A method for preparing a copper-silver electrocatalyst for the preparation of ethylene oxide and its application.

Abstract

This invention discloses a method for preparing a copper-silver electrocatalyst for the production of ethylene oxide and its application. By precisely controlling the molar ratio of copper nitrate to silver nitrate and employing a process of room-temperature dropwise reduction, vacuum drying, and high-temperature calcination within a specific temperature range, a gray-black powder catalyst with excellent electrochemical activity is prepared. The copper-silver bimetallic heterojunction catalyst prepared by this invention, when used in a membrane electrode system for the electrocatalytic epoxidation of ethylene, exhibits higher yield and Faradaic efficiency than previous catalysts. Further optimization of the selectivity of the ethylene epoxidation reaction through copper doping modification results in even higher yields.

Description

Technical Field

[0001] This invention belongs to the technical field, specifically relating to a method for preparing a copper-silver electrocatalyst for the preparation of ethylene oxide and its application. Background Technology

[0002] Ethylene oxide (EO), an important derivative of ethylene, is a key organic intermediate in the chemical industry, widely used in the production of bulk chemicals such as ethylene glycol, epoxy resins, and surfactants. In traditional industry, the epoxidation reaction of ethylene is usually carried out under high temperature (200–270°C) and high pressure (1–3 MPa), using silver-based catalysts to catalyze the reaction of ethylene with oxygen to produce ethylene oxide. This process is not only energy-intensive (approximately 19 MJ / kg EO), but also generates a large amount of carbon dioxide byproducts, making it difficult to balance selectivity and carbon emissions, thus hindering its green and sustainable development.

[0003] To improve catalytic performance, various improved silver catalysts have been proposed in the existing technology. For example, CN202111187708.9 discloses a silver catalyst prepared by regenerating waste α-alumina support, realizing resource recycling; CN202010797846.8 improves epoxidation activity by introducing rhenium, alkali metals, and M-salen complexes as promoters into the silver catalyst. However, these catalysts still face problems such as insufficient activity stability and numerous side reactions in actual operation, limiting their potential for long-term industrial application.

[0004] In recent years, electrochemical catalytic epoxidation of ethylene has gradually become a research hotspot. This method utilizes electrical energy to drive the reaction, which can be carried out at ambient temperature and pressure, and can be directly coupled with green energy sources such as wind power and photovoltaics, possessing the potential for low carbon emissions and high energy efficiency. However, existing electrocatalytic systems mostly rely on halogen media (such as Br₂). - / Cl - As an oxidation mediator, ethylene suffers from serious problems such as equipment corrosion, product contamination, and catalyst deactivation. Furthermore, the low solubility of ethylene in the aqueous phase and its slow reaction kinetics make it difficult to meet industrial-scale requirements in terms of current density and Faraday efficiency. Therefore, developing an electrocatalyst that does not require halogen mediation, can generate active oxygen species in situ, and possesses high ethylene adsorption and intermediate stabilization capabilities is crucial for achieving efficient, stable, and green electrosynthesis of ethylene oxide. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a copper-silver electrocatalyst for preparing ethylene oxide.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a copper-silver electrocatalyst for preparing ethylene oxide, characterized in that it includes: Dissolve copper-containing salts and silver-containing salts in deionized water to obtain a mixed salt solution; Sodium borohydride was dissolved in deionized water to obtain an aqueous solution of sodium borohydride. The mixed salt solution was slowly added to the sodium borohydride aqueous solution while stirring continuously to obtain the mixed aqueous solution; Centrifuge the aqueous solution of the mixture, collect the precipitate, wash until the washing solution is neutral, and then vacuum dry the washed precipitate. The vacuum-dried sample was calcined at high temperature to obtain a gray-black powder, which is the copper-silver electrocatalyst used to prepare ethylene oxide.

[0009] In a preferred embodiment of the preparation method described in this invention, the molar ratio of the copper salt to the silver salt is 5:5.

