Reduction catalyst with double active centers, preparation of reduction catalyst and application of reduction catalyst in electro-catalysis of nitrate
By preparing the CoMo@C NO catalyst supported on the carbon matrix with bimetal oxide, the problems of low catalytic activity and poor stability in the process of electroreduction nitrate ammonia production are solved, and efficient ammonia yield and Faraday efficiency are achieved, which is suitable for industrial applications.
Patent Information
- Application Number
- CN202510639286.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2025-04-17
- Filing Date
- 2025-05-16
- Publication Date
- 2025-08-12
AI Technical Summary
In the process of electroreduction of nitrate ammonia production, existing electrocatalysts have problems such as low catalytic activity, poor stability, high cost and unregulated element content, resulting in low ammonia yield and Faraday efficiency.
The dual active center catalyst formed by bimetal oxide supported on the carbon matrix is prepared by hydrothermal reaction and high-temperature pyrolysis. It is used for electrocatalytic nitrate reduction reaction in alkaline environments, inhibiting hydrogen evolution reaction, and improving catalytic activity and stability.
It achieves efficient ammonia yield and Faraday efficiency, and the catalyst exhibits excellent catalytic activity and stability in alkaline environments, making it suitable for industrial applications.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of electrocatalytic ammonia synthesis, and in particular to a preparation method and application of a catalyst for electrocatalytic nitrate synthesis of ammonia. Background Art
[0002] Ammonia (NH3) is an important carbon-free energy storage inorganic chemical, hydrogen carrier and fertilizer precursor. Modern industrial ammonia synthesis adopts the Haber-Bosch process, which not only requires harsh synthesis conditions but also is accompanied by a large amount of emissions. Nitrate is highly soluble in water and has a low theoretical energy consumption of ammonia synthesis (6.5kWh kg -1 ) has become an extremely attractive nitrogen source. At the same time, nitrate pollution has become increasingly serious with the expansion of industrial scale. Polluted water bodies not only directly threaten human life and health, but also destroy the ecological balance of nature, and have become an environmental hazard that cannot be ignored. Using nitrate as a nitrogen source and reducing nitrate in sewage to ammonia by electrocatalysis is an efficient and sustainable ammonia synthesis technology. This technology can synthesize basic industrial raw material ammonia while treating nitrate pollution in water, realizing waste utilization. The electricity consumed in the electroreduction process can utilize excess electricity generated by intermittent renewable energy sources such as tidal energy, solar energy and wind energy to form a complete green and sustainable ammonia synthesis system. Therefore, the application of electrocatalytic nitrate reduction ammonia production technology is of great significance to the development of the ammonia industry and environmental governance.
[0003] The development and large-scale industrial application of electrocatalytic nitrate reduction to ammonia technology rely on the development of efficient electrocatalysts. In-depth exploration of the intrinsic mechanism of the electrocatalytic nitrate reduction reaction, identification of material active sites, and analysis of structure-activity relationships are the basis for the precise design of highly active and selective electrocatalysts, and are also the top priority of research in the field of electrocatalysis. Most catalysts with a single metal active site have difficulty in adsorption and desorption, slow electron transfer rates, poor conductivity, and slow catalytic rates, resulting in low ammonia yields and Faradaic efficiencies. To address this problem, people have adopted various strategies to modify the catalysts, including precious metal doping, alloying, and defect engineering. However, they still have many disadvantages, such as high price, uncontrollable element content, and low stability. Therefore, it is necessary to find suitable catalysts to improve their electrocatalytic performance. Summary of the Invention
[0004] The present invention aims to provide an electrocatalytic nitrate reduction catalyst and its preparation method and application. The catalyst disclosed in the present invention is used for the electrocatalytic nitrate reduction reaction to produce NH3 in an alkaline environment, and has high catalytic activity and stability.
[0005] In order to achieve the above-mentioned objectives, the first aspect of the present disclosure provides an electrocatalytic nitrate reduction catalyst, wherein the electrocatalytic nitrate reduction catalyst has a dual active center, and the dual active center corresponds to: the dual active center is a bimetallic oxide, and the bimetallic oxide is loaded on a carbon matrix (denoted as M1M2@C NO, where M1M2 corresponds to a bimetal).
