Cu-doped CeO2-CNx catalyst, preparation method and application of Cu-doped CeO2-CNx catalyst in nitrate reduction

Abstract

According to the Cu-doped CeO2-CNx catalyst, the preparation method and the application of the Cu-doped CeO2-CNx catalyst in nitrate reduction, the interaction between reactants and the catalyst is remarkably enhanced through activation and multiple times of heat treatment, the electron transmission capacity is optimized, meanwhile, the adsorption capacity on nitrate is enhanced, the synergistic effect of oxygen vacancies and Cu active sites is optimized, and the Cu-doped CeO2-CNx catalyst is obtained. The obtained catalyst for electrocatalytic reduction of nitrate into ammonia has the characteristics of high activity, high selectivity and stability.

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalysis and relates to a Cu-doped CeO 2 -CN x The invention relates to a catalyst, a preparation method and application thereof in nitrate reduction; in particular, to a preparation method and application of a porous catalytic material with high activity, high selectivity and high stability. Background Art

[0002] As fossil energy is increasingly depleted and the global population continues to grow, environmental problems and energy crises continue to emerge, and the development of sustainable energy resources has become urgent. Most countries are committed to adopting green production chemicals in industry to reduce the consumption of fossil fuels. Among them, ammonia (NH 3 ) is the second largest chemical produced in the world. 3 The global market size exceeds 185 million tons per year; 3 It is also an essential chemical in industrial production and agricultural life. About 50% of the world's food production depends on amino fertilizers, which solves the food problem of nearly 7 billion people. It is also widely used in medicine, textiles, fuel, wastewater treatment and other fields. As the global population continues to grow, to achieve a stable and affordable food supply, sufficient and cost-effective NH 3 In addition, NH 3 It is also an ideal zero-carbon energy carrier and hydrogen storage medium, which is easy to liquefy, has high energy density, high-quality hydrogen content and low transportation and storage costs, and is now also being explored as a future renewable energy alternative. 3 As a carbon-free fuel, NH 3 The production demand will be further upgraded.

[0003] In nature, biological nitrogen fixation provides essential nutrients for organisms, but the biological nitrogen fixation reaction is too slow. 2 Converted to NH 3 Inspired by the electrocatalytic nitrogen reduction reaction (NRR), N 2 As a raw material, it can be used to produce NH 3 Environmentally friendly methods have become the forefront of research. Compared with the HB process, electrocatalytic NRR has the advantages of low energy consumption, mild reaction conditions, and zero carbon emissions. It can also achieve decentralized ammonia production and support distributed long-term energy storage and fuel production. It is a promising circular economy route to replace the HB process.

[0004] Electrochemical nitrate reduction reaction (e-NO 3 RR) is considered a promising environmental NH 3Production pathway, because NO 3 − It has low N=O bond dissociation energy, which ensures faster reaction kinetics; at the same time, its excellent solubility makes NO 3 − The electrocatalyst surface can be fully contacted; and the more positive reaction potential reduces the interference of competitive HER. 3 RR is thermodynamically and kinetically easier than NRR and is expected to be a promising candidate for NH 3 Electrosynthesis provides a practical green approach. On the other hand, NO 3 − It is widely present in industrial wastewater and groundwater. Its excessive discharge and accumulation will destroy the ecological balance and nitrogen cycle system. In addition, NO 3 − It will directly threaten human health and cause a variety of diseases. Therefore, from the perspective of "turning waste into treasure", NO 3 − Transformed into value-added NH 3 , which is of great significance to environmental protection, public health, and restoring the balance of nitrogen cycle. 3 RR uses water as a hydrogen source and is powered by sustainable energy (solar, wind and tidal), reducing consumption and greenhouse gas emissions.

[0005] Excellent e-NO 3 RR performance is closely related to the catalyst, which is mainly reflected in the intrinsic activity of each active site and the density of active sites. The morphology, structure, defects and synergistic effect of electrocatalysts are the factors affecting e-NO 3 RR activity. For example, different crystal structures can be 3 − Activation provides a large number of defect sites and coordination conditions. Heteroatom doping can maximize the absorption free energy of electrocatalysts to different intermediates by adjusting the band gap or intrinsic conductivity. 3 In the RR process, the interaction between the reaction intermediates and the catalyst surface directly affects the subsequent hydrogenation capacity and reaction kinetics, and the selectivity of the final product is largely affected by the electrode material. 3 RR, the researchers studied electrocatalysts including non-metal, noble metal and transition metal-based materials. Transition metal-based materials include Cu-based, Fe-based, Ni-based and Co-based catalysts. 3 NO in RR process 3 − Restore to NO 2 − The slower kinetics may be attributed to the lowest unoccupied molecular π* The orbital has high energy, which is not conducive to the entry of charges. Cu has a unique 3d 10 configuration, whose high d orbital occupancy is similar to the LUMOπ of nitrate * Similar energy levels, can promote e-NO 3 The progress of RR is conducive to becoming NO 3 − Highly active center for reduction reaction.

