Catalyst for electro-catalysis of nitrate and preparation method thereof
By using nickel-molybdenum/foam nickel composite catalyst in the electrocatalytic reduction of nitrate, the problem of insufficient catalytic activity and selectivity in the prior art was solved, efficient and economical ammonia production was achieved, and the catalyst was maintained in the circulation experiment. Good stability.
Patent Information
- Application Number
- CN202411500389.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-24
- Publication Date
- 2025-02-18
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
The prior art has problems such as inhibiting hydrogen-producing competition reactions, improving catalytic activity and selectivity, and effective recovery of product ammonia in the electrocatalytic nitrate reduction process. Moreover, precious metal catalysts are costly and difficult to apply on a large scale.
A nickel-molybdenum/foam nickel foam composite catalyst is used. The catalyst is based on nickel foam and covers nanosheets composed of nickel and molybdenum, and has a large pore frame structure. The molar ratio of nickel to molybdenum is 2:1 to 6:1. This catalyst uses an anion exchange membrane to separate the cathode chamber and anode chamber to achieve efficient reduction of nitrate to ammonia by applying a constant voltage in the H-type double-cavity reaction cell.
High-efficiency electrocatalytic nitrate reduction under normal temperature and pressure was achieved, with high ammonia-yield Faraday efficiency and ammonia yield, with a selectivity of 97% ammonia production, and the activity did not decline significantly in 10 cycle experiments, reducing production costs.
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Abstract
Description
Technical Field
[0001] The present application relates to a catalyst for electrocatalytic nitrate reduction and a preparation method thereof, belonging to the field of electrocatalysis. Background Art
[0002] Ammonia is an important chemical raw material with important applications in agriculture, textiles, plastics and pharmaceuticals. It is a mild, hydrogen-rich energy storage medium with high energy density (4.3kWh kg -1 ), easy to transport, and has broad prospects as the next generation of energy and hydrogen energy carrier. At present, ammonia is mainly obtained through Haber-Bosch industrial synthetic ammonia, which requires high temperature (300-500°C) and high pressure (15-35MPa), and produces a large amount of carbon dioxide greenhouse gas.
[0003] NO 3- It is a common pollutant that is discharged into the surface and groundwater in large quantities, seriously threatening people's health; at the same time, the increase in nitrate concentration in water bodies will cause eutrophication of water bodies and cause damage to the environment. 3- The NO bond energy is low (205 kJ mol -1 ), which is easily broken and converted into ammonia, is a potential nitrogen source for ammonia production. At present, there are still problems in the electrocatalytic reduction of nitrates, including inhibiting the competitive reaction of hydrogen production, improving the activity and selectivity of the catalyst, and effectively recovering the product ammonia.
[0004] Electrocatalytic nitrate reduction is a complex multi-electron and multi-proton transfer process, and the catalyst significantly affects its conversion rate, product selectivity and catalytic stability. At present, many different catalysts have been reported in the literature, including some catalysts containing precious metals such as Au (para-Au / C, Precision Chemistry, 2024), Pt (PtRu, Journal of Catalysis, 2021), and Ru (Ru / RuO2, J.Am.Chem.Soc., 2020). However, due to the high price of precious metals, it is difficult to achieve large-scale application in industry. Some catalysts based on transition metals such as Cu (BiCo@Cu, Advanced Materials, 2023), Co (CoP-CNS, Nature Communications, 2022), Fe (Cu-Fe3O4, Nano Letters, 2023), and Ni (Ni-NSA-VNi, Journal of Materials Chemistry A, 2021) also show high selectivity, but the catalyst stability is poor and the current density is low. Summary of the invention
[0005] The object of the present invention is to provide a nickel-molybdenum / nickel foam catalyst with excellent ammonia production activity, selectivity and cycle stability and a preparation method thereof, which is used for efficient electrocatalytic reduction of nitrate to ammonia.
[0006] According to one aspect of the present application, a catalyst for electrocatalytic nitrate reduction is provided;
[0007] The catalyst is a nickel-molybdenum / nickel foam composite catalyst;
[0008] The catalyst is based on nickel foam and covered with nanosheets composed of nickel and molybdenum;
[0009] The catalyst has a macroporous framework structure;
[0010] In the catalyst, the molar ratio of nickel to molybdenum is 2:1 to 6:1.
