Bimetal MOFs catalyst for electrocatalytic nitrate reduction synthesis of ammonia and preparation method and application thereof

Abstract

The invention relates to a bimetallic MOFs catalyst for electrocatalytic nitrate reduction synthesis of ammonia and a preparation method and application thereof, the bimetallic MOFs catalyst takes quinoline-5-carboxylic acid as a ligand, and has bimetallic active sites of Cu and Co; hydrophobic carbon paper is used as a carrier and is used as a cathode in an electrocatalytic nitrate reduction synthesis ammonia system. The Faraday efficiency of ammonia production of the catalyst reaches 96.4% under the conditions of neutral electrolyte and-0.6 VRHE, and efficient degradation of NO3 <-> and resource recycling of ammonia can be achieved; and the preparation process is simple, the cost is low, the reaction condition is mild, and the industrial application prospect is remarkable.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic nitrate reduction to ammonia synthesis technology, and specifically relates to a bimetallic MOF catalyst for electrocatalytic nitrate reduction to ammonia synthesis, its preparation method and application. Background Technology

[0002] Ammonia (NH3) is not only an important chemical raw material and fertilizer, but also a new type of energy substance with great development potential—a carbon-free, high-energy-density substance. Therefore, adopting new, green, and efficient ammonia production processes has become essential to align with modern sustainable and healthy development trends. To date, industrial NH3 production still primarily relies on the century-old Haber-Bosch process, which requires high-purity hydrogen (H2) and nitrogen (N2) as raw materials, reacting under iron catalysts and high-temperature (400~600 °C) and high-pressure (20~40 MPa) conditions. This not only leads to the massive consumption of fossil fuels and carbon dioxide (CO2) emissions, but its harsh reaction conditions and low conversion rate also become key constraints on the industry's development. The electrocatalytic reduction of nitrate (NO3RR), with its advantages of high efficiency and environmental friendliness, utilizes nitrate (NO3)... - As a raw material, its NO3 - High solubility, dissociation energy (204 kJ / mol) -1 The lower concentration of NO3 effectively reduces the electrochemical resorption of NO3 under mild reaction conditions. - The mass transfer resistance and reaction energy barrier during the conversion to NH3. Furthermore, NO3RR can achieve synergistic treatment of nitrates in industrial wastewater and contaminated groundwater. However, without a catalyst, the reaction rate and Faraday efficiency (FE) of NO3RR are limited by both chemical inertness and the competitive hydrogen evolution reaction in the aqueous electrolyte, making the NO3RR process relatively slow.

[0003] To improve the yield and efficiency of ammonia synthesis, the rational design of catalysts for the electrocatalytic reduction of nitrate is crucial, representing a significant challenge and a key technological breakthrough in this research area. To date, numerous pioneering studies have demonstrated that noble metal nanoparticles, such as ruthenium, rhodium, and palladium, can effectively enhance the performance of electrochemical NH3 synthesis. However, their scarcity and high cost severely limit their large-scale application. Therefore, developing inexpensive and abundant transition metal nanoparticles, such as iron (Fe, Co, Ni, and Cu), has become an important research direction. Among non-noble metal catalysts, Cu-based nanomaterials exhibit advantages due to their electronic structure and affinity for NO3. -The matching of molecular orbitals reveals enormous application potential. Ordinary bulk Cu-based nanomaterials suffer from low metal utilization due to the inertness of internal atoms, thus exacerbating copper resource depletion. Therefore, improving copper atom utilization efficiency through morphological engineering and surface loading has become a core research approach. Metal-organic frameworks (MOFs) possess characteristics such as tunable porous structure, high specific surface area, and good metal site dispersion, making them ideal supports for constructing highly efficient electrocatalysts. Bimetallic MOFs can be formed through heterometallic atom doping, allowing for the regulation of electronic states, band structures, and intermediate adsorption energies, thereby achieving synergistic effects of active sites. However, the application of existing bimetallic MOFs in NO3RR still faces challenges such as complex preparation processes and low concentrations of NO3 under neutral conditions. - Problems such as insufficient degradation and ammonia production efficiency make it difficult to meet the needs of industrial applications. Therefore, it is necessary to design a bimetallic MOF catalyst with a simple synthesis process, while improving the efficiency of low-concentration NO3 under neutral conditions. - Degradation efficiency and ammonia production rate are of great significance for promoting the large-scale application of bimetallic MOF catalysts in the field of electrocatalytic nitrate reduction to ammonia synthesis. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a bimetallic MOF catalyst for the electrocatalytic reduction of nitrate to ammonia, its preparation method and application, so as to realize the reduction of NO3 in industrial wastewater and polluted groundwater. - Highly efficient electrocatalytic degradation; achieving low concentration NO3 under neutral conditions. - It achieves highly selective conversion and completes the resource recovery of ammonia.