[0010] In a preferred embodiment of the preparation method described in this invention, the copper-containing salt includes anhydrous copper nitrate.

[0011] In a preferred embodiment of the preparation method described in this invention, the silver-containing salt includes silver nitrate.

[0012] In a preferred embodiment of the preparation method described in this invention, the mixed salt solution is slowly added to the sodium borohydride aqueous solution and stirred continuously, wherein the molar ratio of the mixed salt solution to the sodium borohydride aqueous solution is 1:5; the stirring temperature is room temperature, and the stirring time is 1-2 hours.

[0013] In a preferred embodiment of the preparation method described in this invention, the vacuum drying temperature is 50~70℃, the heating rate is 2℃ / min, the time is 1~2h, and the vacuum degree is 30Pa.

[0014] In a preferred embodiment of the preparation method described in this invention, the high-temperature calcination temperature is 200~300℃ and the calcination time is 1~3h.

[0015] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of a copper-silver composite catalyst in the electrochemical reaction of a membrane electrode.

[0016] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of a copper-silver electrocatalyst in the preparation of ethylene oxide.

[0017] Beneficial effects of this invention: The copper-silver bimetallic heterojunction catalyst prepared in this invention, when used in a membrane electrode system for the electrocatalytic epoxidation of ethylene, exhibited higher yield and Faraday efficiency than previous catalysts. Further optimization of the selectivity of the ethylene epoxidation reaction through copper doping resulted in even higher yields. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 The present invention describes the synthesis steps of the CuAg catalyst in an embodiment of the present invention.

[0019] Figure 2 The structural characterization of Cu5Ag5 obtained in the embodiments of the present invention includes: a. scanning electron microscope image of Cu5Ag5, b. transmission electron microscope image of Cu5Ag5, c. high-resolution transmission electron microscope image of Cu5Ag5, and d. elemental mapping image of Cu5Ag5.

[0020] Figure 3 The diagram shows the electrochemical performance of the catalyst prepared in the embodiments of the present invention and a schematic diagram of the membrane electrode. Detailed Implementation

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0022] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0024] The raw materials used in this invention were: copper nitrate (Cu(NO3)2, 99%), sodium borohydride (NaBH4), sodium chloride (NaCl), and Nafion 117 solution, purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Silver nitrate (AgNO3), ethylene oxide (99.5%), ethyl acetate, 1,2-dimethoxyethane, disodium hydrogen phosphate (Na2HPO4), and sodium dihydrogen phosphate (NaH2PO4) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Nickel foam and Nafion 117 membrane were purchased from Suzhou Keleng Technology Co., Ltd. Anhydrous ethanol (99.5%) was purchased from Sinopharm Chemical Reagent Co., Ltd. All experiments used ultrapure water (Millipore Milli-Q grade) with a resistivity of 18.2 megohms. All chemical reagents and solvents were used directly without further purification unless otherwise specified.

[0025] The instruments used in this invention embodiment are as follows: Scanning electron microscopy (SEM) images were acquired using a Zeiss Gemini 300 scanning electron microscope with an accelerating voltage of 1.5 kV. X-ray diffraction (XRD) spectra were acquired using a Bruker AXS D8 X-ray diffractometer with Cu Kα radiation (wavelength λ = 1.54056 Å, operating current 100 mA, voltage 40 kV) at a scanning speed of 2° / min. Before X-ray photoelectron spectroscopy (XPS) testing, the samples were deoxygenated in an argon atmosphere for 1 hour, followed by analysis using a Thermo Fisher ESCALAB 250XI spectrometer equipped with an Al Kα X-ray source, and the spectra were calibrated using the C 1s binding energy of 284.6 eV. All electrochemical experiments were performed using a Koster electrochemical workstation. Gas chromatography tests were performed using a Zhejiang Fuli Instruments GC9790PLUS gas chromatograph.

