Confined-range bimetallic catalyst for electrocatalytic reduction reaction as well as preparation method and application of confined-range bimetallic catalyst

Abstract

The invention discloses a confined bimetallic catalyst for electrocatalytic reduction reaction and a preparation method and application thereof, and belongs to the technical field of electrocatalyst.The preparation method comprises the following steps that tetrapropylammonium hydroxide and ultrapure water are mixed, tetraethoxysilane is added, stirring is conducted, and a first mixture is obtained; mixing and stirring nickel chloride hexahydrate, ethylenediamine and ultrapure water to obtain a mixture II; mixing and stirring copper nitrate trihydrate, ethylenediamine and ultrapure water to obtain a mixture III; dropwise adding the mixture II and the mixture III into the mixture I, and performing hydrothermal synthesis to obtain a reaction product; centrifugally separating and collecting the obtained reaction product to obtain a catalyst precursor; and calcining the catalyst precursor in air, and carrying out heat treatment in a flowing hydrogen-argon mixed atmosphere to obtain the confinement bimetallic catalyst. The confinement bimetallic catalyst prepared by the invention is used for electro-catalytic treatment of nitrate in underground water, and can improve the efficiency of electro-catalytic removal of nitrate.

Description

Technical Field

[0001] The present invention relates to the field of electrocatalytic technology, and in particular to a confined bimetallic catalyst for electrocatalytic reduction reaction, and a preparation method and application thereof. Background Art

[0002] Groundwater is an important water resource for human beings. For many countries and regions, groundwater is the main source of water for production, life, industry and agriculture. Among them, nitrate is the main form of nitrogen pollution in groundwater and one of the stable pollutants that is difficult to control in groundwater. The survey data of nitrate in deep and shallow groundwater of 52 basin-scale groundwater systems in China showed that among the shallow aquifers in 36 major basins, 90% of the survey points in 25 basins exceeded the quality standards for drinking water in my country; among the deep or karst aquifers in 37 major basins, 10 basins exceeded the standard. Excessive release of nitrate in groundwater not only affects the quality of environmental components, but also endangers human health through the food chain. Nitrate can be converted into nitrite in the human mouth and gastrointestinal tract. Excessive nitrite can cause methemoglobinemia, which can cause suffocation or even death in severe cases. Infants and young children are more likely to develop methemoglobinemia, commonly known as "blue baby syndrome" after ingesting nitrate. Therefore, it has become an urgent task to decompose or remove nitrate from groundwater through sustainable and effective methods.

[0003] Conventional nitrate treatment technologies mainly include physical, biological and chemical treatment technologies. However, the disadvantages of high cost and low efficiency limit the further development and application of these technologies. Electrochemical treatment technology is a process of removing nitrates by using metal or non-metallic materials as cathodes, and reducing nitrates to nitrogen, ammonia and other products by applying an external current and relying on the electrolytic reaction on the electrode surface during the reaction. Compared with traditional nitrate removal methods, electrochemical methods have the advantages of being environmentally friendly, easy to remotely control, and utilizing renewable energy (such as solar energy, wind energy, and electrical energy). It has become an efficient and promising nitrate removal method.

[0004] Precious metals are widely used in nitrate reduction. However, due to their high cost, easy poisoning and limited lifespan, precious metals such as Pt, Pb and Au are significantly hindered in the large-scale application of nitrate reduction reactions. Transition metal catalytic materials all have a certain degree of nitrate catalytic activity. Among them, Cu has become an important research object for nitrate reduction reaction catalysts due to its unique catalytic properties for nitrates. Compared with other transition metal catalysts, copper-based catalysts have the advantages of stronger binding ability to nitrates, lower potential for driving nitrate catalytic reduction, and relatively low hydrogen evolution activity. Therefore, Cu-based catalysts are the most widely used metal catalysts in nitrate reduction.

[0005] Although the application of copper-based catalysts in nitrate reduction has achieved good results, the kinetics of nitrate reduction by single metal catalysts are slow and the efficiency is poor. Bimetallic catalysts have high denitrification reaction activity and fast reduction kinetics due to the synergistic effect of bimetallic active sites. Precious metals have excellent hydrogen adsorption performance, and copper has good catalytic performance for nitrogen and intermediates. The combination of the two can effectively improve the catalytic activity of the catalyst for nitrate. Researchers have improved the nitrate reduction ability of the catalyst by introducing precious metal doping. For example, Chen et al. synthesized ruthenium-dispersed copper nanowire catalysts (Ru-Cu NW) by cation exchange. The catalyst fully utilized the unique catalytic properties of both Ru and Cu. The highly dispersed Ru atoms can provide highly active nitrate reduction sites, while the surrounding Cu sites can inhibit the competitive hydrogen evolution reaction, making the catalyst have excellent electrocatalytic nitrate reduction performance. However, the price and abundance of precious metals limit their large-scale application. By combining Cu with non-precious metals, not only can the electrode cost be reduced, but also the catalytic activity and stability of the electrode can be enhanced. Considering that Ni atoms are the binding sites of H* and have a strong adsorption effect on key intermediates such as NO2* and NH2*, the addition of Ni atoms on Cu-based catalysts can greatly enhance the hydrogenation capacity of intermediates. In addition, Cu-Ni bimetallic catalysts can effectively regulate the adsorption strength between dual active sites and intermediates through the interatomic synergistic enhancement effect, which can break through the limitation of a single active site and further maximize the catalytic activity. Therefore, the design strategy of stable Cu-Ni bimetallic catalysts is crucial to achieve efficient nitrate removal.

[0006] Bimetallic catalysts have been extensively studied in the electrocatalytic reduction of nitrate. However, the current problem is that due to the increase in surface free energy, metal sites are prone to aggregation, active sites are few and not dispersed enough, the catalyst has poor stability and low life, and the performance of nitrate reduction is significantly reduced. Subnanometals confined in zeolite matrices are a promising special type of catalyst with significant advantages in size control, position regulation and nanostructure design. Yu et al. prepared well-dispersed and small-sized Pd nanoparticles in nano-sized silica (Pd / S-1-in). In the reaction of complete decomposition of formic acid to generate H2, the conversion rate of Pd / S-1-in-K catalyst was the highest, about 1.1 times that of Pd / S-1-in-Na, 1.4 times that of Pd / S-1-in, 5 times that of Pd / S-1-im and 19 times that of Pd / C catalyst. The beauty of zeolite-confined metals lies in their unique confinement effect at the molecular scale, thus achieving spatial confinement catalysis similar to enzyme catalysis. Confined catalysts can optimize the electronic structure of catalysts, improve the synergy between carriers and metal nanoparticles, promote rapid charge transfer, and enhance the catalytic activity, selectivity, and stability of catalysts. Confined engineering has not been reported in the electrocatalytic nitrate reduction reaction, so this study used confined engineering to increase the performance of the catalyst.

