Preparation of Cu / Co bimetallic magnetic catalyst and application of Cu / Co bimetallic magnetic catalyst in electrocatalytic nitrate reduction

Abstract

The invention discloses preparation of a Cu / Co bimetallic magnetic catalyst and application of the Cu / Co bimetallic magnetic catalyst in electro-catalysis nitrate reduction, copper and cobalt bimetallic is uniformly dispersed in nanofibers by adopting an electrostatic spinning technology, and the uniformly dispersed Cu / Co bimetallic magnetic catalyst is generated on the fibers after high-temperature carbonization in a nitrogen atmosphere. The technological operation is simple, and the repeatability is high; according to the process, an electrostatic spinning technology is adopted to prepare the bimetallic catalyst, Cu1Co2 / CNF nanoparticles are well packaged in the prepared nanofibers, the combination mode of the Cu1Co2 / CNF nanoparticles and the nanofibers breaks through a conventional hydrothermal method in the prior art, and the uniformity of the material is greatly improved; the prepared catalyst has good magnetism, regulation and control of active sites and promotion of electron transfer are achieved through an external magnetic field in the process of electro-catalysis nitrate reduction, meanwhile, the stability of the catalyst can be improved, the recycling rate of the catalyst can be increased, and therefore pollution to the environment is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of material chemistry and relates to the preparation of a Cu / Co bimetallic magnetic catalyst and its application in electrocatalytic nitrate reduction. Background Art

[0002] Ammonia (NH3) is an important chemical raw material. In agriculture, ammonia is a key component in the synthesis of nitrogen fertilizers and is crucial for global food production. In industry, ammonia is used to manufacture a variety of products, including explosives, plastics, and fibers. The Haber process is commonly used to synthesize ammonia. However, due to its harsh reaction conditions and the large amount of fossil fuels such as natural gas consumed, it is not only energy-intensive but also produces significant waste. Therefore, the search for a green and sustainable method is crucial.

[0003] Studies have found that electrocatalytic ammonia synthesis has more advantages in terms of renewable energy utilization and adaptability to environmental changes. Compared with the traditional Haber process for ammonia synthesis, it does not require high temperature and high pressure reaction conditions, which greatly reduces energy consumption and equipment requirements. Moreover, the electrocatalytic method uses nitrate, a common pollutant in water, as raw materials, which can greatly improve the green environmental protection of the scheme and has dual environmental protection and economic value. However, traditional catalysts have low active site utilization, resulting in insufficient active hydrogen donors during the reaction process. Existing technologies solve the problem of insufficient active hydrogen supply by introducing precious metals into the catalyst, such as TXiang, et al. Boosting Active Hydrogen Generation via Ruthenium Single Atomsfor Efficient Electrocatalytic Nitrate Reduction to Ammonia. AppliedCatalysis B: Environment and Energy, S0926-3373(24)01257-8. However, the price of precious metal doping is relatively expensive, and doping uniformity is difficult to ensure.

[0004] In recent years, the preparation of bimetallic catalysts has attracted widespread attention compared to conventional noble metal-doped materials. The synergistic effect between the metals in bimetallic catalysts improves reaction performance, and the resulting large amount of hydrogen donors enhances nitrate adsorption. However, common bimetallic catalysts suffer from poor electron transfer and low reaction selectivity, which are major limitations on ammonia synthesis. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a bimetallic modified catalyst with good structural performance, which can improve the electron transfer ability during the reaction and has excellent selectivity for the product ammonia.

[0006] The present invention discloses a Cu / Co bimetallic magnetic catalyst and a preparation method thereof. The method uses electrospinning technology to uniformly disperse copper and cobalt bimetals inside nanofibers, and after high-temperature carbonization under a nitrogen atmosphere, uniformly dispersed bimetallic oxides are generated on the fibers.