[0026] Example 1 This embodiment provides a method for preparing a copper-silver electrocatalyst for the preparation of ethylene oxide, comprising the following steps: (1) Weigh 0.094 g of anhydrous Cu(NO3)2 solid and 0.085 g of AgNO3 solid, add them together to 20 mL of deionized water to dissolve, and stir until homogeneous; (2) Weigh 0.38 g of NaBH4 solid, add it to 20 mL of deionized water and dissolve it, stirring until homogeneous; (3) At room temperature, slowly add the aqueous mixture prepared in step (1) to the aqueous NaBH4 prepared in step (2) while stirring continuously for 1 hour; (4) Centrifuge the mixed solution after the reaction and remove the supernatant. Collect the precipitate and wash it three times with anhydrous ethanol and deionized water respectively until the pH of the supernatant is neutral. Vacuum dry the precipitate for 12 hours. (5) After drying, weigh 100 mg of sample and calcine it at 250°C for 2 hours in a tube furnace at a heating rate of 2°C / min to obtain a gray-black powder. This is the copper-silver catalyst with a molar ratio of 5:5 calcined at 250°C, which is denoted as Cu5Ag5-250.

[0027] Example 2 This embodiment demonstrates the use of the copper-silver catalyst prepared in Example 1 for electrochemical reactions and the preparation of ethylene oxide, specifically including the following steps: (1) Prepare a slurry by mixing 2 mg of Cu5Ag5-250 catalyst with 10 μL of 5 wt% Nafion solution and 1 mL of anhydrous ethanol. Mix the slurry evenly by ultrasonication and then coat it onto the surface of carbon paper (YLS-30T) with a gas diffusion layer (area 4 cm²). 2 After it is completely dried, a gas diffusion electrode carrying an anode catalyst is obtained (5 wt% Nafion solution, the solvent is a mixture of 50 wt% ethanol and 45% water).

[0028] (2) The prepared gas diffusion electrode as the anode, the nickel foam (100PPI 1mm thick) as the cathode, and the ion exchange membrane (Fumasep FKB-PK-130 cation exchange membrane) are assembled together into the membrane electrode reactor.

[0029] (3) Ethylene oxide was prepared by electrochemical method of constant potential polarization (potential is 3.2 V). Ethylene gas was introduced into the anode at a flow rate of 10 mL / min, while 1% mass fraction NaCl solution was pumped into the cathode at a rate of 20 mL / min to carry out hydrogen evolution reaction.

[0030] (4) The product collected at the anode was analyzed by gas chromatography. The yield of ethylene oxide was determined using the internal standard method, with chemically inert and water-soluble ethylene glycol dimethyl ether selected as the internal standard. The amount of product in the test solution could be calculated based on the relative correction factor, as shown in the following formula: Relative correction factor: f = (As / ms) / (Ar / mr); Product quality: mi = f × Ai / (As / ms); In the formula, f is the relative correction factor, As and ms are the added mass of the peak area of ​​the internal standard, Ar and mr are the added mass of the peak area of ​​the product, Ai is the peak area of ​​the product in the test solution, and mi is the mass of the product in the test solution.

[0031] To determine f, a standard sample needs to be prepared, following these steps: Add 10 μL of EO and 10 μL of internal standard to 20 ml of electrolyte. Take 1 μL of the standard sample for gas chromatography detection, repeat the process multiple times, and calculate the average value to obtain f.

[0032] The formulas for calculating output and Faraday efficiency are as follows: The amount of product substance: ni = mi / Mi; Output: P = ni / t / S; Faraday efficiency: FE = ni * z * F / It; In the formula, ni is the amount of substance of the product in the test solution, Mi is the relative molecular mass of ethylene oxide, FE is the Faraday efficiency, S is the area of ​​the anode electrode, z is the number of reaction electrons, F is the Faraday constant, I is the reaction current, and t is the reaction time.

[0033] The measured Faraday efficiency of the reaction was 45.6%, and the yield was 100 μmol / h.

