Preparation method and application of a single-atom transition metal catalyst M1 / CeO2 rich in oxygen vacancies

Abstract

The present invention discloses a preparation method and application of a single-atom transition metal catalyst M1 / CeO2 rich in oxygen vacancies. The preparation method is to weigh phthalocyanine molecules containing single-atom sites of transition metals, trimesic acid, polyvinylpyrrolidone and Ce(NO3)3 and dissolve them in a mixed solution of ethanol and N,N-dimethylformamide; then react the mixed solution at 100-140 °C to form MPc / Ce-MOF powder; finally, place the MPc / Ce-MOF powder in a muffle furnace and calcine it at a temperature of 350-550 °C in an air atmosphere for hours to obtain the M1 / CeO2 catalyst; the obtained catalyst improves the utilization rate of active sites, generates a large number of oxygen vacancies, enhances the adsorption of nitrate and intermediate products, and can effectively improve the activity of electrocatalytic reduction of nitrate and the selectivity of ammonia production, and the ammonia production effect is better.

Description

Technical Field

[0001] The present invention relates to the field of electrochemistry, and specifically relates to a preparation method and application of a single-atom transition metal catalyst M1 / CeO2 with oxygen vacancies. Background Art

[0002] The nitrogen cycle is an important part of the global biogeochemistry. As a pollutant widely present in surface water and groundwater, nitrate nitrogen mainly comes from industrial wastewater discharge, sewage irrigation, farmland fertilization, and aquaculture wastewater. Due to the stable structure of nitrate, it is soluble in water and easy to diffuse. When it enters natural water bodies, it is easy to cause eutrophication of the water, reducing the biodiversity in the water. When it enters the human body, it is easy to be converted into nitrite in the body, causing food poisoning and increasing the probability of suffering from blue baby disease. Therefore, standards such as China's GB 5749-2022 "Sanitary Standards for Drinking Water" stipulate that the nitrate nitrogen content shall not exceed 10 mg / L. So far, there are various methods for treating nitrate, including physical methods, biological methods, chemical methods, and electrochemical methods. Among them, electrochemical catalytic reduction has the advantages of high efficiency, pollution-free, and mild reaction conditions. Moreover, ammonia, one of the products generated by this reaction, is one of the most valuable chemical products in the world and a good source of nitrogen fertilizer in agriculture.

[0003] In the technology of electrocatalytic reduction of nitrate nitrogen, the catalyst material is the focus of research. Among them, copper-based catalysts are favored by current researchers due to their high activity. Therefore, continuously improving copper-based catalysts to enhance their activity, stability, etc. is the current key research area. Summary of the Invention

[0004] In view of this, one of the purposes of the present invention is to provide a preparation method of a single-atom transition metal catalyst M1 / CeO2 with oxygen vacancies. The second purpose of the present invention is to provide a single-atom transition metal catalyst M1 / CeO2 with oxygen vacancies prepared by the above preparation method. The third purpose of the present invention is to provide an electrode containing the single-atom transition metal catalyst M1 / CeO2 with oxygen vacancies. The fourth purpose of the present invention is to provide the application of the catalyst M1 / CeO2 or the electrode in electrocatalytic reduction of nitrate.

[0005] To achieve the above purposes, the present invention provides the following technical solutions:

[0006] 1. A preparation method of a single-atom transition metal catalyst M1 / CeO2 with oxygen vacancies, comprising the following steps:

[0007] (1) Weigh a phthalocyanine molecule containing a single-atom site of a transition metal, trimesic acid, polyvinylpyrrolidone, and Ce(NO3)3 and dissolve them in a mixed solution of ethanol and N,N-dimethylformamide;

[0008] (2) The mixed solution reacts at 100 - 140 °C for 45 - 75 min to form MPc / Ce-MOF powder;

[0009] (3) The MPc / Ce-MOF powder is placed in a muffle furnace and calcined in an air atmosphere at a temperature of 350 - 550 °C for 1.5 - 2.5 hours to obtain the M1 / CeO2 catalyst.