[0007] The method specifically includes the following steps: S1. Ultrasonically dissolve (1-3) mmol of cobalt acetylacetonate and 1 mmol of copper acetylacetonate in 10 ml of N,N-dimethylformamide (DMF), then add 1 g of polyacrylonitrile (PAN) thereto, and stir the mixture overnight after it is completely dissolved; S2. Inject the obtained precursor solution into a 10 ml plastic syringe, perform electrospinning at a rate of 50 μL / min under a voltage of 18 KV, the roller rate is between 380-420 r / min, and the distance between the spinning tip and the roller is maintained in the range of 13-16 cm; S3. Place the electrospun fibers in a muffle furnace and perform low-temperature oxidation pretreatment under air conditions; S4. Place the pretreated sample in S3 in a tubular furnace, introduce nitrogen, and perform high-temperature carbonization. The high-temperature carbonization temperature is 600-800 °C, the heating rate is 3-6 °C / min, and the activation time is 1-3 h; S5. Grind the calcined sample in S4 to obtain the Cu / Co bimetallic magnetic catalyst.

[0008] Preferably, ultrasonic dissolution is used in S1, and the mixture is stirred overnight in a beaker. The concentration of the DMF is 99.9% analytical pure, and the relative molecular mass of the PAN is 150,000.

[0009] During electrospinning in S2, the environmental humidity needs to be controlled below 20% to ensure uniform fiber formation and thus improve the stability of electrospinning.

[0010] Preferably, the specific method of S3 is: place the electrospun fibers in a muffle furnace, raise the temperature to 200 °C at a heating rate of 2 °C / min and hold for 2 h, then cool to room temperature and take out the sample.

[0011] Preferably, the molar ratio of copper acetylacetonate to cobalt acetylacetonate is 1:2.

[0012] The present invention also discloses a Cu / Co bimetallic magnetic catalyst prepared by using any of the above methods.

[0013] The present invention also discloses the application of the above Cu / Co bimetallic magnetic catalyst in electrocatalytic nitrate reduction. Magnets are placed at both ends of the electrode solution, and the distance between the two magnets is controlled between 0-20 cm.

[0014] The NH3 production rate changes with the magnetic distance of the catalyst. Preferably, the optimal magnetic field distance of 20 cm corresponds to a NH3 production rate of 95.09 mg h -1 mg -1 , and the Faraday efficiency reaches 84.72%.

[0015] The preparation process principle of the Cu / Co bimetallic magnetic catalyst described in the present invention lies in: the process adopts oxidation pretreatment and high-temperature carbonization. The purpose of pretreatment is to remove water and volatile substances on the surface of the spinning, so that the active components of the catalyst are better exposed, increasing the number of active sites and preliminarily forming or adjusting some chemical bonds through pre-oxidation, so as to make the catalyst structure more stable and prevent phenomena such as collapse or sintering during subsequent high-temperature carbonization; in addition, metal oxides can be formed and the metal pore structure of the catalyst can be adjusted. During high-temperature carbonization, a part of the metal oxides can enter the pores of the fiber, so as to carry out a more sufficient activation reaction during activation. Through high-temperature carbonization, the carbon source on the catalyst surface decomposes and deposits, further improving the stability and anti-sintering ability of the catalyst; finally, grinding is carried out to reduce the particle size of the catalyst and increase the specific surface area, improving the dispersion uniformity of the active components.

[0016] Beneficial effects: Combining various problems in the current field of electrocatalytic nitrate reduction, the present invention synthesizes the excellent bimetallic synergistic effect and excellent magnetism of Cu / Co bimetals, and the prepared magnetic catalyst significantly improves the reduction performance of nitrate on the copper-based catalyst. The generation of magnetism makes the nitrate ions in the reaction system easier to approach the catalyst surface, increasing the concentration of reactants on the catalyst surface, thereby improving the adsorption capacity and reaction rate of nitrate; the generation of magnetism also causes a magneto-electric effect in the catalyst during the reaction process, thereby increasing the electron migration rate in the reaction and fundamentally improving the problem of insufficient active hydrogen donors in the reaction process; the magnetic catalyst is also easy to be separated and recycled after the reaction due to its own magnetism, which provides a catalyst with good catalytic performance, wide application range, low price and environmental friendliness for the electrocatalytic nitrate reduction synthesis ammonia reaction in the electrocatalytic industry, and has broad application prospects in the field of nitrate catalytic purification in the electrocatalytic industry.

