A copper-based catalyst for electrocatalytic reduction of co2 to produce ch4 and preparation and application thereof

Abstract

The application provides a preparation method of a copper-based catalyst for electrocatalytic reduction of carbon dioxide to prepare methane. The preparation method comprises the following steps: firstly, preparing silica nanospheres with a dendritic morphology and a semi-open pore morphology to obtain an MSN carrier for preparing the copper-based catalyst; and then, precipitating copper salt on the surface of the MSN in a highly dispersed form to obtain a silica nanosphere-supported copper electrocatalyst Cu-MSN-I with semi-open pores. The copper-based catalyst exhibits extremely high selectivity (FE of CH4>60%) and yield (CH4 faradaic efficiency reaches 71.1%) in the electrocatalytic reduction of carbon dioxide to prepare methane, and achieves an unexpected technical effect. The copper-based catalyst not only solves the problems of low yield and low selectivity of the catalyst in the prior art, but also has a simple and easy-to-operate preparation method, and has the prospect of industrial application. In addition, by adjusting the content of the loaded copper salt in the MSN carrier, the electrocatalytic reduction product of carbon dioxide can be freely controlled to be methane or ethylene, different demands can be met, and the application prospect is wider.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and relates to a copper-based catalyst, in particular to a copper-based catalyst for electrocatalytic reduction of carbon dioxide to prepare methane as well as preparation and application thereof. BACKGROUND

[0002] The electrocatalytic reduction of carbon dioxide (CO2RR) to produce methane is an important approach to achieve carbon neutralization. This technology can convert CO2 into valuable chemicals and fuels (such as methane), which not only helps to reduce greenhouse gas emissions, but also provides a solution for the storage of renewable energy. To achieve high efficiency, stability and economy of this process, the selection of a suitable catalyst is crucial. At present, the catalysts studied more mainly include copper-based, gold-based, silver-based, zinc-based metals and their alloy materials, as well as some non-metallic materials such as carbon-based materials, nitrides, phosphides, etc. Among them, copper-based catalysts show high activity and selectivity, and are considered to be the most potential catalyst for the electroreduction of CO2 to methane.

[0003] In order to further improve the activity and stability of copper-based catalysts, researchers have designed and prepared catalysts through various means such as nanocrystallization, alloy formation, defect construction, and surface structure adjustment. For example, by constructing copper nanoparticles or copper alloy nanostructures, the number of active sites can be effectively increased, and the catalytic efficiency can be improved. However, the copper-based catalysts reported in the prior art still have the problems of low yield and low selectivity. This is because: first, the number of active sites on the surface of the catalyst is limited, especially at high current density, the lack of active sites will limit the reaction rate. Secondly, in the CO2RR process, there are also side reactions of competing active sites and electrons, in addition to the production of methane, other by-products such as hydrogen, carbon monoxide, formic acid, etc. may also be produced, thereby reducing the selectivity of methane production. This also means that in practical applications, higher electrical energy consumption is often required to drive the reaction, thereby resulting in a significant increase in cost.

[0004] In addition, the catalyst supports commonly used in the current electrocatalytic reduction of carbon dioxide technology are carbon-based materials (activated carbon, carbon nanotubes, etc.), metal oxides, and conductive polymers. One of the common points of these catalyst supports is that they have good electrical conductivity. This is because, as known to those skilled in the art, if the support does not have electrical conductivity, low current density, excessive side reactions, and other situations may occur during the catalytic process, thereby reducing the catalytic activity and selectivity, and further increasing the cost. Silica nanospheres are a kind of porous silica material with small particle size, large specific surface area, porous structure, and high chemical stability, which has been widely used in separation, drug release, analysis and detection, etc. However, silica does not have electrical conductivity, as mentioned earlier, if it is used as a catalyst support, low current density, excessive side reactions, and other situations may occur during the electrocatalytic process.

[0005] At present, in the field of electrocatalytic reduction of carbon dioxide, there is no related report on the catalyst using silica nanospheres as a carrier. SUMMARY

[0006] In view of the problems of low yield and low selectivity of the catalyst in the preparation of methane by electrocatalytic reduction of carbon dioxide in the prior art, the application provides a preparation method of a copper-based catalyst for electrocatalytic reduction of carbon dioxide to prepare methane. The copper-based catalyst uses silica nanospheres with semi-open pores as a carrier, has good performance of electrocatalytic reduction of CO2 to CH4, not only shows extremely high CH4 selectivity in a wide potential range, but also significantly improves the yield, and achieves unexpected technical effects. In addition, the preparation method of the copper-based catalyst is simple and easy to operate, and has the prospect of industrial application.

[0007] The technical scheme of the application is as follows:

[0008] A preparation method of a silica nanosphere supported copper-based catalyst, comprising the following steps:

[0009] (1) Preparation of silica nanospheres: a certain amount of water, butyl aldehyde and CTAB are added to a closed reaction device, and stirred to be uniformly mixed under alkaline conditions. Then a certain amount of TEOS is added, and the stirring state is maintained at room temperature for 20-28h. Liquid-solid separation is performed, and the obtained white solid is washed, dried and calcined to obtain a yellow solid, i.e. silica nanospheres with semi-open pore morphology, which is an MSN carrier. In this step, a certain concentration of CTAB aqueous solution is used in an alkaline solution to realize the regulation of the growth of silica nanospheres, and finally a semi-open pore morphology with a dendritic shape is formed, so that the MSN carrier for preparing a copper-based catalyst is obtained. The application initiatively uses non-conductive silica nanospheres as a catalyst carrier for electrocatalytic reduction of carbon dioxide, which overcomes the technical prejudice.

