MOF (Metal Organic Framework) catalyst containing high-valence copper as well as preparation method and application of MOF catalyst

Abstract

The invention belongs to the technical field of material chemistry, and particularly relates to an MOF catalyst containing high-valence copper and a preparation method and application of the MOF catalyst. According to the invention, Ag is doped on a Cu-based metal organic framework material framework through an ion exchange method, then the Ag is mixed with a binder solution to prepare slurry, the slurry is coated on an electrode substrate, the electrode substrate is dried to serve as a working electrode, constant potential or circulating potential is applied to the working electrode in a preset voltage range in an electrochemical system containing an electrolyte, and thus the Cu-based metal organic framework material is obtained. Cu (III) is generated in situ through electrochemical reconstruction, and the MOF catalyst containing high-valence copper is obtained. The MOF catalyst containing high-valence copper has excellent ammoxidation reaction activity and stability, is especially suitable for high-conversion-rate and high-selectivity ammoxidation reaction to prepare nitrite, and is suitable for industrial induced production application.

Description

Technical Field

[0001] The present application belongs to the field of material chemistry technology, and more specifically, relates to a MOF catalyst containing high-valent copper, a preparation method thereof, and an application thereof. Background Art

[0002] With the proposal of the "dual carbon" strategic goals of carbon peak and carbon neutrality, the energy structure is facing a major demand for transformation from traditional fossil energy to clean energy. Among the many secondary energy carriers, ammonia energy has the advantages of abundant sources, high combustion calorific value, and zero carbon emissions. Therefore, achieving efficient conversion of ammonia is crucial to fully utilizing ammonia energy. However, the current ammonia oxidation reaction has problems such as slow kinetics and large overpotential, which seriously restricts the development and utilization of ammonia energy. In addition, the high corrosiveness of ammonia and the strong complexing ability between the current precious metal-based catalytic materials and nitrogen-containing intermediates can easily lead to poisoning and deactivation of precious metal-based catalytic materials, resulting in poor durability, thereby reducing the rate of ammonia electrocatalytic oxidation reaction, which has become an important bottleneck restricting the development of this technology.

[0003] Therefore, the development of low-cost, highly active and efficient electrocatalytic ammonia oxidation catalysts is a key issue that needs to be urgently addressed in this field. Summary of the Invention

[0004] In response to the defects of the prior art, the purpose of this application is to provide a MOF catalyst containing high-valent copper and its preparation method and application, aiming to solve the problems of low catalytic activity, low ammonia conversion efficiency, and unsuitability for industrial application of existing catalysts used for electrocatalytic ammonia oxidation reactions. It is particularly suitable for high-efficiency, low-energy consumption electrocatalytic ammonia oxidation to produce nitrite.

[0005] To achieve the above objectives, in a first aspect, the present application provides a method for preparing a MOF catalyst containing high-valent copper, comprising the following steps: S1. Mixing a water-soluble divalent copper salt, an organic ligand, and a dispersing solvent to conduct a hydrothermal reaction, then collecting the precipitate by centrifugation, washing, and drying to obtain a Cu-based metal-organic framework material; S2, mixing the Cu-based metal-organic framework material, a water-soluble divalent silver salt, and a reaction solvent to perform an ion exchange reaction, then collecting the precipitate by centrifugation, washing, and drying to obtain a Ag-doped Cu-based metal-organic framework material; S3. The Ag-doped Cu-based metal-organic framework material, a conductive agent and a binder solution are mixed to form a composite slurry, and the slurry is coated on at least one surface of the electrode substrate and dried to obtain a working electrode. The working electrode is then placed in an electrochemical system containing an electrolyte, and a constant potential or a cyclic potential is applied to the working electrode within a preset voltage range, so that the Ag-doped Cu-based metal-organic framework material undergoes in-situ electrochemical reconstruction to generate Cu(III). The reconstructed working electrode is washed and dried to obtain the MOF catalyst containing high-valent copper.

[0006] Preferably, the molar ratio of the water-soluble divalent inorganic copper salt to the organic ligand is (1.5-2):1.

[0007] Preferably, the molar ratio of the copper element in the water-soluble divalent inorganic copper salt to the silver element in the water-soluble inorganic silver salt is (20-25):1.

[0008] Preferably, the water-soluble divalent copper salt is one or more of copper chloride, copper sulfate, copper acetate, copper nitrate and copper nitrate hydrate; and / or, The above organic ligand is trimesic acid; and / or, The above-mentioned dispersing solvent is one or more of methanol, ethanol, N,N-dimethylformamide, N,N-diethylformamide and deionized water; The water-soluble divalent silver salt is one or more of silver nitrate and silver nitrate hydrate.

[0009] Preferably, in step S1, the temperature of the hydrothermal reaction is 50° C. to 100° C., and the time of the hydrothermal reaction is 12 h to 24 h.

[0010] Preferably, in step S2, the ion exchange reaction time is 10 h to 15 h.

[0011] Preferably, in step S3, the conductive agent is a conductive agent selected from carbon black, graphite, carbon fiber, graphene, and carbon nanotubes.

[0012] Preferably, the binder solution is formed by uniformly mixing the binder and the dispersing solvent, wherein the binder is Nafion and / or polyvinylidene fluoride.

[0013] Preferably, in step S3, the electrode substrate is carbon fiber paper, nickel foam or titanium sheet; and / or, The electrolyte is an alkaline solution selected from potassium hydroxide solution or sodium hydroxide solution.