[0017] Specific advantages: (1) The process of the present invention is simple to operate, highly repeatable, the waste catalyst is easy to recycle, and it is environmentally friendly; (2) The process uses electrospinning to assemble the bimetal, and its mixing method for the two breaks the conventional hydrothermal technology in the prior art, greatly improving the mixing uniformity of the two; (3) The catalyst prepared by the process has excellent magnetism, has a strong adsorption capacity for nitrate ions, promotes the transfer of electrons in the reaction process, increases the reaction rate and reaction conversion rate; (4) Both copper and cobalt elements involved in the present invention are rich in resources, inexpensive and easy to obtain, and the catalyst preparation process in the reaction process is simple and convenient, suitable for large-scale production. Description of the Drawings

[0018] Figure 1 Powder diffraction characterization of the products of Example 1 and Comparative Examples 1-2; Figure 2 Statistical chart of the grain size of the product of Example 1; Figure 3 Element mapping diagram of the product of Example 1; Figure 4 X-ray photoelectron spectroscopy diagrams of the products of Example 1 and Comparative Example 1; Figure 5 X-ray photoelectron spectroscopy diagrams of the products of Example 1 and Comparative Example 2; Figure 6 IT curve diagram of different magnetic field distances in Example 4; Figure 7 Faraday efficiency and ammonia production rate of different magnetic field distances in Example 4; Figure 8 LSV curve diagrams of Example 4 at magnetic field distances of 0 and 15 cm; Figure 9 Schematic diagram of the setup of the external magnetic field catalytic device in Example 4. Detailed Embodiments

[0019] The following examples further illustrate the content of the present invention, but should not be construed as limiting the present invention. Without departing from the spirit and essence of the present invention, modifications and substitutions made to the methods, steps or conditions of the present invention all fall within the scope of the present invention.

[0020] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

[0021] Preparation of Cu / Co Bimetal Magnetic Catalyst in Example 1 Weigh 1 mmol of copper acetylacetonate and dissolve it in 10 ml of DMF solution. After it is completely dissolved, dissolve 2 mmol of cobalt acetylacetonate in it. Then add 1 g of PAN and stir for 12 h overnight until it is completely dissolved. Inject the obtained mixture into a 10 ml plastic syringe and perform electrospinning at a voltage of 18 kV in an environment with a humidity of less than 20%. The electrospinning rate of the electrospinning machine is 50 μL / min, the roller rate is 400 r / min, and the distance from the electrospinning tip to the roller is 15 cm. After electrospinning, place the obtained fibrous solid in a muffle furnace and pre-treat it at 200 °C for 2 h with a heating rate of 2 °C / min. Finally, carbonize the obtained product at 700 °C in a tube furnace under a nitrogen atmosphere for 2 h with a heating rate of 5 °C / min. Finally, collect the sample and grind it to obtain the catalyst Cu1Co2 / CNF. Example 2

[0022] Prepare the Cu / Co bimetallic magnetic catalyst using the same method as in Example 1, except that weigh 1 mmol of copper acetylacetonate and 1 mmol of cobalt acetylacetonate; the roller rate is 380 r / min, and the distance from the electrospinning tip to the roller is 13 cm; carbonize at 600 °C for 3 h with a heating rate of 3 °C / min. Example 3

[0023] Prepare the Cu / Co bimetallic magnetic catalyst using the same method as in Example 1, except that weigh 1 mmol of copper acetylacetonate and 3 mmol of cobalt acetylacetonate; the roller rate is 420 r / min, and the distance from the electrospinning tip to the roller is 16 cm; carbonize at 800 °C for 1 h with a heating rate of 6 °C / min. Comparative Example 1

[0024] Weigh 3 mmol of copper acetylacetonate and dissolve it in 10 ml of DMF solution. Then add 1 g of PAN and stir for 12 h overnight until it is completely dissolved. Inject the obtained mixture into a 10 ml plastic syringe and perform electrospinning at a voltage of 18 kV in an environment with a humidity of less than 20%. The electrospinning rate of the electrospinning machine is 50 μL / min, the roller rate is 400 r / min, and the distance from the electrospinning tip to the roller is 15 cm. After electrospinning, place the obtained fibrous solid in a muffle furnace and pre-treat it at 200 °C for 2 h with a heating rate of 2 °C / min. Finally, carbonize the obtained product at 700 °C in a tube furnace under a nitrogen atmosphere for 2 h with a heating rate of 5 °C / min. Finally, collect the sample and grind it to obtain the catalyst Cu3 / CNF. Comparative Example 2