[0005] This invention provides a bimetallic MOF catalyst for the electrocatalytic reduction of nitrate to ammonia, which uses quinoline-5-carboxylic acid as a ligand, has Cu and Co bimetallic active sites, and produces a synergistic effect; the bimetallic MOF catalyst uses hydrophobic carbon paper as a support and serves as the cathode in the electrocatalytic reduction of nitrate to ammonia system.

[0006] This invention provides a method for preparing a bimetallic MOF catalyst for the electrocatalytic reduction of nitrate to ammonia, comprising:

[0007] Co(NO3)3·6H2O (cobalt nitrate hexahydrate) and Cu(NO3)2·3H2O (copper nitrate trihydrate) were mixed, and then quinoline-5-carboxylic acid (Qc-5) was added and dissolved in a mixed solvent of dimethylformamide and anhydrous ethanol. The mixed solution was continuously sonicated at room temperature, followed by a solvothermal reaction. After cooling, the solution was washed and dried to obtain a bimetallic MOF catalyst, denoted as Qc-5-CuCo.

[0008] Preferably, the molar ratio of quinoline-5-carboxylic acid: Cu(NO3)2·3H2O: Co(NO3)3·6H2O is 2:0.1~2:0.1~2.

[0009] Preferably, the volume ratio of dimethylformamide to anhydrous ethanol in the mixed solvent is 1:1.

[0010] Preferably, the ultrasonic treatment power is 53~80 W, the ultrasonic time is 15~30 min, and the temperature of the mixed solution is controlled at 15~30 ℃ during the ultrasonic process.

[0011] Preferably, the solvothermal reaction temperature is 100~120 ℃ and the reaction time is 24~60 hours.

[0012] Preferably, the washing and drying process specifically involves: centrifuging and washing with dimethylformamide and anhydrous ethanol 2-4 times each, followed by vacuum drying at 100-115°C for 6-12 hours.

[0013] The present invention also provides an application of the above-mentioned bimetallic MOF catalyst in the electrocatalytic reduction of nitrate to ammonia, comprising: loading the bimetallic MOF catalyst onto hydrophobic carbon paper as the cathode in the electrocatalytic system.

[0014] Furthermore, the electrocatalysis is carried out in an H-type electrolytic cell; a bimetallic MOF catalyst supported on hydrophobic carbon paper is used as the cathode, a platinum sheet as the anode, and an Ag / AgCl electrode filled with saturated KCl solution is used as the reference electrode; the anolyte is Na2SO4 solution, and the catholyte is NaNO3+Na2SO4 solution; Nafion 117 is used as the membrane, and the operating potential is -0.4 ~ -0.8 V. RHE .

[0015] Preferably, the concentration of NaNO3 in the cathode electrolyte is 0.05~0.2 mol / L; the concentration of Na2SO4 is 0.1~0.3 mol / L; the electrocatalytic reaction temperature is 20~35 ℃; and the reaction lasts for 2~12 hours.