[0010] Preferably in the present invention, the mass ratio of the phthalocyanine molecule containing transition metal single-atom sites to trimesic acid is 200 - 400:1.

[0011] Preferably in the present invention, the mass ratio of the phthalocyanine molecule containing transition metal single-atom sites to PVP is 20 - 25:1.

[0012] Preferably in the present invention, the mass ratio of the phthalocyanine molecule containing transition metal single-atom sites to Ce(NO3)3 is 1 - 1.5:1.

[0013] Preferably in the present invention, the volume ratio of ethanol to N,N-dimethylformamide in the mixed solution of ethanol and N,N-dimethylformamide is 5 - 7:3.

[0014] More preferably, it is calcined at 450 °C - 500 °C.

[0015] 2. The oxygen-rich vacancy single-atom transition metal catalyst M1 / CeO2 prepared by the said preparation method.

[0016] 3. An electrode containing the oxygen-rich vacancy single-atom transition metal catalyst M1 / CeO2. Mix the M1 / CeO2 catalyst and carbon powder with ethanol and isopropanol, then add Nafion as an adhesive and ultrasonicate it to a uniform ink-like state; under the heating of an infrared lamp, apply the uniformly dispersed ink-like catalyst solution on both sides of the carbon paper to obtain the electrode.

[0017] 4. The application of the catalyst M1 / CeO2 or the said electrode in the electrocatalytic reduction of nitrate.

[0018] Preferably in the present invention, the voltage for the electrocatalytic reduction of nitrate is -1.30 V to -1.50 V, and the reference electrode is Ag / AgCl, 3.0 M, KCl.

[0019] The beneficial effects of the present invention are as follows: The present invention discloses a preparation method of an oxygen-rich vacancy single-atom transition metal catalyst M1 / CeO2. This method can improve the utilization rate of active sites, generate a large number of oxygen vacancies, enhance the adsorption of nitrate and intermediate products, and can effectively improve the activity of electrocatalytic reduction of nitrate and the selectivity of ammonia production, with better ammonia production effect. Description of the Drawings

[0020] To make the objectives, technical solutions, and beneficial effects of the present invention clearer, the present invention provides the following attached drawings for description:

[0021] Figure 1 It is the TEM image of the Cu1 / CeO2 catalyst;

[0022] Figure 2 It is the SEM image of Cu1 / CeO2;

[0023] Figure 3 It is the Cu 2p xps spectrum of Cu1 / CeO2 ( Figure 3 a), and the O 1s xps spectrum ( Figure 3 b);

[0024] Figure 4 It is the graph of the removal rate of NO3 - -N varying with time in the electrocatalytic NRR reaction;

[0025] Figure 5 It is the graph of the product distribution of NO3 - -N varying with time in the electrocatalytic NRR reaction;

[0026] Figure 6 It is the graph of the continuous flow reaction stability of the catalyst electrode in the electrocatalytic NRR reaction. Specific Embodiments

[0027] The present invention will be further described below in conjunction with the attached drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0028] Example 1: Preparation of the Cu1 / CeO2 catalyst electrode

[0029] (1) Weigh 20 mg of CuPc, 6.0 g of H3BTC, 0.3 g of PVP, and 0.6 g of Ce(NO3)3 and dissolve them in a mixed solution of 50 mL of ethanol and 25 mL of DMF (75 mL);

[0030] (2) Transfer the mixed solution to a hydrothermal reactor, heat it to 120 °C and react for 1.0 hour to form MPc / Ce-MOF powder;

[0031] (3) Place the powder material in a muffle furnace and calcine it at 450 °C for 2.0 hours in an air atmosphere to obtain the Cu1 / CeO2 catalyst;

[0032] (4) Take 30 mg of the Cu1 / CeO2 powder and 4 mg of carbon powder from step (3), add 3.6 mL of ethanol and 0.4 mL of isopropanol and mix them evenly. Then add 40 μL of Nafion as a binder, and ultrasonically treat it until it becomes a uniform ink-like state. Under the heating of an infrared lamp, apply the evenly dispersed ink-like catalyst solution on both sides of the carbon paper to serve as the working electrode.