[0010] The mass ratio of the water, butyl aldehyde, CTAB and TEOS is 100-140: 104-136: 5-8: 20-22. The alkaline condition is that pH=11-12. The washing is specifically performed by washing 3-5 times with water or ethanol. The drying is specifically performed at 70-90 DEG C for 12-18h. The calcination is specifically performed by increasing the temperature to 500-550 DEG C at a temperature increasing rate of 10 DEG C / min, and calcining for 5-7h. Compared with ordinary nanospheres, the MSN prepared in the application is a mesoporous SiO2 carrier, which has a more excellent pore structure, not only provides more abundant Si-OH, which is conducive to the combination of Cu and the formation of more catalytic sites for subsequent electrocatalytic reduction reaction, but also is more conducive to the diffusion of CO2 molecules compared with the solid structure of ordinary nanospheres.

[0011] (2) Loading of copper-based catalyst: take appropriate amount of MSN carrier prepared in step (1) and divalent copper salt in water, stir until the copper salt is dissolved and uniformly dispersed. Then add urea, stir at 60-100℃ under alkaline conditions for 3-5h. Liquid-solid separation, the obtained blue solid is washed, dried, calcined to obtain blue-green powder, namely silica nanosphere supported copper-based catalyst Cu-MSN-I. In this step, according to the chemical precipitation of cations, the copper salt is precipitated on the surface of the MSN in a highly dispersed form, and a silica nanosphere supported copper electrocatalyst Cu-MSN-I with semi-open pores is obtained.

[0012] The amount of divalent copper salt is 1.4-1.6 mmol of copper salt / g of MSN carrier, and the amount of urea is 11-13 mmol of urea / g of MSN carrier; the alkaline condition is pH=10-11. The washing is specifically 3-5 times with water. The drying is specifically 12-18 hours at 50-70℃. The calcination is specifically heating to 300-350℃ at a heating rate of 10℃ / min, and calcining for 4h-6h. The inventors have unexpectedly found that only at a specific content, the copper salt can be fixed on the surface of the MSN carrier in a fine and highly dispersed form; thereby further making the prepared copper-based catalyst have more significant methane catalytic effect (FE>70%, CH4faraday efficiency reaches 71.1%) compared with ordinary catalysts. In addition, too high or too low content of copper salt in the loading process will cause a change in morphology and cannot achieve the expected results.

[0013] Preferably, the divalent copper salt is copper chloride, copper nitrate or copper sulfate.

[0014] The catalyst Cu-MSN-I prepared by the foregoing method has an unexpected technical effect in the electrocatalytic CO2 reduction reaction to produce methane. The inventors have speculated that this is because the composite catalyst formed by combining silica nanospheres and copper metal, at a specific loading amount, provides an electron conduction path through the conductive material, and the silica nanospheres provide structural support and specific catalytic active sites, realizing the synergistic effect of the two, thereby showing excellent selectivity and yield.

[0015] The application of the catalyst Cu-MSN-I in the electrocatalytic CO2 reduction to produce CH4.

[0016] The present application also provides another catalyst. The inventors have found in research that when the amount of divalent copper salt in step (1) is 7-8 mmol of copper salt / g of MSN carrier, a silica nanosphere supported copper-based catalyst Cu-MSN-II is obtained.

[0017] The catalyst Cu-MSN-II is prepared by the method described above. Different from the copper-based catalyst Cu-MSN-I, the product of the electrocatalytic CO2 reduction reaction using the copper-based catalyst Cu-MSN-II is ethylene.

[0018] Application of the catalyst Cu-MSN-II as described above in the electrocatalytic CO2 reduction to produce C2H4.

[0019] Advantages of the present application:

[0020] (1) The silica nanosphere loaded copper-based catalyst described in the present application exhibits extremely high selectivity (FE of CH4>60%) and yield (CH4faradaic efficiency reaches 71.1%) in the electrocatalytic reduction of carbon dioxide to produce methane, solving the problem of low yield and low selectivity of the catalyst in the prior art, and making significant progress.

[0021] (2) The silica nanosphere loaded copper-based catalyst described in the present application uses non-conductive silica nanospheres as a carrier for the first time, and exhibits excellent performance under a certain copper salt content, producing unexpected technical effects.

[0022] (3) The present application provides a preparation method of the silica nanosphere loaded copper-based catalyst, which has simple steps and mild conditions, and is more convenient than other catalyst synthesis processes, which is of great significance for practical application.

[0023] (4) The preparation method described in the present application can freely realize the regulation of the product of the electrocatalytic reduction of carbon dioxide by regulating the content of the loaded copper salt in the MSN carrier, i.e., methane or ethylene, which can meet different needs and has a broader application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The scanning electron microscope picture of the copper-based catalyst Cu-MSN-I prepared in Example 2 of the present application.

[0025] Figure 2 The transmission electron microscope picture of the copper-based catalyst Cu-MSN-I prepared in Example 2 of the present application.

[0026] Figure 3 The scanning electron microscope picture of the copper-based catalyst Cu-MSN-II prepared in Example 5 of the present application.

[0027] Figure 4 The transmission electron microscope picture of the copper-based catalyst Cu-MSN-II prepared in Example 5 of the present application.

[0028] Figure 5The energy dispersive X-ray spectrogram of the copper-based catalyst Cu-MSN-I prepared in Example 2 of the present application.

[0029] Figure 6 The energy dispersive X-ray spectrogram of the copper-based catalyst Cu-MSN-II prepared in Example 5 of the present application.

[0030] Figure 7 The X-ray powder diffraction pattern of the copper-based catalyst Cu-MSN-I prepared in Example 2 of the present application and the copper-based catalyst Cu-MSN-II prepared in Example 5 of the present application.

[0031] Figure 8 The N2 adsorption-desorption isotherm graph of the copper-based catalyst Cu-MSN-I prepared in Example 2 of the present application and the copper-based catalyst Cu-MSN-II prepared in Example 5 of the present application.

[0032] Figure 9 The pore size distribution graph of the copper-based catalyst Cu-MSN-I prepared in Example 2 of the present application and the copper-based catalyst Cu-MSN-II prepared in Example 5 of the present application.