[0014] Preferably, in step S3, the electrochemical system is a three-electrode system, comprising the working electrode, the counter electrode and the reference electrode.

[0015] Preferably, in step S3, the preset voltage range is 1-1.8 V RHE The potential was applied in the form of cyclic voltammetry scanning.

[0016] Preferably, the scan rate of the cyclic voltammetry scan is 5 mV / s to 100 mV / s, and the number of cycles is 10 to 100 times.

[0017] Further preferably, the scan rate of the cyclic voltammetry scan is 30 mV / s to 80 mV / s, and the number of cycles is 30 to 80 times.

[0018] In a second aspect, the present application provides a MOF catalyst containing high-valent copper prepared by the above-mentioned preparation method.

[0019] In a third aspect, the present application provides an application of the above-mentioned MOF catalyst containing high-valent copper in an electrocatalytic ammonia oxidation reaction.

[0020] Preferably, the product of the electrocatalytic ammonia oxidation reaction includes nitrite.

[0021] This application intends to construct a high-valent copper-based MOF catalyst through a multi-level structural design, which aims to solve the competitive adsorption of reactants and hydroxyl anions at the active sites and provide technical and economic support for the industrialization of ammonia energy.

[0022] In general, the above technical solutions conceived by this application have the following technical advantages compared with the existing technologies: (1) In this application, Ag is doped on the skeleton of a Cu-based metal organic framework material by an ion exchange method, and then the slurry is mixed with a binder solution to form a slurry, which is then coated on an electrode substrate. After drying, it is used as a working electrode. A constant potential or a cyclic potential is applied to the working electrode in an electrochemical system containing an electrolyte within a preset voltage range. The doped Ag can effectively adjust the electronic structure of the Cu site under the application of an external electric field, significantly reduce the energy barrier for the conversion of Cu(II) to Cu(III), and promote the conversion of Cu(II) to Cu(III). Cu(III) is generated in situ through electrochemical reconstruction to obtain a MOF catalyst containing high-valent copper (abbreviated as CuAg-OH-BTC). At the same time, the in situ generated Cu(III) can effectively enhance the electron density of CuAg-OH-BTC near the Fermi level, making CuAg-OH-BTC have excellent ammonia oxidation reaction activity and durability, which is beneficial to the adsorption / decomposition of ammonia oxidation reaction intermediates and inhibits the progress of competing reactions such as oxygen evolution reaction (OER), especially improving the efficiency of ammonia oxidation to prepare nitrite. The preparation method provided in this application has the advantages of simple process, low cost, and easy industrial production.

[0023] (2) The MOF catalyst containing high-valent copper provided in this application is used for electrocatalytic ammonia oxidation reaction, has excellent catalytic activity, can achieve high conversion rate and high selectivity of ammonia oxidation reaction to prepare nitrite, and is suitable for industrial induced production application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 1 is a schematic flow chart of a method for preparing a MOF catalyst containing high-valent copper provided in an embodiment of the present application; Figure 2 This is a scanning electron microscope image of CuAg-OH-BTC prepared in Example 1 of the present application; Figure 3 This is a transmission electron micrograph of CuAg-OH-BTC prepared in Example 1 of the present application, wherein the scale of content (a) is 50 nm and the scale of content (b) is 2 nm; Figure 4 This is the EDS graph of CuAg-OH-BTC prepared in Example 1 of the present application; Figure 5 This is a scanning electron micrograph of the CuAg-BTC prepared in Comparative Example 2 of the present application, wherein the scale of content (a) is 500 nm and the scale of content (b) is 200 nm; Figure 6 FTIR images of the catalysts prepared in Example 1 and Comparative Examples 1 to 3 of the present application; Figure 7 1 is the XRD pattern of the catalysts prepared in Example 1 and Comparative Examples 1 to 3 of the present application; wherein (a) is CuAg-OH-BTC and CuAg-BTC, and (b) is Cu-BTC and Cu-OH-BTC MOF; Figure 8 1 is the XPS graph of the catalysts prepared in Example 1 and Comparative Examples 1 to 3 of the present application; Figure 9 This is an XPS fine image of Cu in the catalysts prepared in Example 1 and Comparative Examples 1 to 3 of the present application; wherein content (a) is CuAg-OH-BTC and Cu-OH-BTC, and content (b) is Cu-BTC and CuAg-BTC; Figure 10 This is the XPS fine map of Ag in the CuAg-OH-BTC prepared in Example 1 of the present application and the CuAg-BTC prepared in Comparative Example 2; Figure 11 d-band diagrams of the catalysts prepared in Example 1 and Comparative Examples 1 to 3 of the present application; Figure 12 1 is a graph showing the change in capacitance current of the catalysts prepared in Example 1 and Comparative Examples 1 to 3 of the present application at different scan rates; Figure 13The catalyst prepared in Example 1 and Comparative Examples 1 to 3 of the present application reacts with nitrite (NO2 - ) selectivity and yield; Figure 14 The catalyst prepared in Example 1 and Comparative Examples 1 to 3 of the present application is effective for ammonia (NH4 + ) conversion rate and content; Figure 15 The CuAg-OH-BTC prepared in Example 1 of the present application is at 1.6V RHE The constant voltage test was carried out under the conditions of different time periods of ammonia (NH4 + ) conversion rate and content; Figure 16 The CuAg-OH-BTC prepared in Example 1 of the present application is at 1.6V RHE The constant voltage test was carried out under the conditions of different time periods, and the nitrite (NO2 - ) selectivity and cumulative yield. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0026] In the description of this application, it should be understood that the term "and / or" describes an association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. The symbol " / " herein indicates that the associated objects are in an "or" relationship, for example, A / B means either A or B.