[0006] The first metal element is selected from any one of nickel, cobalt and iron, preferably cobalt;
[0007] The second metal element is selected from any one of molybdenum, vanadium, tungsten and niobium, preferably molybdenum.
[0008] The molar ratio of the first metal element to the second metal element is (2-10):1.
[0009] A second aspect of the present disclosure provides a method for preparing a catalyst for electrocatalytic nitrate synthesis of ammonia, the method comprising:
[0010] S1, dissolving a compound containing an aminocarboxylic acid derivative in an organic solvent to obtain a first solution;
[0011] S2, dissolving a compound containing the first metal source and an acid compound containing the second metal in an organic solvent to obtain a second solution;
[0012] S3, stirring the first solution of step S1 and the second solution of step S2, transferring them to a reactor, mixing them, and reacting them at high temperature, centrifuging and washing them after the reaction to obtain a compound having a bimetallic precursor, and then drying them to obtain a first solid;
[0013] S4, pyrolyzing the first solid under the protection of an inert gas at a high temperature, and obtaining a second solid, i.e., a reduction catalyst having dual active centers, after natural cooling;
[0014] In step S1, the aminocarboxylic acid derivative is 2-aminoterephthalic acid;
[0015] In step S2, the first metal element is selected from any one or more of nickel, cobalt and iron, preferably containing cobalt; the compound of the first metal source is selected from nickel salts, cobalt salts and iron salts, for example, the Co salt is a hydrate containing CoCl2, the nickel salt is nickel nitrate, and the iron salt is ferric nitrate, ferric chloride, etc.
[0016] The second metal element is selected from any one or more of molybdenum, tungsten, vanadium and niobium, preferably molybdenum; the acid compound of the second metal is preferably a compound containing phosphomolybdic acid or a compound containing phosphotungstic acid;
[0017] In steps S1 and S2, the organic solvent is N,N-dimethyldiamide;
[0018] In step S3, the molar ratio of the aminocarboxylic acid derivative to the total metal is 1:(1-2), the high temperature reaction temperature is 110-180° C., and the reaction time is 2-5 h.
[0019] In step S4, the calcination temperature is 700-900° C., the calcination time is 5-6 hours, and the inert gas is nitrogen.
[0020] A third aspect of the present disclosure provides an application of a catalyst for catalyzing the reaction of nitrate to ammonia in an alkaline environment.
[0021] Furthermore, the electrolyte environment is alkaline, which is conducive to inhibiting the occurrence of hydrogen evolution reaction, thereby promoting the occurrence of electrocatalytic nitrate synthesis reaction of ammonia.
[0022] The electrocatalytic nitrate reduction method comprises an electrolytic cell comprising a working electrode cathode containing the catalyst of the present invention, a reference electrode, a counter electrode, and an electrolyte. The working electrode is the electrode containing the catalyst, the reference electrode is a Hg / HgO electrode, and the counter electrode is a platinum mesh. Argon is passed through the working electrode as a protective gas. The reaction temperature for the electrocatalytic nitrate to ammonia reaction is 25-40°C.
[0023] Through the above technical solution, the method disclosed herein prepares a precursor of bimetallic active sites by hydrothermal reaction, and then obtains an electrocatalytic reduction catalyst having bimetallic active sites by high-temperature pyrolysis. The method disclosed herein is beneficial for adjusting the electronic structure and local coordination environment of the catalyst, providing more active sites, reducing the surface Gibbs free energy of the reaction intermediates, and thus improving the catalytic activity of the catalyst; it can also inhibit the occurrence of competitive hydrogen evolution reaction in the electrocatalytic nitrate reduction reaction, effectively improving the ammonia yield, and showing stability in long-term testing. The method disclosed herein has simple steps and mild conditions, which is conducive to industrialization.
[0024] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 This is a multiple performance test of Example 1 at -0.2V vs. RHE;
[0026] Figure 2 This is the long-term stability test of Example 1;
[0027] Figure 3 This is the X-ray diffraction pattern of Example 1. DETAILED DESCRIPTION
[0028] The technical solution of the present invention is further described below through specific embodiments.