[0033] Figure 10 The faradaic efficiency graph of the copper-based catalyst Cu-MSN-I prepared in Example 2 of the present application for electrocatalytic CO2 reduction.

[0034] Figure 11 The faradaic efficiency graph of the copper-based catalyst Cu-MSN-II prepared in Example 5 of the present application for electrocatalytic CO2 reduction.

[0035] Figure 12 The in-situ infrared spectrogram of the copper-based catalyst Cu-MSN-I prepared in Example 2 of the present application for electrocatalytic CO2 reduction.

[0036] Figure 13 The in-situ infrared spectrogram of the copper-based catalyst Cu-MSN-II prepared in Example 5 of the present application for electrocatalytic CO2 reduction.

[0037] Figure 14 The scanning electron microscope picture of the smooth surface spherical nanoball supported copper catalyst prepared in Comparative Example 2.

[0038] Figure 15 is the faradaic efficiency graph of the smooth surface spherical nanoball supported copper catalyst prepared in Comparative Examples 1-2 for electrocatalytic CO2 reduction.

[0039] Figure 16 is the faradaic efficiency graph of the Cu-MSN catalysts with different Cu loadings prepared in Comparative Examples 3-5 for electrocatalytic CO2 reduction. DETAILED DESCRIPTION

[0040] The application will be further described in connection with the following examples.

[0041] The raw materials used in the present application are commercially available, unless otherwise specified. Among them, copper nitrate (Cu(NO3)2·3H2O, 99%), tetraethyl orthosilicate (TEOS, >99%), urea (99.5%), ammonia (NH4OH, 25-28%), and cetyltrimethylammonium bromide (CTAB) were purchased from China National Pharmaceutical Group Chemical Reagent Co., Ltd. Butyraldehyde (C4H8O, 99%) was purchased from Shanghai Macklin Biochemical Co., Ltd. Copper chloride, copper nitrate, and copper sulfate were purchased from China National Pharmaceutical Group Chemical Reagent Co., Ltd. All materials were used directly without further purification. Deionized water was used in all synthesis processes.

[0042] Example 1: Preparation of silica nanosphere-supported copper-based catalyst Cu-MSN-I

[0043] (1) Preparation of silica nanospheres: 10 g of water, 10.4 g of butyraldehyde, and 0.5 g of CTAB were added to a sealed reaction device and stirred until uniform under alkaline conditions. Then 2 g of TEOS was added and stirred at room temperature for 20 h. The liquid-solid was separated, and the obtained white solid was washed, dried, and calcined to obtain a yellow solid, i.e., silica nanospheres with semi-open pore morphology, which was the MSN carrier.

[0044] The alkaline condition was pH = 11 (appropriate amount of NH4OH was added). The washing was specifically 3 times with ethanol. The drying was specifically at 70°C for 18 hours. The calcination was specifically heating at a rate of 10°C / min to 500°C and calcining for 7 h.

[0045] (2) Loading of copper-based catalyst: 0.35 g of the MSN carrier prepared in step (1) and an appropriate amount of copper chloride were taken in water and stirred until the copper salt was dissolved and uniformly dispersed. Then urea was added, and the mixture was stirred at 60°C under alkaline conditions for 5 h. The liquid-solid was separated, and the obtained blue solid was washed, dried, and calcined to obtain a blue-green powder, i.e., silica nanosphere-supported copper-based catalyst Cu-MSN-I.

[0046] The amount of copper chloride was 1.4 mmol of copper salt per gram of MSN carrier, and the amount of urea was 11 mmol of urea per gram of MSN carrier. The alkaline condition was pH = 10. The washing was specifically 3 times with water. The drying was specifically at 50°C for 18 hours. The calcination was specifically heating at a rate of 10°C / min to 300°C and calcining for 6 h.

[0047] Example 2: Preparation of silica nanosphere-supported copper-based catalyst Cu-MSN-I

[0048] Different from example 1, (1) preparation of silica nanospheres: 12 g of water, 12 g of butyl aldehyde and 0.64 g of CTAB were added into a closed reaction device, and stirred until mixed uniformly under alkaline conditions. Then 2.1 g of TEOS was added, and reacted at room temperature under stirring for 24 h. Liquid-solid separation was performed, and the obtained white solid was washed, dried and calcined to obtain a yellow solid, i.e. silica nanospheres with a semi-open channel morphology, namely the MSN carrier.

[0049] The alkaline condition is pH = 11. The washing is specifically 4 times of ethanol washing. The drying is specifically drying at 75 °C for 14 h. The calcination is specifically heating at a heating rate of 10 °C / min to 510 °C, and calcining for 5.5 h.

[0050] (2) Loading of copper-based catalyst: 0.35 g of the MSN carrier prepared in step (1) and an appropriate amount of copper nitrate were taken in water, and stirred until the copper salt was dissolved and uniformly dispersed. Then urea was added, and stirred at 70 °C under alkaline conditions for 3.5 h. Liquid-solid separation was performed, and the obtained blue solid was washed, dried and calcined to obtain a blue-green powder, i.e. the silica nanosphere loaded copper-based catalyst Cu-MSN-I.

[0051] The amount of copper nitrate is 1.5 mmol of copper salt per g of MSN carrier, and the amount of urea is 11.5 mmol of urea per g of MSN carrier. The alkaline condition is pH = 10. The washing is specifically 4 times of water washing. The drying is specifically drying at 55 °C for 14 h. The calcination is specifically heating at a heating rate of 10 °C / min to 320 °C, and calcining for 4.5 h.