[0034] Comparative Example 1 This comparative example provides a method for preparing a copper oxide precursor, including the following steps: (1) Weigh 0.188 g of anhydrous Cu(NO3)2 solid, add it to 20 mL of deionized water to dissolve it, and stir until homogeneous; (2) Weigh 0.38 g of NaBH4 solid, add it to 20 mL of deionized water and dissolve it, stirring until homogeneous; (3) At room temperature, slowly add the Cu(NO3)2 aqueous solution prepared in step (1) to the NaBH4 aqueous solution prepared in step (2) while stirring continuously for 1 hour; (4) Centrifuge the mixed solution after the reaction and remove the supernatant. Collect the precipitate and wash it three times with anhydrous ethanol and deionized water respectively until the pH of the supernatant is neutral. Vacuum dry the precipitate for 12 hours. (5) After drying, weigh 100 mg of the sample and calcine it at 250°C for 2 hours in a tube furnace at a heating rate of 2°C / min to obtain a gray-black powder, which is denoted as CuO-250.

[0035] The CuO-250 catalyst prepared in Example 2 was used for electrochemical reactions and the preparation of ethylene oxide. The final measured Faradaic efficiency was 22.6%, and the yield was 49.48 μmol / h. Compared with the Cu5Ag5-250 catalyst, the Faradaic efficiency of the CuO-250 catalyst was significantly reduced. This is because copper oxide has a lower adsorption capacity for ethylene, resulting in poorer epoxidation catalytic activity and thus a lower yield of ethylene oxide.

[0036] Comparative Example 2 This comparative example provides a method for preparing a silver precursor, including the following steps: (1) Weigh 0.170 g of AgNO3 solid, add it to 20 mL of deionized water and dissolve it, stirring until homogeneous; (2) Weigh 0.38 g of NaBH4 solid, add it to 20 mL of deionized water and dissolve it, stirring until homogeneous; (3) At room temperature, slowly add the AgNO3 aqueous solution prepared in step (1) to the NaBH4 aqueous solution prepared in step (2) while stirring continuously for 1 hour; (4) Centrifuge the mixed solution after the reaction and remove the supernatant. Collect the precipitate and wash it three times with anhydrous ethanol and deionized water respectively until the pH of the supernatant is neutral. Vacuum dry the precipitate for 12 hours. (5) After drying, weigh 100 mg of sample and calcine it at 250 °C for 2 h in a tube furnace at a heating rate of 2 °C / min to obtain silver-gray powder, which is denoted as Ag-250.

[0037] The Ag-250 prepared using the method in Example 2 was used for electrochemical reactions and the preparation of ethylene oxide. The final measured Faraday efficiency was 31.3%, and the yield was 54.33 μmol / h. This efficiency is significantly lower than that of Cu5Ag5-250. This is because elemental silver has poor hydrophilicity, and reactive oxygen species are not sufficiently stable on the silver surface. Under high current densities, they are prone to desorption or conversion, leading to side reactions such as oxygen evolution reactions, resulting in poor selectivity for ethylene oxide and thus low epoxidation efficiency.

[0038] Comparative Example 3 The difference between this comparative example and Example 1 is that the raw materials in step (1) are replaced with 0.057 g of anhydrous Cu(NO3)2 solid and 0.119 g of AgNO3 solid. The remaining steps are the same as in Example 1. A copper-silver catalyst with a molar ratio of 3:7, calcined at 250°C, is obtained and is denoted as Cu3Ag7-250.

[0039] The Cu3Ag7-250 prepared using the method in Example 2 was used for electrochemical reactions and the preparation of ethylene oxide. The final measured Faraday efficiency was 32.7%, and the yield was 56.8 μmol / h. Its efficiency was slightly lower than that of Cu5Ag5-250. This is because the Cu content in the catalyst is slightly lower, making the catalyst more hydrophobic, which in turn leads to poorer stability of active oxygen and thus lower catalyst performance.