[0007] In summary, electrocatalytic reduction of nitrate has the advantages of being environmentally friendly, easy to remotely control, and utilizing renewable energy (such as solar energy, wind energy, and electric energy), and has become an efficient and promising method for nitrate removal. However, common catalyst materials face problems such as slow single metal catalytic kinetics, few catalytic active sites, poor catalyst stability, and side reactions affecting catalytic efficiency. Summary of the invention

[0008] The object of the present invention is to provide a method for preparing a confined bimetallic catalyst for an electrocatalytic reduction reaction to solve the problems raised in the above background technology.

[0009] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions: A method for preparing a confined bimetallic catalyst for an electrocatalytic reduction reaction comprises the following steps: Tetrapropylammonium hydroxide and ultrapure water are mixed, and ethyl orthosilicate is added and stirred to obtain a mixture 1; Mixing and stirring nickel chloride hexahydrate, ethylenediamine and ultrapure water to obtain a mixture II; Copper nitrate trihydrate, ethylenediamine and ultrapure water are mixed and stirred to obtain a mixture three; Adding mixture 2 and mixture 3 dropwise into mixture 1, stirring without precipitation, and then putting into an autoclave, performing hydrothermal synthesis at 165-175° C. to obtain a reaction product; The obtained reaction product is centrifuged and collected, and then washed and dried to obtain a catalyst precursor; The catalyst precursor is first placed in air for calcination, and then placed in a flowing hydrogen-argon mixed atmosphere for heat treatment to obtain the confined bimetallic catalyst.

[0010] Preferably, the molar ratio of the nickel chloride hexahydrate to the copper nitrate trihydrate is 1:(0.8-1.2).

[0011] Preferably, the drying temperature is 75-85°C.

[0012] Preferably, the calcination temperature is 500-600°C.

[0013] Preferably, the heat treatment temperature is 350-450°C.

[0014] Preferably, the volume ratio of hydrogen to argon in the hydrogen-argon mixed atmosphere is 3:97-7:93.

[0015] Another object of an embodiment of the present invention is to provide a confined bimetallic catalyst prepared by the above preparation method.

[0016] Another object of an embodiment of the present invention is to provide an application of the above-mentioned confined bimetallic catalyst in the electrocatalytic reduction of nitrates.

[0017] Another object of an embodiment of the present invention is to provide an application of the above-mentioned confined bimetallic catalyst in removing nitrate from water.

[0018] Another object of an embodiment of the present invention is to provide an electrocatalytic reduction device, comprising a cathode and an anode, wherein the cathode is made of the above-mentioned confined bimetallic catalyst.

[0019] The present invention prepares a subnanometer hybrid bimetallic cluster catalyst in pure siliceous S-1 zeolite nanocrystals, and uses the catalyst for electrocatalytic treatment of nitrate in groundwater, thereby improving the efficiency of electrocatalytic removal of nitrate and providing a more economical and effective method for achieving high-efficiency removal of nitrate pollution in groundwater. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A technical schematic diagram of electrocatalytic removal of nitrate from water using a confined bimetallic catalyst provided in an embodiment of the present invention; Figure 2 It is a synthetic roadmap for different materials; Figure 3 A schematic diagram of the structure of an electrocatalytic reduction device provided in an embodiment of the present invention; in the figure, 1-external power supply; 2-single-chamber electrolytic cell; 3-electrolyte; 4-anode; 5-cathode; Figure 4SEM images of S-1 (a) and Cu-Ni / S-1 (b); Figure 5 (a) is the SEM image of Cu-Ni@S-1, (b) is the element distribution map of Cu-Ni@S-1; Figure 6 is the XPS spectrum of Cu-Ni@S-1; Figure 7 is the XRD pattern of Cu-Ni@S-1; Figure 8 BET results of S-1 (a) and Cu-Ni@S-1 (b); Fig. 9 Electrochemical impedance spectra of Cu-Ni@S-1, Cu-Ni / S-1 and S-1; Fig.10 Linear sweep voltammetry curves of different materials; Fig.11 Comparison of Tafel slope (vs. RHE) of different materials; Fig.12 Comparison chart of (a) nitrate removal efficiency, (b) nitrite generation efficiency and (c) ammonia nitrogen generation efficiency of different catalyst materials; Fig.13 This is a graph showing the cycle performance test results of the Cu-Ni@S-1 catalyst; Fig.14 This is a comparison chart of metal leaching amounts from different materials; Fig.15 The effect of different current density on the electrocatalytic reduction of nitrate; Fig.16 The effect of different pH on the electrocatalytic reduction of nitrate; Fig.17 The effect of different initial nitrate concentrations on the electrocatalytic reduction of nitrate; Fig.18 This is a diagram showing the effect of different chloride ion concentrations on the electrocatalytic reduction of nitrate; Fig.19 The effect of different TBA concentrations on the electrocatalytic reduction of nitrate; Fig. 20 This is the reaction pathway diagram of Cu-Ni@S-1 electrocatalytic reduction of nitrate; Fig.21 It is the reaction process and Gibbs free energy change diagram; Fig. 22 The overall differential charge and adsorption energy comparison of adsorbed nitrate of Cu-Ni / S-1 and Cu-Ni@S-1; Fig.23Partial wave density of states of (a) Cu 3d orbital and (b) Ni 3d orbital of Cu-Ni@S-1 and Cu-Ni / S-1. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Conventional treatment technologies for nitrates mainly include physical, biological and chemical treatment technologies. Physical treatment technologies have high treatment costs, and nitrates are only transferred or concentrated but not completely removed, which is likely to cause secondary pollution. Biological treatment technologies are easily affected by the surrounding environment due to the large size of the reactor and the slow treatment cycle, so this method has many limitations in practical applications. The disadvantage of chemical methods is that they cannot completely convert nitrates into non-toxic and harmless nitrogen, and they will also produce pollutants such as metal ions, causing secondary pollution to the environment.

[0023] Electrocatalytic nitrate reduction reaction driven by renewable energy is a promising method for removing nitrate (NO 3- ) technology. It is popular among the public due to its environmental friendliness, easy remote automation control, and the use of renewable energy (such as solar energy, wind energy, and electric energy). Cathode catalyst is one of the main factors affecting the electrochemical reduction of nitrates. However, single metal catalysts have problems such as slow kinetics, few catalytic active sites, poor catalyst stability, and side reactions affecting catalytic efficiency.

[0024] In order to improve the reaction rate of electrocatalytic nitrate removal technology, the cathode nitrate reduction mechanism was studied. Specifically, the nitrate reduction mechanism can be explained by two types of reactions: (I) involving electrons; (II) involving hydrogen atoms.

[0025] Type (I) reaction of electrocatalytic removal of nitrate at different potentials: NO3 - +H2O+2e - →NO2 - +2OH - , E 0 =0.01V (1) NO3 - +3H2O+5e - →0.5N2+6OH - , E 0 =0.26V (2) NO3- +6H2O+8e - →NH3+9OH - , E 0 =-0.12V (3) NO3 - +2H2O+3e - →0.5N2+4OH - , E 0 =-0.406V (4) NO3 - +5H2O+6e - →NH3+7OH - , E 0 =-0.165V (5) NO3 - +4H2O+4e - →NH2OH+5OH - , E 0 =-0.45V (6) According to the first type of reaction, nitrate reacts on the cathode surface under the catalysis of electrons, which may involve nitrite, nitrogen and other redox products.