[0016] Preferably, the specific steps for supporting the bimetallic MOF catalyst on hydrophobic carbon paper include:

[0017] (1) Preparation of hydrophobic carbon paper:

[0018] First, the carbon paper is immersed in a polytetrafluoroethylene solution with a mass concentration of 10%~30%, dried in an oven, and then calcined in a muffle furnace to remove the surfactant contained in the polytetrafluoroethylene. At the same time, the polytetrafluoroethylene is uniformly dispersed on the surface of the carbon paper through hot melting and sintering, thus producing hydrophobic carbon paper.

[0019] (2) Hydrophobic carbon paper supported catalyst:

[0020] The above-mentioned bimetallic MOF catalyst was added to a mixture of isopropanol and Nafion solution, and after sonication, a catalyst slurry was obtained. Then, it was sprayed onto the surface of hydrophobic carbon paper to obtain a supported bimetallic MOF catalyst.

[0021] Preferably, in step (1), the drying temperature of the carbon paper in the oven is 50~70 ℃ and the drying time is 1~3 hours.

[0022] Preferably, in step (1), the muffle furnace calcination temperature is 100~115 ℃, the calcination time is 24~48 hours, and the heating rate is 5~20 ℃ / min.

[0023] Preferably, in step (2), the volume ratio of isopropanol to Nafion solution in the mixed solvent is 100:1~2; and the mass concentration of Nafion solution is 5%~10%.

[0024] Preferably, in step (2), the spray gun pressure is 0.2~0.4 MPa, the spraying distance is 15~25 cm, and the spraying is carried out in 3~5 uniform sprayings.

[0025] Preferably, in step (2), the loading of the catalyst slurry on the surface of the hydrophobic carbon paper is 1.5~3.5 mg / cm². 2 .

[0026] Beneficial effects

[0027] (1) The catalytic performance synthesized in this invention is excellent, at -0.6 V RHE Under these conditions, the Faraday efficiency of ammonia production reaches 96.4%, which is far higher than the current Faraday efficiency of ammonia production.

[0028] (2) The reaction conditions of this invention are mild, and low concentrations of NO3 can be achieved under neutral electrolyte, room temperature and pressure. - The efficient conversion does not require harsh high-temperature and high-pressure conditions, and its energy consumption is only 1 / 3 to 1 / 2 of that of the Haber-Bosch process, significantly reducing production costs.

[0029] (3) This invention has both environmental and economic benefits, achieving the removal of NO3 from industrial wastewater and polluted groundwater. - Pollution control was achieved, and the resource recovery of ammonia was completed (ammonia can be used as an energy carrier or chemical raw material).

[0030] (4) The present invention uses a solvothermal method to prepare the catalyst, which is simple and has low raw material cost; the hydrophobic carbon paper carrier has good stability and is not easily corroded, which can ensure the long-term use of the catalyst and is suitable for large-scale production and application, showing great industrial potential. Attached Figure Description

[0031] Figure 1 The supported Qc-5-CuCo catalyst in this invention is used for the electrocatalysis of NO3. - A schematic diagram illustrating the principle of ammonia synthesis.

[0032] Figure 2 SEM images of the Qc-5-CuCo catalysts prepared in the embodiments and comparative examples of the present invention are shown; where (a), (b), (c), and (d) correspond to Example 1, Example 2, Comparative Example 1, and Comparative Example 2, respectively.

[0033] Figure 3 This is a flowchart illustrating the preparation process of the Qc-5-CuCo catalyst in this embodiment of the invention.

[0034] Figure 4 The supported catalyst in Example 1 was used at -0.4 to -0.8 V. RHE The yields of ammonia and nitrite and the Faraday efficiency under the given conditions. Detailed Implementation

[0035] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0036] The microstructure of the products in the embodiments or comparative examples of this invention was tested using SEM (Hitachi S-4800). Electrochemical tests were conducted in an H-type electrolytic cell using a three-electrode method, with the supported catalyst prepared in the embodiments or comparative examples as the cathode, a platinum sheet as the anode, and an Ag / AgCl electrode filled with saturated KCl solution as the reference electrode. The cathode and anode were separated by a Nafion 117 membrane. Electrochemical performance was tested on a Chenhua CHI760D electrochemical workstation. The synthesized ammonia and nitrite were detected using a UV spectrophotometer (Shanghai Shunzi Hengping Scientific Instruments Co., Ltd. UV2200PC).