[0040] Comparative Example 4 The difference between this comparative example and Example 1 is that the raw materials in step (1) are replaced with 0.131 g of anhydrous Cu(NO3)2 solid and 0.051 g of AgNO3 solid. The remaining steps are the same as in Example 1. A copper-silver catalyst with a molar ratio of 7:3, calcined at 250°C, is obtained and is denoted as Cu7Ag3-250.

[0041] The Cu7Ag3-250 catalyst prepared using the method in Example 2 was used for electrochemical reactions and the preparation of ethylene oxide. The final measured Faraday efficiency was 21.5%, and the yield was 38.6 μmol / h. Its efficiency is significantly lower than that of Cu5Ag5-250. This is because the Cu content in the catalyst is too high, and the single-metal copper catalyst itself has insufficient adsorption capacity for ethylene, resulting in lower epoxidation efficiency and poorer catalyst performance.

[0042] Comparative Example 5 The difference between this comparative example and Example 1 is that the calcination temperature in step (5) is replaced with 100°C, while the rest of the steps are the same as in Example 1. A copper-silver catalyst with a molar ratio of 5:5 calcined at 100°C is obtained and is denoted as Cu5Ag5-100.

[0043] The Cu5Ag5-100 prepared using the method in Example 2 was used for electrochemical reactions and the preparation of ethylene oxide. The final measured Faraday efficiency of the reaction was 15.8%, and the yield was 32.7 μmol / h. This is because the low sintering temperature prevented the catalyst from fully forming a high-valence copper oxide structure, and the low-valence elemental copper as a catalyst had insufficient oxidation capacity, resulting in poorer activity in the epoxidation reaction.

[0044] Comparative Example 6 The difference between this comparative example and Example 1 is that the calcination temperature in step (5) is replaced with 400°C, while the rest of the steps are the same as in Example 1. A copper-silver catalyst with a molar ratio of 5:5 calcined at 400°C is obtained and is denoted as Cu5Ag5-400.

[0045] The Cu5Ag5-400 catalyst prepared in Example 2 was used for electrochemical reactions and the preparation of ethylene oxide. The final measured Faradaic efficiency was 25.6%, and the yield was 42.8 μmol / h. The Faradaic efficiency of the Cu5Ag5-400 catalyst was significantly lower than that of the Cu5Ag5-250 catalyst. This is because the calcination temperature in the tube furnace was too high, leading to catalyst sintering and agglomeration into larger blocky structures, which reduced the electrochemical active area of ​​the reaction and thus lowered the catalyst performance. This is consistent with the results of SEM morphology testing.

[0046] In summary, this invention provides a copper-silver bimetallic heterojunction electrocatalyst synthesized via a co-reduction method for use in the epoxidation of ethylene in a membrane electrode. Figure 1 This is a schematic diagram of the synthesis of CuAg catalyst.

[0047] Example 3 This example describes the characterization of the synthesized catalyst using scanning electron microscopy (SEM), and the results are as follows: Figure 2As shown, the surface size of the Cu5Ag5 catalyst calcined at 250℃ was found to be around 50 nm, exhibiting an irregular coral-like structure and a relatively loose distribution. Figure 2 a) Compared with microspherical catalysts obtained by calcination of single metals, it can provide a larger specific surface area, thereby providing abundant active sites for epoxidation reaction.

[0048] The heterointerface Cu5Ag5 catalyst was further characterized using transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). TEM results showed a clear heterointerface between the two, with silver clusters encapsulated within copper oxides. Figure 2 b).

[0049] The detailed crystal structure of the Cu5Ag5 catalyst was analyzed by HRTEM. Figure 2 c) The observed lattice spaces are 0.232 nm and 0.236 nm, corresponding to the CuO (111) and Ag (111) planes, respectively. These data indicate that CuO and Ag coexist on the Cu5Ag5 sample, and a clear heterojunction interface exists between CuO and Ag. Furthermore, the corresponding... Figure 2 High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) elemental mapping showed that Cu and O were uniformly distributed on the catalyst, and Ag existed in the form of tiny clusters, confirming the successful synthesis of the catalyst.