[0026] According to the type (II) reaction, the reaction starts with the adsorption of H2O (Equation 7) and nitrate (Equation 9) onto the catalyst electrode (*) and quickly reaches a dynamic equilibrium. When a constant current is applied to the electrode surface, the adsorbed H2O can be reduced to adsorbed hydrogen atoms (*H). A series of subsequent hydrogenation reactions are then completed. Therefore, *H plays a major role in the entire process of nitrate electrocatalytic reduction.

[0027] *H participates in the reaction (II) of electrocatalytic removal of nitrate: 2H2O+2e - →H2+2OH - (7) H2+2*→2*H (8) NO3 - +*H→*NO2+OH - (9) *NO2 - +*H→*NO+OH - (10) *NO+*→*N+*O (11) *N+*N→2*+N2(12) *NH+*H→*NH2+* (13) *NH2+*H→*NH3+* (14) *NH3→NH3+* (15) The electrocatalytic reduction mechanisms of nitrates at different electrodes are different, which leads to different effects. For example, when Pt, Fe, and Ni are used as cathodes, type (II) reactions are more likely to occur. These metals have empty d-orbital outer electron structures, which can be attributed to the adsorption of hydrogen atoms to form *H. Of course, the intermediate steps of type (II) reactions are not completely consistent under different materials and different reaction conditions, and specific analysis is required depending on the specific situation. The nitrate reduction reaction on the Cu electrode mainly follows the type (I) reaction because the Cu electrode has a strong adsorption capacity for nitrates. Therefore, designing efficient and highly selective electrode materials is the key to the electrocatalytic reduction of nitrates.

[0028] In order to solve the above technical problems, the present invention prepares a new Cu-Ni@S-1 catalytic material for electrocatalytic treatment of nitrate in groundwater (such as Figure 1 ), effectively solves the following problems: (1) Conventional single metal catalysts face the problem of slow kinetics during electrocatalytic reduction. However, this study used a Cu-Ni metal ethylenediamine complex mixture as a precursor and prepared a subnanometer hybrid bimetallic cluster catalyst Cu-Ni@S-1 in pure siliceous S-1 zeolite nanocrystals through a hydrothermal synthesis method. Due to the synergistic effect of the bimetallic, the electron transport of the catalytic reaction was accelerated, the problem of slow kinetics of the nitrate reduction reaction was solved, and the performance of the catalyst was enhanced.

[0029] (2) Conventional metal catalysts have high surface free energy, and active sites are prone to agglomeration, resulting in a reduction in active sites, thereby reducing catalytic activity. Confinement engineering can well disperse the Cu-Ni bimetallic active sites, increase the number of active sites, and generate smaller sub-nano particles. Sub-nano-sized metal clusters have better catalytic activity or selectivity than nano-sized metal clusters, solving the problem of low catalytic activity of the catalyst.

[0030] (3) Harsh external environments may cause corrosion, deactivation or structural changes of the catalyst. Based on the confinement effect, the active sites of Cu and Ni can be encapsulated in the nanopores of the zeolite molecular sieve to avoid direct contact with the harsh external environment (such as strong acids, strong bases, etc.), thereby delaying and preventing the deactivation of the active sites, extending the service life of the catalyst, and solving the problem of poor catalyst stability.

[0031] (4) In transition metal-based catalysts, the interaction between the adsorbed state and the surface d electrons usually produces bonding orbitals and antibonding orbitals. The higher the d-band center, the higher the antibonding state, and the stronger the adsorption force. The confinement effect causes the d-band center of Cu and Ni to shift upward, thereby promoting the adsorption of nitrate in water by Cu-Ni@S-1, significantly reducing the reaction energy barrier of electrocatalytic reduction of nitrate, inhibiting the occurrence of side reactions, and solving the problem of side reactions affecting catalytic efficiency.

[0032] (5) The rate-limiting step in the electrocatalytic nitrate removal process is NH3 synthesis. The Cu-Ni bimetallic structure reduces the gap between the Ni 3d orbital d-band center and the N 2p orbital, resulting in enhanced interactions between metal atoms and key NOH* intermediates, lowering the selective NH3 synthesis limiting potential, accelerating the reaction rate, and solving the problem of the rate-limiting step affecting the efficiency of electrocatalytic nitrate removal.

[0033] Specifically, in one embodiment of the present invention, a method for preparing a confined bimetallic catalyst for an electrocatalytic reduction reaction is provided, which comprises the following steps: S1, mixing tetrapropylammonium hydroxide and ultrapure water, adding ethyl orthosilicate and stirring to obtain a mixture 1; S2, mixing nickel chloride hexahydrate, ethylenediamine and ultrapure water to obtain a mixture 2; S3, mixing copper nitrate trihydrate, ethylenediamine and ultrapure water to obtain mixture three; wherein the molar ratio of nickel chloride hexahydrate to copper nitrate trihydrate is 1: (0.8-1.2), preferably 1: 1; S4, adding mixture 2 and mixture 3 dropwise to mixture 1, stirring without precipitation, and then placing in an autoclave, performing hydrothermal synthesis at 165-175° C. to obtain a reaction product; S5, centrifugally separating and collecting the obtained reaction product, and then washing and drying it to obtain a catalyst precursor; wherein the drying temperature is 75-85°C; S6. The catalyst precursor is first placed in air at 500-600 °C for calcination, and after cooling, it is placed in a flowing hydrogen-argon mixed atmosphere and linearly heated to 350-450 °C for heat treatment to obtain a confined bimetallic catalyst; wherein the volume ratio of hydrogen to argon in the hydrogen-argon mixed atmosphere is 3:97-7:93, preferably 5:95.

[0034] Example 1: Figure 2 As shown, this embodiment provides a method for preparing a confined bimetallic catalyst for an electrocatalytic reduction reaction, which comprises the following steps: S1. Mix 13 g of tetrapropylammonium hydroxide and 15.45 g of ultrapure water, stir continuously for 10 min on a magnetic stirrer, then add 8.32 g of ethyl orthosilicate and stir for 6 h to obtain a clear mixture 1. S2, 1.19 g of nickel chloride hexahydrate, 2 mL of ethylenediamine and 8 mL of ultrapure water were mixed and stirred for 10 min to obtain a mixture II; S3, 1.21 g of copper nitrate trihydrate, 2 mL of ethylenediamine and 8 mL of ultrapure water were mixed and stirred for 10 min to obtain mixture three; S4, respectively taking 1 mL of the above mixture 2 and mixture 3 and adding them dropwise to the above mixture 1, stirring for 30 min without precipitation, and then putting them into an autoclave, and performing hydrothermal synthesis at 170 ° C for 4 days to obtain a reaction product; S5, the obtained reaction product was centrifuged and collected, then washed with ethanol 3 times, washed with ultrapure water 3 times, and then dried at 80 °C overnight to obtain catalyst precursor A-Cu-Ni@S-1; S6. The catalyst precursor A-Cu-Ni@S-1 was first calcined in air at 550 °C for 8 h. After cooling, it was placed in a flowing hydrogen-argon mixed atmosphere (the volume ratio of hydrogen to argon was 5:95) and linearly heated to 400 °C within 2 h for heat treatment and maintained for 2 h. It was then ground to obtain a confined bimetallic catalyst, named Cu-Ni@S-1.