[0052] Example 3: Preparation of silica nanosphere loaded copper-based catalyst Cu-MSN-I

[0053] Different from example 1, (1) preparation of silica nanospheres: 12 g of water, 12 g of butyl aldehyde and 0.64 g of CTAB were added into a closed reaction device, and stirred until mixed uniformly under alkaline conditions. Then 2.1 g of TEOS was added, and reacted at room temperature under stirring for 24 h. Liquid-solid separation was performed, and the obtained white solid was washed, dried and calcined to obtain a yellow solid, i.e. silica nanospheres with a semi-open channel morphology, namely the MSN carrier.

[0054] The alkaline condition is pH = 11. The washing is specifically 4 times of ethanol washing. The drying is specifically drying at 75 °C for 14 h. The calcination is specifically heating at a heating rate of 10 °C / min to 510 °C, and calcining for 5.5 h.

[0055] (2) Copper-based catalyst loading: take 0.35g MSN carrier prepared in step (1) and an appropriate amount of copper sulfate in water, stir until the copper salt is dissolved and uniformly dispersed. Then add urea, stir at 80°C under alkaline conditions for 4h. Liquid-solid separation, the blue solid obtained is washed, dried, calcined to obtain blue-green powder, namely silica nanosphere supported copper-based catalyst Cu-MSN-I.

[0056] Wherein, the amount of copper sulfate is 1.5mmol copper salt / g MSN carrier, and the amount of urea is 12mmol urea / g MSN carrier; the alkaline condition is: pH=11. The washing is specifically: washing with water for 4 times. The drying is specifically: drying at 65°C for 16 hours. The calcination is specifically: heating to 340°C at a heating rate of 10°C / min, and calcining for 5h.

[0057] Example 4: Preparation of silica nanosphere supported copper-based catalyst Cu-MSN-I

[0058] (1) Preparation of silica nanospheres: 14g water, 13.6g butyl aldehyde and 0.8g CTAB were added to a sealed reaction device, and stirred under alkaline conditions until the mixture was uniform. Then 2.2g TEOS was added, and stirred at room temperature for 20-28h. Liquid-solid separation, the white solid obtained was washed, dried and calcined to obtain yellow solid-silica nanospheres with semi-open pore morphology, namely MSN carrier.

[0059] Wherein, the alkaline condition is: pH=12 (add an appropriate amount of NH4OH). The washing is specifically: washing with ethanol for 5 times. The drying is specifically: drying at 90°C for 12 hours. The calcination is specifically: heating to 550°C at a heating rate of 10°C / min, and calcining for 5h.

[0060] (2) Copper-based catalyst loading: take 0.35g MSN carrier prepared in step (1) and an appropriate amount of copper nitrate in water, stir until the copper salt is dissolved and uniformly dispersed. Then add urea, stir at 100°C under alkaline conditions for 3h. Liquid-solid separation, the blue solid obtained is washed, dried, calcined to obtain blue-green powder, namely silica nanosphere supported copper-based catalyst Cu-MSN-I.

[0061] Wherein, the amount of copper nitrate is 1.6mmol copper salt / g MSN carrier, and the amount of urea is 13mmol urea / g MSN carrier; the alkaline condition is: pH=11. The washing is specifically: washing with water for 5 times. The drying is specifically: drying at 70°C for 12 hours. The calcination is specifically: heating to 350°C at a heating rate of 10°C / min, and calcining for 4h.

[0062] Example 5: Preparation of silica nanosphere supported copper-based catalyst Cu-MSN-II

[0063] (1) Preparation of silica nanospheres: 10 g of water, 10.4 g of butyl aldehyde and 0.5 g of CTAB were added to a closed reaction device, and stirred to mix uniformly under alkaline conditions. Then 2 g of TEOS was added, and stirred at room temperature for 20 h. Liquid-solid separation was performed, and the obtained white solid was washed, dried and calcined to obtain a yellow solid, i.e. silica nanospheres with a semi-open pore morphology, namely the MSN carrier.

[0064] The alkaline condition is pH = 11. The washing is specifically 3 times of ethanol washing. The drying is specifically 18 hours of drying at 70°C. The calcination is specifically heating at a heating rate of 10°C / min to 500°C, and calcining for 7 h.

[0065] (2) Loading of copper-based catalyst: 0.35 g of the MSN carrier prepared in step (1) and an appropriate amount of copper chloride were taken in water, and stirred until the copper salt was dissolved and uniformly dispersed. Then urea was added, and stirred at 60°C under alkaline conditions for 5 h. Liquid-solid separation was performed, and the obtained blue solid was washed, dried and calcined to obtain a blue-green powder, i.e. silica nanosphere supported copper-based catalyst Cu-MSN-I.

[0066] The amount of copper chloride is 7 mmol of copper salt per g of MSN carrier, and the amount of urea is 11 mmol of urea per g of MSN carrier. The alkaline condition is pH = 10. The washing is specifically 3 times of water washing. The drying is specifically 18 hours of drying at 50°C. The calcination is specifically heating at a heating rate of 10°C / min to 300°C, and calcining for 6 h.

[0067] Example 6: Preparation of silica nanosphere supported copper-based catalyst Cu-MSN-II

[0068] Different from Example 4, (1) Preparation of silica nanospheres: 11.5 g of water, 11.5 g of butyl aldehyde and 0.6 g of CTAB were added to a closed reaction device, and stirred to mix uniformly under alkaline conditions. Then 2.05 g of TEOS was added, and stirred at room temperature for 24 h. Liquid-solid separation was performed, and the obtained white solid was washed, dried and calcined to obtain a yellow solid, i.e. silica nanospheres with a semi-open pore morphology, namely the MSN carrier.

[0069] The alkaline condition is pH = 11. The washing process specifically involves washing four times with ethanol. The drying process specifically involves drying at 80°C for 15 hours. The calcination process specifically involves heating to 520°C at a rate of 10°C / min and calcining for 6 hours.