[0025] Weigh 3 mmol of cobalt acetylacetonate and dissolve it in 10 ml of DMF solution. Then add 1 g of PAN to it. After it is completely dissolved, stir it for 12 h overnight. Inject the obtained mixture into a 10 ml plastic syringe and perform electrospinning at a voltage of 18 kV in an environment with a humidity of less than 20%. The electrospinning rate of the electrospinning machine is 50 μL / min, the roller rate is 400 r / min, and the distance between the electrospinning tip and the roller is 15 cm. After electrospinning, place the obtained fibrous solid in a muffle furnace and pre-treat it at 200 °C for 2 h with a heating rate of 2 °C / min. Finally, carbonize the obtained product at 700 °C in a tube furnace under a nitrogen atmosphere for 2 h with a heating rate of 5 °C / min. Finally, collect the sample and grind it to obtain the catalyst Co3 / CNF.

[0026] Application of Cu / Co Bimetallic Magnetic Catalyst in Electrochemical Reduction of Nitrate Weigh 4 mg of the Cu / Co bimetallic magnetic catalyst prepared in Example 1. Immerse the carbon cloth in concentrated nitric acid for 20 h and then rinse it thoroughly with a large amount of deionized water. Mix 500 μL of deionized water, 450 μL of absolute ethanol, and 50 μL of naphthol to prepare a solution for dissolving the catalyst. After mixing evenly, ultrasonicate it for 30 min to prepare the ink.

[0027] First, fix the carbon cloth with an electrode clamp. Drop 50 μL of the prepared ink onto the front side of the carbon cloth and dry it. After drying, continue to drop 50 μL onto the back side of the carbon cloth. Fix the electrode clamp in the reaction chamber. Add 50 ml of 0.1 mol potassium sulfate solution to the anode and 50 ml of a mixed solution of 0.1 mol potassium sulfate and potassium nitrate to the cathode. Place two magnets at both ends of the electrode and measure and record the distance between the two magnets.

[0028] Perform an IT curve test at this distance, further calculate the Faraday efficiency and ammonia production rate under an external magnetic field, and then adjust the distance. Select 0 cm, 6 cm, 9 cm, 12 cm, 15 cm, and 20 cm respectively for multiple measurements and calculations. As Figure 7 shown, as the distance of the external magnetic field increases, the ammonia production rate increases, and the change trend of the Faraday efficiency cannot be judged. The optimal magnetic field distance of 20 cm corresponds to a catalyst NH3 production rate of 95.09 mg h -1 mg -1 , and the Faraday efficiency reaches 84.72%.

[0029] Figure 1Powder diffraction characterization was performed on the different metal catalysts (Cu1Co2 / CNF, Cu3 / CNF, Co3 / CNF) obtained in Example 1 and Comparative Examples 1-2. Powder diffraction data collection was completed on a Shimadzu XRD6000 diffractometer in Japan, with a tube voltage of 40 KV, a tube current of 30 mA, and graphite-monochromated Cu Kα radiation. Data collection was performed in θ / 2θ scanning mode, continuously scanned in the range of 10° to 80°, and the scanning speed was 3° / min. The powder diffraction results are shown in Figure 1 , and the three peaks at 43.2, 50.4, and 74.1 represent the (111) and (200) diffraction peaks of copper, and the three peaks at 44.2, 51.5, and 75.9 represent the (2) diffraction peaks of cobalt. Compared with the samples Cu3 / CNF and Co3 / CNF, the appearance of the copper and cobalt double peaks in Cu1Co2 / CNF proves that the bimetal is well doped into the Cu1Co2 / CNF sample.

[0030] Figure 2 , 3 are the grain size statistical chart and element mapping diagram of the product of Example 1. It can be well reflected from the size statistical chart that the average metal particle size is about 17.2 nm. The element mapping diagram shows that Cu in Cu1Co2 / CNF shows a highly dispersed state, and Co exists in the form of nanoparticles, which is consistent with the results of X-ray powder diffraction characterization.

[0031] Figure 4 , 5 are the X-ray photoelectron spectroscopy diagrams of the products of Example 1 and Comparative Examples 1-2 respectively, further indicating that the doping of the bimetal Cu1Co2 can make the catalyst have richer valence states. Compared with Comparative Examples 1-2, the doping of the bimetal causes changes in the surface active sites of the catalyst, forming a good bimetal synergistic effect, and due to the magnetic influence of cobalt itself, it can generate a magnetic composite material with better performance.