[0035] The key point of the embodiment of the present invention is to confine the sub-nano bimetallic Cu and Ni in the zeolite molecular sieve, reduce the metal leaching of Cu and Ni and block the direct contact between the active sites of Cu and Ni and the highly corrosive environment, thereby delaying and preventing the deactivation of the catalyst and improving the stability of the catalyst. And the confinement engineering can well disperse the Cu-Ni bimetallic active sites, increase the number of active sites, and at the same time move the d-band center of the metal upward to improve the adsorption performance of nitrates. The synergistic effect of the Cu-Ni bimetallic accelerates the kinetics of the reaction, and the bimetallic structure reduces the gap between the Ni 3d orbital d-band center and the N 2p orbital, reducing the limiting potential of the selective NH3 synthesis, thereby improving the removal rate of nitrates.

[0036] Example 2: This example provides a method for preparing a confined bimetallic catalyst for an electrocatalytic reduction reaction, which comprises the following steps: S1. Mix 13 g of tetrapropylammonium hydroxide and 15.45 g of ultrapure water, stir continuously for 10 min on a magnetic stirrer, then add 8.32 g of ethyl orthosilicate and stir for 6 h to obtain a clear mixture 1. S2, 5 mmol nickel chloride hexahydrate, 2 mL ethylenediamine and 8 mL ultrapure water were mixed and stirred for 10 min to obtain a mixture II; S3, 4 mmol of copper nitrate trihydrate, 2 mL of ethylenediamine and 8 mL of ultrapure water were mixed and stirred for 10 min to obtain mixture 3; S4, respectively taking 1 mL of the above mixture 2 and mixture 3 and adding them dropwise to the above mixture 1, stirring for 30 min without precipitation, and then putting them into an autoclave, and performing hydrothermal synthesis at 165 ° C for 4 days to obtain a reaction product; S5, centrifugally separating and collecting the obtained reaction product, then washing it with ethanol for 3 times, washing it with ultrapure water for 3 times, and then drying it at 75° C. overnight to obtain a catalyst precursor; S6. The catalyst precursor is first calcined in air at 500 °C for 8 h. After cooling, it is then placed in a flowing hydrogen-argon mixed atmosphere (the volume ratio of hydrogen to argon is 3:97) and linearly heated to 350 °C within 2 h for heat treatment and maintained for 2 h. It is then ground to obtain a confined bimetallic catalyst.

[0037] Example 3: This example provides a method for preparing a confined bimetallic catalyst for an electrocatalytic reduction reaction, which comprises the following steps: S1. Mix 13 g of tetrapropylammonium hydroxide and 15.45 g of ultrapure water, stir continuously for 10 min on a magnetic stirrer, then add 8.32 g of ethyl orthosilicate and stir for 6 h to obtain a clear mixture 1. S2, 5 mmol nickel chloride hexahydrate, 2 mL ethylenediamine and 8 mL ultrapure water were mixed and stirred for 10 min to obtain a mixture II; S3, 6 mmol of copper nitrate trihydrate, 2 mL of ethylenediamine and 8 mL of ultrapure water were mixed and stirred for 10 min to obtain mixture 3; S4, respectively taking 1 mL of the above mixture 2 and mixture 3 and adding them dropwise to the above mixture 1, stirring for 30 min without precipitation, and then putting them into an autoclave, and performing hydrothermal synthesis at 175 ° C for 4 days to obtain a reaction product; S5, centrifugally separating and collecting the obtained reaction product, then washing it with ethanol for 3 times, washing it with ultrapure water for 3 times, and then drying it at 85° C. overnight to obtain a catalyst precursor; S6. The catalyst precursor is first calcined in air at 600 °C for 8 h. After cooling, it is then placed in a flowing hydrogen-argon mixed atmosphere (the volume ratio of hydrogen to argon is 7:93) and linearly heated to 450 °C within 2 h for heat treatment and maintained for 2 h. It is then ground to obtain a confined bimetallic catalyst.

[0038] Example 4: Figure 3 As shown, this embodiment provides an electrocatalytic reduction device, including an external power supply 1, a cathode 5 and an anode 4; the two ends of the external power supply 1 are respectively connected to the cathode 5 and the anode 4; the cathode 5 and the anode 4 are arranged in a single-chamber electrolytic cell 2; the single-chamber electrolytic cell 2 is also filled with an electrolyte 3, and the electrolyte 3 can be nitrate wastewater; the anode 4 can be made of a platinum sheet, and the cathode 5 is made of the above-mentioned confined bimetallic catalyst; specifically, the preparation method of the cathode 5 is as follows: First, the Cu-Ni@S-1 confined bimetallic catalyst, conductive carbon black and polyvinylidene fluoride prepared in Example 1 were weighed and mixed in a mass ratio of 8:1:1, and then the mixture was dissolved in N-methyl-2-pyrrolidone (concentration of 10 g / L) to prepare a catalyst ink; then, the ink was coated on a carbon cloth (CC, 1.0×2.0 cm), ensuring that both sides were evenly coated, and finally dried at 60°C for 30 minutes to obtain a cathode 5.

[0039] In an embodiment of the present invention, the electrocatalytic reduction test of nitrate is carried out in a single-chamber electrolytic cell 2 using a two-electrode system. The electrode sheet and platinum sheet prepared using Cu-Ni@S-1 are used as the cathode 5 and the anode 4, respectively, and the distance between the two plates is controlled to be maintained at 0.5-2.0 cm. The electrolyte 3 can be a nitrate solution prepared with NaNO3 at a concentration of 50 mg / L (in terms of N) for experiment. The reason for selecting a concentration of 50 mg / L is that the concentration of nitrate in the nitrate-contaminated groundwater actually collected is 55 mg / L, which is approximately 50 mg / L in the simulation experiment. The nitrate content of the water sample at each time point is measured using ion chromatography, and the nitrate removal rate is calculated.

[0040] The electrocatalytic removal of nitrate by the above device has enhanced degradation effect and significantly improved efficiency; specifically, the electrocatalytic removal of nitrate was carried out in a single-chamber electrolytic cell 2 (50 mL) using a GPS305D DC regulated power supply. 30 mL of electrolyte 3 contained 50 mg / L nitrate (in terms of N). A current of 50 mA was applied to the system, and samples were taken every 30 min. The nitrate content of the water samples at each time point was measured using ion chromatography, and the nitrate removal rate was calculated. Under the optimal conditions, 94.99% of nitrate can be degraded within 3 h. At the same time, the Cu-Ni@S-1 catalyst has good cyclic stability, and there is still a degradation rate of 91.92% after repeated use for 5 times, as shown in Table 1.