[0011] The electrocatalytic reduction of nitrate is carried out in an H-type double-chamber reaction cell, wherein the cathode chamber and the anode chamber are separated by an anion exchange membrane, a nickel-molybdenum / nickel foam catalyst is used as a working electrode, and a constant voltage is applied to allow the nitrate in the cathode chamber solution to synthesize ammonia through an electrochemical reduction reaction.
[0012] According to the second aspect of the present application, a method for preparing a nickel-molybdenum / nickel foam composite catalyst is provided, comprising at least the following steps:
[0013] Step I: placing a mixed solution containing nickel salt, molybdenum salt, and nickel foam in a sealed container, and performing reaction I to obtain a nickel foam sample;
[0014] Step II: reducing the nickel foam sample obtained in step I in a mixed atmosphere of argon and hydrogen to obtain the catalyst.
[0015] Optionally, in step I, the nickel salt is selected from at least one of nickel nitrate, nickel sulfate, and nickel chloride;
[0016] The molybdenum salt is selected from at least one of sodium molybdate, potassium molybdate and ammonium molybdate.
[0017] Optionally, the molar ratio of the nickel salt to the molybdenum salt is 1:8 to 8:1.
[0018] Optionally, the molar ratio of the nickel salt to the molybdenum salt is 1:4 to 4:1.
[0019] Optionally, the conditions of reaction I are as follows:
[0020] The temperature of the reaction I is 120-180°C;
[0021] The reaction time is 5 to 10 hours.
[0022] Optionally, in step II, the mixed atmosphere includes argon and hydrogen.
[0023] Optionally, in step II, the ventilation rate of the argon gas is 100 to 300 sccm.
[0024] Optionally, in step II, the hydrogen gas flow rate is 10 to 50 sccm.
[0025] Optionally, in step II, the reduction conditions are as follows:
[0026] The heating rate of the reduction is 3-5°C / min;
[0027] The reduction temperature is 25-550°C;
[0028] The reduction time is 30 min to 2 h.
[0029] Optionally, a method for preparing a nickel-molybdenum / nickel foam catalyst for electrocatalytic reduction of nitrate to ammonia comprises the following steps:
[0030] 1) The nickel foam substrate was ultrasonically cleaned in acetone, isopropanol, ethanol and ultrapure water for 30 min and then dried;
[0031] 2) preparing 30 mL of a mixed solution of nickel nitrate hexahydrate and sodium molybdate dihydrate, wherein the molar ratio of nickel to molybdenum is in the range of 1:4 to 4:1;
[0032] 3) pouring the mixed solution into a reaction kettle, placing the nickel foam therein, and hydrothermalizing at 150° C. for 6 h. After hydrothermal treatment, ultrasonically treating the obtained nickel foam sample and vacuum drying the obtained nickel foam sample;
[0033] 4) The vacuum-dried sample was heated from room temperature to 550° C. at a rate of 3° C. / min in a mixed atmosphere of argon and hydrogen (200 sccm of argon and 30 sccm of hydrogen) and subjected to hydrogen reduction at this temperature for 1 h to obtain the nickel-molybdenum / foamed nickel composite catalyst.
[0034] The beneficial effects of this application include:
[0035] 1) The catalyst prepared in this application is a new type of non-precious metal catalyst, which uses clean electric energy to electrocatalyze nitrate reduction under normal temperature and pressure conditions, and has a high ammonia production Faraday efficiency and ammonia yield. Compared with the precious metal catalysts reported in previous studies, it is conducive to reducing production costs.
[0036] 2) The catalyst described in the present application can achieve up to 97% ammonia production selectivity at a relatively low overpotential, and can maintain activity without significant degradation in a stability experiment of 10 cycles.
