A porous carbon supported nickel catalyst, a preparation method and application thereof

Abstract

The application discloses a porous carbon supported nickel catalyst and a preparation method and application thereof, and belongs to the technical field of water treatment. The non-noble metal catalyst with high-dispersed active sites, rich multi-level pores and stable composite structure is constructed by taking the metal organic framework Ni-MOF-74 with a clear structure as a precursor and through a pyrolysis and reduction process which is accurately controlled. The catalyst can efficiently catalyze the hydrogen reduction of nitrate under mild conditions, realizes high conversion rate and high nitrogen selectivity, and has good cycle stability and anti-interference ability. The method is controllable in process and good in repeatability, and is suitable for actual wastewater treatment scenes.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a porous carbon-supported nickel catalyst, its preparation method, and its application. Background Technology

[0002] Currently, excessive accumulation of nitrates in industrial wastewater and agricultural drainage leads to eutrophication of water bodies and threatens human health. Existing nitrate treatment methods mainly include biological denitrification, physical adsorption, electrochemical reduction, and chemical catalytic reduction. Among them, catalytic hydrogenation reduction technology has attracted much attention due to its fast reaction rate, lack of secondary pollution, and ability to convert nitrates into nitrogen or ammonia.

[0003] Currently, commonly used nitrate reduction catalysts are mainly supported catalysts of noble metals (such as Pd and Pt) or transition metals (such as Ni and Cu). However, noble metal catalysts are expensive and difficult to apply on a large scale; while traditional non-noble metal catalysts suffer from low activity, poor stability, easy aggregation, and high ammonia selectivity. In recent years, metal-organic frameworks (MOFs) have become a research hotspot for high-performance catalyst precursors due to their high specific surface area, tunable structure, and abundant metal sites. However, the application of their derivatives in nitrate reduction still faces technical bottlenecks such as complex preparation processes, uneven distribution of active sites, and insufficient cycle stability.

[0004] In the prior art, CN114695852A discloses a carbon-coated cathode material, but it is mainly used in the battery field, and carbon coating leads to a reduction in capacity; CN114628663A discloses a cerium-doped modified cathode material, but its improvement on problems such as high residual alkali content and poor air stability is limited. Therefore, developing a nitrate reduction catalyst that combines high activity, high selectivity, high stability, and low cost is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The main objective of this invention is to propose a porous carbon-supported nickel catalyst, its preparation method, and its application. The catalyst has the characteristics of simple preparation process, low cost, uniform dispersion of active sites, large specific surface area, and stable structure. It can efficiently catalyze the hydrogenation reduction of nitrate under mild conditions, achieving high conversion rate and high nitrogen selectivity. At the same time, it has good cycle stability and anti-interference ability, and is suitable for practical wastewater treatment scenarios.

[0006] To achieve the above objectives, this invention proposes a method for preparing a porous carbon-supported nickel catalyst, comprising the following steps:

[0007] S1. The nickel source and the organic ligand 2,5-dihydroxyterephthalic acid are dissolved in a mixed solvent composed of N,N-dimethylformamide, ethanol and deionized water to obtain a mixture. The mixture is then transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction is completed, the solid product is collected by cooling. The solid product is washed and dried to obtain Ni-MOF-74 precursor powder.

[0008] S2. Ni-MOF-74 precursor powder was pyrolyzed at high temperature under an inert atmosphere to obtain Ni@C intermediate;

[0009] S3. The Ni@C intermediate is transferred to the reactor and reduced under a reducing gas atmosphere by programmed temperature increase to obtain reduced Ni@C;

[0010] S4. Reduced Ni@C was dispersed in an aqueous ethanol solution, vinylsilane coupling agent was added, the mixture was stirred and reacted, the solid was collected by filtration, washed and dried, and then added to N,N-dimethylformamide, 2-vinylimidazole and azobisisobutyronitrile were added, and the mixture was heated under a nitrogen atmosphere. After the reaction was completed, the solid was collected by filtration, washed and dried to obtain a porous carbon-supported nickel catalyst.