[0027] In the specification and claims of this application, the terms "first" and "second" and so on are used to distinguish different objects rather than to describe the specific order of objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0028] In the description of the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0029] In the description of the embodiments of the present application, unless otherwise specified, “plurality” means two or more.

[0030] The present application provides a method for preparing a MOF catalyst containing high-valent copper, comprising the following steps: S1, mixing a water-soluble divalent copper salt, an organic ligand, and a dispersing solvent for a hydrothermal reaction, then collecting the precipitate by centrifugation, washing, and drying to obtain a Cu-based metal-organic framework material, i.e., Cu-BTC; S2, mixing the Cu-based metal-organic framework material, a water-soluble divalent silver salt and a reaction solvent to carry out an ion exchange reaction, then collecting the precipitate by centrifugation, washing and drying to obtain a Cu-based metal-organic framework material doped with Ag, i.e., CuAg-BTC; S3. The Ag-doped Cu-based metal-organic framework material, a conductive agent and a binder solution are mixed to form a composite slurry, and the slurry is coated on at least one surface of the electrode substrate and dried to obtain a working electrode. The working electrode is then placed in an electrochemical system containing an electrolyte, and a constant potential or a cyclic potential is applied to the working electrode within a preset voltage range, so that the Ag-doped Cu-based metal-organic framework material undergoes in-situ electrochemical reconstruction to generate Cu(III). The reconstructed working electrode is washed and dried to obtain a MOF catalyst containing high-valent copper, i.e., CuAg-OH-BTC.

[0031] In some embodiments, in step S1, the molar ratio of the water-soluble divalent inorganic copper salt and the organic ligand is (1.5~2):1. By regulating the molar ratio of the copper salt and the organic ligand, the copper content in the MOF material can be regulated, the morphology, pore structure and stability of the material can be controlled, and the catalytic activity of the material can be improved.

[0032] In some embodiments, in step S1, the water-soluble divalent inorganic copper salt is one or more of copper chloride, copper sulfate, copper acetate, copper nitrate and copper nitrate hydrate.

[0033] In some embodiments, the copper nitrate hydrate includes but is not limited to Cu(NO3)2·2H2O, Cu(NO3)2·3H2O, Cu(NO3)2·5H2O, Cu(NO3)2·6H2O, etc.

[0034] In some embodiments, in step S1, the organic ligand is trimesic acid (H3BTC).

[0035] In the present application, the above-mentioned dispersing solvent can ensure that all reactants can be evenly dispersed, which is conducive to the full and uniform progress of the reaction. The present application does not limit the specific type of the above-mentioned dispersing solvent, and a solvent with good solubility is preferred. In some embodiments, the above-mentioned dispersing solvent is one or more of methanol, ethanol, N,N-dimethylformamide, N,N-diethylformamide and deionized water.

[0036] In some embodiments, the dispersion solvent is a mixed solution of N,N-dimethylformamide, ethanol and deionized water.

[0037] In some embodiments, in order to allow the hydrothermal reaction to proceed fully, the water-soluble divalent inorganic copper salt and the organic ligand can be dispersed in a dispersion solvent respectively to prepare a water-soluble divalent inorganic copper salt solution and an organic ligand solution, and then the two solutions are mixed for hydrothermal treatment.

[0038] In some embodiments, in step S1, the temperature of the hydrothermal reaction is 50° C. to 100° C., and the time of the hydrothermal reaction is 12 h to 24 h.

[0039] It is understood that this application does not limit the drying method described above. It is understood that selecting an appropriate drying method and adjusting the drying time and temperature appropriately based on the solvent used are all within the scope of this application. In some embodiments, the drying temperature may be 50°C to 70°C, and the drying time may be 10 to 15 hours.

[0040] In some embodiments, the molar ratio of the copper element in the water-soluble divalent inorganic copper salt to the silver element in the water-soluble inorganic silver salt is (20-25):1. By adjusting the ratio of the two, the doping amount of Ag in the Cu-based metal-organic framework material is controlled.

[0041] In some embodiments, the water-soluble divalent silver salt is one or more of silver nitrate and silver nitrate hydrate.

[0042] In some embodiments, in step S2, the reaction solvent can provide a reaction environment suitable for the ion exchange reaction and can disperse the Cu-based metal-organic framework material and the water-soluble divalent silver salt. The reaction solvent can be, but is not limited to, an alcohol solvent or deionized water. In some embodiments, the alcohol solvent can be ethanol or propanol.

[0043] In some embodiments, in step S2, the ion exchange reaction time is 10 h to 15 h.

[0044] In some embodiments, in order to make the ion exchange reaction more gentle, the above-mentioned Cu-based metal-organic framework material can be dispersed in deionized water, and then a water-soluble divalent silver salt is added to carry out the ion exchange reaction; or the water-soluble divalent silver salt can be dispersed in deionized water, and then the Cu-based metal-organic framework material is added to carry out the ion exchange reaction. In some embodiments, in order to improve the efficiency of the ion exchange reaction, the reaction can be promoted by stirring. It is understandable that the present application has no special limitation on the amount of deionized water used. As long as the ion exchange reaction can be fully carried out, it is within the scope of protection of this application.