[0033] The TEM image of the Cu1 / CeO2 catalyst prepared in Example 1 is as Figure 1 shown, and the SEM detection results are as Figure 2 shown. It can be seen that the microscopic morphology of Cu1 / CeO2 is a rod-like structure.

[0034] The XPS detection results of the oxygen-rich vacancy single-atom copper catalyst Cu1 / CeO2 prepared in Example 1 are as Figure 3 shown. It can be seen from the figure that the catalyst contains a large number of oxygen vacancies.

[0035] In the present invention, the mixture solution can react at 100 - 140 °C. When the calcination temperature is controlled at 350 - 550 °C, the mass ratio of phthalocyanine molecules to trimesic acid is 200 - 400:1, the mass ratio of phthalocyanine molecules to PVP is 20 - 25:1, the mass ratio of phthalocyanine molecules to Ce(NO3)3 is 1 - 1.5:1, and the volume ratio of ethanol to N,N-dimethylformamide is 5 - 7:3

[0036] Removal effect of the Cu1 / CeO2 catalyst electrode on the pollutant nitrate in Example 2

[0037] (1) The construction of the electrocatalytic NRR reaction device is as follows:

[0038] a) For the electrocatalytic NRR reaction, an H-type two-compartment electrochemical cell is used, and the anode chamber and the cathode chamber are separated by a cation exchange membrane (Nafion-117). Add 100 mL of sodium sulfate (50 mM) electrolyte solution to both the anode and cathode chambers. Before the reaction, nitrogen gas (for more than 10 minutes) needs to be introduced into both the cathode and anode chambers to remove dissolved oxygen; then add 2 mL of nitrate nitrogen stock solution (5 g / L NO3 - ) to the cathode electrolysis chamber, and the initial concentration of NO3 - -N is 22.5 mg / L, and then stir with a magnetic stirrer for 10 minutes to mix evenly;

[0039] b) According to the principle of the three-electrode system, construct an electrocatalytic reduction nitrate device, using the Cu1 / CeO2 catalyst electrode as the working electrode, a platinum electrode (30 mm × 30 mm) as the counter electrode, and Ag / AgCl 3.0 M KCl as the reference electrode;

[0040] c) Evaluation of the electrocatalytic NRR reaction effect, detecting the concentrations of target pollutants (NO3 - -N), intermediate products (NO2 - -N) and final products (NH3-N) through a UV spectrophotometer (UV1000).

[0041] (2) Operation of the electrocatalytic NRR reaction device, steps are as follows:

[0042] a) Place the entire electrochemical denitrification reaction device in a 25°C constant temperature water bath magnetic stirrer, control the reaction temperature at 25°C, set the magnetic stirring rate at 400 rpm, and maintain uniform stirring;

[0043] b) Set the parameters of the electrochemical workstation, select chronoamperometry, set the voltages to -1.3V, -1.35V, -1.40V, -1.45V, -1.50V, and start the program for electrochemical reduction of nitrate.

[0044] (3) Determination of the electrocatalytic NRR reaction activity, steps are as follows:

[0045] a) At 0 min, 60 min, 120 min, 180 min, 240 min, 300 min and 360 min during the reaction, take samples (about 2.5 mL), and pipette 1 mL of the sample solution into a colorimetric tube to dilute the sample 20 times;

[0046] c) Use a UV spectrophotometer (UV1000) to measure the concentrations of target pollutants (NO3 - -N), final products (NH3-N) and intermediate products (NO2 - -N) at 220 nm, 420 nm and 540 nm respectively;

[0047] d) The nitrate removal rate (η) = (1 - C t / C0) * 100%;

[0048] The selectivity S of ammonia nitrogen NH4 + is expressed as: S NH4 + = C NH4 + / (C0 - C t ) * 100%;

[0049] Among them, C NH4 + represents the concentration of NH4 + -N (mg·L -1 ) after electrolysis for t time, C0 represents the initial concentration of NO3 - -N (mg·L -1 ); Ct represents NO3 at time t- -N concentration (mg·L -1 ).

