Catalyst for reduction of nitrate to produce ammonia, and preparation method and application thereof

Abstract

The application discloses a catalyst capable of reducing nitrate to prepare ammonia, a preparation method and application thereof. The catalyst comprises a nitrogen-doped carbon carrier and copper tri-atoms loaded on the nitrogen-doped carbon carrier. The catalyst has excellent electrochemical catalytic nitrate reduction performance and can be used for reducing nitrate to prepare ammonia.

Description

Technical Field

[0001] This invention belongs to the field of materials, specifically relating to a catalyst that can be used to reduce nitrate ions to produce ammonia, its preparation method, and its application. Background Technology

[0002] Nitrogen is a fundamental element in living organisms, and the nitrogen cycle plays a crucial role in maintaining the balance of elements in the biosphere, directly impacting human life. However, excessive human intervention and industrial development have led to an increase in nitrate (NO3) in water. - Pollution gradually disrupts the balance of the microbial-mediated nitrogen cycle, leading to excessive release of NO3. - NO3 poses a significant threat to the ecological environment and public health. - Accumulation of NO3 in rivers and lakes leads to eutrophication, which is harmful to aquatic life; NO3 in drinking water - The presence of NO3 can damage the human endocrine system and lead to serious diseases; - The generated nitrite (NO2) - NO3 is a carcinogenic compound. Therefore, removing NO3 from water is crucial. - It is of utmost importance.

[0003] Traditional biological, physical, and chemical methods have been used to remove NO3 from water bodies. - However, these methods generate secondary pollution, requiring subsequent treatment, which limits their widespread use. Compared to these methods, electrocatalytic nitrate reduction reaction (NO3RR) is a promising alternative because it uses renewable electricity, operates under mild conditions, and does not produce harmful residues.

[0004] NO3 - As a major nitrogen pollutant in surface and groundwater, converting it into the more valuable ammonia (NH3) is an effective way to balance the disrupted nitrogen cycle and has attracted widespread attention from researchers over the past few decades. NO3RR involves the transfer of 9 protons and 8 electrons, a kinetically slow process. Furthermore, byproducts generated during NO3RR, such as NO2... - Hydrazine (N₂H₄) and nitrogen (N₂) can affect the selectivity of NH₃. Furthermore, the electrocatalytic hydrogen production process HER competes with NO₃RR, resulting in lower Faraday efficiency.

[0005] To address these challenges, there is an urgent need to develop highly selective and efficient electrocatalysts for ammonia production. Summary of the Invention

[0006] To address the shortcomings and deficiencies of existing technologies, this invention provides catalysts with different copper species configurations on nitrogen-doped carbon (NC) supported by copper metal-organic frameworks (Cu-BTC) using precursor coordination environment regulation and high-temperature carbonization strategies. These catalysts are used for the electrochemical catalytic reduction of nitrate to remove nitrate contaminants from water. To obtain catalysts with different copper species configurations, the amounts of copper source and 1,3,5-benzenetriacrylic acid were controlled. Experiments show that this method can easily and efficiently synthesize catalysts for the reduction of nitrate to ammonia, and the prepared catalysts exhibit good catalytic performance for electrochemical nitrate reduction.

[0007] According to a first aspect of the present invention, a catalyst is provided for reducing nitrate ions to prepare ammonia, the catalyst comprising a nitrogen-doped carbon support and copper triatoms supported on the nitrogen-doped carbon support.

[0008] In some embodiments, the catalyst has a nanosheet structure.

[0009] In some embodiments, the distance between two adjacent copper atoms in the three copper atoms is... For example, Or any value between them.

[0010] In some embodiments, the distances between two adjacent copper atoms in the three copper atoms are respectively and

[0011] In some embodiments, the catalyst contains 15% to 40% copper by mass, preferably 15% to 20%. In some embodiments, the catalyst contains 15%, 16%, 17%, 18%, 19%, 20%, 25%, 30%, 35%, 40% copper by mass, or any value between these values.

[0012] According to a second aspect of the present invention, a method for preparing a catalyst that can be used to reduce nitrate ions to produce ammonia is provided, the method comprising the following steps:

[0013] S1: Mix solution A containing a copper source with solution B containing 1,3,5-benzenetricarboxylic acid and then react them.