[0070] (2) Supporting the copper-based catalyst: Take 0.35g of the MSN support prepared in step (1) and an appropriate amount of copper nitrate in water, and stir until the copper salt is dissolved and evenly dispersed. Then add urea and stir the reaction at 60-100℃ under alkaline conditions for 3-5 hours. Separate the liquid and solid, and wash, dry and calcine the obtained blue solid to obtain a blue-green powder, namely the copper-based catalyst Cu-MSN-I supported on silica nanospheres.

[0071] The dosage of copper nitrate was 7.2 mmol copper salt / g MSN carrier, and the dosage of urea was 11.5 mmol urea / g MSN carrier; the alkaline condition was pH = 10. The washing process involved washing with water four times. The drying process involved drying at 60℃ for 13 hours. The calcination process involved heating to 330℃ at a rate of 10℃ / min and calcining for 5 hours.

[0072] Example 7: Preparation of Cu-MSN-II copper-based catalyst supported on silica nanospheres

[0073] Unlike Example 4, (1) the preparation of silica nanospheres: 12.5g of water, 13g of butyraldehyde and 0.72g of CTAB were added to a closed reaction apparatus and stirred under alkaline conditions until uniformly mixed. Then 2.11g of TEOS was added and the mixture was stirred at room temperature for 26h. After liquid-solid separation, the obtained white solid was washed, dried and calcined to obtain a yellow solid—silica nanospheres with a semi-open pore morphology, i.e., MSN carrier.

[0074] The alkaline condition is pH = 12. The washing process specifically involves washing four times with ethanol. The drying process specifically involves drying at 85°C for 17 hours. The calcination process specifically involves heating to 540°C at a rate of 10°C / min and calcining for 6.5 hours.

[0075] (2) Supporting the copper-based catalyst: Take 0.35g of the MSN support prepared in step (1) and an appropriate amount of copper sulfate in water, and stir until the copper salt is dissolved and evenly dispersed. Then add urea and stir the reaction at 80℃ under alkaline conditions for 4.5h. After liquid-solid separation, wash, dry and calcine the obtained blue solid to obtain a blue-green powder, namely the copper-based catalyst Cu-MSN-I supported on silica nanospheres.

[0076] The amount of copper sulfate is 7.6 mmol of copper salt per gram of the MSN carrier, and the amount of urea is 12.3 mmol of urea per gram of the MSN carrier; the basic condition is pH = 11. The washing is specifically 4 times of washing with water. The drying is specifically 15 hours of drying at 65°C. The calcination is specifically heating to 340°C at a heating rate of 10°C / min, and calcination for 5.5 hours.

[0077] Example 8: Preparation of the copper-based catalyst Cu-MSN-II supported by silica nanospheres

[0078] Different from Example 4, (1) preparation of the silica nanospheres: 14 g of water, 13.6 g of butyl aldehyde and 0.8 g of CTAB were added into a closed reaction device, and stirred to be uniformly mixed under a basic condition. Then, 2.2 g of TEOS was added, and the stirring was continued at room temperature for 28 hours. After liquid-solid separation, the obtained white solid was washed, dried and calcined to obtain a yellow solid, i.e. the silica nanospheres with a semi-open pore structure, which was the MSN carrier.

[0079] The basic condition is pH = 12. The washing is specifically 5 times of washing with ethanol. The drying is specifically 12 hours of drying at 90°C. The calcination is specifically heating to 550°C at a heating rate of 10°C / min, and calcination for 5 hours.

[0080] (2) loading of the copper-based catalyst: 0.35 g of the MSN carrier prepared in step (1) and an appropriate amount of copper nitrate were taken in water, and stirred until the copper salt was dissolved and uniformly dispersed. Then, urea was added, and the stirring was continued at 100°C under a basic condition for 3 hours. After liquid-solid separation, the obtained blue solid was washed, dried and calcined to obtain a blue-green powder, i.e. the copper-based catalyst Cu-MSN-I supported by silica nanospheres.

[0081] The amount of copper nitrate is 8 mmol of copper salt per gram of the MSN carrier, and the amount of urea is 13 mmol of urea per gram of the MSN carrier; the basic condition is pH = 11. The washing is specifically 5 times of washing with water. The drying is specifically 12 hours of drying at 70°C. The calcination is specifically heating to 350°C at a heating rate of 10°C / min, and calcination for 4 hours.

[0082] Comparative Example 1: smooth surface spherical nanospheres SSN as a carrier (control with Cu-MSN-I).

[0083] Different from Example 1, the self-prepared spherical silica nanospheres were used as the carrier of the copper-based catalyst.

[0084] Preparation method: the spherical silica nanospheres were prepared by sol-gel method. The specific operation was as follows: 25.5 g of deionized water and 11.8 g of ethanol were thoroughly stirred in a round-bottom flask at a stirring speed of 800 rpm for 15 minutes. 0.08 g of CTAB, 0.5 g of TEOS and 0.55 g of ammonia were added, and stirring was performed for 180 minutes. The whole experiment was carried out at room temperature. The obtained white product was washed with deionized water and ethanol for 5 times, and was placed in an oven at 80°C overnight. Then, calcination was performed as follows: first, calcination was performed at 200°C for 2 h, and then calcination was performed at 600°C at a temperature rising rate of 10°C / min for 4 h, to obtain the final product, smooth surface spherical nanospheres SSN.

[0085] Comparative Example 2: smooth surface spherical nanospheres as carrier (control with Cu-MSN-II).

[0086] Different from Example 4, the smooth surface spherical nanospheres SSN prepared by Comparative Example 1 were used as the carrier of the copper-based catalyst.

[0087] Comparative Example 3: low copper-based catalyst loading

[0088] Different from Example 1, the amount of copper nitrate in the step (2) was 0.3 mmol of copper salt / g of the MSN carrier.

[0089] Comparative Example 4: medium copper-based catalyst loading

[0090] Different from Example 1, the amount of copper nitrate in the step (2) was 4.4 mmol of copper salt / g of the MSN carrier.