[0029] In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the embodiments, unless otherwise specified, are all conventional methods in the art.
[0030] Example 1
[0031] A method for preparing a CoMo@C NO nanocomposite material, comprising the following steps:
[0032] a. Preparation of Precursors
[0033] 272 mg (1.5 mmol) of 2-aminoterephthalic acid was dissolved in 15 mL of N,N-dimethyldiamide and then sonicated for 10 min to obtain solution A. 356.90 mg (1.5 mmol) of cobalt chloride hexahydrate and 114.09 mg (0.063 mmol) of phosphomolybdic acid hydrate were dissolved in 15 mL of N,N-dimethyldiamide and sonicated for 10 min to obtain solution B. Solutions A and B were vigorously stirred for 30 min and then transferred to a reactor. The mixture was reacted at 110°C for 2 h. After cooling to room temperature, the precipitate was centrifuged, washed three times with ethanol and water, and then dried in vacuo at 60°C for 12 h.
[0034] b. CoMo@C NO nanocomposite
[0035] Under nitrogen atmosphere, the temperature was raised from room temperature to 900 °C at a rate of 5 °C / min and maintained for 5 h. The black powder obtained after natural cooling was CoMo@C NO nanooctahedron.
[0036] The catalyst was then electrocatalyzed in a three-electrode system to synthesize ammonia from nitrate, with the anolyte being 30 mL of 1 M KOH solution and the cathode being 30 mL of 1 M KOH + 0.1 M KNO3 solution.
[0037] Performance characterization:
[0038] like Figure 1 As shown, the catalyst prepared in Example 1 was subjected to multiple (3) parallel tests at -0.2 V vs. RHE; Figure 2 The catalyst was subjected to a long-term stability test, and the results showed that the catalyst had excellent catalytic activity and stability.
[0039] like Figure 3As shown, the composition and structure of CoMo@C NO were characterized by X-ray diffraction (XRD). In the figure, the diffraction peaks observed at 23.47 nm, 26.68 nm, and 27.75 nm can be attributed to the crystal planes (021), (002), and (-202) of CoMoO4 (JCPDS No. 21-0868), respectively. This confirms the successful synthesis of the bimetallic compound.
[0040] application:
[0041] The prepared CoMo@C NO nanocomposite material is used to catalyze the nitrate synthesis of ammonia in an alkaline environment, and the steps are as follows:
[0042] Electrochemical tests were performed using an H cell. First, 0.2 mg of CoMo@C NO nanocomposite was loaded on carbon paper. The electrolyte on the left was 30 mL of 1 M KOH, and the electrolyte on the right was 30 mL of 1 M KOH + 0.1 M KNO3. After the reaction was carried out in an electrolytic cell at a voltage of -0.2 V vs. RHE for 1 hour, the catalytic efficiency of the reaction system CoMo@C NO nanocomposite was measured by UV spectrophotometry to be 9335.55 μg h. -1 mg cat. -1 ,FE is 99.99%.
[0043] Example 2
[0044] a. Preparation of Precursors
[0045] 272 mg (1.5 mmol) of 2-aminoterephthalic acid was dissolved in 15 mL of N,N-dimethyldiamide and then sonicated for 10 min to obtain solution A. 356.90 mg (1.5 mmol) of cobalt chloride hexahydrate and 114.09 mg (0.063 mmol) of phosphomolybdic acid hydrate were dissolved in 15 mL of N,N-dimethyldiamide and sonicated for 10 min to obtain solution B. Solutions A and B were mixed and vigorously stirred for 30 min before being transferred to a reactor and reacted at 130°C for 4 h. After cooling to room temperature, the precipitate was centrifuged, washed three times with ethanol and water, and then dried in vacuo at 60°C for 12 h.
[0046] b. CoMo@C NO nanocomposite
[0047] Under nitrogen atmosphere, the temperature was increased from room temperature to 900 °C at a rate of 5 °C / min and maintained for 5 h. The black powder obtained after natural cooling was CoMo@C NO nanooctahedron.