[0014] S2: The reaction product obtained in step S1 is subjected to solid-liquid separation and drying to obtain a metal-organic framework material;

[0015] S3: The mixture of the metal-organic framework material obtained in step S2 and dicyandiamide is calcined in an inert atmosphere to obtain the catalyst.

[0016] In some embodiments, in step S1, the molar ratio of the 1,3,5-benzenetricarboxylic acid to the copper element in the copper source is 1:(2.2-2.8), for example, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8 or any value between them.

[0017] In some embodiments, in step S1, the copper source includes at least one of copper chloride, copper nitrate, copper sulfate, and copper acetate.

[0018] In some embodiments, in step S1, the solvent in solution A and / or solution B includes a C1-C3 alcohol compound, preferably one or more of methanol, ethanol, and propanol.

[0019] In some embodiments, in step S1, the reaction temperature is 15-40°C and the reaction time is 10-40 hours. In some embodiments, in step S1, the reaction temperature is 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, or any value between them. In some embodiments, in step S1, the reaction time is 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, or any value between them.

[0020] In some embodiments, in step S2, the metal-organic framework material is characterized by X-ray diffraction, showing characteristic peaks at 2θ of 5.8°±0.2°, 6.7°±0.2°, 9.5°±0.2°, 11.6°±0.2°, 13.4°±0.2°, 17.5°±0.2°, and 19.0°±0.2°.

[0021] In some embodiments, in step S3, the mass ratio of the metal-organic framework material to dicyandiamide is 1:(8-15), preferably 1:(8-12). In some embodiments, the mass ratio of the metal-organic framework material to dicyandiamide is 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, or any value between them.

[0022] In some embodiments, in step S3, the calcination temperature is 700-1000°C, preferably 750-850°C. In some embodiments, the calcination temperature is 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, or any value between them.

[0023] In some embodiments, the roasting time in step S3 is 1-5 hours, preferably 1-3 hours. In some embodiments, the roasting time is 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 4 hours, 5 hours, or any value between them.

[0024] In some embodiments, the preparation method further includes cooling the calcined product and then acid washing and drying it.

[0025] According to a third aspect of the present invention, the application of the catalyst described in the first aspect or the catalyst prepared by the preparation method described in the second aspect in the electrochemical catalytic reduction of nitrate to ammonia is provided.

[0026] In some embodiments, the reaction is carried out in an aqueous phase.

[0027] The material synthesis method in this invention is simple and easy to operate, and the prepared copper triatomic catalyst exhibits excellent electrochemical catalytic performance for nitrate reduction. This superior electrocatalytic NO3RR property benefits from the unique configuration of fully exposed triatomic Cu supported on an ultrathin NC substrate (Cu3 / NC). This structure provides the catalyst with abundant active sites and enables the synergistic effect of adjacent Cu sites to rapidly promote the deoxygenation and hydrogenation steps in the NO3RR process, avoiding the byproduct NO2. - The accumulation of [agents] also inhibits competitive HER; at the same time, the electronic configuration and d-band center of the catalyst are adjusted, optimizing the adsorption and desorption capabilities of reaction intermediates on its surface, giving Cu3 / NC excellent NO3RR performance. Attached Figure Description

[0028] Figure 1 The images shown are scanning electron microscope images (a) and XRD patterns (b) of Cu-BTC according to Embodiment 1 of the present invention.

[0029] Figure 2 The image shows the XRD pattern of Cu3 / NC in Example 1 of the present invention.

[0030] Figure 3 The images shown are transmission electron microscope (A) and aberration-corrected high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image (B) of Cu3 / NC according to Embodiment 1 of the present invention.

[0031] Figure 4 The image shows a high-angle annular dark-field scanning transmission electron microscope image of Cu3 / NC according to Embodiment 1 of the present invention, and the corresponding elemental distribution mapping diagram of Cu, C and N.

[0032] Figure 5The figures are the NH3 yield (a) and the Faraday efficiency FE (b) of NH3 at different potentials in Example 1 of the present invention.

[0033] Figure 6 To illustrate the NO3 in solution at -0.8V in Example 1 of the present invention - NO2 - and NH4 + The concentration of [something] changes over time.

[0034] Figure 7 The yield of NH3 and the Faraday efficiency (FE) of Cu3 / NC at -0.8V for 7 cycles in Example 1 of the present invention are given.