[0050] Using the Cu1 / CeO2 catalyst electrode prepared in Example 1 as the working electrode, the electrocatalytic NRR reaction was carried out according to the above steps.

[0051] In the electrocatalytic NRR reaction, the reduction activity of NO3 - -N changes with time as Figure 4 shown. The results show that during the electrocatalytic NRR process of the Cu1 / CeO2 catalyst electrode, the reduction activity of NO3 - -N increases with the extension of time, and the reduction activity of NO3 - -N reaches 100% at 6 h.

[0052] In the electrocatalytic NRR reaction, the product distribution of N species after a 6-h reaction cycle is as Figure 5 shown. The results show that after a 6-h reaction cycle of the Cu1 / CeO2 catalyst electrode, the main nitrogen species in the products exist in the form of ammonia nitrogen, and there is no obvious accumulation of the intermediate product NO2 - -N.

[0053] The above experimental data prove that the Cu1 / CeO2 catalyst electrode has higher activity and ammonia production in electrocatalytic NRR.

[0054] The working electrode uses the single-atom copper catalyst electrode with rich oxygen vacancies prepared in Example 1. The electrocatalytic reduction of nitrate reaction is carried out according to the above steps. Additionally, the voltage setting conditions are changed, and the voltages are set to -1.30 V, -1.35 V, -1.40 V, -1.45 V, -1.50 V, and 5 reactions are carried out. The results of the electrocatalytic reduction of nitrate by the Cu1 / CeO2 catalyst electrode at different voltages are shown in Table 1. As the voltage increases to -1.45 V, the removal rate of nitrate reaches 100%, and the selectivity of ammonia nitrogen reaches the highest. As the voltage continues to increase, the enhancement of the hydrogen evolution side reaction leads to a decrease in both the removal rate of nitrate and the selectivity of ammonia nitrogen.

[0055] Table 1. Nitrate removal rate, ammonia selectivity and Faraday efficiency of Cu1 / CeO2 electrode at different voltages

[0056]

[0057] The working electrode uses the single-atom copper catalyst electrode with rich oxygen vacancies prepared in Example 1. The electrocatalytic reduction of nitrate reaction is carried out according to the above steps. In addition, the initial concentration of nitrate is changed, and the initial concentrations are determined to be 50 mg / L, 100 mg / L, 200 mg / L, and 400 mg / L. The results are shown in Table 2. It can be seen that as the initial nitrate concentration increases, the removal rate of nitrate by the electrode prepared with this catalyst slightly decreases, and the selectivity for ammonia nitrogen also shows a decreasing trend.

[0058] Table 2. Removal efficiency, ammonia selectivity, and Faraday current efficiency for nitrates at different concentrations

[0059] Nitrate concentration (mg / L) 50 100 200 400 Removal efficiency (η) 100％ 99.3％ 99.3％ 94.4％ Ammonia selectivity (S) 90.6％ 91.6％ 90.0％ 78.8％ Faraday current efficiency (FE) 24.4％ 44.4％ 56.9％ 72.4％

[0060] The working electrode uses the single-atom copper catalyst electrode with rich oxygen vacancies prepared in Example 1. The electrocatalytic reduction of nitrate reaction is carried out according to the above steps, and the electrocatalytic reduction reaction is continuously carried out for 30 h. The results are shown in Table 3 and Figure 6 as shown. After 30 h of continuous flow experiment, the removal rate of nitrate is above 90%, and the selectivity for ammonia nitrogen also fluctuates around 90%, indicating that the stability and repeatability of the single-atom copper catalyst with rich oxygen vacancies are good.