[0011] Preferably, in step S1, the nickel source is at least one of Ni(CH3COO)2·4H2O, Ni(NO3)2·6H2O, and NiCl2·6H2O; the molar ratio of the nickel source to 2,5-dihydroxyterephthalic acid is 1:0.28-0.32.

[0012] In this step, a high-purity, highly crystalline MOF precursor was obtained through a hydrothermal reaction, laying the foundation for the ordered porous structure and highly dispersed metal sites of the subsequent derived materials. Ni-MOF-74 was chosen as the precursor because it possesses one-dimensional hexagonal channels, a high specific surface area, and periodically arranged nickel sites. During pyrolysis, this ordered structure partially transforms into a highly interconnected porous carbon network, providing not only a large specific surface area and abundant mass transfer channels, but also effectively limiting and dispersing the in-situ generated nickel species, preventing severe agglomeration at high reduction temperatures, thereby achieving high density and high dispersion of the metal active sites.

[0013] Preferably, the flow rate of the inert gas in step S2 is controlled at 30-100 mL / min; by controlling the flow rate of the inert gas, the gaseous byproducts generated during pyrolysis are ensured to be discharged in a timely manner, avoiding adverse effects on the structure of the carbon matrix, and the intermediate product after pyrolysis has a high specific surface area (greater than 200 m²). 2 / g) and a porous structure dominated by mesopores.

[0014] Preferably, in step S2, the pyrolysis process involves a programmed heating rate of 2-5°C / min to 500-650°C, followed by holding at that temperature for 2-6 hours.

[0015] In this step, pyrolysis aims to carbonize the organic ligands in the MOF framework under anaerobic conditions, transforming them into amorphous carbon or partially graphitized carbon matrix with good conductivity. Simultaneously, nickel ions in the framework are partially reduced and converted in situ into highly dispersed nickel oxide (NiO) nanoparticles or nickel-carbon composite species. After pyrolysis, the mixture is naturally cooled to room temperature to obtain an intermediate product (denoted as Ni@C intermediate). This step is crucial for forming porous carbon supports and immobilizing metal species; the pyrolysis temperature directly affects the degree of graphitization of the carbon matrix, the pore structure, and the initial state of the metal particles.

[0016] Preferably, the reducing gas in step S3 is one of hydrogen or a mixture of hydrogen and an inert gas; the flow rate of the reducing gas is 20-60 mL / min to ensure a sufficient reducing atmosphere and promote heat and mass transfer. In the reduced catalyst, metallic nickel nanoparticles are uniformly embedded in the carbon matrix, with a particle size distribution in the range of 5-20 nm, and the carbon support surface contains an appropriate amount of oxygen-containing functional groups (such as -OH, C=O, etc.), which is beneficial to improving its hydrophilicity and subsequent reactions.

[0017] Preferably, in step S3, the reduction process is carried out at a heating rate of 2-10℃ / min to 320-440℃, and the reduction time is 1-4 hours.

[0018] In this step, the nickel species (mainly NiO) in the precursor are fully reduced to catalytically active zero-valent nickel (Ni) nanoparticles. If the reduction temperature is too low (e.g., 300℃), NiO reduction will be incomplete, and the residual nickel oxide will cover some active sites. If the reduction temperature is too high (e.g., 450℃), the nickel nanoparticles are prone to migration and agglomeration, resulting in a decrease in the active specific surface area. This step directly determines the valence state, dispersion, and particle size of the active metal on the catalyst surface, and is the core to obtaining high catalytic activity.

[0019] Preferably, in step S4, the mass ratio of reduced Ni@C, vinylsilane coupling agent, 2-vinylimidazole, and azobisisobutyronitrile is 10:0.3-0.5:5-8:0.05-0.1; the heating temperature is 60-80℃, and the heating time is 12-24h.