[0041] Table 1 Comparison of nitrate reduction performance of different electrocatalytic materials

[0042] As shown in Table 1, the nitrate reduction performance of different electrocatalytic materials was compared. The nitrate removal rate of the catalytic material Cu-Ni@S-1 prepared in the embodiment of the present invention reached 94.99%, and in just 3 hours, which is much shorter than the time required by other catalytic materials. The nitrate removal efficiency is much higher than other iron-based and metal catalysts, and the ammonia selectivity is also 75.38%. This shows the excellent performance of Cu-Ni@S-1 and the amazing nitrate removal efficiency.

[0043] Comparative Example 1: This comparative example provides a method for preparing zeolite molecular sieve S-1, which is carried out by hydrothermal method. The synthesis process is as follows Figure 2 As shown, the specific steps include: 13 g of tetrapropylammonium hydroxide was mixed with 15.45 g of ultrapure water. After continuous stirring on a magnetic stirrer for 10 min, 8.32 g of tetraethyl orthosilicate was added and stirred for 6 h to obtain a clear mixture. The mixture was then placed in an autoclave and subjected to hydrothermal synthesis at 170 °C for 4 days. The obtained product was centrifuged and collected, washed with ethanol 3 times, washed with ultrapure water 3 times, and dried at 80 °C overnight to obtain the precursor AS-1. The precursor AS-1 was then calcined at 550 °C for 8 h to obtain a white solid, which was the zeolite molecular sieve, named S-1.

[0044] Comparative Example 2: This comparative example provides a method for preparing a Cu-Ni / S-1 catalyst. The synthesis process is as follows Figure 2 As shown, the specific steps include: The zeolite molecular sieve S-1 obtained in Comparative Example 1 was first impregnated and calcined with 1 mL of 0.8 M nickel chloride solution and 1 mL of 0.8 M copper nitrate solution. The solid was then dried in an oven at 80 °C overnight, and then linearly heated to 400 °C within 2 h in a flowing hydrogen-argon mixed atmosphere (the volume ratio of hydrogen to argon was 5:95) and maintained for 2 h. After grinding, the catalyst material was obtained, named Cu-Ni / S-1.

[0045] Performance test: The Cu-Ni@S-1 prepared in Example 1 and the S-1 and Cu-Ni / S-1 catalysts prepared in Comparative Examples 1-2 were subjected to relevant performance tests, and the results are as follows: 1. The scanning electron microscope (SEM) images of the S-1 catalyst and the Cu-Ni / S-1 catalyst prepared in the above comparative examples 1-2 are as follows: Figure 4 as shown in (a) and (b). Figure 4 (a) The hexagonal structure of the S-1 catalyst can be clearly observed. Figure 4(b) shows the SEM image of Cu-Ni / S-1, in which it can be clearly seen that it has sharp edges and corners, regular shape, and a very standard hexagonal structure, which is highly similar to the SEM image of S-1 molecular sieve, and does not show the influence of the interaction between Cu and Ni and the molecular sieve.

[0046] The SEM image of Cu-Ni@S-1 prepared in Example 1 is as follows: Figure 5 As shown in (a), the material is hexahedral in shape. At the same time, the surface of the material is rough due to the entry of Cu and Ni into the zeolite. The metal clusters are evenly distributed in the nanoscale zeolite molecular sieve, indicating that the morphology is successfully synthesized. The element distribution of the Cu-Ni@S-1 sample was determined by X-ray energy dispersive spectroscopy (EDX), as shown in Figure 5 As shown in (b). It can be seen that O, Si, Cu and Ni elements are evenly distributed in almost the same position, indicating that Cu and Ni are successfully confined into the S-1 molecular sieve. Among them, O and Si elements appear more dense, because they are the components of the molecular sieve. Cu and Ni elements are more dispersed than the former two, which indicates that Cu and Ni confined in the molecular sieve will not gather together to form clusters, which is beneficial to increase the reaction contact area and improve the catalyst activity.

[0047] The valence states of Cu and Ni were carefully analyzed by X-ray photoelectron spectroscopy (XPS). Figure 6 shown. Figure 6 (a) shows the XPS spectrum of Cu 2p. At the binding energy of about 933.0 eV (Cu 2p 3 / 2 ) and 952.0 eV (Cu 2p 1 / 2 ) indicates that Cu 0 and Cu 2+ At about 932.2 eV (Cu 2p 3 / 2 ) and 951.4 eV (Cu 2p 1 / 2 ) corresponds to the Cu 0 , at about 933.4 eV (Cu 2p 3 / 2 ) and 952.7 eV (Cu 2p 1 / 2 ) corresponds to the Cu 2+ . Figure 6 (b) shows the Ni 2p XPS spectra. Both Cu-Ni / S-1 and Cu-Ni@S-1 show a pair of peaks with binding energies of 853.0 eV and 856.0 eV, which are assigned to Ni 0 or Ni 2+ state.

[0048] Cu-Ni@S-1 was characterized by X-ray diffraction (XRD). Figure 7 As shown. It can be seen that Cu-Ni@S-1 has all six main characteristic peaks of S-1 (7.9 ◦ , 8.9 ◦ , 14.9 ◦ , 23.1 ◦ , 24.0 ◦ , 30.0 ◦ ), which proves that Cu-Ni@S-1 has the expected S-1 zeolite structure and has been successfully synthesized, and the introduction of metal substances does not interfere with the crystallization of zeolite. By comparing the standard XRD patterns of Cu-Ni@S-1 with those of Cu and Ni, it is proved that the material contains Cu and Ni. The diffraction peaks of Cu and Ni are not obvious, indicating that the Cu and Ni clusters are evenly distributed.

[0049] pass Figure 8 From the BET results, it can be seen that the curves of Cu-Ni@S-1 and S-1 are consistent with the type I adsorption isotherm, proving that they are both microporous structures. The curves of Cu-Ni@S-1 and S-1 are quite different. Since Cu and Ni are confined inside the molecular sieve, the structure of the molecular sieve is affected and the pore size of the molecular sieve is reduced, resulting in a different adsorption curve of Cu-Ni@S-1. The internal figure is the pore size distribution curve of the material. The results show that the pore size of Cu-Ni@S-1 (2.37 nm) is smaller than the pore size of S-1 (4.37 nm), indicating that Cu and Ni are successfully confined in the molecular sieve. And the BET specific surface area of ​​Cu-Ni@S-1 is 358.49 m 2 / g is much higher than the BET specific surface area of ​​S-1 (232.89 m 2 / g, Cu-Ni@S-1 has a higher specific surface area and more active sites, which is more conducive to improving the catalytic activity.

[0050] In order to obtain the electrochemical performance of Cu-Ni@S-1 catalyst, the catalytic materials Cu-Ni@S-1, Cu-Ni / S-1, and S-1 were applied to carbon cloth (1.0×2.0 cm) to obtain working electrodes (Cu-Ni@S-1 / CC, Cu-Ni / S-1 / CC, and S-1 / CC). The electrochemical characterization of Cu-Ni@S-1 catalyst and other catalysts was carried out by electrochemical workstation. EIS results are shown in Figure 2. Fig. 9 As shown, Cu-Ni@S-1 has lower charge transfer resistance, further demonstrating the excellent effect of confined materials.