[0037] Example 1

[0038] This embodiment provides a supported Qc-5-CuCo catalyst for the electrocatalytic reduction of nitrate to ammonia, and the specific preparation method is as follows:

[0039] 1) The synthesis process of Qc-5-CuCo catalyst is as follows: Figure 3 As shown:

[0040] Weigh 0.1 mol Co(NO3)3·6H2O (29.1 g) and 0.1 mol Cu(NO3)2·3H2O (24.2 g), and mix thoroughly. Add 0.4 mol quinoline-5-carboxylic acid (69.2 g) and dissolve in 2000 mL of a 1:1 dimethylformamide-anhydrous ethanol mixture. Sonicate at 100 W for 30 minutes at room temperature (solution temperature 25 ℃), transfer to a polytetrafluoroethylene-lined autoclave, and react at 105 ℃ for 48 hours. After cooling, wash three times each with dimethylformamide and anhydrous ethanol (8000 rpm, 5 minutes each time), and vacuum dry at 105 ℃ for 12 hours to obtain a brownish-red powder, designated as Qc-5-CuCo catalyst, with the morphology as shown in the figure. Figure 2 As shown in figure a, it exhibits a cluster structure, through Cu 2+ With Co 2+ The formation of hybrid coordination structures results in a larger active specific surface area, which is beneficial for improving catalytic efficiency.

[0041] 2) Preparation of hydrophobic carbon paper:

[0042] Take a 10 cm x 10 cm piece of carbon paper, immerse it in a 30% polytetrafluoroethylene solution for 5 minutes, dry it in a 60 ℃ oven for 2 hours; then transfer it to a muffle furnace, heat it to 350 ℃ at a rate of 5 ℃ / min, calcine it with air for 24 hours, and then cool it for later use.

[0043] 3) Catalyst support:

[0044] Take 0.5 g of Qc-5-CuCo catalyst, add 10 mL of isopropanol and 2 mL of 5% Nafion solution, and sonicate at 100 W for 30 minutes to prepare a catalyst slurry; spray it onto hydrophobic carbon paper in 4 layers using an air spray gun (0.3 MPa pressure, 15~25 cm distance), with a loading of 2.0 mg / cm³. 2 The catalyst was dried and vacuum-sealed for later use, thus obtaining the supported Qc-5-CuCo catalyst.

[0045] Using the above-mentioned supported catalyst as the cathode, a platinum sheet as the anode, and an Ag / AgCl electrode filled with saturated KCl solution as the reference electrode, the cathode and anode were separated by a Nafion 117 membrane; the anode electrolyte was Na2SO4 solution, and the cathode electrolyte was 0.1 mol / L NaNO3 + 0.3 mol / L Na2SO4, and the electrochemical performance was tested.

[0046] -0.4 ~ -0.8 V RHE The yields of ammonia and nitrite and the Faraday efficiency under the given conditions are as follows: Figure 4 As shown.

[0047] At -0.6 VRHE The Faraday efficiency (FE) of NH3 was measured under the following conditions. NH3 ): 96.4%;

[0048] NH3 yield: 355 µmol h -1 cm -2 ;

[0049] Cycle stability: After 12 hours of continuous electrolysis, FE remains at 94.5%, and yield decay is ≤3%.

[0050] Example 2

[0051] This embodiment provides a supported Qc-5-CuCo catalyst for the electrocatalytic reduction of nitrate to ammonia. The specific preparation method is the same as in Example 1, except that the amount of metal source is adjusted to 0.1 mol Cu(NO3)2·3H2O (24.2 g) and 0.15 mol Co(NO3)3·6H2O (43.7 g). The morphology of the obtained Qc-5-CuCo catalyst is as follows. Figure 2 As shown in b, it exhibits a plate-like aggregated structure, which increases the active surface area of ​​the catalyst and is beneficial to improving catalytic efficiency.