[0048] application
[0049] The prepared CoMo@C NO nanocomposite material was used to catalyze the nitrate synthesis ammonia reaction in an alkaline environment. The steps were the same as in Example 1. The catalytic efficiency of the reaction system CoMo@C NO nanocomposite material was measured to be 8255.46 μg h -1 mg cat. -1 , FE is 92.01%.
[0050] Example 3
[0051] A method for preparing a CoMo@C NO nanocomposite material, comprising the following steps:
[0052] a. Preparation of Precursors
[0053] 272 mg (1.5 mmol) of 2-aminoterephthalic acid was dissolved in 15 mL of N,N-dimethyldiamide and then sonicated for 10 min to obtain solution A. 356.90 mg (1.5 mmol) of cobalt chloride hexahydrate and 114.09 mg (0.063 mmol) of phosphomolybdic acid hydrate were dissolved in 15 mL of N,N-dimethyldiamide and sonicated for 10 min to obtain solution B. Solutions A and B were vigorously stirred for 60 min and then transferred to a reactor. The mixture was reacted at 110°C for 2 h. After cooling to room temperature, the precipitate was centrifuged, washed three times with ethanol and water, and then dried in vacuo at 60°C for 12 h.
[0054] b. CoMo@C NO nanocomposite
[0055] Under nitrogen atmosphere, the temperature was increased from room temperature to 700°C at a rate of 5°C / min and maintained for 5 h. The black powder obtained after natural cooling was CoMo@C NO nanooctahedron.
[0056] application
[0057] The prepared CoMo@C NO nanocomposite material was used to catalyze the nitrate synthesis ammonia reaction, and the steps were the same as those in Example 1. The catalytic efficiency of the reaction system CoMo@C NO nanocomposite material was measured to be 8364.85 μg / h. -1 mg cat. -1 , FE is 89.03%.
[0058] Example 4
[0059] The electrocatalytic nitrate reduction catalyst was prepared by the method of Example 1, except that cobalt chloride hexahydrate in step a was replaced by ferric chloride hexahydrate, and the temperature in step b was changed from 900° C. to 800° C.
[0060] The prepared FeMo@C NO nanocomposite material was used to catalyze the nitrate synthesis ammonia reaction, and the steps were the same as in Example 1. The catalytic efficiency of the reaction system FeMo@C NO nanocomposite material was measured to be 7562.87 μg h -1 mg cat. -1 , FE is 88.09%.
[0061] Example 5
[0062] The electrocatalytic nitrate reduction catalyst was prepared by the method of Example 1, except that 114.09 mg of phosphomolybdic acid hydrate in step a was replaced by 178.26 mg of phosphotungstic acid hydrate, and the temperature in step b was changed from 900° C. to 700° C.
[0063] The prepared CoW@C NO nanocomposite material was used to catalyze the nitrate synthesis ammonia reaction, and the steps were the same as in Example 1. The catalytic efficiency of the reaction system CoW@C NO nanocomposite material was measured to be 7526.24 μg h -1 mg cat. -1 , FE is 86.06%.
[0064] Comparative Example 1
[0065] The difference from Example 1 is that the electrolyte is different. The anode is 30 mL of 0.5 M sulfuric acid solution, and the cathode is 30 mL of 0.5 M sulfuric acid solution and 0.1 M potassium nitrate solution. The prepared CoMo@C NO nanocomposite material is used to catalyze the nitrate synthesis reaction of ammonia. The steps are the same as those in Example 1. The catalytic efficiency of the reaction system CoMo@C NO nanocomposite material is measured to be 312.49 μg h -1 mg cat. -1 , FE is 42.66%.
[0066] Comparative Example 2
[0067] The difference from Example 1 is that the electrolyte is different. The anode is 30 mL of 0.5 M sodium sulfate, and the cathode is 30 mL of 0.5 M sodium sulfate solution and 0.1 M potassium nitrate solution. The prepared CoMo@C NO nanocomposite material is used to catalyze the nitrate synthesis reaction of ammonia. The steps are the same as those in Example 1. The catalytic efficiency of the reaction system CoMo@C NO nanocomposite material is measured to be 9614.18 μg h -1 mg cat. -1 , FE is 6.77%.