[0032] Figure 6 is the IT curve diagram of Example 4. It can be seen that as the magnetic field distance changes, the current density will also change to a certain extent, and the IT curve diagram is relatively flat, indicating that the catalyst has high stability. Subsequently, the Faraday efficiency and ammonia production rate can be calculated according to the IT curve diagram, and the results are as shown in Figure 7 . It can be found that as the applied magnetic field distance increases, the ammonia production rate increases, indicating that controlling the magnetic field distance can make the electrocatalytic reaction proceed more thoroughly.

[0033] Figure 8It is the LSV curve diagram of Example 4 when the magnetic field distance is 0 and 15 cm. It can be observed that the current density becomes larger under the condition of adding a magnetic field, making its performance more excellent. This further illustrates that magnetism can enable the electrocatalytic reaction to proceed at a higher rate, and also reflects the superiority and foresight of the magnetic bimetallic catalyst prepared by the present invention.

[0034] Figure 9 It is a schematic diagram of the specific device for adding an external magnetic field to the catalyst in Example 4. Since the metal itself has some magnetism, we tried to directly place an external magnetic field outside the reaction chamber. We placed two magnets on both sides of the reaction chamber and adjusted the magnetic field strength around the metal catalyst by changing the distance between the magnets. The distance between the two magnets was set from 0 to 20 cm, resulting in the generation of electromagnetic induction, increasing the electron transfer ability and the electro-migration rate. Experiments found that as the distance between the magnets increased, the ammonia production rate gradually increased, and the change trend of the Faraday efficiency was not very obvious.

Claims

1. A preparation method of a Cu / Co bimetallic magnetic catalyst, characterized in that, The method uses electrospinning technology to uniformly disperse copper-cobalt bimetals inside the nanofibers. After high-temperature carbonization under a nitrogen atmosphere, a uniformly dispersed Cu / Co bimetallic magnetic catalyst is generated on the fibers.

2. The preparation method of the Cu / Co bimetallic magnetic catalyst according to claim 1, wherein The method specifically includes the following steps: S1. Ultrasonically dissolve (1-3) mmol of cobalt acetylacetonate and 1 mmol of copper acetylacetonate in 10 ml of N,N-dimethylformamide, and then add 1 g of polyacrylonitrile thereto. After it is completely dissolved, stir the mixture overnight to obtain a precursor solution; S2. Inject the obtained precursor solution into a 10 ml plastic syringe, and perform electrospinning at a rate of 50 μL / min under a voltage of 18 KV. The roller speed is between 380-420 r / min, and the distance between the spinning tip and the roller is maintained in the range of 13-16 cm; S3. Place the electrospun fibers in a muffle furnace and perform low-temperature oxidation pretreatment under air conditions; S4. Place the pretreatment sample of S3 in a tubular furnace, introduce nitrogen, and perform high-temperature carbonization. The high-temperature carbonization temperature is 600-800 °C, the heating rate is 3-6 °C / min, and the activation time is 1-3 h; S5. Take the calcined sample of S4 and grind it to obtain a Cu / Co bimetallic magnetic catalyst.

3. The preparation method of the Cu / Co bimetallic magnetic catalyst according to claim 2, characterized in that, The N,N-dimethylformamide used in S1 has a concentration of 99.9% analytical pure, and the relative molecular mass of polyacrylonitrile is 150,000.

4. The preparation method of the Cu / Co bimetallic magnetic catalyst according to claim 2, characterized in that, The molar ratio of the copper acetylacetonate: cobalt acetylacetonate is 1:

2.

5. The preparation method of the Cu / Co bimetallic magnetic catalyst according to claim 2, characterized in that, During electrospinning in S2, the environmental humidity needs to be controlled below 20%.

6. The preparation method of the Cu / Co bimetallic magnetic catalyst according to claim 2, characterized in that, The specific method of S3 is: Take the spun fibers in a muffle furnace, heat them to 200 °C at a heating rate of 2 °C / min and hold for 2 h, cool to room temperature and then take out the sample.

7. The Cu / Co bimetallic magnetic catalyst prepared by the preparation method described in any one of claims 1-6.

8. The application of the Cu / Co bimetallic magnetic catalyst described in claim 7 in electrocatalytic nitrate reduction.

9. The application according to claim 8, wherein Place a magnet at both ends of the electrode solution and control the distance between the two magnets to be between 0-20 cm.

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