[0052] Example 3

[0053] This embodiment provides a supported Qc-5-CuCo catalyst for the electrocatalytic reduction of nitrate to ammonia. The specific preparation method is the same as in Example 1, except that the amount of metal source is adjusted to 0.1 mol Cu(NO3)2·3H2O (24.2 g) and 0.2 mol Co(NO3)3·6H2O (58.2 g).

[0054] Example 4

[0055] This embodiment provides a supported Qc-5-CuCo catalyst for the electrocatalytic reduction of nitrate to ammonia. The specific preparation method is the same as in Example 1, except that the amount of metal source is adjusted to 0.15 mol Cu(NO3)2·3H2O (36.3 g) and 0.1 mol Co(NO3)3·6H2O (29.1 g).

[0056] Example 5

[0057] This embodiment provides a supported Qc-5-CuCo catalyst for the electrocatalytic reduction of nitrate to ammonia. The specific preparation method is the same as in Example 1, except that the amount of metal source is adjusted to 0.2 mol Cu(NO3)2·3H2O (48.4 g) and 0.1 mol Co(NO3)3·6H2O (29.1 g).

[0058] Example 6

[0059] In this embodiment, the same supported Qc-5-CuCo catalyst as in Example 1 was used for electrocatalytic performance testing. The difference is that the cathode electrolyte used was a 0.1 mol / L NaNO3 + 0.2 mol / L Na2SO4 solution.

[0060] Comparative Example 1

[0061] This comparative example prepares a supported catalyst using the same method as in Example 1, except that the metal source is adjusted to 0.1 mol Cu(NO3)2·3H2O (24.2 g). The morphology of the obtained catalyst is as follows. Figure 2 As shown in c, it exhibits a uniform aggregation of polygonal particles, with the crystal stacking mode deviating from layered growth, forming a regular granular morphology.

[0062] Comparative Example 2

[0063] This comparative example prepares a supported catalyst using the same method as in Example 1, except that the metal source is adjusted to 0.1 mol Co(NO3)3·6H2O (29.1 g). The morphology of the obtained catalyst is as follows. Figure 2 As shown in d, with Figure 2 Similar to c, it exhibits uniform polygonal particle aggregation, forming a more regular granular morphology.

[0064] Comparative Example 3

[0065] This comparative example uses the same supported Qc-5-CuCo catalyst as Example 1 for electrocatalytic performance testing, the difference being that: the cathode electrolyte used is only 0.1 mol / L NaNO3 solution (pH 7.0, no Na2SO4 electrolyte).

[0066] Using the supported catalyst prepared in the above examples or comparative examples as the cathode, electrocatalytic reduction of nitrate to ammonia was carried out. The specific parameters and performance test results are shown in Table 1.

[0067] like Figure 1 As shown, the Qc-5-CuCo catalyst, through Cu-Co bimetallic synergy, quinoline-5-carboxylic acid electron channels, and hydrophobic carbon paper interface modulation, achieves high performance at -0.6 V. RHE NO3 is achieved under neutral conditions - →Reduction of NH3 (NO3) - + 8e - + 9H + → NH3 + 3H2O), Cathode core process: Cu sites selectively adsorb NO3 - Co sites regulate electronic states; ligands transfer electrons from the external circuit, activating NO bonds; intermediates (NO2) -→NO→N2H4) Stepwise protonation reduction; NH3 rapid desorption, site regeneration. Based on the test data from the embodiments and comparative examples of this application, the Cu / Co molar ratio, by regulating the balance of bimetallic synergistic effects, determines the distribution of active sites, electron transport efficiency, and side reaction suppression ability of the catalyst; the cathode electrolyte system, by changing NO3... - The concentration, ionic strength, and conductivity of the supporting electrolyte affect reaction mass transfer, proton supply, and interfacial charge transfer. These factors collectively determine the electrochemical reaction efficiency (FE), ammonia yield, and cycle stability of the electrocatalytic reduction of nitrate to ammonia (NO3RR). This application achieves the core effects of "high selectivity, high activity, and strong adaptability" by optimizing the Cu / Co ratio and adapting electrolyte systems for various scenarios.