[0068] Comparative Example 3
[0069] The difference from Example 1 is that cobalt chloride hexahydrate is not used, and the Mo@C NO composite material is finally prepared. The prepared Mo@C NO composite material is used to catalyze the nitrate synthesis ammonia reaction. The steps are the same as those in Example 1. The catalytic efficiency of the reaction system Mo@C NO composite material is measured to be 300.19 μg h -1 mg cat. -1 , FE is 42.76%.
[0070] Comparative Example 4
[0071] The difference from Example 1 is that phosphomolybdic acid hydrate is not used, and the final product is Co@C NO composite material. The prepared Co@C NO composite material is used for the electrocatalytic nitrate synthesis of ammonia reaction. The steps are the same as those in Example 1. The catalytic efficiency of the reaction system Co@C NO composite material is measured to be 6365.81 μg h -1 mg cat. -1 , FE is 76.54%.
[0072] Performance Testing
[0073] 1. Catalytic efficiency of catalytic nitrogen fixation and ammonia synthesis
[0074] The application results of the above embodiments and comparative examples are summarized in Table 1. Table 1 Catalytic efficiency of catalytic nitrogen fixation and ammonia synthesis reaction of embodiments 1 to 4 and comparative examples 1 to 2 (time: 1 h)
[0075]
[0076]
[0077] As can be seen from Table 1: Comparative Examples 1 and 2 show that when the solution environment is acidic and neutral, the catalytic performance of the catalyst is far inferior to that of the solution environment when the solution environment is alkaline. This is mainly because when the solution pH decreases, the competitive hydrogen evolution reaction (HER) increases, which reduces the FE of the NRA reaction. Comparative Examples 3 and 4 show that when the catalyst contains only Co or Mo, its catalytic effect is inferior to that of the catalyst containing Co and Mo bimetallic sites. This is because NRA has a two-step conversion process, the first step is the conversion of nitrate to nitrite, and the second step is the conversion of nitrite to ammonia. The active site of the Co element is mainly the conversion of nitrite to ammonia, and the active site of the Mo element is mainly the conversion of nitrate to nitrite. The presence of only Co or Mo active sites will cause the other step of the two-step reaction to proceed slowly, resulting in reduced efficiency of ammonia synthesis.
[0078] The results of Examples 2 and 3 show that when the catalytic reaction conditions change, the ammonia yield and Faradaic efficiency decrease to varying degrees. This may be because when the reaction conditions change, the active sites formed by the catalyst are reduced, resulting in a decrease in the efficiency of ammonia synthesis. Examples 4 and 5 show that when other metal elements are used as bimetallic active sites, their catalytic effect is not as good as that of catalysts containing Co and Mo bimetallic active sites. This may be because the bimetallic sites formed by other elements may over-stabilize certain intermediates (such as NO or N), resulting in difficulty in desorption or the formation of byproducts (such as N2) instead of the target product NH3.
[0079] 2. Reuse rate test method:
[0080] The CoMo@C NO nanocomposites obtained in Examples 1 to 3 and the FeMo@C NO nanocomposites obtained in Example 4 were used in the electrocatalytic nitrate synthesis reaction for several cycles. The catalysts loaded with the composite materials were then used again in the electrocatalytic nitrate synthesis reaction for several cycles under the same conditions. The changes in the catalytic activity of the CoMo@C NO nanocomposites after repeated use were detected. The results are shown in Table 2.