[0045] In some embodiments, in step S3, the conductive agent is one or more of carbon black, graphite, carbon fiber, graphene, and carbon nanotubes.

[0046] In some embodiments, in step S3, the binder solution is formed by mixing a binder and the dispersing solvent, which can regulate the fluidity of the composite slurry. In some embodiments, the binder solution is formed by mixing a binder and an alcohol / water mixed solution. In some embodiments, the binder is Nafion and / or polyvinylidene fluoride, which can enhance the adhesion of the Ag-doped Cu-based metal-organic framework material to the surface of the electrode substrate and prevent it from falling off.

[0047] In some embodiments, in step S3, the electrode substrate is carbon fiber paper, nickel foam or titanium sheet.

[0048] In some embodiments, in step S3, the method of coating the above-mentioned coating on at least one surface of the electrode substrate includes but is not limited to drip coating, coating, spraying, dipping, roller coating, etc.

[0049] In some embodiments, in step S3, the electrolyte is an alkaline solution, which provides an ionic environment and participates in the electrochemical reconstruction process. In some embodiments, the alkaline solution is selected from potassium hydroxide solution or sodium hydroxide solution, and the concentration of the alkaline solution is 0.5 mmol / L to 2 mmol / L.

[0050] In some embodiments, in step S3, the electrochemical system is a three-electrode system, comprising the working electrode, a counter electrode, and a reference electrode. In some embodiments, the counter electrode is a platinum electrode, a gold electrode, or a graphite electrode, preferably a platinum electrode. In some embodiments, the reference electrode is a silver / silver chloride electrode.

[0051] In some embodiments, in step S3, the preset voltage range is 1-1.8 V. RHE The potential is applied in a cyclic voltammetric scanning manner, which can cause Cu(II) to undergo electrochemical reconstruction and generate high-valent copper, namely Cu(III), in situ.

[0052] In some embodiments, the scan rate of the cyclic voltammetry scan is 5 mV / s to 100 mV / s, and the number of cycles is 10 to 100 times.

[0053] In a preferred embodiment, the scan rate of the cyclic voltammetry scan is 30 mV / s~80 mV / s, and the number of cycles is 30~80 times. The electrochemical reaction rate and the degree of reconstruction are regulated by controlling the scan rate and the number of cycles. When the scan rate is too low / the number of cycles is too small, Cu(III) cannot be effectively generated in situ by electrochemical reconstruction, resulting in insignificant improvement in the performance of the catalyst; when the scan rate is too high / the number of cycles is too large, the structure of the catalyst is severely damaged, the structural stability deteriorates, and it is not conducive to recycling.

[0054] This application utilizes an ion exchange method to dope Ag onto the Cu-based metal-organic framework (MOF) framework. This slurry is then mixed with a binder solution to form a slurry, coated onto an electrode substrate, and dried to serve as a working electrode. In an electrochemical system containing an electrolyte, a constant potential or cycling potential is applied to the working electrode within a preset voltage range. The doped Ag effectively modulates the electronic structure of the Cu sites, significantly reducing the energy barrier for the conversion of Cu(II) to Cu(III). This electrochemical reconstruction generates Cu(III) in situ, yielding a MOF catalyst containing high-valent copper (abbreviated as CuAg-OH-BTC). Furthermore, the in situ generated Cu(III) effectively enhances the electron density of the CuAg-OH-BTC near the Fermi level, facilitating the adsorption and cleavage of intermediates in the ammonia oxidation reaction and inhibiting competing reactions such as the oxygen evolution reaction (OER). This results in CuAg-OH-BTC exhibiting excellent ammonia oxidation activity and durability, particularly improving the efficiency of ammonia conversion to nitrite. The preparation method provided herein offers advantages such as simplicity, low cost, and ease of industrial production.

[0055] Based on this, the present application provides a MOF catalyst containing high-valent copper prepared by the above preparation method, namely CuAg-OH-BTC.

[0056] The CuAg-OH-BTC provided in the present application can be used as a catalyst for the electrocatalytic oxidation reaction of ammonia. Based on this, the present application also provides the use of the above-mentioned MOF catalyst containing high-valent copper in the electrocatalytic ammonia oxidation reaction.

[0057] In some embodiments, the product of the electrocatalytic ammonia oxidation reaction includes nitrite.

[0058] In some embodiments, the MOF catalyst containing high-valent copper is RHE A 12-h constant voltage test was carried out under the same conditions, and the conversion rate of ammonia could reach 92.8%, and the selectivity of nitrite could reach more than 90%. It is possible to achieve high conversion rate and high selectivity of ammonia oxidation reaction to prepare nitrite, has excellent stability, and is suitable for industrial induced labor applications.

[0059] It should be understood that materials of the same or similar type, model, quality, properties, or functions as the reagents and instruments used in the following examples can be used to implement this application. The experimental methods used in the following examples are all conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial sources.