[0006] For example, CN118513042A is a single-atom transition metal catalyst CeO rich in oxygen vacancies. 2 The preparation method and application of the invention are as follows: the preparation method is to weigh phthalocyanine molecules containing transition metal single atom sites and trimesic acid, polyvinyl pyrrolidone and Ce(NO 3 ) 3 ; dissolved in a mixed solution of ethanol and N, N-dimethylformamide; then reacting the mixed solution at 100-140°C to form MPc / Ce-MOF powder; finally placing the MPc / Ce-MOF powder in a muffle furnace and calcining it at a temperature of 350-550°C in an air atmosphere for 1.5 hours to obtain M 1 / CeO 2 Catalyst; The obtained catalyst improves the utilization rate of active sites, generates a large number of oxygen vacancies, enhances the adsorption of nitric acid and intermediates, can effectively improve the activity of electrocatalytic reduction of nitrate and the selectivity of ammonia production, and has a better ammonia production effect. Summary of the invention

[0007] Based on the above content, the present invention provides a Cu-doped CeO 2 -CN x Catalyst, preparation method and application thereof in nitrate reduction. Through multiple heat treatments, the interaction between reactants and catalysts is significantly enhanced, the electron transfer capacity is optimized, the adsorption capacity of nitrate is enhanced, and the synergistic effect of oxygen vacancies and Cu active sites is optimized. The obtained catalyst has high dispersion, high selectivity and stability, and provides an innovative strategy for the development of efficient nitrate reduction catalysts, as follows: A Cu-doped CeO 2 -CN x The preparation method of the catalyst comprises the following preparation method: (1) Preparation of bimetallic MOF materials: Solution A: add solid copper nitrate and cerium nitrate into methanol solution and stir magnetically to fully dissolve; Solution B: Add dimethylimidazole solid and citric acid into methanol solution and stir magnetically to fully dissolve; Pour solution A into solution B, adjust the pH value to 5.5±0.2 with sodium hydroxide or ammonia water, stir magnetically at 500-800 rpm for 12-36 h at a water bath temperature of 25-30° C., filter, wash, and dry to obtain a copper-cerium bimetallic MOF material; (2) Preparation of nitrogen-doped carbon material: the product obtained in step (1) is mixed with melamine in a certain proportion and ground sufficiently, then subjected to nitrogen calcination in a tubular furnace, and then naturally cooled to room temperature and ground sufficiently; (3) Activation: placing the product prepared in step (2) in a hydrothermal reactor containing 6-8 wt% KOH, and performing activation treatment at 170-180° C. for 4-5 h. After cooling, filtering and drying, a high specific surface area nitrogen-doped porous carbon carrier is obtained; (4) After secondary nitrogen calcination treatment, the mixture is ground evenly to obtain Cu-doped CeO 2 -CN x catalyst.

[0008] In certain embodiments, 0.06-0.08 mol copper nitrate and 0.03-0.04 mol cerium nitrate solids are added to 100-150 mL methanol solution and magnetically stirred for 5-10 min to fully dissolve.

[0009] In certain embodiments, 0.8-1.2 mol of dimethylimidazole solid and 0.04-0.06 mol of citric acid are added to 140-160 mL of methanol solution and magnetically stirred for 5-10 min to fully dissolve.

[0010] In certain embodiments, the weight ratio of the product obtained in step (1) to melamine is 2:(1.2-1.4).

[0011] In some embodiments, the tubular furnace is subjected to a nitrogen calcination treatment once: the temperature is increased at 3-5°C / min to 490-510°C and kept at this temperature for 50-70min, and then the temperature is increased at 3-5°C / min to 950-1000°C and kept at this temperature for 110-130min.

[0012] In certain embodiments, the secondary nitrogen calcination treatment is performed by heating the temperature at 3-5°C / min to 200-500°C and maintaining the temperature for 120-140 min.