[0051] The LSV curves of Cu-Ni@S-1, Cu-Ni / S-1 and S-1 were measured by linear sweep voltammetry (LSV). Fig.10 As shown. It can be seen that the Cu-Ni@S-1 material has a lower overpotential and a larger current density. Fig. 9 The electrochemical impedance spectrum shows that the Cu-Ni@S-1 catalyst has a smaller impedance and a larger current, which indicates that the Cu-Ni@S-1 catalyst has excellent conductivity, which is conducive to the transfer of electrons from the cathode to the surface of the Cu-Ni@S-1 catalyst, indicating that the Cu-Ni@S-1 material has good catalytic activity.

[0052] The Tafel slopes of Cu-Ni@S-1, Cu-Ni / S-1 and S-1 were calculated based on the LSV curves. Fig.11 The Tafel slope indicates the change in overpotential required when the current changes tenfold, so the smaller the absolute value of the slope, the better. The smaller the slope, the smaller the voltage rise and the lower the energy consumption. Fig.11 It can be seen that Cu-Ni@S-1 has the lowest Tafel slope (63.87 mV / dec), indicating that Cu-Ni@S-1 has the best reaction kinetics in the nitrate reduction reaction.

[0053] 2. The electrocatalytic removal of nitrate was carried out in a single-chamber electrolytic cell (50 mL) using a GPS305D DC regulated power supply. In the two-electrode system, the platinum sheet served as the anode, and the prepared different catalytic materials were coated on a 1.0×2.0 cm carbon cloth as the cathode, so that the distance between the two plates was controlled in the range of 0.5-2.0 cm. 30 mL of the electrolyte contained 50 mg / L nitrate (in terms of N). A current of 50 mA was applied to the system, and samples were taken every 30 min. The nitrate content of the water samples at each time point was determined by ion chromatography, and the nitrate removal rate was calculated. The ammonia nitrogen concentration during the reaction process was determined by Nessler's reagent spectrophotometry, and the ammonia nitrogen conversion rate was calculated.

[0054] Depend on Fig.12 As shown in (a), after 180 min of reaction, the degradation rate of nitrate by Cu-Ni@S-1 catalyst has reached 94.99%, while the degradation rate of nitrate by Cu-Ni / S-1 catalyst after 180 min of reaction is only 59.14%. As for the S-1 molecular sieve alone and the carbon cloth alone, the degradation rates of nitrate after 180 min are 30.22% and 24.40%, respectively. The S-1 molecular sieve itself has no catalytic activity. Like the carbon cloth, it can only reduce the nitrate in the solution by cathode current, so the degradation effect is poor. The Cu-Ni@S-1 catalyst removed up to 94.99% of nitrate within 180 min, showing an amazing removal efficiency, far exceeding other similar catalysts. Therefore, Cu-Ni@S-1 is an excellent electrocatalytic reduction nitrate catalytic material. Fig.12 (b) and Fig.12(c) shows the changing trend of the products produced by the removal of nitrate. With the increase of electrolysis time, nitrate is gradually removed, nitrite is first produced and then consumed, and the concentration of ammonia nitrogen continues to increase. Nitrate is mainly reduced to ammonia nitrogen. Since many intermediates generated in the process of nitrate reduction are negatively charged, they are easily repelled by the electric field and difficult to accumulate on the cathode, thus inhibiting the occurrence of nitrogen generation reaction. In addition, the generated nitrite is unstable and easily oxidized to nitrate. Therefore, the main product of nitrate reduction is ammonia nitrogen.

[0055] During the use of Cu-Ni@S-1 catalyst, if the catalyst active sites are deactivated due to the influence of the external environment, the reaction efficiency will be greatly reduced, affecting the continuous progress of the catalytic reaction. In order to test the stability of the Cu-Ni@S-1 catalyst, 5 cycle experiments were carried out. During the experiment, the electrode sheet was carefully cleaned and dried after each electrocatalytic degradation, and then the electrode sheet was continued to be put into the electrocatalytic reduction system to repeatedly degrade new nitrate. The experimental conditions were 50 mg / L (in terms of N) nitrate, 50 mA / cm 2 The experimental results are shown in Fig.13 As shown. Fig.13 It can be seen that the nitrate degradation rates of the Cu-Ni@S-1 catalyst within 180 min after five cycles were 97.7%, 95.6%, 94.5%, 92.7%, and 91.9%, respectively. After five cycles, the catalyst still maintained a high degradation effect, indicating that the Cu-Ni@S-1 catalyst has good cyclic stability.

[0056] Atomic absorption test was performed on the water body after 180 minutes of reaction to obtain the concentration of heavy metal ions in the water body after the reaction, in order to explore whether the confinement effect improves the stability of the catalyst and reduces the metal leaching of the catalyst. Fig.14 shown.

[0057] from Fig.14 It can be seen that after 180 seconds of reaction, the copper ion content in the water of the Cu-Ni@S-1 catalyst is 0.029 mg / L, and the nickel ion content is 0.079 mg / L, which is much lower than the copper ion content of 0.153 mg / L and the nickel ion content of 0.443 mg / L in the water of the Cu-Ni / S-1 catalyst. The comparison shows that the confinement effect improves the stability of the catalyst and reduces the amount of metal leaching from the catalyst. The copper ion concentration reaches the Class II standard for groundwater quality (≤0.05), and the nickel ion concentration also reaches the Class IV standard for groundwater quality (≤0.1). This shows the excellent effect of confinement.

[0058] 3. In the process of electrocatalytic reduction, current density is undoubtedly an important factor affecting the reaction. In order to verify the effect of current density on the electrocatalytic reduction of nitrate, the current density was controlled to 1 mA / cm 2 , 10 mA / cm 2 , 25 mA / cm 2 , 50mA / cm 2 and 100 mA / cm 2 , and reacted for 180 min. The degradation experiment was carried out while keeping the operation steps and other degradation conditions unchanged, and the nitrate conversion rate and various product selectivities were obtained as follows: Fig.15 shown.

[0059] from Fig.15 It can be seen that when the current density is as low as 1 mA / cm 2 The nitrate removal rate is quite slow when the current density is 100 mA / cm 2 When the current density is increased to a certain level, the removal rate does not increase significantly. When the current density is 50 mA / cm 2 When the current density is 100 mA / cm 2 The current density of the reactor was 1.19% lower than that of the reactor at 100 °C. This may be due to the fact that the mass transfer of nitrates limits the reaction rate. Therefore, it is particularly important to choose a suitable current density in order to balance the degradation of nitrates and the amount of energy consumption.

[0060] 4. As we all know, the initial pH of the reaction system has an important influence on the reaction process. The pH of the system will affect the reduction kinetics and the selectivity of by-products. In order to explore the effect of the initial pH of the reaction system on the electrocatalytic reduction degradation of nitrates, the embodiment of the present invention uses appropriate amounts of H2SO4 and NaOH to adjust the pH of the reaction system in order to avoid side reactions. Under different conditions of pH 3, 5, 7, 9, and 11, the degradation experiment was carried out while keeping the operating steps and other degradation conditions unchanged, and the nitrate conversion rate and various product selectivity were obtained as follows: Fig.16 shown.