[0060] The following are examples and comparative examples: Example 1 (1) Preparation of Cu-BTC by hydrothermal method 1.25 g of the water-soluble divalent inorganic copper salt Cu(NO₃)₂·3H₂O and 0.625 g of the organic ligand 1,3,5-benzenetricarboxylic acid (H₃BTC) were dissolved in 15 mL of a dispersion solution containing DMF, CH₃CH₂OH, and H₂O in a 1:1:1 volume ratio. This yielded a water-soluble divalent inorganic copper salt solution (Cu(NO₃)₂·3H₂O solution) and an organic ligand solution (H₃BTC solution). The water-soluble divalent inorganic copper salt solution was slowly added to the organic ligand solution and stirred for 30 minutes. The mixture was then sealed in a hydrothermal autoclave, heated to 80°C for 24 hours, and cooled to room temperature. The mixture was then centrifuged to obtain a light blue precipitate, which was washed alternately with DMF, CH₃CH₂OH, and H₂O. The washed precipitate was then dried in a vacuum oven at 60°C for 12 hours to obtain a Cu-based metal-organic framework (Cu-BTC).

[0061] (2) Preparation of CuAg-BTC 1 g of the above-mentioned Cu-BTC was ultrasonically dispersed in water, and then 0.036 g of water-soluble divalent inorganic silver salt AgNO3 was added. After stirring for 12 h, the precipitate was collected by centrifugation and washed alternately with anhydrous ethanol and deionized water. The washed precipitate was then vacuum dried at 60°C for 12 h to obtain an Ag-doped Cu-based metal-organic framework material, referred to as CuAg-BTC.

[0062] (3) Preparation of CuAg-OH-BTC by in situ electrochemical reconstruction 4 mg of the above-mentioned CuAg-BTC was dispersed in 1 mL of a mixture (the volume ratio of C3H8O, H2O, and Nafion in the mixture was 30:69:1) and 20% by weight of carbon black was added. The mixture was ultrasonicated for 30 min to obtain a uniform slurry. 200 μL of the above-mentioned slurry was drop-coated on a conductive substrate (carbon fiber paper CFP with a length and width of 1 cm × 1 cm) to obtain a CuAg-BTC loading of 800 μL / cm 2 The CFP was dried and used as the working electrode, platinum as the counter electrode, and Ag / AgCl as the reference electrode. Cyclic voltammetry (CV) was performed 60 times in an alkaline electrolyte (1 mmol / L KOH solution) at a scan rate of 50 mV / s in the voltage range of 1-1.8 V. RHE , causing the CuAg-BTC loaded on the CFP working electrode to undergo in situ electrochemical reconstruction, and then dried at 40~80℃ to obtain a MOF catalyst containing high-valent copper, referred to as CuAg-OH-BTC.

[0063] Comparative Example 1 The catalyst provided in this comparative example is a catalyst that has not been Ag-doped and has not been subjected to in-situ electrochemical reconstruction, namely, Cu-BTC, and its preparation method is the same as step (1) of Example 1.

[0064] Comparative Example 2 The catalyst provided in this comparative example is a catalyst that is Ag-doped but not subjected to in-situ electrochemical reconstruction, namely, CuAg-BTC, and its preparation method is the same as step (1) and step (2) of Example 1.

[0065] Comparative Example 3 The catalyst provided in this comparative example is a catalyst that is not Ag-doped but undergoes in-situ electrochemical reconstruction, namely, Cu-OH-BTC, and its preparation method comprises the following steps: (1) Preparation of Cu-BTC by hydrothermal method is the same as step (1) in Example 1.

[0066] (2) Preparation of Cu-OH-BTC by in situ electrochemical reconstruction 4 mg of the above Cu-BTC was dispersed in 1 mL of the mixture (the volume ratio of C3H8O, H2O and Nafion in the mixture was 30:69:1), and ultrasonicated for 30 min to obtain a uniform slurry. 200 μL of the above slurry was drop-coated on a conductive substrate (carbon fiber paper CFP with a length and width of 1 cm × 1 cm) to obtain a Cu-BTC loading of 800 μL / cm 2 The CFP was then used as the working electrode, the platinum sheet as the counter electrode, and the Ag / AgCl as the reference electrode. Cyclic voltammetry (CV) was performed 60 times in an alkaline electrolyte (1 mmol / L KOH solution) at a scan rate of 50 mV / s. The voltage range was 1-1.8 V. RHE , so that the Cu-BTC loaded on the CFP working electrode undergoes in situ electrochemical reconstruction, and then is dried at 40~80℃ to obtain Cu-OH-BTC.

[0067] Example 2 The CuAg-OH-BTC prepared in Example 1 was characterized.

[0068] Figure 2 This is the scanning electron microscope image of CuAg-OH-BTC. Figure 3 Content (a) is a transmission electron microscope image of CuAg-OH-BTC at a scale of 50nm. Figure 3 Content (b) is a transmission electron microscopy image of CuAg-OH-BTC at a scale of 2 nm. It can be seen that CuAg-OH-BTC has a nanorod-like structure with a diameter of about 50~100 nm.

[0069] Figure 4This is the EDS image of CuAg-OH-BTC. It can be seen that C, O, Ag and Cu elements exist in CuAg-OH-BTC and are uniformly dispersed.

[0070] Figure 5 Content (a) is a scanning electron microscope image of CuAg-BTC at a scale of 500nm. Figure 5 Content (b) is a scanning electron micrograph of CuAg-BTC at a scale of 200 nm. It can be seen that compared with CuAg-BTC, the CuAg-OH-BTC after in situ electrochemical reconstruction in Example 1 still maintains its original nanorod structure without obvious structural damage, indicating that in situ electrochemical reconstruction does not significantly change the microstructure of the catalyst.