[0091] Comparative Example 5: high copper-based catalyst loading

[0092] Different from Example 1, the amount of copper nitrate in the step (2) was 10.5 mmol of copper salt / g of the MSN carrier.

[0093] Example 9: structural characterization of the copper-based catalyst

[0094] The copper-based catalysts prepared in Examples 1-4 (Cu-MSN-I) and Examples 5-8 (Cu-MSN-II) were subjected to structural characterization. Since the results were similar, the copper-based catalyst prepared in Example 2 (Cu-MSN-I) and the copper-based catalyst prepared in Example 5 (Cu-MSN-II) were taken as examples for illustration. At the same time, the samples prepared in Comparative Examples 1-2 were subjected to scanning electron microscope detection, and the results were consistent. The sample prepared in Comparative Example 2 was taken as an example for illustration.

[0095] (1) Scanning electron microscope detection

[0096] The copper-based catalyst Cu-MSN-I prepared in Example 2 was examined using a scanning electron microscope, such as... Figure 1 As shown, the semi-open pore structure on the MSN surface is clearly visible. The copper-based catalyst Cu-MSN-I prepared in Example 5 was examined using a scanning electron microscope, as shown... Figure 3 As shown, the semi-open pore structure is almost entirely occupied by Cu species. Figure 1 and Figure 3 It can be seen that the copper-based catalysts Cu-MSN-I and Cu-MSN-II prepared in this application both have clearly visible semi-open channels. This is because both of them use MSN as the support, which has semi-open channels.

[0097] Figure 14 Scanning electron microscope (SEM) images of the copper catalyst supported on smooth-surfaced spherical nanospheres prepared in Comparative Example 2. Figure 14 It can be seen that the SSN carrier is a smooth spherical shape, and the Cu species were successfully loaded onto the surface of the silicon sphere.

[0098] (2) Transmission electron microscopy detection

[0099] The copper-based catalyst Cu-MSN-I prepared in Example 2 was examined using transmission electron microscopy, such as... Figure 2 As shown, the semi-open pore structure on the MSN surface is clearly visible. The copper-based catalyst Cu-MSN-II prepared in Example 5 was examined using transmission electron microscopy, as shown... Figure 4 As shown, the semi-open pore structure is almost entirely occupied by Cu species. Figure 2 and Figure 4 It can be seen that both the copper-based catalysts Cu-MSN-I and Cu-MSN-II prepared in this application have clearly visible semi-open channels, consistent with the results of scanning electron microscopy. However, in the copper-based catalyst Cu-MSN-II, the amount of catalytic addition in the channel structure also increases due to the increase in copper loading.

[0100] (3) Energy dispersive X-ray spectroscopy

[0101] The copper-based catalyst Cu-MSN-I prepared in Example 2 was tested using energy-dispersive X-ray spectroscopy, such as... Figure 5 As shown. The copper-based catalyst Cu-MSN-II prepared in Example 5 was tested using energy-dispersive X-ray spectroscopy, as shown. Figure 6 As shown. By Figure 5 A very weak characteristic signal of Cu element was observed on the Cu-MSN-I surface, indicating that Cu species are immobilized in a highly dispersed form on the surface and within the pores of the silica nanospheres. This result was unexpected before the synthesis of the catalyst.Figure 6 It can be observed that there is a strong characteristic signal of Cu element on the surface of Cu-MSN-II, and the Cu species fills the pores of the silica nanospheres in the form of aggregation. This is because the concentration of copper nitrate solution during synthesis is different, resulting in different aggregation forms of Cu loaded on the carrier.

[0102] (4) X-ray powder diffraction instrument detection

[0103] The copper-based catalyst Cu-MSN-I prepared in Example 2 and the copper-based catalyst Cu-MSN-II prepared in Example 5 were detected by an X-ray powder diffraction instrument, as shown in Figure 7 It can be seen that there is no obvious wave peak in the XRD spectrum, indicating that the copper-based catalyst Cu-MSN-I and Cu-MSN-II are mainly amorphous structures. Figure 7

[0104] (5) Physical adsorbent test

[0105] The copper-based catalyst Cu-MSN-I prepared in Example 2 and the copper-based catalyst Cu-MSN-II prepared in Example 5 were subjected to physical adsorbent test, and the N2 adsorption-desorption isotherm graph Figure 8 ) and the pore size distribution graph Figure 9 ) of the catalyst were obtained. As can be seen from Figure 8 , unlike the copper-based catalyst Cu-MSN-II, the copper-based catalyst Cu-MSN-I shows a clear H3 type hysteresis loop, indicating that it retains the mesoporous structure of MSN. As can be seen from Figure 9 , the copper-based catalyst Cu-MSN-I has a small micropore ratio and more mesopores above 10 nm; the copper-based catalyst Cu-MSN-II has a sharp increase in micropore ratio and more mesopores below 10 nm. Therefore, (a) the copper-based catalyst Cu-MSN-I retains the mesoporous structure of MSN; (b) fine micropores appear in the aggregated Cu species of the copper-based catalyst Cu-MSN-II.

[0106] Example 10: Electrochemical CO2 reduction test

[0107] The copper-based catalyst Cu-MSN-I prepared in Examples 1-4, the copper-based catalyst Cu-MSN-II prepared in Examples 5-8, and the silica nanosphere supported copper-based catalyst prepared in Comparative Examples 1-5 were subjected to electrochemical CO2 reduction test.

[0108] (1) Electrochemical experiment

[0109] ​Test method: Electrochemical experiments were conducted using a Gamry interface 1010E electrochemical workstation and an H-type battery (using a Nafion 117 proton exchange membrane). In the electrochemical system, the catalyst Ag / Ag... + (The saturated solution was KCl) and platinum sheets were used as the working electrode, reference electrode, and counter electrode, respectively. CO2 reduction at different potentials was also performed in a 0.1M saturated KHCO3 solution containing CO2. The experiment required a continuous flow of 100% CO2 gas at a flow rate of 30 ml / min. 25 ml of 0.1M KHCO3 solution was injected into both the positive and negative electrodes of the electrolytic cell. Gas chromatographs (GC, Huifen 7820) were used to detect the gaseous products.