[0035] Figure 8 The image shows the XRD pattern of Cu1 / NC in Embodiment 2 of the present invention.

[0036] Figure 9 The images shown are transmission electron microscope (a) and aberration-corrected HAADF-STEM (b) images of Cu1 / NC according to Embodiment 2 of the present invention.

[0037] Figure 10 The image shows the HAADF-STEM image of Cu1 / NC with spherical aberration correction according to Embodiment 2 of the present invention, and the corresponding mapping diagram.

[0038] Figure 11 The figures are NH3 yield (a) and Faraday efficiency FE (b) of NH3 at different potentials in Example 2 of the present invention.

[0039] Figure 12 Cu in Embodiment 3 of the present invention p XRD pattern of / NC.

[0040] Figure 13 Cu in Embodiment 3 of the present invention p Transmission electron microscopy (a) and HRTEM (b) images of / NC.

[0041] Figure 14 The image shown is a HAADF-STEM image with spherical aberration correction according to Embodiment 3 of the present invention, and the corresponding mapping diagram.

[0042] Figure 15 The figures are the NH3 yield (a) and the Faraday efficiency FE (b) of NH3 at different potentials in Example 3 of the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention in any way. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure. Such structures and techniques have also been described in many publications.

[0044] In this invention, "copper triatoms" refers to three adjacent copper atoms loaded on a nitrogen-doped carbon support. These three copper atoms are bonded together by electrostatic attraction to form metallic bonds, and the distance between any two adjacent copper atoms is [missing information].

[0045] The reagents and / or pharmaceuticals used in the following examples are all commercially available or can be synthesized by known methods.

[0046] The detection methods used in the following embodiments are as follows:

[0047] (1) Detection of NH3 yield and Faraday efficiency (FE)

[0048] The NO3RR process was carried out in an H-type electrolytic cell. 50 mL of 1 M KOH solution was poured into one side as the anolyte, and 50 mL of 1 M KOH + 0.1 M KNO3 solution was poured into the other side as the catholyte. The anolyte and cathode chambers were separated by a Nafion membrane. A platinum sheet electrode was inserted into the anolyte as the counter electrode, and an Hg / HgO electrode and a carbon paper loaded with the catalyst sandwiched between stainless steel electrodes were inserted into the cathode chamber as the reference and working electrodes, respectively. The reaction was conducted on a CHI760E electrochemical workstation. The NO3RR process was driven by an I / O device, with the reaction time set to 30 minutes and the reaction voltage set. Samples of the reacted solution were taken, and subsequent dilution, color development, and UV absorbance testing were performed to obtain the NH3 yield and Faradaic efficiency (FE) of the catalyst used.

[0049] (2) NO3 - NO2 - and NH4 +The NO3RR concentration detection process was carried out in an H-type electrolytic cell. 50 mL of 1 M KOH solution was poured into one side as the anolyte, and 50 mL of 1 M KOH + 0.1 M KNO3 solution was poured into the other side as the catholyte. The anolyte and cathode chambers were separated by a Nafion membrane. A platinum sheet electrode was inserted into the anolyte as the counter electrode, and an Hg / HgO electrode and a carbon paper containing the catalyst sandwiched between stainless steel electrodes were inserted into the cathode chamber as the reference and working electrodes, respectively. The reaction was carried out on a CHI760E electrochemical workstation. The NO3RR process was driven by an I / O circuit, with a reaction time of 8 hours and a reaction voltage set. Samples were taken every hour. All solutions after the reaction were diluted, developed, and tested with UV absorbance to obtain the NO3 concentration. - NO2 - and NH4 + The concentration.