[0050] Example 4 This example describes electrochemical experiments on the Cu5Ag5-250 catalyst and several comparative examples. The reactions were carried out under neutral conditions, and the electrolyte was 0.1M phosphate buffered saline (PBS). Furthermore, to ensure sufficient ethylene in the anolyte for the olefin epoxidation reaction, high-purity ethylene was continuously bubbled into the system for 30 minutes before each test.

[0051] like Figure 3 As shown in figure a, linear sweep voltammetry (LSV) tests were first performed on three different catalysts. Comparison revealed that the reaction initiation potentials of the three catalysts were the same, all at 1.31 V (vs Ag / AgCl). With increasing reaction potential, the current density of the CuAg material increased rapidly, and its growth efficiency was significantly higher than that of Ag and CuO. This indicates that the CuAg catalyst exhibits significantly better reactivity than Ag and CuO. This can be attributed to the formation of the heterojunction in the CuAg material, which effectively expands the specific surface area of ​​the catalyst, providing more active sites. Simultaneously, the formation of the heterojunction optimizes the local electronic environment, accelerating electron transfer and thus improving the electrocatalytic epoxidation performance of the catalyst.

[0052] To investigate the conditions for achieving optimal ethylene oxide yield, further electrocatalytic experiments were conducted on the CuAg catalyst. The optimal yield was sought by varying the copper-silver ratio in the feedstock and different potentials. Potentially constant polarization experiments were performed on self-made CuAg catalysts with different copper-silver ratios (Cu7Ag3, Cu5Ag5, and Cu3Ag7) at 2V. The results are as follows: Figure 3 As shown in b, the Faradaic efficiency of the Cu7Ag3 catalyst is only 21.5%. This is because the copper content in this catalyst is too high, and while single-metal copper catalysts themselves have low efficiency in catalyzing epoxidation, they are more active in side reactions such as oxygen evolution reaction. The Cu5Ag5 catalyst exhibits extremely high FE for the electrocatalytic ethylene epoxidation reaction during the 4-hour reaction, and the reaction current is relatively stable. Furthermore, the yield and Faradaic efficiency of the Cu3Ag7 catalyst are close to those of Cu5Ag5, with only a slight decrease.

[0053] To further improve the yield and continuous production capacity of ethylene oxide, a membrane electrode reactor suitable for electrocatalytic ethylene epoxidation was designed, such as... Figure 3 As shown in c. Potentially constant polarization experiments were performed at different potentials using the membrane electrode assembly, and the product analysis is as follows. Figure 3 As shown in Figure d, as the voltage increases from 2.5V to 3.2V, both the EO yield and Faraday efficiency gradually increase, reaching their highest values ​​at 3.2V (Faraday efficiency of 45.6% and yield of 100 μmol / h). When the voltage increases to 3.4V, both decrease. This is likely due to increased side reactions at higher voltages, resulting in the production of more oxygen and carbon dioxide, rather than ethylene oxide. Therefore, different voltages significantly affect the yield and FE; higher voltage does not necessarily lead to higher yields and FE.

[0054] Different calcination temperatures also affect the performance of CuAg catalysts. Potentiostatic polarization experiments were conducted on three catalysts (CuAg-100, CuAg-250, and CuAg-400) calcined at 3.2 V. The results are as follows: Figure 3 As shown in e, the CuAg-100 catalyst exhibits a Faraday efficiency of only 15% and the lowest yield. This is because the low sintering temperature prevents the catalyst from fully forming a high-valence copper oxide structure. Furthermore, while single-metal copper catalysts generally have low efficiency in catalyzing epoxidation, they are more active in side reactions such as oxygen evolution reaction.