[0110] Test results: The copper-based catalyst Cu-MSN-I prepared in Example 2 and the copper-based catalyst Cu-MSN-II prepared in Example 5 are used as examples for illustration.

[0111] Figure 10 The image shows the Faradaic efficiency of the copper-based catalyst Cu-MSN-I for CO2 reduction prepared in Example 2 of this invention. Figure 10 As shown, the copper-based catalyst Cu-MSN-I exhibits excellent electrocatalytic reduction of CO2 to CH4, demonstrating extremely high CH4 selectivity (FE>60%) over a wide potential range, with the highest CH4 Faradaic efficiency reaching 71.1%. The Faradaic efficiencies of the byproducts H2 and CO are extremely low, with optimal potentials of H2 <10% and CO <2%.

[0112] Figure 11 The image shows the Faradaic efficiency of the copper-based catalyst Cu-MSN-II for CO2 reduction prepared in Example 5. Figure 11 As shown, the copper-based catalyst Cu-MSN-II exhibits excellent electrocatalytic reduction of CO2 to C2H4, demonstrating extremely high C2H4 selectivity (FE>60%) within a specific potential range, with the highest CH4 Faradaic efficiency reaching 66.4%. The Faradaic efficiencies of the byproducts H2 and CO are extremely low, with optimal potentials of H2 <10% and CO <2%.

[0113] As shown in Example 9, although the mesoporous channels of MSN in the copper-based catalyst Cu-MSN-II are filled, the newly generated micropores can still improve the catalytic efficiency. It is well known that porous materials possess highly ordered pore structures, which not only increase the specific surface area of ​​the material but also provide more exposure opportunities for the active sites of the catalyst. Specifically, regarding the copper-based catalysts Cu-MSN-I and Cu-MSN-II prepared in this application, on the one hand, the high surface area means that more active sites can contact the reactants, thereby improving the catalytic efficiency; on the other hand, the highly ordered pore structure allows reactants to rapidly enter the pores and reach the active sites, while products can also rapidly exit from the pores, avoiding the influence of diffusion limitation on the reaction rate. Furthermore, the microenvironment inside the pores may also have a protective effect on the catalyst surface, slowing down the poisoning and sintering processes.

[0114] (2) In-situ ATR-FTIR spectroscopy

[0115] Test methods: Results were obtained using a spectrometer (Thermo Fisher Nicolet IS 50) equipped with a mercury cadmium telluride (MCT / B) detector and a VeeMAX III ATR accessory (Pike Technologies). A three-electrode spectroelectrochemical cell (Jackfish) was used as the electrolytic cell. Catalyst drops were cast onto a sputtered gold-silicon prism as the working electrode, and a standard Ag / AgCl electrode and platinum wire were used as the reference and counter electrodes, respectively. The electrolyte was a 0.1M CO2-saturated KHCO3 solution. The electrochemical cell was connected to an electrochemical station and electrolysis was performed at a constant potential from 0V to -2.4V relative to the RHE.

[0116] Test results: The copper-based catalyst Cu-MSN-I prepared in Example 2 and the copper-based catalyst Cu-MSN-II prepared in Example 5 are used as examples for illustration.

[0117] Figure 12 This is the in-situ infrared spectrum of the copper-based catalyst Cu-MSN-I. Figure 12 It can be known that 2063cm -1 The peak at that point is attributed to linearity (CO). L The stretching of C≡O, and the higher reduction potential, the higher intensity of the *CO peak. At 1739 cm⁻¹ -1 The fluctuation at this point suggests the possible presence of a *CHO intermediate, which previous studies have shown to be an important precursor for CH4 formation. 2860cm -1 and 2930cm -1 The fluctuation at that point is attributed to *CH x The symmetric and asymmetric stretching vibrations of the group suggest a possible continuous hydrogenation process during the conversion of the *CHO intermediate to CH4. At 10¹⁰ cm⁻¹-1 A weak intermediate signal of *COH was observed at 1230 cm⁻¹, while at 1230 cm⁻¹... -1 and 1067cm -1 No significant carbon-carbon coupling intermediate signal was observed, indicating that Cu-MSN-I, which contains abundant Cu-O-Si sites, tends to stabilize *CHO hydrogenation to CH4.

[0118] Figure 13 This is the in-situ infrared spectrum of the copper-based catalyst Cu-MSN-II. Figure 13 As shown, at 1391cm -1 The strong fluctuations at 1010, 1067, and 1230 cm⁻¹ suggest the possible presence of a *COOH intermediate, while the Cu-MSN-I spectrum of the copper-based catalyst shows no *COOH intermediate. -1 The peaks at these locations are attributed to *COH, *COCOH, and *OCCOH, respectively. The presence of the two key intermediates for carbon-carbon coupling, *COCOH and *OCCOH, indicates that the copper-based catalyst Cu-MSN-II, which contains abundant Cu-O-Cu sites, facilitates the coupling of *CO and *COH adsorbed on adjacent Cu surfaces, thereby improving the selectivity for C2H4 generation.

[0119] Figure 15 shows the Faradaic efficiency of the copper catalysts supported on smooth-surface spherical nanospheres prepared in Comparative Examples 1-2 for the electrocatalytic reduction of CO2. As shown in Figure 15, it can be seen that the copper-based catalysts prepared in Comparative Examples 1-2 exhibit extremely low Faradaic efficiency and low current density in the electrocatalytic reduction of CO2 to the target product, while the Faradaic efficiencies of the byproducts H2 and CO are very high, indicating that these catalysts do not have the potential to be highly efficient electrocatalysts. Therefore, it can be concluded that only by using non-conductive silica nanospheres with semi-open pores as a support can copper-based catalysts potentially exhibit excellent performance.