[0050] (3) Detection of NH3 yield and Faraday efficiency (FE) after 7 cycles

[0051] The NO3RR process was carried out in an H-type electrolytic cell. 50 mL of 1M KOH solution was poured into one side as the anolyte, and 50 mL of 1M KOH + 0.1M KNO3 solution was poured into the other side as the catholyte. The anolyte and cathode chambers were separated by a Nafion membrane. A platinum electrode was inserted into the anolyte as the counter electrode, and an Hg / HgO electrode and a carbon paper loaded with the catalyst sandwiched between stainless steel electrodes were inserted into the cathode chamber as the reference and working electrodes, respectively. The reaction was carried out on a CHI760E electrochemical workstation. The NO3RR process was driven by an iterative process (it), with the reaction time set to 30 minutes and the reaction voltage set. After the reaction, a sample was taken and retained. The catholyte and anolyte were then replaced with 50 mL of 1M KOH + 0.1M KNO3 solution, and the anolyte was replaced with 50 mL of 1M KOH solution. The iterative process was repeated, and the resulting solution was sampled and retained. After 7 cycles, the retained sample solution was diluted, developed, and its UV absorbance was measured to obtain the NH3 yield and Faraday efficiency (FE) of the catalyst used.

[0052] Example 1: Preparation of nitrogen-doped carbon-supported copper triatomic Cu3 / NC catalyst

[0053] (1) Synthesis of Cu-BTC:

[0054] 4.832 g of Cu(NO3)2·3H2O (0.02 mol) was dissolved in 100 mL of methanol to form solution A; 1.681 g of 1,3,5-benzenetricarboxylic acid (BTC) (0.008 mol) was dissolved in 100 mL of methanol to form solution B. Solution A was then slowly added to solution B, and the mixture was stirred at 400 rpm for 10 minutes to obtain a blue solution. The blue solution was left at room temperature for 24 hours. Subsequently, it was washed five times with methanol at 8000 rpm for 5 minutes each time, and the obtained solid was the Cu-BTC precursor. Finally, the Cu-BTC precursor was freeze-dried.

[0055] (2) Synthesis of Cu3 / NC:

[0056] The Cu-BTC precursor was mixed with dicyandiamide at a mass ratio of 1:10 and directly carbonized under an argon atmosphere at 800 °C with a heating rate of 5 °C / min. After holding at this temperature for 2 hours, the mixture was naturally cooled to room temperature. Subsequently, the product was soaked in 5 wt.% hydrochloric acid for 4 hours with stirring, followed by washing with ethanol by centrifugation at 8000 rpm five times for 5 minutes each time. Finally, the Cu3 / NC was freeze-dried.

[0057] like Figure 1 As shown in Figure a, the scanning electron microscope image reveals that the precursor Cu-BTC has a clear octahedral morphology. The XRD pattern of Cu-BTC is consistent with the fitted results. Figure 1 b) Typical peaks were observed at 2θ = 5.8° (111), 6.7° (200), 9.5° (220), 11.6° (222), 13.4° (400), 17.5° (511) and 19.0° (440), indicating that it was successfully synthesized.

[0058] Figure 2 The diffraction pattern of Cu3 / NC is similar to that of broad graphite peaks, indicating that no metal or oxide nanocrystals were formed.

[0059] exist Figure 3 In a, Cu3 / NC exhibits a nanosheet-like structure. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image ( Figure 3 b) shows that in Cu3 / NC, adjacent three-atom structures are clearly visible. The raster image in the inset directly shows three representative metal atoms in the blue box area, with distances between adjacent atoms of [missing information]. and

[0060] from Figure 4 The elemental distribution map of Cu3 / NC shows that Cu, C, and N elements are uniformly distributed on the material surface.

[0061] Figure 5 Figure a shows the yield of NH3 in the voltage range of -0.6V to -1.0V. It can be seen from the figure that the NH3 yield increases with a negative shift of the applied potential from -0.6V, reaching a maximum of 24816 μg h at -0.8V. -1 mg -1 The yield subsequently decreased slightly with further increases in the applied potential, likely because a more negative applied potential promotes the competitive hydrogen evolution reaction, thus reducing the NH3 yield. The highest ammonia yield achieved at -0.8V was superior to most reported materials (5000-15000 μgh). -1 mg -1 between).

[0062] Figure 5 Figure b shows the Faraday efficiency FE over a voltage range of -0.6V to -1.0V. As can be seen from the figure, the Faraday efficiency of Cu3 / NC exhibits a volcano-like trend, reaching a maximum of 95.4% at -0.8V. The overall Faraday efficiency remains above 70%, indicating that Cu3 / NC is effective against NO3- ions over a wide voltage range. - The degradation process for producing ammonia has good energy efficiency.