[0071] Figure 6 The FTIR images of the catalysts prepared in Example 1 and Comparative Examples 1-3 show that the Ag atoms introduced into CuAg-BTC partially replace the Cu atoms in Cu-BTC to form CuAg-BTC, resulting in a slight decrease in the intensity of the MO peak. After in situ electrochemical reconstruction of CuAg-BTC, the functional group types of CuAg-OH-BTC remain unchanged, but the intensities differ slightly, indicating that the MOF structure of CuAg-OH-BTC has undergone some changes.

[0072] Figure 7 Content (a) and Figure 7 Content (b) is the XRD pattern of the catalysts prepared in Example 1 and Comparative Examples 1 to 3. It can be seen that CuAg-OH-BTC still retains characteristic peaks similar to those of the other three catalysts, but the intensity of the corresponding characteristic peaks is slightly weakened.

[0073] Figure 8 The XPS graphs of the catalysts prepared in Example 1 and Comparative Examples 1 to 3 show that C, O, Ag, and Cu are present in CuAg-OH-BTC and CuAg-BTC; and C, O, and Cu are present in Cu-BTC and Cu-OH-BTC.

[0074] Figure 9 Content (a) and Figure 9 Content (b) is the XPS fine map of Cu in the catalysts prepared in Example 1 and Comparative Examples 1 to 3. It can be seen that the Cu 3+ / Cu 2+ The peak area ratio of Cu(II) is significantly higher than that of Cu-OH-BTC, which indicates that the introduced Ag atoms may interact with Cu and promote the conversion of Cu(II) to Cu(III) under the application of an external electric field.

[0075] Figure 10The XPS fine images of Ag in the catalysts prepared in Example 1 and Comparative Example 2 show that the valence state of Ag in the CuAg-OH-BTC that underwent in-situ electrochemical reconstruction did not change significantly.

[0076] Figure 11 The d-band center spectra of the catalysts prepared in Example 1 and Comparative Examples 1 to 3 show that the d-band of CuAg-OH-BTC is closer to the Fermi level.

[0077] Example 3 The electrocatalytic ammonia oxidation activity of the CuAg-OH-BTC prepared in Example 1 and the Cu-BTC, CuAg-BTC, and Cu-OH-BTC prepared in Comparative Examples 1 to 3 was tested. Specifically: 4 mg of each catalyst was dispersed in 1 mL of a mixture (the volume ratio of C3H8O, H2O, and Nafion in the mixture was 30:69:1) and ultrasonicated for 30 min to obtain a uniform slurry. 200 μL of the slurry was drop-coated on a conductive substrate (carbon fiber paper (CFP) with a length and width of 1 cm × 1 cm), resulting in a loading of 800 μL / cm for each catalyst. 2 The CFP, or catalyst electrode, was used. Electrochemical tests were performed using different catalyst electrodes as working electrodes, platinum foil as the counter electrode, and Ag / AgCl (saturated KCl aqueous solution) as the reference electrode in an electrolyte of 0.5 M KOH and 55 mM NH₄OH. A CHI 760E electrochemical workstation was used. CV tests were performed at a scan rate of 50 mV / s to estimate the reaction kinetics of the different catalysts. The results were then compared at 1.6 V. RHE The electrocatalytic reaction was carried out for 60 min under the appropriate conditions to evaluate the conversion of ammonia and the selectivity of nitrite for different catalysts.

[0078] (1) Determination of selectivity and content of nitrite 4 g of sulfanilamide and 0.2 g of naphthylethylenediamine hydrochloride were dissolved in a mixture of 14 mL of phosphoric acid and 50 mL of deionized water to prepare a nitrite colorimetric reagent. A mixed solution of 0.5 mol / L KOH and 55 mmol / L NH₄Cl was used as the solvent, and a certain amount of dry NaNO₂ was dissolved in the solvent to prepare standard solutions of nitrosamine salts with concentrations of 0, 0.4, 0.8, 1.6, 3.2, and 6.4 mg / L. 5 µL of the nitrosamine salt standard solutions of varying concentrations, 4995 µL of deionized water, and 100 µL of the nitrite colorimetric reagent were mixed. After standing in the dark for 20 minutes, the absorbance of the nitrosamine salt standard solutions of varying concentrations at 540 nm was measured using a UV-visible spectrophotometer to construct a nitrite concentration-absorbance standard curve.

[0079] 5 μL of the electrolyte after the electrocatalytic reaction, 4995 μL of deionized water and 100 μL of nitrite color developer were mixed and allowed to stand in the dark for 20 min. The absorbance of the electrolyte at 540 nm was measured using a UV-visible spectrophotometer and then substituted into the above nitrite concentration-absorbance curve to obtain the nitrite content in the electrolyte after the electrocatalytic reaction.

[0080] The selectivity of nitrite (N,%) is calculated as follows: N=(C N / (C0-C A ))×100, where C0 (mmol / L) is the initial concentration of ammonia, C N (mmol / L) is the concentration of ammonia, C A is the concentration of nitrite produced in the electrolyte.

[0081] (2) Determination of ammonia conversion rate Ammonia standard solutions with concentrations of 0, 5, 10, 50, and 100 mmol / L were prepared by dissolving a certain amount of dry NH4Cl in a mixed solution of 0.5 mol / L KOH and 55 mmol / L NH4Cl as the solvent. 10 µL of each ammonium standard solution with different concentrations was mixed with 4990 µL of deionized water and 100 µL of potassium sodium tartrate as a color developer. After standing in the dark for 20 minutes, the absorbance of the various ammonium standard solutions at 370 nm was measured using a UV-Vis spectrophotometer to construct a standard curve of ammonium concentration versus absorbance.