[0020] In this step, the vinyl silane coupling agent undergoes hydrolysis in an aqueous ethanol solution to generate highly active silanol groups, which then undergo dehydration condensation with the hydroxyl groups on the surface of the reduced Ni@C material to form stable silicon-oxygen-carbon covalent bonds, thereby firmly anchoring the vinyl groups to the carbon matrix surface. Under the action of the initiator azobisisobutyronitrile, it undergoes a free radical polymerization reaction with 2-vinylimidazolium, thereby forming a functionalized polymer brush on the carbon support surface. This hydrophilic polymer layer not only improves the dispersion and mass transfer efficiency of the catalyst, but also utilizes the electrostatic attraction of the protonated imidazole groups to specifically enrich nitrate ions, significantly increasing the reaction rate. At the same time, its steric hindrance and coordination anchoring effect effectively inhibits the agglomeration and loss of nickel particles, and the weakly alkaline microenvironment inhibits the formation of byproduct ammonia nitrogen, endowing the catalyst with excellent activity, selectivity and stability.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1) This invention provides a porous carbon-supported nickel catalyst and its preparation method. Using a well-defined metal-organic framework Ni-MOF-74 as a precursor, a non-noble metal catalyst with highly dispersed active sites, abundant hierarchical pores, and a stable composite structure is constructed through precisely controlled pyrolysis and reduction processes. It can efficiently catalyze the hydrogenation reduction of nitrate under mild conditions, achieving high conversion and high nitrogen selectivity, while also exhibiting good cycle stability and anti-interference ability. This method is process-controllable, has good repeatability, and is suitable for practical wastewater treatment scenarios.

[0023] 2) This invention employs a two-step method of pyrolysis followed by reduction, rather than direct high-temperature reduction. The first step, pyrolysis, carbonizes the organic framework at a relatively mild temperature, forming a stable carbon support and initially fixing nickel species. The second step, selective reduction, is performed at a lower temperature, which can precisely reduce nickel oxide to the metallic state while avoiding excessive graphitization or structural collapse of the carbon support. This stepwise control strategy enables the synergistic optimization of metal particle size, carbon support properties, and the interface between the two.

[0024] 3) This invention utilizes a vinylsilane coupling agent to surface-treat reduced Ni@C materials, constructing abundant reactive double bonds on the surface. These bonds serve as anchor points for in-situ free radical polymerization of 2-vinylimidazole, successfully building a functionalized polymer brush. This polymer layer not only significantly enhances the catalyst's hydrophilicity and dispersibility and reduces liquid-solid mass transfer resistance through the formation of a broad hydrogen bond network and protonation effect, but more importantly, it utilizes the positive charge of the protonated imidazole groups to specifically capture and enrich nitrate ions in water through strong electrostatic attraction, greatly increasing the local substrate concentration and reaction rate at the active sites. Furthermore, the steric hindrance effect of the polymer layer and the coordination anchoring effect of the imidazole nitrogen atoms synergistically lock in metallic nickel particles, effectively preventing their aggregation and loss. The weakly alkaline microenvironment on the surface helps optimize the reaction pathway and inhibit the formation of the byproduct ammonia nitrogen, ultimately endowing the catalyst with excellent adsorption-catalysis synergistic performance, high nitrogen selectivity, and long-term cycling stability. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The XRD patterns of reduced Ni@C obtained in Examples 1-4 and Comparative Example 2 of this invention are shown.

[0027] Figure 2 The images show the FT-IR spectra of reduced Ni@C obtained in Examples 1-4 and Comparative Example 2 of this invention.

[0028] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0029] To avoid unnecessary details, unless otherwise specified, all items used in the following examples are commercially available products, and all methods used are conventional methods unless otherwise specified.

[0030] Example 1

[0031] A method for preparing a porous carbon-supported nickel catalyst includes the following steps:

[0032] S1. Weigh 1.525 g (6.13 mmol) of nickel acetate tetrahydrate and 0.36 g (1.817 mmol) of 2,5-dihydroxyterephthalic acid, and add them to a mixed solvent consisting of 50 mL DMF, 50 mL anhydrous ethanol, and 50 mL deionized water. Sonicate the mixture for 30 minutes to form a homogeneous suspension. Transfer the suspension to a 200 mL polytetrafluoroethylene-lined high-pressure reactor and react in a 100 °C oven for 24 hours. After the reaction, cool the mixture, collect the solid by filtration, and wash it three times each with DMF and ethanol. Dry the solid in an 80 °C vacuum drying oven for 12 hours to obtain a light brown Ni-MOF-74 precursor powder.