[0063] like Figure 6 As shown, when the initial NO3 - At a concentration of 100 mmol / L, NO3 - It degrades almost completely after 7 hours. A small amount of toxic byproduct NO2 is produced after 2 hours of reaction. - NO2 is produced, but after 5 hours of reaction, the intermediate product NO2 is produced. - Almost all of it is converted, and the final products are all ammonia, an important chemical, and nitrogen gas, which is pollution-free.

[0064] from Figure 7 As can be seen, after seven NO3RR cycles at -0.8V, the NH3 yield and Faraday efficiency FE did not show significant decline, indicating that Cu3 / NC has good electrocatalytic NO3RR stability.

[0065] Example 2: Preparation of nitrogen-doped carbon-supported single-atom copper Cu1 / NC catalyst:

[0066] 0.966 g of Cu(NO3)2·3H2O (0.004 mol) was dissolved in 100 mL of methanol to form solution A; 1.681 g of 1,3,5-benzenetricarboxylic acid (0.008 mol) was dissolved in 100 mL of methanol to form solution B. Solution A was then slowly added to solution B, and the mixture was stirred at 400 rpm for 10 minutes to obtain a blue solution. The blue solution was left at room temperature for 24 hours. Subsequently, it was washed five times with methanol at 8000 rpm for 5 minutes each time. The Cu-BTC precursor was then freeze-dried.

[0067] Subsequently, the Cu-BTC precursor was mixed with dicyandiamide at a mass ratio of 1:10 and directly carbonized under an argon flow at 800°C with a heating rate of 5°C / min. After holding at this temperature for 2 hours, it was naturally cooled to room temperature. The product was then soaked in 5 wt.% hydrochloric acid for 4 hours under stirring, followed by washing with ethanol by centrifugation at 8000 rpm five times for 5 minutes each time. Finally, the Cu1 / NC was freeze-dried.

[0068] Diffraction pattern of Cu1 / NC ( Figure 8 Similar to the broad graphite peaks, this indicates the absence of metal or oxide nanocrystal formation.

[0069] Transmission electron microscope images of Cu1 / NC ( Figure 9 a) Showing its nanosheet morphology, aberration-corrected HAADF-STEM image ( Figure 9 Dispersed bright spots can be observed on b), corresponding to dispersed Cu single atoms. Furthermore, from... Figure 10 The mapping diagram shows that Cu, C, and N elements are uniformly distributed on the material surface.

[0070] Example 3: Preparation of nitrogen-doped carbon-supported copper nanoclusters Cu p / NC catalyst:

[0071] 1.82 g of Cu(NO3)2·3H2O (0.0075 mol) was dissolved in 50 mL of methanol to form solution A; 0.8575 g of 1,3,5-benzenetricarboxylic acid (0.0041 mol) was dissolved in 50 mL of methanol to form solution B. While sonicating, solution A was slowly added to solution B, forming a blue solution. The process continued until precipitation was complete. The precipitate was collected by centrifugation and washed five times with methanol at 8000 rpm for 5 minutes each time to remove reaction residues. Finally, the powder was freeze-dried.

[0072] The powder was then mixed with dicyandiamide powder at a mass ratio of 1:10, and directly carbonized under an argon flow at 800°C at a heating rate of 5°C / min. After holding at this temperature for 2 hours, it was naturally cooled to room temperature to obtain a solid, namely Cu. p / NC; Finally, for Cu p / NC is freeze-dried.

[0073] like Figure 12 As shown, Cu p / NC shows weak diffraction peaks at 43.3°, 50.2° and 73.6°, which correspond to the (111), (200) and (220) planes of metallic Cu, respectively (PDF 1-1241).

[0074] Cu p / NC TEM image ( Figure 13 In image a), copper clusters aggregated on nanosheets are observed, as shown in the high-resolution transmission electron microscope (HRTEM) image. Figure 13 b) 0.21 nm lattice fringes were measured, corresponding to the Cu(111) crystal plane. Obvious white spots were observed on the HAADF-STEM, representing aggregated copper clusters. Figure 14 The mapping diagram shows that Cu aggregates, while C and N elements are uniformly distributed.

[0075] Figure 11 a and 11b show the electrochemical catalytic nitrate reduction performance of Cu1 / NC; Figure 15 a and 15b show Cu p Electrochemical catalytic nitrate reduction performance of / NC.