[0013] In some embodiments, a Cu-doped CeO 2 -CN x Catalyst used in the field of electrochemical reduction of nitrate to synthesize ammonia.

[0014] An electrode material, wherein the electrode material is formed by doping CeO with Cu 2 -CN x The catalyst is prepared by compounding with a conductive substrate, and the conductive substrate is selected from one of foamed nickel, carbon paper and carbon cloth.

[0015] A method for preparing an electrode material, wherein Cu is doped with CeO 2 -CN x The catalyst and Nafion dispersion are dispersed in an organic solvent, the obtained dispersion is drop-coated on carbon paper, and then dried to obtain the result.

[0016] The present invention first prepares a Cu-Ce bimetallic MOF material, and uses citric acid instead of oxalic acid as a complexing agent. Citric acid regulates the size distribution of metal clusters through steric hindrance, wherein the tricarboxylic acid structure can chelate Cu 2+ and Ce 3+ , to avoid heterogeneous precipitation or phase separation, see the attached Figure 1 The prepared bimetallic MOF material has a hexagonal morphology and a smooth surface, indicating that the bimetallic MOF was successfully prepared without any technical problems of dual-phase deposition.

[0017] Next, the nitrogen-doped carbon material is prepared: during the roasting process, the MOF organic ligand (dimethylimidazole) is carbonized at high temperature to form a porous carbon matrix, retaining part of the MOF pore structure, which is mainly micro-mesoporous; during the roasting process, the nitrogen source melamine is also introduced, and finally the nitrogen-doped carbon porous carrier is obtained by roasting. The nitrogen-doped carbon material is used as a catalyst carrier. In the process of preparing ammonia by nitrate electroreduction, the catalytic efficiency and reaction performance are significantly improved through structural modification, conductivity improvement and intermediate state stabilization. This material not only accelerates the reaction rate, but also ensures the effective stability of the intermediate state substance, making the overall reaction process more efficient and reliable.

[0018] Activation: The original specific surface area of ​​the bimetallic MOF material is relatively high, which decreases significantly after calcination and carbonization, but the porous carbon still retains a relatively high value. However, in order to obtain a higher specific surface area, pore expansion activation is required. KOH reacts with carbon to etch the carbon skeleton to generate new pores, forming a rough or porous structure and enhancing the surface active sites.

[0019] The last step is secondary nitrogen calcination. The secondary nitrogen calcination treatment plays multiple key roles in the preparation of the catalyst and has significant technical advantages in improving the performance of electrochemical reduction of nitrate to ammonia: (1) secondary calcination can make CeO 2 Oxygen vacancies in the lattice are further formed and stabilized. Oxygen vacancies serve as key active sites for nitrate adsorption and activation, which can significantly enhance the interaction between reactants and catalysts. (2) Since the present invention does not require subsequent noble metal impregnation loading, secondary calcination can effectively remove residual oxygen-containing groups (such as -COOH) activated by KOH, reduce inactive sites, and improve conductivity. (3) The electron rearrangement induced by secondary calcination enhances the Cu-CeO 2The charge transfer efficiency at the heterogeneous interface promotes the conversion of intermediates in the rate-determining step; (4) thermal treatment can eliminate the internal stress formed during the pre-treatment of porous carbon, avoid the structural collapse of the carbon skeleton during the electrochemical cycle, and relieve the volume expansion stress during the electrochemical cycle, thereby improving the stability and life of the catalyst.

[0020] See attached Figure 1 and attached Figure 2 , including Figure 1 (C) and (d) in the figure are the morphologies after activation and secondary nitrogen calcination heat treatment, which are porous morphologies. Figure 1 Neutralization Figure 2 From the TEM-Mapping results, it can be seen that the copper and cerium are evenly dispersed and coupled in the form of an alloy, the lattice spacing is 0.27nm, and the C, N, O, Cu, and Ce species elements are evenly distributed in the catalyst.

[0021] Beneficial technical effects: The present invention significantly enhances the interaction between reactants and catalysts through multiple heat treatments, optimizes the electron transfer capacity, and at the same time enhances the adsorption capacity of nitrate ions, optimizes the synergistic effect of oxygen vacancies and Cu active sites, and the obtained catalyst has high NH 3 Yield and high NH 3 Selectivity and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Attached Figure 1 Bimetallic MOF materials and Cu-doped CeO 2 -CN x Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the catalyst, and the corresponding elemental mapping images.