[0037] 3) The synergistic effect of nickel and molybdenum in the catalyst described in the present application, nickel can effectively promote the activation of water under alkaline conditions, thereby providing protons for nitrate reduction to react. Molybdenum makes the conversion process of nitrate more convenient and efficient, especially conducive to the conversion of nitrate to nitrite. BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Figure 1 This is a SEM image of nickel-molybdenum / nickel foam in Example 1 of the present application;
[0039] Figure 2 This is the standard curve diagram in Example 2 of the present application;
[0040] Figure 3 The selectivity and activity diagram of ammonia production of the catalyst at different voltages in Example 3 of the present application;
[0041] Figure 4 The nitrate reduction selectivity and activity diagram of nickel-molybdenum catalysts with different ratios in Example 5 of the present application;
[0042] Figure 5 This is a test diagram of the electrocatalytic ammonia production cycle stability of the catalyst in Example 6 of the present application. DETAILED DESCRIPTION
[0043] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.
[0044] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels;
[0045] The analysis method in Example 1 of the present application is as follows:
[0046] The morphology of the catalysts was analyzed using Quanta 200F and HT7700 instruments.
[0047] The analysis of the product ammonia in the examples of the present application is as follows:
[0048] The product ammonia was detected by UV-visible spectrophotometry.
[0049] The calculation formula of the product ammonia in the embodiment of the present application is as follows:
[0050] Ammonia production Faraday efficiency = nFc(NH3)V / it;
[0051] Ammonia production rate = Vc(NH3) / tS.
[0052] Where n is the number of electrons transferred when nitric acid is reduced to ammonia, which is 8; F is the Faraday constant, which is 96485C mol -1; c(NH3) is the concentration of product ammonia in the solution; V is the volume of the cathode solution, which is 10 mL; i is the average current of nitrate reduction to produce ammonia; t is the time for nitrate reduction to produce ammonia, which is 40 min; S is the projected area of the catalyst on the electrode, which is 0.36 cm 2 .
[0053] Example 1 Preparation of Nickel-Molybdenum / Nickel Foam Working Electrode
[0054] The nickel-molybdenum / nickel foam working electrode for electrocatalytic reduction of nitrate to ammonia was prepared by the following steps:
[0055] 1) The nickel foam was ultrasonically cleaned with different cleaning solutions for 30 min and then dried;
[0056] 2) preparing a mixed solution of nickel salt and molybdenum salt: mixing 20 mL 0.06 mol / L nickel nitrate hexahydrate and 10 mL 0.08 mol / L sodium molybdate dihydrate, wherein the molar ratio of nickel to molybdenum in the formed mixed solution is 1.2:0.8;
[0057] 3) pouring the mixed solution into a reaction kettle, placing the nickel foam therein, and hydrothermalizing at 150° C. for 6 h. After hydrothermal treatment, ultrasonically treating the obtained nickel foam sample and vacuum drying the obtained nickel foam sample;
[0058] 4) The vacuum-dried nickel foam sample was heated from room temperature to 550°C at a rate of 3°C / min in a mixed atmosphere of argon and hydrogen and then subjected to hydrogen reduction at this temperature for 1 hour to obtain the nickel-molybdenum / nickel foam composite catalyst, i.e., the electrocatalytic nitrate reduction catalyst. Its surface morphology is as follows Figure 1 The figure shows that nickel and molybdenum are densely distributed on the surface of the base nickel foam to form a nano-sheet structure.
[0059] Example 2 Detection of product ammonia
[0060] The product ammonia was detected by UV-visible spectrophotometry. This method is Nesslers' method, and the specific process is as follows: Take an appropriate amount of the reaction solution and dilute it to 2mL, and use 2mL of 0.5M sulfuric acid solution to neutralize it. After the reaction is complete, add 200μL of Nessler reagent, let it stand for 20min, record its absorbance at 450nm and compare it with the standard curve as shown in Figure 2 Compare the amount of ammonia generated by nitrate reduction.
[0061] Example 3 Nitrate reduction activity test of nickel-molybdenum / nickel foam
[0062] The nickel-molybdenum / nickel foam catalyst prepared in Example 1 was encapsulated with 706 glue to an exposed area of 0.6*0.6 cm 2, as the working electrode, platinum sheet as the counter electrode, and Ag / AgCl saturated with potassium chloride as the reference electrode. In a standard three-electrode system double-chamber electrolytic cell, before the experiment, 1M potassium hydroxide solution was used as the electrolyte, and it was pretreated at -1.52V vs. Ag / AgCl for 30min. Then, a mixed solution of 0.5M potassium nitrate and 1M potassium hydroxide was used as the electrolyte, and the electrolyte was at -0.1V at 30℃ water bath and normal pressure. RHE The reaction was carried out under voltage for 40 min. The ammonia concentration in the electrolyte was determined by spectrophotometry. The Faradaic efficiency of nitrate production was 97%, and the ammonia production rate was 6.08 mmol cm -2 h -1 , Figure 3 is the ammonia production rate and Faraday efficiency of the catalyst at different voltages.