[0033] S2. Take 2.0 g of the dried Ni-MOF-74 precursor powder and spread it evenly in an alumina boat, then place it in a tube furnace. Under a nitrogen atmosphere (flow rate 50 mL / min), heat to 550 °C at a rate of 5 °C / min, and calcine at this temperature for 4 hours. After the process is complete, allow it to cool naturally to room temperature under nitrogen protection to obtain a black Ni@C intermediate.

[0034] S3. Take about 1.5g of Ni@C intermediate and place it in a quartz tube reactor, then place it in another tube furnace. Purge with a hydrogen / argon mixture (5% H2 / Ar, flow rate 40 mL / min), and heat to 400℃ at a rate of 5℃ / min. Maintain this temperature at 400℃ for 2 hours. After reduction, continue cooling to room temperature under a hydrogen / argon mixture atmosphere to obtain reduced Ni@C-400.

[0035] S4. Weigh 1.0 g of reduced Ni@C-400 and disperse it in 50 mL of 50 wt% ethanol aqueous solution. After ultrasonic dispersion for 10 minutes, add 0.04 g of vinyltriethoxysilane dropwise and react at 40 °C for 4 h. Filter and collect the solid, wash and dry it, and disperse it in 100 mL of N,N-dimethylformamide. Add 0.6 g of 2-vinylimidazole and 0.01 g of azobisisobutyronitrile. Purge the reaction system with nitrogen gas for 30 minutes to remove oxygen. Then heat to 70 °C under nitrogen protection and stir magnetically for 18 hours. After the reaction is completed, cool, collect the solid product, wash and dry it to obtain a porous carbon-supported nickel catalyst.

[0036] Example 2

[0037] A method for preparing a porous carbon-supported nickel catalyst, similar to that in Example 1, except that the reduction temperature in step S3 is 300℃, specifically including the following steps:

[0038] S1. Weigh 1.525 g (6.13 mmol) of nickel acetate tetrahydrate and 0.36 g (1.817 mmol) of 2,5-dihydroxyterephthalic acid, and add them to a mixed solvent consisting of 50 mL DMF, 50 mL anhydrous ethanol, and 50 mL deionized water. Sonicate the mixture for 30 minutes to form a homogeneous suspension. Transfer the suspension to a 200 mL polytetrafluoroethylene-lined high-pressure reactor and react in a 100 °C oven for 24 hours. After the reaction, cool the mixture, collect the solid by filtration, and wash it three times each with DMF and ethanol. Dry the solid in an 80 °C vacuum drying oven for 12 hours to obtain a light brown Ni-MOF-74 precursor powder.

[0039] S2. Take 2.0 g of the dried Ni-MOF-74 precursor powder and spread it evenly in an alumina boat, then place it in a tube furnace. Under a nitrogen atmosphere (flow rate 50 mL / min), heat to 550 °C at a rate of 5 °C / min, and calcine at this temperature for 4 hours. After the process is complete, allow it to cool naturally to room temperature under nitrogen protection to obtain a black Ni@C intermediate.

[0040] S3. Take approximately 1.5 g of Ni@C intermediate and place it in a quartz tube reactor, then place it in another tube furnace. Purge with a hydrogen / argon mixture (5% H2 / Ar, flow rate 40 mL / min), and heat to 300℃ at a rate of 5℃ / min. Maintain this temperature at 300℃ for 2 hours. After reduction, continue cooling to room temperature under a hydrogen / argon mixture atmosphere to obtain reduced Ni@C-300.

[0041] S4. Weigh 1.0 g of reduced Ni@C-300 and disperse it in 50 mL of 50 wt% ethanol aqueous solution. After ultrasonic dispersion for 10 minutes, add 0.04 g of vinyltriethoxysilane dropwise and react at 40 °C for 4 h. Filter and collect the solid, wash and dry it, and disperse it in 100 mL of N,N-dimethylformamide. Add 0.6 g of 2-vinylimidazole and 0.01 g of azobisisobutyronitrile. Purge the reaction system with nitrogen gas for 30 minutes to remove oxygen. Then heat to 70 °C under nitrogen protection and stir magnetically for 18 hours. After the reaction is completed, cool, collect the solid product, wash and dry it to obtain a porous carbon-supported nickel catalyst.