[0023] Attached Figure 2 Cu doped CeO 2 -CN x Elemental mapping of multiple elements in catalysts.

[0024] Attached Figure 3 At different secondary calcination temperatures, the catalyst NH 3 Faradaic efficiency and yield.

[0025] Attached Figure 4 Linear sweep voltammetry (LSV), chronoamperometry (CA) curves and NH 3 Faradaic efficiency and yield.

[0026] Attached Figure 5 Catalyst spectroscopy testing.

[0027] Attached Figure 6 Catalyst stability testing. DETAILED DESCRIPTION

[0028] Example 1 A Cu-doped CeO 2 -CN x The preparation method of the catalyst comprises the following preparation method: (1) Preparation of bimetallic MOF materials.

[0029] Solution A: Add 0.06 mol copper nitrate and 0.03 mol cerium nitrate solid into 100 mL methanol solution and stir magnetically for 5 min to fully dissolve.

[0030] Solution B: Add 0.8 mol of solid dimethylimidazole and 0.04 mol of citric acid into 140 mL of methanol solution and stir magnetically for 5 min to fully dissolve.

[0031] Solution A was poured into solution B, and the pH value was adjusted to 5.5±0.2 using sodium hydroxide or ammonia water. The solution was stirred magnetically at 500 rpm for 12 h at a water bath temperature of 25°C, filtered, washed, and dried to obtain a copper-cerium bimetallic MOF material.

[0032] (2) Preparation of nitrogen-doped carbon materials: The product obtained in step (1) was mixed with melamine in a weight ratio of 2:(1.2) and ground thoroughly, and then subjected to nitrogen calcination in a tubular furnace: the temperature was raised to 490°C at 3°C / min and kept constant for 50 min, and then the temperature was further raised to 950°C at 3°C / min and kept constant for 110 min. The mixture was naturally cooled to room temperature and then ground thoroughly.

[0033] (3) Activation: The product prepared in step (2) was placed in a hydrothermal reactor containing 6 wt % KOH and activated at 170 ° C for 4 h. After cooling, it was filtered and dried to obtain a nitrogen-doped porous carbon carrier with a high specific surface area.

[0034] (4) Secondary nitrogen calcination treatment: heating at 3°C / min to 200°C and maintaining constant temperature for 120 min. After calcination, grinding is performed evenly to obtain Cu-doped CeO 2 -CN x catalyst.

[0035] Example 2 A Cu-doped CeO 2 -CN x The preparation method of the catalyst comprises the following preparation method: (1) Preparation of bimetallic MOF materials.

[0036] Solution A: Add 0.07 mol copper nitrate and 0.035 mol cerium nitrate solid into 125 mL methanol solution and stir magnetically for 7.5 min to fully dissolve.

[0037] Solution B: Add 1.0 mol of solid dimethylimidazole and 0.05 mol of citric acid into 150 mL of methanol solution and stir magnetically for 7.5 min to fully dissolve.

[0038] Solution A was poured into solution B, and the pH value was adjusted to 5.5±0.2 using sodium hydroxide or ammonia water. The solution was stirred magnetically at 650 rpm for 24 h at a water bath temperature of 27.5°C, filtered, washed, and dried to obtain a copper-cerium bimetallic MOF material.

[0039] (2) Preparation of nitrogen-doped carbon materials: The product obtained in step (1) was mixed with melamine in a weight ratio of 2:(1.3) and ground thoroughly, and then subjected to nitrogen calcination in a tubular furnace: the temperature was increased to 500°C at 4°C / min and kept constant for 60 min, and then the temperature was continued to be increased to 975°C at 4°C / min and kept constant for 120 min, and then naturally cooled to room temperature and ground thoroughly.

[0040] (3) Activation: The product prepared in step (2) was placed in a hydrothermal reactor containing 7 wt % KOH and activated at 175° C. for 4.5 h. After cooling, the product was filtered and dried to obtain a nitrogen-doped porous carbon carrier with a high specific surface area.

[0041] (4) Secondary nitrogen calcination treatment: heating at 4°C / min to 350°C and maintaining the temperature for 130 min. After calcination, grinding is performed evenly to obtain Cu-doped CeO 2 -CN x catalyst.

[0042] Example 3 A Cu-doped CeO 2 -CN x The preparation method of the catalyst comprises the following preparation method: (1) Preparation of bimetallic MOF materials.

[0043] Solution A: Add 0.08 mol copper nitrate and 0.04 mol cerium nitrate solid into 150 mL methanol solution and stir magnetically for 10 min to fully dissolve.