[0068] Table 1. Performance parameters of the supported catalysts prepared in Examples 1-6 and Comparative Examples 1-3 under different conditions.

[0069]

Claims

1. A bimetallic MOF catalyst for the electrocatalytic reduction of nitrate to ammonia, characterized in that, The bimetallic MOF catalyst uses quinoline-5-carboxylic acid as a ligand and has Cu and Co bimetallic active sites; the bimetallic MOF catalyst uses hydrophobic carbon paper as a support and serves as the cathode in the electrocatalytic nitrate reduction to ammonia synthesis system.

2. A method for preparing a bimetallic MOF catalyst for the electrocatalytic reduction of nitrate to ammonia, comprising: Co(NO3)3·6H2O and Cu(NO3)2·3H2O were mixed, and then quinoline-5-carboxylic acid was added and dissolved in a mixed solvent of dimethylformamide and anhydrous ethanol. The mixed solution was continuously sonicated at room temperature, followed by a solvothermal reaction. After cooling, the solution was washed and dried to obtain a bimetallic MOF catalyst.

3. The preparation method according to claim 2, characterized in that, The molar ratio of quinoline-5-carboxylic acid: Cu(NO3)2·3H2O: Co(NO3)3·6H2O is 2:0.1~2:0.1~2; the volume ratio of dimethylformamide to anhydrous ethanol in the mixed solvent is 1:

1.

4. The preparation method according to claim 2, characterized in that, The ultrasonic treatment power is 53~80 W, the ultrasonic time is 15~30 min, and the temperature of the mixed solution is controlled at 15~30 ℃ during the ultrasonic process; the solvothermal reaction temperature is 100~120 ℃, and the reaction time is 24~60 hours.

5. The application of the bimetallic MOF catalyst as described in claim 1 in the electrocatalytic reduction of nitrate to ammonia, characterized in that, The application includes: loading the bimetallic MOF catalyst onto hydrophobic carbon paper as a cathode in an electrocatalytic system.

6. The application according to claim 5, characterized in that, The electrocatalysis was carried out in an H-type electrolytic cell; a bimetallic MOF catalyst supported on hydrophobic carbon paper was used as the cathode, a platinum sheet as the anode, and an Ag / AgCl electrode filled with saturated KCl solution as the reference electrode; the anolyte was Na₂SO₄ solution, and the catholyte was NaNO₃ + Na₂SO₄ solution; Nafion 117 was used as the membrane, and the operating potential was -0.4 ~ -0.8 V. RHE .

7. The application according to claim 6, characterized in that, The concentration of NaNO3 in the cathode electrolyte is 0.05~0.2 mol / L; the concentration of Na2SO4 is 0.1~0.3 mol / L; the electrocatalytic reaction temperature is 20~35 ℃; and the reaction lasts for 2~12 hours.

8. The application according to claim 5, characterized in that, The specific steps for loading the bimetallic MOF catalyst onto hydrophobic carbon paper include: (1) First, immerse the carbon paper in a polytetrafluoroethylene solution with a mass concentration of 10%~30%, dry it in an oven, and then calcine it in a muffle furnace to obtain hydrophobic carbon paper. (2) The bimetallic MOF catalyst is added to a mixture of isopropanol and Nafion solution, and after sonication, a catalyst slurry is obtained. Then, it is sprayed onto the surface of hydrophobic carbon paper to obtain a supported bimetallic MOF catalyst.

9. The application according to claim 8, characterized in that, In step (1), the drying temperature of the carbon paper in the oven is 50~70 ℃ and the drying time is 1~3 hours; the calcination temperature of the muffle furnace is 100~115 ℃ and the calcination time is 24~48 hours, with a heating rate of 5~20 ℃ / min.

10. The application according to claim 8, characterized in that, In step (2), the loading of the catalyst slurry on the surface of the hydrophobic carbon paper is 1.5~3.5 mg / cm². 2 .

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