[0061] Table 3. Removal efficiency and ammonia selectivity of the same electrode in continuous reaction for 30 h

[0062] Reaction time (h) 2 4 6 10 14 18 22 26 30 Removal efficiency (η) 94.5％ 97.6％ 96.7％ 94.9％ 96.3％ 90.4％ 94.5％ 94.9％ 94.5％ Ammonia selectivity (S) 93.8％ 87.9％ 94.6％ 89.6％ 93.6％ 96.5％ 88.6％ 86.6％ 90.1％

[0063] Example 3. Removal effect of Cu1 / CeO2 catalysts prepared at different calcination temperatures on the pollutant nitrate

[0064] (1) Weigh 20 mg of CuPc and 6.0 g of H3BTC, 0.3 g of PVP and 0.6 g of Ce(NO3)3 and dissolve them in a mixed solution of 50 mL of ethanol and 25 mL of DMF (75 mL);

[0065] (2) Transfer the mixed solution to a hydrothermal reactor, heat it to 120 °C and react for 1.0 hour to form MPc / Ce-MOF powder;

[0066] (3) Place the powder material in a muffle furnace and calcine it at 450 °C for 2.0 hours in an air atmosphere to obtain the Cu1 / CeO2 catalyst;

[0067] (4) Take 30 mg of Cu1 / CeO2 powder and 4 mg of carbon powder from step (3), add 3.6 mL of ethanol and 0.4 mL of isopropanol and mix them evenly. Then add 40 μL of Nafion as a binder, and ultrasonicate it until it becomes a homogeneous ink-like state. Under the heating of an infrared lamp, apply the evenly dispersed ink-like catalyst solution to both sides of the carbon paper to obtain the working electrode.

[0068] Adjust the calcination temperature in step (3) to 300 °C and 400 °C respectively to prepare the catalysts. Then prepare the working electrodes from the catalysts prepared at different temperatures according to the method in step (4), and carry out the NRR reaction according to the following steps.

[0069] (1) Setup of the electrocatalytic NRR reaction device, the specific steps are as follows:

[0070] a) For the electrocatalytic NRR reaction, use an H-type two-compartment electrochemical reaction cell, and separate the anode compartment and the cathode compartment with a cation exchange membrane (Nafion-117). Add 100 mL of sodium sulfate (50 mM) electrolyte solution to both the anode and cathode compartments. Before the reaction, nitrogen gas (for more than 10 min) needs to be introduced into both the cathode and anode compartments to remove dissolved oxygen; then add 2 mL of nitrate nitrogen stock solution (5 g / L NO3 - ) to the cathode electrolysis compartment, with the initial concentration of NO3 - -N being 22.5 mg / L, and then stir with a magnetic stirrer for 10 min to mix evenly;

[0071] b) According to the principle of the three-electrode system, set up an electrocatalytic nitrate reduction device, using the Cu1 / CeO2 catalyst electrode as the working electrode, a platinum electrode (30 mm × 30 mm) as the counter electrode, and Ag / AgCl 3.0 M KCl as the reference electrode;

[0072] c) Evaluation of the electrocatalytic NRR reaction effect, detect the concentrations of the target pollutant (NO3 - -N), intermediate product (NO2 - -N) and final product (NH3-N) through a UV spectrophotometer (UV1000).

[0073] (2) Operation of the electrocatalytic NRR reaction device, the steps are as follows:

[0074] e) Place the entire electrochemical denitrification reaction device in a 25 °C constant temperature water bath magnetic stirrer, control the reaction temperature at 25 °C, set the magnetic stirring rate at 400 rpm, and maintain uniform stirring;

[0075] f) Set the parameters of the electrochemical workstation, select chronoamperometry, and set the voltage to -1.40 V to start the program for electrochemically reducing nitrate.