[0076] according to Figure 5 and Figure 11 , Figure 15 It can be seen that Cu1 / NC, Cu3 / NC, Cu p Both NC and NH4+ can be used for the electrochemical catalytic synthesis of ammonia from nitrate ions, and can effectively convert NO3 pollutants in water bodies. - .

[0077] Experimental results show that the Cu3 / NC catalyst prepared in Example 1 exhibits the best electrochemical catalytic performance for nitrate reduction. Its Faradaic efficiency remains above 70% over a wide voltage range (-0.6V to -1.0V), reaching a maximum of 95.4% at -0.8V, while simultaneously achieving a maximum ammonia yield of 24816 μg / h. -1 mg -1 The Cu3 / NC method exhibited excellent electrocatalytic stability in seven cycles, with no significant decrease in NH3 yield and Faraday efficiency (FE). Furthermore, the Cu3 / NC preparation method is simple, requires low metal usage, and significantly improves atom utilization, which is beneficial for large-scale production and application.

[0078] In summary, the synthesis method of the catalyst in this invention is simple and easy to operate, and the prepared Cu3 / NC exhibits excellent electrochemical catalytic nitrate reduction performance.

[0079] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A catalyst for reducing nitrate to prepare ammonia, the catalyst comprising a nitrogen-doped carbon support and three copper atoms supported on the nitrogen-doped carbon support, the three copper atoms being three adjacent copper atoms supported on the nitrogen-doped carbon support, the three copper atoms forming a metallic bond, the distance between two adjacent copper atoms being 1.5 Å - 5 Å.

2. The catalyst according to claim 1, characterized in that, The catalyst has a nanosheet structure; and / or In the three copper atoms, the distances between two adjacent copper atoms are 2.2 Å ± 0.2 Å, 2.5 Å ± 0.2 Å, and 3.0 Å ± 0.2 Å, respectively.

3. The catalyst according to claim 1 or 2, characterized in that, The catalyst contains 15% to 40% copper by mass.

4. The catalyst according to claim 1 or 2, characterized in that, The catalyst contains 15% to 20% copper by mass.

5. A method for preparing a catalyst that can be used to reduce nitrate ions to produce ammonia, comprising the following steps: S1: Mix solution A containing a copper source with solution B containing 1,3,5-benzenetricarboxylic acid and then react them. S2: The reaction product obtained in step S1 is subjected to solid-liquid separation and drying to obtain a metal-organic framework material; S3: The mixture of the metal-organic framework material obtained in step S2 and dicyandiamide is calcined in an inert atmosphere to obtain the catalyst; In step S1, the molar ratio of 1,3,5-benzenetricarboxylic acid to copper in the copper source is 1:(2.2-2.8); and / or In step S1, the copper source includes at least one of copper chloride, copper nitrate, copper sulfate, and copper acetate; and / or In step S1, the solvent in solution A and / or solution B includes one or more of methanol, ethanol, and propanol; and / or In step S1, the reaction temperature is 15-40℃ and the time is 10-40h.

6. The preparation method according to claim 5, characterized in that, In step S2, X-ray diffraction characterization revealed that the metal-organic framework material exhibited characteristic peaks at 2θ values ​​of 5.8°±0.2°, 6.7°±0.2°, 9.5°±0.2°, 11.6°±0.2°, 13.4°±0.2°, 17.5°±0.2°, and 19.0°±0.2°.

7. The preparation method according to claim 5, characterized in that, In step S3, the mass ratio of the metal-organic framework material to dicyandiamide is 1:(8-15); and / or In step S3, the calcination temperature is 700-1000℃; and / or In step S3, the roasting time is 1-5 hours.

8. The preparation method according to claim 5, characterized in that, In step S3, the mass ratio of the metal-organic framework material to dicyandiamide is 1:(8-12); and / or In step S3, the calcination temperature is 750-850℃; and / or In step S3, the roasting time is 1-3 hours.

9. The preparation method according to any one of claims 5-8, characterized in that, The preparation method further includes cooling the calcined product and then acid washing and drying it.

10. The application of the catalyst according to any one of claims 1-4 or the catalyst prepared by the preparation method according to any one of claims 5-9 in the electrochemical catalytic reduction of nitrate to ammonia.

11. The application according to claim 10, characterized in that, The reaction takes place in the aqueous phase.

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