[0042] Example 3

[0043] A method for preparing a porous carbon-supported nickel catalyst is similar to that in Example 1, except that the reduction temperature in step S3 is 350°C, and specifically includes the following steps:

[0044] S1. Weigh 1.525 g (6.13 mmol) of nickel acetate tetrahydrate and 0.36 g (1.817 mmol) of 2,5-dihydroxyterephthalic acid, and add them to a mixed solvent consisting of 50 mL DMF, 50 mL anhydrous ethanol, and 50 mL deionized water. Sonicate the mixture for 30 minutes to form a homogeneous suspension. Transfer the suspension to a 200 mL polytetrafluoroethylene-lined high-pressure reactor and react in a 100 °C oven for 24 hours. After the reaction, cool the mixture, collect the solid by filtration, and wash it three times each with DMF and ethanol. Dry the solid in an 80 °C vacuum drying oven for 12 hours to obtain a light brown Ni-MOF-74 precursor powder.

[0045] S2. Take 2.0 g of the dried Ni-MOF-74 precursor powder and spread it evenly in an alumina boat, then place it in a tube furnace. Under a nitrogen atmosphere (flow rate 50 mL / min), heat to 550 °C at a rate of 5 °C / min, and calcine at this temperature for 4 hours. After the process is complete, allow it to cool naturally to room temperature under nitrogen protection to obtain a black Ni@C intermediate.

[0046] S3. Take approximately 1.5 g of Ni@C intermediate and place it in a quartz tube reactor, then place it in another tube furnace. Purge with a hydrogen / argon mixture (5% H2 / Ar, flow rate 40 mL / min), and heat to 350℃ at a rate of 5℃ / min. Maintain this temperature at 350℃ for 2 hours. After reduction, continue cooling to room temperature under a hydrogen / argon mixture atmosphere to obtain reduced Ni@C-350.

[0047] S4. Weigh 1.0 g of reduced Ni@C-350 material and disperse it in 50 mL of 50 wt% ethanol aqueous solution. After ultrasonic dispersion for 10 minutes, add 0.04 g of vinyltriethoxysilane dropwise and react at 40 °C for 4 h. Filter and collect the solid, wash and dry it, and disperse it in 100 mL of N,N-dimethylformamide. Add 0.6 g of 2-vinylimidazole and 0.01 g of azobisisobutyronitrile. Purge the reaction system with nitrogen gas for 30 minutes to remove oxygen. Then heat to 70 °C under nitrogen protection and stir magnetically for 18 hours. After the reaction is completed, cool, collect the solid product, wash and dry it to obtain a porous carbon-supported nickel catalyst.

[0048] Example 4

[0049] A method for preparing a porous carbon-supported nickel catalyst, similar to that in Example 1, except that the reduction temperature in step S3 is 450℃, specifically including the following steps:

[0050] S1. Weigh 1.525 g (6.13 mmol) of nickel acetate tetrahydrate and 0.36 g (1.817 mmol) of 2,5-dihydroxyterephthalic acid, and add them to a mixed solvent consisting of 50 mL DMF, 50 mL anhydrous ethanol, and 50 mL deionized water. Sonicate the mixture for 30 minutes to form a homogeneous suspension. Transfer the suspension to a 200 mL polytetrafluoroethylene-lined high-pressure reactor and react in a 100 °C oven for 24 hours. After the reaction, cool the mixture, collect the solid by filtration, and wash it three times each with DMF and ethanol. Dry the solid in an 80 °C vacuum drying oven for 12 hours to obtain a light brown Ni-MOF-74 precursor powder.

[0051] S2. Take 2.0 g of the dried Ni-MOF-74 precursor powder and spread it evenly in an alumina boat, then place it in a tube furnace. Under a nitrogen atmosphere (flow rate 50 mL / min), heat to 550 °C at a rate of 5 °C / min, and calcine at this temperature for 4 hours. After the process is complete, allow it to cool naturally to room temperature under nitrogen protection to obtain a black Ni@C intermediate.