[0044] Solution B: Add 1.2 mol of solid dimethylimidazole and 0.06 mol of citric acid into 160 mL of methanol solution and stir magnetically for 10 min to fully dissolve.

[0045] Solution A was poured into solution B, and the pH value was adjusted to 5.5±0.2 using sodium hydroxide or ammonia water. The solution was stirred magnetically at 800 rpm for 36 h at a water bath temperature of 30° C., filtered, washed, and dried to obtain a copper-cerium bimetallic MOF material.

[0046] (2) Preparation of nitrogen-doped carbon material: The product obtained in step (1) was mixed with melamine in a weight ratio of 2: (1.4) and ground thoroughly, and then subjected to nitrogen calcination in a tubular furnace: the temperature was increased at 5°C / min to 510°C and kept constant for 70 min, and then the temperature was increased at 5°C / min to 1000°C and kept constant for 130 min, and then naturally cooled to room temperature and ground thoroughly.

[0047] (3) Activation: The product prepared in step (2) was placed in a hydrothermal reactor containing 8 wt % KOH and activated at 180° C. for 5 h. After cooling, the product was filtered and dried to obtain a nitrogen-doped porous carbon carrier with a high specific surface area.

[0048] (4) Secondary nitrogen calcination treatment: Heating at 5°C / min to 500°C and maintaining constant temperature for 140 min. After calcination, grinding is performed evenly to obtain Cu-doped CeO 2 -CN x catalyst.

[0049] Comparative Example 1 A method for preparing a Cu / C catalyst comprises the following preparation method: (1) Preparation of bimetallic MOF materials.

[0050] Solution A: Add 0.07 mol of solid copper nitrate into 125 mL of methanol solution and stir magnetically for 7.5 min to fully dissolve.

[0051] Solution B: Add 1.0 mol of solid dimethylimidazole and 0.05 mol of citric acid into 150 mL of methanol solution and stir magnetically for 7.5 min to fully dissolve.

[0052] Pour solution A into solution B, adjust the pH value to 5.5±0.2 with sodium hydroxide or ammonia water, stir magnetically at 650 rpm for 24 h at a water bath temperature of 27.5°C, filter, wash and dry to obtain MOF material.

[0053] (2) The product obtained in step (1) was subjected to a nitrogen calcination treatment in a tubular furnace: the temperature was increased to 500°C at 4°C / min and kept constant for 60 min, the temperature was further increased to 975°C at 4°C / min and kept constant for 120 min, and the product was naturally cooled to room temperature and then fully ground to obtain a Cu / C catalyst.

[0054] Electrochemical measurement: The three-electrode system test was performed on a CHI 660E electrochemical workstation. A platinum sheet was used as the counter electrode and a saturated Hg / HgO electrode was used as the reference electrode. The potential was converted to the potential relative to the reversible hydrogen electrode (RHE), E(RHE)=E(Hg / HgO)+0.197+0.0591∗pH. The working electrode was prepared by dropping 150μL of catalyst ink (2mg of catalyst prepared in the examples and comparative examples, 240μL of isopropanol, 60μL of water and 25μL of Nafion solution) on carbon paper (area: 1cm 2 )superior.

[0055] The catalyst prepared in Example 2 was used as the reference, and the secondary nitrogen calcination treatment was adjusted respectively: the temperature was raised to 200°C, 300°C, 400°C, and 500°C at 4°C / min, and the mixture was ground evenly after calcination to obtain Cu-doped CeO 2 -CN x Catalyst, see Appendix Figure 3 At different secondary calcination temperatures, the catalyst NH 3 FE and yield, among which when the calcination temperature in Example 2 was modified to 500°C, the catalytic performance of the corresponding catalyst was the best.

[0056] See attached Figure 4 , tested based on Example 2 and Comparative Example 1, wherein the attached Figure 4 (a) is the preparation of Cu-doped CeO in Example 2 2 -CN x The chronoamperometric CA curve of (Ce-Cu / C) catalyst; Figure 4 (b) is the CA curve of the Cu / C catalyst prepared in Comparative Example 1. The following conclusions can be drawn: (1) the current density increases significantly after Ce doping; (2) the FE of Example 2 NH3 The overall yield is higher than that of comparative example 1, and the highest yield can reach 96.01%; (3) The yield of example 2 is much higher than that of Cu / C, and the highest yield can reach 25.12 mmol . h -1 cm -2 .