[0061] from Fig.16It can be seen that good performance can be obtained under both acidic and neutral conditions. The degradation effect is best under pH=3, and 100% of nitrate can be degraded after 180 minutes of reaction. There is a slight effect at pH=7, but the final degradation effect can reach 97.70% after 180 minutes of degradation. However, as the pH further increases to alkaline conditions, the removal rate of nitrate decreases. At pH=11, the degradation rate after 180 minutes of degradation dropped to 60.40%, indicating that pH has a certain effect on the degradation process. This may be because acidic conditions are conducive to the electrocatalytic generation of *H, thereby improving the removal rate of nitrate. Therefore, the optimal pH value for electrocatalytic removal of nitrate using the catalytic material Cu-Ni@S-1 is 3.

[0062] 5. In order to explore the effect of initial nitrate concentration on the electrocatalytic reduction degradation process of nitrate, electrocatalytic degradation tests were carried out under the conditions of nitrate concentrations of 30 mg / L, 50 mg / L, and 100 mg / L (all in terms of N), and the degradation experiments were carried out while keeping the operating steps and other degradation conditions unchanged. The nitrate conversion rate and various product selectivities were obtained as follows: Fig.17 shown.

[0063] from Fig.17 It can be seen that different initial concentrations within a certain range have an effect on the nitrate degradation effect. As the nitrate concentration increases, the nitrate removal rate decreases. This may be due to the excessive nitrate in the electrolyte, which leads to incomplete nitrate reduction reaction and increases the formation of gas N (N2, N2O) through intermediate contact. This leads to a decrease in nitrate removal rate and an increase in gaseous nitride selectivity.

[0064] 6. In order to explore the effect of different initial chloride ion concentrations on the electrocatalytic reduction degradation process of nitrate, electrocatalytic degradation tests were carried out under the conditions of controlling chloride ion concentrations of 0 mg / L, 10 mg / L, 50 mg / L and 100 mg / L, and the degradation experiments were carried out while keeping the operating steps and other degradation conditions unchanged. The nitrate removal rate and ammonia nitrogen yield were obtained as follows: Fig.18 shown.

[0065] from Fig.18 It can be seen that different chloride ion concentrations have a certain effect on the nitrate degradation effect. After 180 min of reaction, the nitrate removal rates under the conditions of 10 mg / L, 50 mg / L and 100 mg / L chloride ions were 90.30%, 78.54% and 72.87%, respectively. This may be due to the fact that the active sites are occupied by Cl - Occupies, because Cl - The presence of will cause a side reaction in the reaction system to generate Cl2, thus affecting the removal effect of nitrate. -As the concentration increases, the ammonia nitrogen concentration decreases, and more ammonia nitrogen is oxidized into nitrogen gas. This is due to the presence of Cl in water. - In the case of Cl - It will generate Cl2 at the anode and further combine with H2O to generate HClO / ClO - , is a typical strong oxidant that can convert ammonia nitrogen into nitrogen gas.

[0066] VII. Electrocatalytic reduction of nitrate is a complex process, including direct reduction mediated by electron transfer and indirect reduction mediated by atomic H*. Since tert-butyl alcohol (TBA) can be used as a quencher of H*, in order to explore the effect of indirect reduction mediated by atomic H* on the electrocatalytic reduction of nitrate, electrocatalytic degradation tests were carried out under the conditions of controlling the concentration of tert-butyl alcohol to be 0 mM / L, 5 mM / L and 10 mM / L, and the degradation experiments were carried out while keeping the operation steps and other degradation conditions unchanged. The nitrate removal rate and ammonia nitrogen yield were obtained as follows: Fig.19 shown.

[0067] from Fig.19 It can be seen that different TPA concentrations have a certain effect on the nitrate degradation effect. After 120 min of reaction, the nitrate removal rate was 61.09% under the condition of 5 mM / L tert-butanol, and the nitrate removal rate was only 49.48% under the condition of 10 mM / L tert-butanol, which was 45.58% lower than that of 0 mM / L tert-butanol. With the increase of tert-butanol concentration, the nitrate removal rate decreased significantly. This shows that most of the H* is captured by tert-butanol and cannot participate in the hydrogenation reaction process of nitrate reduction intermediates, which further proves that H* plays a key role in promoting nitrate conversion. As the nitrate degradation effect deteriorates, the production of ammonia nitrogen also weakens. This shows that H* plays an important role in the electrocatalytic reduction of nitrate in the Cu-Ni@S-1 catalyst.

[0068] 8. In order to better understand the superior electrocatalytic performance and catalytic reaction mechanism of Cu-Ni@S-1 for nitrate reduction, the present invention further introduces DFT calculations to compare the changes in electronic structure and the differences in reaction energy barriers and nitric acid reduction. The reaction pathway of electrocatalytic reduction of nitrate by catalytic material Cu-Ni@S-1 is as follows: Fig. 20 , Fig.21 shown.

[0069] The reduction of nitrate to ammonia is accompanied by the transfer of nine protons and eight electrons. Fig. 20 The demonstrated reaction pathway is applicable to the electrocatalytic reduction of nitrate to generate ammonia over Cu-Ni@S-1 catalyst. The first step is NO3 - During this process, NO3 -When adsorbed to the catalyst Cu-Ni@S-1, no electron transfer is required. The subsequent step is the gradual reduction of *NO3, which is converted into *NO2, *NO, *NOH, *N, *NH, *NH2 in sequence, and finally desorbed to obtain the catalyst *. The specific reaction formula is as follows: *+NO3 - +9H + →*NO3+9H + (16) *NO3+9H + →*NO2+7H + +H2O (17) *NO2+7H + +H2O→*NO+5H + +2H2O (18) *NO+5H + +2H2O→*NOH+4H + +2H2O (19) *NOH+4H + +2H2O→*N+3H + +3H2O (20) *N+3H + +3H2O → *NH+2H + +3H2O (21) *NH+2H + +3H2O→*NH2+H + +3H2O (22) *NH2+H + +3H2O→*+3H2O+NH3(23) Fig.21 The Gibbs free energy change diagram (ΔG) of Cu-Ni@S-1 and Cu-Ni / S-1 accompanying nitrate reduction is presented. For Cu-Ni@S-1, the rate-limiting step from *NH2 to NH3 is its reaction rate, and the ΔG upslope of this step is small, which is 2.4 eV; while for Cu-Ni / S-1, the rate-limiting step of its reaction rate is *NO to *NOH, and the ΔG upslope is larger, reaching 2.6 eV. Therefore, the energy barrier of the rate-limiting step of Cu-Ni@S-1 is lower than that of the rate-limiting step of Cu-Ni / S-1, so Cu-Ni@S-1 has a higher nitrate removal efficiency. Based on DFT calculations, it can be seen that Cu-Ni@S-1 has good conductivity, strong adsorption capacity for nitrate ions, and no large reaction barrier for nitrate reduction, thus showing significant electrocatalytic activity.

