to perform a hydrothermal reaction, and obtaining a reaction product after the reaction is completed; (5) centrifuging the reaction product obtained in step (4), and then centrifugally washing and drying the solid product obtained by centrifugation to obtain a dry solid product; (6) The dried solid product obtained in step (5) is calcined and then ground to obtain an aluminum-modified copper-based catalyst.

2. The preparation method according to claim 1, wherein: In the step (1), the molar ratio of copper nitrate hydrate to aluminum nitrate hydrate is copper nitrate hydrate:aluminum nitrate hydrate=1:(0.07-2).

3. The preparation method according to claim 1, wherein: In the step (2), the molar concentration of the anhydrous sodium citrate solution is 0.3-0.7 mmol / L, and the amount of the anhydrous sodium citrate solution added is 0.05-0.15 times the volume of the metal solution.

4. The preparation method according to claim 1, wherein: The molar concentration of sodium carbonate in the aqueous mixture in step (3) is 1.0-1.4 mol / L, and the molar ratio of sodium carbonate to sodium hydroxide in the aqueous mixture is sodium carbonate:sodium hydroxide=2:

1.

5. The preparation method according to claim 1, wherein: In the step (3), the mixed solution with a stable pH after titration is kept at room temperature and pressure and stirred for at least 2 hours.

6. The preparation method according to claim 1, wherein: In the step (4), the hydrothermal reaction temperature is 50-80° C., and the reaction time is 6-10 hours.

7. The preparation method according to claim 1, wherein: In the step (5), the solid product is washed alternately by centrifugation using deionized water and ethanol.

8. The preparation method according to claim 1, wherein: In the step (6), the calcination temperature is 400-600° C., and the calcination time is 1-3 hours.

9. An aluminum-modified copper-based catalyst, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 8.

10. The use of an aluminum-modified copper-based catalyst according to claim 9, characterized in that: The aluminum-modified copper-based catalyst is used for electrochemical catalytic reduction of carbon dioxide to produce methane and ethylene products. When the molar ratio of the copper nitrate hydrate to the aluminum nitrate hydrate is 1:0.07≤copper nitrate hydrate:aluminum nitrate hydrate<1:0.7, the selectivity of the ethylene product is higher than the selectivity of the methane product; when the molar ratio of the copper nitrate hydrate to the aluminum nitrate hydrate is 1:0.7<copper nitrate hydrate:aluminum nitrate hydrate≤1:2, the selectivity of the methane product is higher than the selectivity of the ethylene product.

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