[0057] See attached Figure 5 , catalyst (a) N 2 H 4 UV spectrum of (b) NO 2 - UV spectrum of (c) N 2 H 4 , NO 2 - , NH 3From the FE, it can be concluded that the catalyst of the present invention has a high selectivity, that is, the yield of the corresponding by-products and the Faraday efficiency are very low.

[0058] See attached Figure 6 It can be seen that in the ten cycle tests, NH 3 The FE of the test was always above 93%, and the NH 3 The absorbance curves of the it and NH 3 The yield also remained stable, demonstrating the stability of the catalyst.

[0059] It should be noted that the above example is only one of the preferred embodiments of the present invention. It is very easy for professionals to change or modify some of its parameters. Therefore, meaningless modifications based only on the design concept of the main body of the present invention are futile, and these changes are still within the scope of protection of the present invention.

Claims

1. A Cu-doped CeO2-CN x The method for preparing a catalyst is characterized in that The invention comprises the following preparation method: (1) Preparation of bimetallic MOF materials: Solution A: add copper nitrate and cerium nitrate solids into methanol solution and stir magnetically to fully dissolve; Solution B: Add dimethylimidazole solid and citric acid into methanol solution and stir magnetically to fully dissolve; Pour solution A into solution B, adjust the pH value to 5.5±0.2 with sodium hydroxide or ammonia water, stir magnetically at 500-800 rpm for 12-36 h at a water bath temperature of 25-30° C., filter, wash, and dry to obtain a copper-cerium bimetallic MOF material; (2) Preparation of nitrogen-doped carbon material: the product obtained in step (1) is mixed with melamine in a certain proportion and ground sufficiently, then subjected to nitrogen calcination in a tubular furnace, and then naturally cooled to room temperature and ground sufficiently; (3) Activation: placing the product prepared in step (2) in a hydrothermal reactor containing 6-8 wt% KOH, and performing activation treatment at 170-180° C. for 4-5 h. After cooling, filtering and drying, a high specific surface area nitrogen-doped porous carbon carrier is obtained; (4) After secondary nitrogen calcination treatment, the mixture was ground evenly to obtain Cu-doped CeO2-CN x catalyst.

2. A Cu-doped CeO2-CN as claimed in claim 1 x The method for preparing a catalyst is characterized in that Add 0.06-0.08 mol of copper nitrate and 0.03-0.04 mol of cerium nitrate solid into 100-150 mL of methanol solution and stir magnetically for 5-10 minutes to fully dissolve.

3. A Cu-doped CeO2-CN as claimed in claim 1 x The method for preparing a catalyst is characterized in that Add 0.8-1.2 mol of dimethylimidazole solid and 0.04-0.06 mol of citric acid into 140-160 mL of methanol solution and stir magnetically for 5-10 minutes to fully dissolve.

4. A Cu-doped CeO2-CN as claimed in claim 1 x The method for preparing a catalyst is characterized in that The weight ratio of the product obtained in step (1) to melamine is 2:(1.2-1.4).

5. A Cu-doped CeO2-CN as claimed in claim 1 x The method for preparing a catalyst is characterized in that Tubular furnace primary nitrogen calcination treatment: heat up to 490-510°C at 3-5°C / min and keep constant temperature for 50-70min, then continue to heat up to 950-1000°C at 3-5°C / min and keep constant temperature for 110-130min.

6. A Cu-doped CeO2-CN as claimed in claim 1 x The method for preparing a catalyst is characterized in that Secondary nitrogen calcination treatment: heat up at 3-5℃ / min to 200-500℃ and keep constant temperature for 120-140min.

7. A Cu-doped CeO2-CN x Catalyst, characterized in that A catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. A Cu-doped CeO2-CN as claimed in claim 7 x The use of a catalyst is characterized in that Used in the field of electrochemical reduction of nitrate to synthesize ammonia.

9. An electrode material, comprising the Cu-doped CeO2-CN as claimed in claim 7 x Catalyst, characterized in that The electrode material is Cu doped CeO2-CN x The catalyst is prepared by compounding with a conductive substrate, and the conductive substrate is selected from one of foamed nickel, carbon paper and carbon cloth.

10. A method for preparing an electrode material, characterized in that The Cu-doped CeO2-CN prepared in claim 7 x The catalyst and Nafion dispersion are dispersed in an organic solvent, the obtained dispersion is drop-coated on carbon paper, and then dried to obtain the result.

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