[0070] Fig. 22The adsorption differential charge of nitrate on Cu-Ni / S-1 and Cu-Ni@S-1 is shown. The electron-accepting ability of Cu-Ni@S-1 is significantly higher than that of Cu-Ni / S-1, and the bond length of Cu-Ni@S-1 for adsorbing nitrate is smaller than that of Cu-Ni / S-1. The shorter the bond length, the more stable the bond, and the more stable the molecule formed. In addition, the adsorption energy of Cu-Ni@S-1 and Cu-Ni / S-1 is calculated. The adsorption energy of Cu-Ni@S-1 for nitrate is -3.069 eV, which is stronger than that of Cu-Ni / S-1. Therefore, Cu-Ni@S-1 has a stronger adsorption capacity for nitrate, so Cu-Ni@S-1 is easier to react with nitrate and be reduced.

[0071] The partial wave density of states of the d orbitals of Cu and Ni atoms in the two catalysts Cu-Ni@S-1 and Cu-Ni / S-1 were calculated respectively. Fig.23 In the figure, (a) is the partial wave density of states of the 3d orbital of Cu atoms, and (b) is the partial wave density of states of the 3d orbital of Ni atoms. The dotted line represents the d-band center of the two catalysts. In transition metal-based catalysts, the interaction between the adsorbed state and the surface d electrons usually forms bonding orbitals and antibonding orbitals, where the bonding orbitals are below the Fermi level, have lower energy and are fully filled, while the antibonding orbitals are also below the Fermi level, have higher energy but are only partially filled. The higher the d-band center, the higher the antibonding state and the stronger the adsorption force. The d-band center of Cu atoms in the Cu-Ni@S-1 catalyst is -1.879 eV, which is closer to the Fermi level than Cu-Ni / S-1. This indicates that it has a better adsorption capacity for nitrates. The d-band center of Ni atoms in the Cu-Ni@S-1 catalyst is also higher than that of Cu-Ni / S-1, which adjusts the gap between the d-band center of the Ni 3d orbital and the N 2p orbital, and increases the energy of the N 2p antibonding state above the Fermi level. Ultimately, the interaction between metal atoms and the key *NOH intermediate is enhanced, reducing the limiting potential for selective NH3 synthesis. Therefore, the catalytic activity of Cu-Ni@S-1 is significantly better than that of Cu-Ni / S-1, which is consistent with the experimental results above.

[0072] In summary, the present invention prepares subnanometer-scale hybrid bimetallic cluster catalysts in pure siliceous S-1 zeolite nanocrystals, which are used for electrocatalytic treatment of nitrates in groundwater, thereby improving the efficiency of electrocatalytic removal of nitrates and providing a more economical and effective method for achieving high-efficiency removal of nitrate pollution in groundwater. Specifically, the present invention has the following technical effects: (1) Using a mixture of Cu-Ni metal ethylenediamine complexes as catalyst precursors, a sub-nanometer hybrid bimetallic cluster catalyst was prepared in pure siliceous S-1 zeolite nanocrystals by a hydrothermal synthesis method. Due to the synergistic effect of the bimetallics, the sub-nanometer hybrid bimetallic cluster catalyst solved the problem of slow nitrate reduction reaction kinetics and enhanced the performance of the catalyst.

[0073] (2) Sub-nanometer-sized metal clusters have better catalytic activity or selectivity than nano-sized metal clusters. Confinement engineering can effectively disperse the Cu-Ni bimetallic active sites, increase the number of active sites, and generate smaller sub-nanometer particles, solving the problem of low catalytic activity of the catalyst, thereby improving the removal rate of nitrates.

[0074] (3) Based on the confinement effect, the Cu and Ni active sites can be encapsulated in the nanopores of the zeolite molecular sieve to avoid direct contact with the external harsh environment (such as strong acids, strong bases, etc.), thereby delaying and preventing the deactivation of the active sites, extending the service life of the catalyst, and solving the problem of poor catalyst stability.

[0075] (4) Due to the confinement effect of zeolite, the d-band centers of Cu and Ni move upward, thereby promoting the adsorption of nitrate in water by Cu-Ni@S-1, significantly reducing the reaction energy barrier of electrocatalytic reduction of nitrate, inhibiting the occurrence of side reactions, and solving the problem of side reactions affecting catalytic efficiency. The efficiency of the electrocatalytic nitrate reduction reaction is significantly improved.

[0076] (5) The Cu-Ni bimetallic structure reduces the gap between the Ni 3d orbital d-band center and the N 2p orbital, resulting in enhanced interactions between metal atoms and key NOH* intermediates. At the same time, since NH3 synthesis is the rate-limiting step of the reaction, the overall electrocatalytic removal efficiency of nitrate is limited. The bimetallic structure reduces the Gibbs free energy of NH3 synthesis, lowers the limiting potential of selective NH3 synthesis, accelerates the reaction rate, and solves the problem of the rate-limiting step affecting the efficiency of electrocatalytic removal of nitrate.

[0077] Based on the above-mentioned ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above-mentioned description. The technical scope of the present invention is not limited to the contents of the specification.

Claims

1. A method for preparing a confined bimetallic catalyst for electrocatalytic reduction reaction, characterized in that: The following steps are involved: Tetrapropylammonium hydroxide and ultrapure water are mixed, and ethyl orthosilicate is added and stirred to obtain a mixture 1; Mixing and stirring nickel chloride hexahydrate, ethylenediamine and ultrapure water to obtain a mixture II; Copper nitrate trihydrate, ethylenediamine and ultrapure water are mixed and stirred to obtain a mixture three; Adding mixture 2 and mixture 3 dropwise into mixture 1, stirring without precipitation, and then putting into an autoclave, performing hydrothermal synthesis at 165-175° C. to obtain a reaction product; The obtained reaction product is centrifuged and collected, and then washed and dried to obtain a catalyst precursor; The catalyst precursor is first placed in air for calcination, and then placed in a flowing hydrogen-argon mixed atmosphere for heat treatment to obtain the confined bimetallic catalyst.

2. The method for preparing the confined bimetallic catalyst for electrocatalytic reduction reaction according to claim 1, characterized in that: The molar ratio of the nickel chloride hexahydrate to the copper nitrate trihydrate is 1:(0.8-1.2).

3. The method for preparing a confined bimetallic catalyst for electrocatalytic reduction reaction according to claim 1, characterized in that: The drying temperature is 75-85°C.

4. The method for preparing a confined bimetallic catalyst for electrocatalytic reduction reaction according to claim 1, characterized in that: The calcination temperature is 500-600°C.

5. The method for preparing a confined bimetallic catalyst for electrocatalytic reduction reaction according to claim 1, characterized in that: The heat treatment temperature is 350-450°C.

6. The method for preparing a confined bimetallic catalyst for electrocatalytic reduction reaction according to claim 1, characterized in that: The volume ratio of hydrogen to argon in the hydrogen-argon mixed atmosphere is 3:97-7:

93.

7. A confined bimetallic catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the confined bimetallic catalyst as claimed in claim 7 in the electrocatalytic reduction of nitrates.

9. Use of the confined bimetallic catalyst as claimed in claim 7 in removing nitrate from water.

10. An electrocatalytic reduction device, comprising a cathode and an anode, characterized in that: The cathode is made of the confined bimetallic catalyst described in claim 7.

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