[0081] Table 2 Catalytic efficiency of the nitrate reduction reaction to synthesize ammonia by the catalysts of Examples 1 to 4 after several cycles of catalysis
[0082]
[0083] As shown in Table 2, the catalytic efficiency of the catalysts of Examples 1-4 only slightly changed after ten hours of cyclic catalytic nitrate reduction to ammonia synthesis. After ten cycles, the CoMo@C NO nanocomposite of Example 1 still retained 98.3% of its initial catalytic efficiency. The CoMo@C NO nanocomposite of Example 2 still retained 97.2% of its initial catalytic efficiency. The CoMo@C NO nanocomposite of Example 3 still retained 97.6% of its initial catalytic efficiency. The FeMo@C NO nanocomposite of Example 4 still retained 96.8% of its initial catalytic efficiency. This is primarily due to the stable structure of the catalysts synthesized using this method, the mild catalytic reaction conditions, the absence of strong acids, strong bases, or strong oxidizing substances involved in the catalytic reaction or their generation, and the fact that the catalytic activity of the catalysts did not significantly change after cyclic use. Therefore, the CoMo@C NO nanocomposite of the present invention is highly reusable and practical.
[0084] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are within the scope of the technical solution of the present invention.
Claims
1. A reduction catalyst having dual active centers, characterized in that: The electrocatalytic nitrate reduction catalyst has a dual active center, wherein the dual active center corresponds to: a first metal site corresponding to a transition metal and a second metal site corresponding to a metallic acid; the dual active center is a bimetallic oxide, and the bimetallic oxide is supported on a carbon matrix; The first metal element is selected from any one of nickel, cobalt and iron, preferably cobalt; The second metal element is selected from any one of molybdenum, vanadium and niobium, preferably molybdenum.
2. A reduction catalyst having dual active centers according to claim 1, characterized in that: The molar ratio of the first metal element to the second metal element is (2-10):
1.
3. The method for preparing a reduction catalyst having dual active centers according to claim 1 or 2, characterized in that: The following steps are involved: S1, dissolving a compound containing an aminocarboxylic acid derivative in an organic solvent to obtain a first solution; S2, dissolving a compound containing the first metal source and an acid compound containing the second metal in an organic solvent to obtain a second solution; S3, stirring the first solution of step S1 and the second solution of step S2, transferring them to a reactor, mixing them, and reacting them at high temperature, centrifuging and washing them after the reaction to obtain a compound having a bimetallic precursor, and then drying them to obtain a first solid; S4. The first solid is subjected to high-temperature pyrolysis under the protection of an inert gas, and after natural cooling, a second solid, i.e., a reduction catalyst having dual active centers, is obtained.
4. The method according to claim 3, characterized in that In step S1, the aminocarboxylic acid derivative is 2-aminoterephthalic acid.
5. The method according to claim 3, characterized in that In step S2, the first metal element is selected from any one or more of nickel, cobalt and iron, preferably containing cobalt; the compound of the first metal source is selected from nickel salts, cobalt salts and iron salts, for example, the Co salt is a hydrate containing CoCl2, the nickel salt is nickel nitrate, and the iron salt is ferric nitrate, ferric chloride, etc. The second metal element is selected from any one or more of molybdenum, tungsten, vanadium and niobium, preferably molybdenum; the acid compound of the second metal is preferably a compound containing phosphomolybdic acid or a compound containing phosphotungstic acid.
6. The method according to claim 3, characterized in that The organic solvent in steps S1 and S2 is N,N-dimethyldiamide.
7. The method according to claim 3, characterized in that In step S3, the molar ratio of the aminocarboxylic acid derivative to the total metal is 1:(1-2), the high temperature reaction temperature is 110-180° C., and the reaction time is 2-5 h.
8. The method according to claim 3, characterized in that In step S4, the calcination temperature is 700-900° C., the calcination time is 5-6 hours, and the inert gas is nitrogen.
9. Use of the reduction catalyst with dual active centers according to claim 1 or 2 for catalyzing the synthesis of ammonia from nitrate in an alkaline environment.
10. The use according to claim 9, wherein an electrolytic cell is formed by a working electrode cathode containing a reduction catalyst having dual active centers according to claim 1 or 2, a reference electrode, a counter electrode, and an electrolyte, wherein the working electrode is an electrode containing the catalyst, the reference electrode is a Hg / HgO electrode, and the counter electrode is a platinum mesh; argon is passed through the working electrode as a protective gas; and the reaction temperature of the electrocatalytic nitrate synthesis reaction is 25-40°C.