[0063] Example 4 Synthesis and characterization of nickel-molybdenum / nickel foam catalysts in different ratios
[0064] According to the synthesis method in Example 1, nickel-molybdenum / nickel foam catalysts with different proportions were obtained by changing the molar ratio of nickel and molybdenum elements. These catalysts were characterized to obtain the atomic ratios of nickel and molybdenum in the catalysts under different feed ratios. The results are shown in Table 1. In NiMo-xy, x represents x mmol of nickel nitrate added during the synthesis process, and y represents y mmol of sodium molybdate added during the synthesis process.
[0065] Example 5 Comparison of Nitrate Reduction Activity of Nickel-Molybdenum / Nickel Foam in Different Ratios
[0066] The nickel-molybdenum / nickel foam catalysts of different ratios in Example 4 were used for nitrate reduction test, and the experimental method was the same as that in Example 3. Figure 4 As shown, at -0.1V RHE Under the conditions, the feed ratio is 1.2:0.8 and the Ni 2.44 Mo has the best activity and selectivity.
[0067] Example 6 Nitrate reduction stability test of nickel-molybdenum / nickel foam
[0068] The material in Example 1 was tested for its electrocatalytic reduction of NO3 according to the test method of Example 3. - The cycling stability of the Ni-Mo / Ni foam catalyst was tested continuously at a constant current potential of -1.72V vs.Ag / AgCl. Figure 5 As shown, the test conditions remained the same as before, and 15 cycles were performed continuously, each cycle was 40 minutes, and the ammonia production efficiency was almost unchanged.
[0069] Table 1
[0070]
[0071] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.
Claims
1. A catalyst for electrocatalytic nitrate reduction, characterized in that: The catalyst is a nickel-molybdenum / nickel foam composite catalyst; The catalyst is based on nickel foam and covered with nanosheets composed of nickel and molybdenum; The catalyst has a macroporous framework structure; In the catalyst, the molar ratio of nickel to molybdenum is 2:1 to 6:
1.
2. A method for preparing a nickel-molybdenum / nickel foam composite catalyst, characterized in that: At least the following steps are included: Step I: placing a mixed solution containing nickel salt, molybdenum salt, and nickel foam in a sealed container, and performing reaction I to obtain a nickel foam sample; Step II: reducing the nickel foam sample obtained in step I in a mixed atmosphere of argon and hydrogen to obtain the catalyst.
3. The preparation method according to claim 2, characterized in that: In step I, the nickel salt is selected from at least one of nickel nitrate, nickel sulfate, and nickel chloride; The molybdenum salt is selected from at least one of sodium molybdate, potassium molybdate and ammonium molybdate.
4. The preparation method according to claim 2, characterized in that: In step I, the molar ratio of the nickel salt to the molybdenum salt is 1:8 to 8:
1.
5. The preparation method according to claim 4, characterized in that: In step I, the molar ratio of the nickel salt to the molybdenum salt is 1:4 to 4:
1.
6. The preparation method according to claim 2, characterized in that: In step I, the conditions of reaction I are as follows: The temperature of the reaction I is 120-180°C; The reaction time is 5 to 10 hours.
7. The preparation method according to claim 2, characterized in that: In step II, The mixed atmosphere includes argon and hydrogen.
8. The preparation method according to claim 2, characterized in that: In step II, the ventilation rate of the argon gas is 100-300 sccm.
9. The preparation method according to claim 2, characterized in that: In step II, the hydrogen gas flow rate is 10 to 50 sccm.
10. The preparation method according to claim 2, characterized in that: In step II, the reduction conditions are as follows: The heating rate of the reduction is 3-5°C / min; The reduction temperature is 25 to 550° C. The reduction time is 30min to 2h.