[0120] Figure 16 shows the Faradaic efficiency of the Cu-MSN catalysts with different Cu loadings prepared in Comparative Examples 3-5 for the electrocatalytic reduction of CO2. Figure 16a As can be seen, the catalyst prepared in Comparative Example 3 exhibits lower Faraday efficiency in the electrocatalytic reduction of CO2 to CH4, indicating that this loading is clearly suboptimal. Figure 16b As can be seen, the Faradaic efficiency of the catalyst prepared in Comparative Example 4 for the electrocatalytic reduction of CO2 to C2H4 and CH4 is lower than that of Cu-MSN-Ⅰ and Cu-MSN-Ⅱ, indicating that this loading is clearly not optimal. Figure 16cIt can be seen that the faradic efficiency of the catalyst prepared in Comparative Example 5 for electrocatalytic reduction of CO2 to C2H4 is lower than that of Cu-MSN-II, and apparently the loading amount is not the optimal loading amount. It can be known that even if the non-conductive silica nanospheres with semi-open pores are used as the carrier, only when the copper-based catalyst loading amount is specific, the high selectivity (FE of CH4>60%) and yield (faradic efficiency of CH4 reaches 71.1%) can be exhibited in the electrocatalytic reduction of carbon dioxide to prepare methane.

[0121] In summary, (1) the silica nanosphere loaded copper-based catalyst described in the present application initiatively uses the non-conductive silica nanospheres as the carrier, and exhibits excellent performance at a certain copper salt content, and produces unexpected technical effects, i.e. high selectivity (FE of CH4>60%) and yield (faradic efficiency of CH4 reaches 71.1%) in the electrocatalytic reduction of carbon dioxide to prepare methane. (2) The silica nanosphere loaded copper-based catalyst described in the present application not only has simple preparation steps and mild conditions, and is of important significance for practical application, but also can freely realize the regulation of the electrocatalytic reduction of carbon dioxide to prepare products, i.e. methane or ethylene, by regulating the content of the loaded copper salt in the MSN carrier, so that different demands can be met, and the application prospect is more broad.

Claims

1. A method for the preparation of a copper-based catalyst for the electrocatalytic reduction of CO2 to CH4, characterized in that: It comprises the following steps: (1) Preparation of silica nanospheres: a certain amount of water, butyl aldehyde and CTAB are added into a closed reaction device, and stirred until mixed uniformly under alkaline conditions; then a certain amount of TEOS is added, and stirred at room temperature for 20-28 hours; liquid-solid separation is performed, and the solid is washed, dried and calcined to obtain silica nanospheres with semi-open pore morphology, namely MSN carrier; wherein the mass ratio of water, butyl aldehyde, CTAB and TEOS is 100-140: 104-136: 5-8: 20-22; (2) Loading of copper-based catalyst: a certain amount of MSN carrier prepared in step (1) and divalent copper salt are taken in water, and stirred until the copper salt is dissolved and uniformly dispersed; then urea is added, and stirred at 60-100°C under alkaline conditions for 3-5 hours; liquid-solid separation is performed, and the solid is washed, dried, calcined to obtain silica nanospheres loaded copper-based catalyst Cu-MSN-I; wherein the amount of divalent copper salt is 1.4-1.6 mmol of copper salt per gram of MSN carrier, and the amount of urea is 11-13 mmol of urea per gram of MSN carrier.

2. The method of claim 1, wherein: The alkaline conditions in step (1) are pH=11-12; the alkaline conditions in step (2) are pH=10-11.

3. The method of claim 2, wherein: The divalent copper salt is copper chloride, copper nitrate or copper sulfate.

4. The method of any one of claims 1-3, wherein: In step (1), the washing is specifically 3-5 times with water or ethanol; the drying is specifically 12-18 hours at 70-90°C; and the calcination is specifically heating to 500-550°C at a heating rate of 10°C / min, and calcining for 5-7 hours.

5. The method of any one of claims 1-3, wherein: In step (2), the washing is specifically 3-5 times with water; the drying is specifically 12-18 hours at 50-70°C; and the calcination is specifically heating to 300-350°C at a heating rate of 10°C / min, and calcining for 4-6 hours.

6. The catalyst Cu-MSN-I prepared by the method of any one of claims 1-5.

7. The use of the catalyst Cu-MSN-I of claim 6 in electrocatalytic reduction of CO2 to produce CH4.

8. A method for the preparation of a copper-based catalyst for the electrocatalytic reduction of CO2 to C2H4, characterized in that: It comprises the following steps: (1) Preparation of silica nanospheres: a certain amount of water, butyl aldehyde and CTAB are added into a closed reaction device, and stirred until mixed uniformly under alkaline conditions; then a certain amount of TEOS is added, and stirred at room temperature for 20-28 hours; liquid-solid separation is performed, and the solid is washed, dried and calcined to obtain silica nanospheres with semi-open pore morphology, namely MSN carrier; wherein the mass ratio of water, butyl aldehyde, CTAB and TEOS is 100-140: 104-136: 5-8: 20-22; (2) Loading of copper-based catalyst: take the MSN carrier prepared in step (1) and a divalent copper salt in water, stir until the copper salt is dissolved and uniformly dispersed; then add urea, stir under alkaline conditions at 60-100°C for 3-5h; liquid-solid separation, wash, dry and calcine the solid to obtain a silica nanosphere loaded copper-based catalyst Cu-MSN-II; wherein the amount of divalent copper salt is 7-8mmol of copper salt per gram of MSN carrier, and the amount of urea is 11-13mmol of urea per gram of MSN carrier.

9. The catalyst Cu-MSN-II prepared by the method of claim 8.

10. Use of the catalyst Cu-MSN-II of claim 9 in electrocatalytic reduction of CO2 to produce C2H4.

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