[0082] 10 μL of the electrolyte after the electrocatalytic reaction, 4990 μL of deionized water, and 100 μL of potassium sodium tartrate color developer were mixed and allowed to stand in the dark for 20 min. The absorbance of the electrolyte at 370 nm was measured using a UV-visible spectrophotometer and then substituted into the above ammonium salt concentration-absorbance curve to obtain the concentration of ammonium salt in the electrolyte after the electrocatalytic reaction.

[0083] The calculation formula of ammonia conversion rate (A,%) is: A=((C0-C A ) / C0)×100, where C0 (mmol / L) is the initial concentration of ammonia, C A is the concentration of nitrite produced in the electrolyte.

[0084] Figure 12 The corresponding graph of the capacitance current of different catalysts with different scanning speeds, that is, the double layer capacitance (Cdl) graph, shows that the Tafel slope of CuAg-OH-BTC is much lower than that of comparative examples 1 to 3. When the scanning rate is 25 mV / s, its double layer capacitance value is the largest, which is 50.3 mF / cm2 , indicating that CuAg-OH-BTC has faster reaction kinetics and better ammoxidation activity.

[0085] Figure 13 and Figure 14 The selectivity and yield of the catalysts prepared in Example 1 and Comparative Examples 1 to 3 for nitrite and ammonia conversion rate show that CuAg-OH-BTC has the highest nitrite yield, which also indicates that it has the best ammonia oxidation reaction activity and is selective for nitrite.

[0086] Example 4 According to the steps of Example 3, the CuAg-OH-BTC prepared in Example 1 was electrochemically tested. RHE A 12-h constant voltage test was carried out under the same conditions. During the test, the electrolyte was collected at different time periods, and the absorbance of the electrolyte at 370 nm and 540 nm was measured by color reaction and UV-visible spectrophotometer to evaluate its durability.

[0087] Figure 15 At 1.6V RHE Constant voltage tests under these conditions investigated the effect of CuAg-OH-BTC on ammonia conversion efficiency. The color of the electrolyte collected at different time points gradually faded with increasing treatment time, indicating that ammonia was gradually consumed. At a constant voltage test time of 12 hours, the residual ammonia in the electrolyte was less than 3.5 mmol / L, and the ammonia conversion rate reached 92.8%.

[0088] Figure 16 For 1.6 V RHE Constant voltage tests were conducted under these conditions to examine the effect of CuAg-OH-BTC on the cumulative nitrite production. The color development of the electrolyte collected at different time points gradually deepened with increasing treatment time, indicating a significant accumulation of nitrite in the electrolyte. At a constant voltage test time of 12 hours, the nitrite concentration in the electrolyte reached 38.7 mmol / L, and the selectivity for nitrite was greater than 80%.

[0089] Example 5 The preparation method of the MOF catalyst containing high-valent copper provided in this embodiment comprises the following steps: (1) Preparation of Cu-BTC by hydrothermal method is the same as step (1) in Example 1.

[0090] (2) Preparation of CuAg-BTC was carried out in the same manner as in step (2) of Example 1.

[0091] (3) In situ electrochemical reconstruction to prepare CuAg-OH-BTC was the same as in Example 1, except that 30 cyclic voltammetry treatments were performed at a scan rate of 30 mV / s.

[0092] Example 6 The preparation method of the MOF catalyst containing high-valent copper provided in this embodiment comprises the following steps: (1) Preparation of Cu-BTC by hydrothermal method is the same as step (1) in Example 1.

[0093] (2) Preparation of CuAg-BTC was carried out in the same manner as in step (2) of Example 1.

[0094] (3) In situ electrochemical reconstruction to prepare CuAg-OH-BTC was the same as in Example 1, except that cyclic voltammetry was performed 80 times at a scan rate of 30 mV / s.

[0095] Example 7 The preparation method of the MOF catalyst containing high-valent copper provided in this embodiment comprises the following steps: (1) Preparation of Cu-BTC by hydrothermal method is the same as step (1) in Example 1.

[0096] (2) Preparation of CuAg-BTC was carried out in the same manner as in step (2) of Example 1.

[0097] (3) In situ electrochemical reconstruction to prepare CuAg-OH-BTC was the same as in Example 1, except that cyclic voltammetry was performed 30 times at a scan rate of 80 mV / s.

[0098] Example 8 The preparation method of the MOF catalyst containing high-valent copper provided in this embodiment comprises the following steps: (1) Preparation of Cu-BTC by hydrothermal method is the same as step (1) in Example 1.

[0099] (2) Preparation of CuAg-BTC was carried out in the same manner as in step (2) of Example 1.

[0100] (3) In situ electrochemical reconstruction to prepare CuAg-OH-BTC was the same as in Example 1, except that 80 cyclic voltammetry treatments were performed at a scan rate of 80 mV / s.

[0101] Electrochemical testing of the Cu-OH-BTC prepared in Examples 5 to 8 was performed according to the method provided in Example 4. The test results showed that when the constant voltage test time was 12 h, the ammonia conversion rate in the electrolyte could reach 88% or above, and the selectivity of nitrite was greater than 80%.

[0102] Comparative Example 4 (1) Preparation of Cu-BTC by hydrothermal method is the same as step (1) in Example 1.