[0076] (3) Measure the electrocatalytic NRR reaction activity, and the steps are as follows:

[0077] a) At 0 min, 60 min, 120 min, 180 min, 240 min, 300 min, and 360 min during the reaction, take samples (about 2.5 mL), and draw 1 mL of the sample solution to dilute the sample 20 times in a volumetric flask;

[0078] g) Use a UV-visible spectrophotometer (UV1000) to measure the concentrations of the target pollutant (NO3 - -N), the end product (NH3-N), and the intermediate product (NO2 - -N) at 220 nm, 420 nm, and 540 nm respectively;

[0079] h) The removal rate of nitrate (η) = (1 - C t / C0) * 100%;

[0080] The selectivity of ammonia nitrogen S NH4 + is expressed as: S NH4 + = C NH4 + / (C0 - C t ) * 100%;

[0081] wherein, C NH4 + represents the concentration of NH4 + -N (mg·L -1 ) after electrolysis for t time, C0 represents the initial concentration of NO3 - -N (mg·L -1 ), and Ct represents the concentration of NO3 - -N at time t (mg·L -1 ).

[0082] Table 4. Removal efficiency and ammonia selectivity of catalysts prepared at different temperatures

[0083] Calcination temperature 300℃ 400℃ 450℃ 500℃ Removal rate 90.3％ 92.5％ 99.3％ 99.2％ Selectivity of ammonia 56.2％ 62.7％ 91.6％ 91.9％

[0084] The above-described embodiments are merely preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. Application of a single-atom transition metal catalyst M1 / CeO2 with rich oxygen vacancies in electrocatalytic reduction of nitrate radicals, characterized in that, The preparation method of the catalyst M1 / CeO2 includes the following steps: (1) Weigh a phthalocyanine molecule containing a transition metal single-atom site, trimesic acid, polyvinylpyrrolidone, and Ce(NO3)3 and dissolve them in a mixed solution of ethanol and N,N-dimethylformamide; the phthalocyanine molecule containing a transition metal single-atom site is CuPc; the volume ratio of ethanol to N,N-dimethylformamide in the mixed solution of ethanol and N,N-dimethylformamide is 5-7:3, and each 75 mL of the mixed solution contains 20 mg of CuPc, 6.0 g of H3BTC, 0.3 g of PVP, and 0.6 g of Ce(NO3)3; (2) React the mixed solution at 100-140 °C for 45-75 min to form MPc / Ce-MOF powder; (3) Place the MPc / Ce-MOF powder in a muffle furnace and calcine it in an air atmosphere at a temperature of 350-550 °C for 1.5-2.5 hours to obtain the M1 / CeO2 catalyst.

2. Application of the electrode of the single-atom transition metal catalyst M1 / CeO2 containing oxygen-rich vacancies in the electrocatalytic reduction of nitrate, which is characterized in that: The preparation method of the catalyst M1 / CeO2 includes the following steps: (1) Weigh a phthalocyanine molecule containing a transition metal single-atom site, trimesic acid, polyvinylpyrrolidone, and Ce(NO3)3 and dissolve them in a mixed solution of ethanol and N,N-dimethylformamide; the phthalocyanine molecule containing a transition metal single-atom site is CuPc; the volume ratio of ethanol to N,N-dimethylformamide in the mixed solution of ethanol and N,N-dimethylformamide is 5-7:3, and each 75 mL of the mixed solution contains 20 mg of CuPc, 6.0 g of H3BTC, 0.3 g of PVP, and 0.6 g of Ce(NO3)3; (2) React the mixed solution at 100-140 °C for 45-75 min to form MPc / Ce-MOF powder; (3) Place the MPc / Ce-MOF powder in a muffle furnace and calcine it in an air atmosphere at a temperature of 350-550 °C for 1.5-2.5 hours to obtain the M1 / CeO2 catalyst; The preparation method of the electrode is as follows: Mix the M1 / CeO2 catalyst and carbon powder with ethanol and isopropanol, then add Nafion as an adhesive and ultrasonicate it to a uniform ink-like state; under infrared lamp heating, apply the uniformly dispersed ink-like catalyst solution on both sides of the carbon paper to obtain the electrode.

3. The application according to claim 2, wherein: The voltage for the electrocatalytic reduction of nitrate is -1.30 V to -1.50 V, and the reference electrode is Ag / AgCl, 3.0 M, KCl.

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