[0055] Furthermore, analysis of the results for the CuAg-400 catalyst revealed that while its current density remained stable, it decreased compared to the CuAg-250 catalyst, and its Faradaic efficiency also declined. This is attributed to the excessively high calcination temperature in the tube furnace, which led to catalyst sintering and agglomeration into larger blocky structures with relatively smooth surfaces and blurred particle boundaries, thereby reducing the active surface area for the reaction and resulting in lower catalyst performance. This aligns with the previous SEM morphology analysis results. In contrast, the CuAg-250 catalyst exhibited extremely high reaction efficiency and relatively stable reaction current during the 4-hour reaction.

[0056] Subsequently, long-term stability tests were conducted on the membrane electrode assembly. For example... Figure 3 As shown in f, the catalyst operated stably in the MEA system for 60 hours, during which the current density remained stable. The prepared CuAg catalyst exhibits good stability in the membrane electrode reactor and has the potential for commercial application.

[0057] Silver-based catalysts have shown good catalytic potential in the electrocatalytic ethylene epoxidation reaction, but in practical applications, they still suffer from problems such as insufficient ethylene adsorption strength, low surface coverage of key electrophilic oxygen intermediates, and susceptibility to competitive oxygen evolution side reactions, making it difficult to further improve ethylene oxide yield and Faraday efficiency. Copper oxide (CuO), due to its tunable electronic structure, excellent H2O adsorption and oxygen-containing intermediate stabilization capabilities, and intrinsic inertness to oxygen evolution reactions, has significant advantages in regulating oxygen species pathways and inhibiting over-oxidation. Therefore, this invention constructs a Cu-Ag bimetallic catalyst with a heterogeneous interface structure and integrates it into a membrane electrode reaction system, aiming to synergistically enhance ethylene adsorption, stabilize key oxygen intermediates, and inhibit oxygen evolution side reactions, thereby achieving a highly selective, high current density, and highly stable electrocatalytic ethylene epoxidation reaction.

[0058] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing a copper-silver electrocatalyst for the preparation of ethylene oxide, characterized in that: include, Copper-containing and silver-containing salts are dissolved in a solvent to obtain a mixed salt solution; Sodium borohydride was dissolved in deionized water to obtain an aqueous solution of sodium borohydride. The mixed salt solution was slowly added to the sodium borohydride aqueous solution while stirring continuously to obtain the mixed aqueous solution; Centrifuge the aqueous solution of the mixture, collect the precipitate, wash until the washing solution is neutral, and then vacuum dry the washed precipitate. The vacuum-dried sample was calcined at high temperature to obtain a gray-black powder, which is the copper-silver electrocatalyst used to prepare ethylene oxide.

2. The preparation method according to claim 1, characterized in that: The molar ratio of the copper-containing salt to the silver-containing salt is 5:

5.

3. The preparation method according to claim 1, characterized in that: The copper-containing salt includes anhydrous copper nitrate; the silver-containing salt includes silver nitrate.

4. The preparation method according to claim 1, characterized in that: The solvent includes at least one of deionized water and ethanol.

5. The preparation method according to claim 1, characterized in that: The mixed salt solution is slowly added to the sodium borohydride aqueous solution while stirring continuously. The molar ratio of the mixed salt solution to the sodium borohydride aqueous solution is 1:

5. The stirring temperature is room temperature, and the stirring time is 1-2 hours.

6. The preparation method according to claim 1, characterized in that: The vacuum drying temperature is 50~70℃, the heating rate is 2℃ / min, the time is 1~2h, and the vacuum degree is 30Pa.

7. The preparation method according to claim 1, characterized in that: The high-temperature calcination temperature is 200~300℃, and the calcination time is 1~3h.

8. The copper-silver electrocatalyst prepared by any one of the preparation methods described in claims 1 to 7.

9. The application of the copper-silver composite catalyst as described in claim 8 in the electrochemical reaction of the membrane electrode.

10. The application of the copper-silver electrocatalyst as described in claim 8 in the preparation of ethylene oxide.

Images