[0103] (2) Preparation of CuAg-BTC was carried out in the same manner as in step (2) of Example 1.

[0104] (3) In situ electrochemical reconstruction to prepare CuAg-OH-BTC is the same as in Example 1, except that cyclic voltammetry treatment is performed five times.

[0105] Comparative Example 5 (1) Preparation of Cu-BTC by hydrothermal method is the same as step (1) in Example 1.

[0106] (2) Preparation of CuAg-BTC was carried out in the same manner as in step (2) of Example 1.

[0107] (3) In situ electrochemical reconstruction to prepare CuAg-OH-BTC is the same as in Example 1, except that 150 cyclic voltammetry treatments are performed.

[0108] The Cu-OH-BTC prepared in Comparative Examples 4 and 5 were tested for electrocatalytic ammonia oxidation activity according to the method provided in Example 3.

[0109] The test results show that the conversion rate of ammonia of Cu-OH-BTC prepared in Comparative Example 4 is only 8%, and the selectivity for nitrite is 78%. Its electrocatalytic ammonia oxidation reaction activity is slightly better than that of CuAg-BTC prepared in Comparative Example 2, but still significantly worse than that of Cu-OH-BTC prepared in Example 1. Analysis shows that the reason may be that the number of cyclic voltammetry treatments in Comparative Example 4 is relatively small (5 times), which cannot effectively improve the electrocatalytic ammonia oxidation reaction activity of the catalyst.

[0110] The conversion rate of ammonia to Cu-OH-BTC prepared in Comparative Example 5 was only 5%, and the selectivity for nitrite was 70%. Its electrocatalytic ammonia oxidation reaction activity was slightly better than that of Cu-BTC prepared in Comparative Example 1, but still significantly worse than that of Cu-OH-BTC prepared in Example 1. Analysis showed that the reason may be that the number of cyclic voltammetry treatments in Comparative Example 5 was too many (150 times), resulting in poor structural stability of the catalyst, which is not conducive to recycling.

[0111] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a MOF catalyst containing high-valent copper, characterized in that: The steps include: S1. Mixing a water-soluble divalent copper salt, an organic ligand, and a dispersing solvent to conduct a hydrothermal reaction, then collecting the precipitate by centrifugation, washing, and drying to obtain a Cu-based metal-organic framework material; S2, mixing the Cu-based metal-organic framework material, a water-soluble divalent silver salt, and a reaction solvent to perform an ion exchange reaction, then collecting the precipitate by centrifugation, washing, and drying to obtain a Cu-based metal-organic framework material doped with Ag; S3. Mix the Ag-doped Cu-based metal-organic framework material, a conductive agent, and a binder solution to form a composite slurry, and apply it on at least one surface of an electrode substrate. Dry it to obtain a working electrode, then place the working electrode in an electrochemical system containing an electrolyte, apply a constant potential or a cyclic potential to the working electrode within a preset voltage range, so that the Ag-doped Cu-based metal-organic framework material undergoes in-situ electrochemical reconstruction to generate Cu(III), wash and dry the reconstructed working electrode to obtain the MOF catalyst containing high-valent copper.

2. The preparation method according to claim 1, characterized in that The molar ratio of the water-soluble divalent inorganic copper salt to the organic ligand is (1.5-2):1; and / or, The molar ratio of the copper element in the water-soluble divalent inorganic copper salt to the silver element in the water-soluble inorganic silver salt is (20-25):

1.

3. The preparation method according to claim 2, characterized in that The water-soluble divalent copper salt is one or more of copper chloride, copper sulfate, copper acetate, copper nitrate and copper nitrate hydrate; and / or, The organic ligand is trimesic acid; and / or, The dispersing solvent is one or more of methanol, ethanol, N,N-dimethylformamide, N,N-diethylformamide and deionized water; The water-soluble divalent silver salt is one or more of silver nitrate and silver nitrate hydrate.

4. The preparation method according to claim 1, wherein In step S1, the temperature of the hydrothermal reaction is 50°C to 100°C, and the time of the hydrothermal reaction is 12 h to 24 h; and / or, In step S2, the ion exchange reaction time is 10 h to 15 h.

5. The preparation method according to claim 1, characterized in that In step S3, the conductive agent is a conductive agent selected from carbon black, graphite, carbon fiber, graphene, and carbon nanotubes; The binder solution is formed by mixing a binder and the dispersing solvent, wherein the binder is Nafion and / or polyvinylidene fluoride.

6. The preparation method according to claim 1, characterized in that In step S3, the electrode substrate is carbon fiber paper, nickel foam or titanium sheet; and / or, The electrolyte is an alkaline solution selected from potassium hydroxide solution or sodium hydroxide solution; and / or, The electrochemical system is a three-electrode system, comprising the working electrode, the counter electrode and the reference electrode; The preset voltage range is 1~1.8 V RHE The potential was applied in the form of cyclic voltammetry scanning.

7. The preparation method according to claim 6, wherein The scanning rate of the cyclic voltammetry scan is 5 mV / s to 100 mV / s, and the number of cycles is 10 to 100 times.

8. A MOF catalyst containing high-valent copper prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the MOF catalyst containing high-valent copper according to claim 8 in an electrocatalytic ammonia oxidation reaction.

10. The use according to claim 9, characterized in that The product of the electrocatalytic ammonia oxidation reaction includes nitrite.

Images