[0052] S3. Take approximately 1.5 g of Ni@C intermediate and place it in a quartz tube reactor, then place it in another tube furnace. Purge with a hydrogen / argon mixture (5% H2 / Ar, flow rate 40 mL / min), and heat to 450℃ at a rate of 5℃ / min. Maintain this temperature at 450℃ for 2 hours. After reduction, continue cooling to room temperature under a hydrogen / argon mixture atmosphere to obtain reduced Ni@C-450.

[0053] S4. Weigh 1.0 g of reduced Ni@C-450 material and disperse it in 50 mL of 50 wt% ethanol aqueous solution. After ultrasonic dispersion for 10 minutes, add 0.04 g of vinyltriethoxysilane dropwise and react at 40 °C for 4 h. Filter and collect the solid, wash and dry it, and disperse it in 100 mL of N,N-dimethylformamide. Add 0.6 g of 2-vinylimidazole and 0.01 g of azobisisobutyronitrile. Purge the reaction system with nitrogen gas for 30 minutes to remove oxygen. Then heat to 70 °C under nitrogen protection and stir magnetically for 18 hours. After the reaction is completed, cool, collect the solid product, wash and dry it to obtain a porous carbon-supported nickel catalyst.

[0054] Comparative Example 1

[0055] A method for preparing a nickel catalyst, similar to that in Example 1, differs in that nickel acetate tetrahydrate is directly pyrolyzed and reduced, specifically including the following steps:

[0056] S1. Take 2.0 g of nickel acetate tetrahydrate, spread it evenly in an alumina boat, and place it in a tube furnace. Under a nitrogen atmosphere (flow rate 50 mL / min), heat to 550 °C at 5 °C / min, and calcine at this temperature for 4 hours. After the process is completed, allow it to cool naturally to room temperature under nitrogen protection to obtain the intermediate product;

[0057] S2. Take about 1.5g of intermediate product and put it into a quartz tube reactor, which is then placed in another tube furnace. A hydrogen / argon mixture (5% H2 / Ar, flow rate 40mL / min) is introduced, and the temperature is increased to 400℃ at a rate of 5℃ / min. The temperature is then maintained at 400℃ for 2 hours for reduction. After the reduction is completed, the mixture is cooled to room temperature under a hydrogen / argon mixture atmosphere to obtain the nickel catalyst.

[0058] Comparative Example 2

[0059] A method for preparing a catalyst for wastewater treatment, wherein the catalyst is Ni-MOF-74, specifically includes the following steps:

[0060] Weigh 1.525 g (6.13 mmol) of nickel acetate tetrahydrate and 0.36 g (1.817 mmol) of 2,5-dihydroxyterephthalic acid, and add them to a mixed solvent consisting of 50 mL DMF, 50 mL anhydrous ethanol, and 50 mL deionized water. Sonicate the mixture for 30 minutes to form a homogeneous suspension. Transfer the suspension to a 200 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE) and react in an oven at 100 °C for 24 hours. After the reaction is complete, cool the mixture, collect the solid by filtration, and wash it three times each with DMF and ethanol. Dry the solid in a vacuum oven at 80 °C for 12 hours to obtain a light brown Ni-MOF-74.

[0061] Comparative Example 3

[0062] A method for preparing a porous carbon-supported nickel catalyst, similar to that in Example 1, except that 2-ethyleneimidazole is not grafted onto it, specifically includes the following steps:

[0063] S1. Weigh 1.525 g (6.13 mmol) of nickel acetate tetrahydrate and 0.36 g (1.817 mmol) of 2,5-dihydroxyterephthalic acid, and add them to a mixed solvent consisting of 50 mL DMF, 50 mL anhydrous ethanol, and 50 mL deionized water. Sonicate the mixture for 30 minutes to form a homogeneous suspension. Transfer the suspension to a 200 mL polytetrafluoroethylene-lined high-pressure reactor and react in a 100 °C oven for 24 hours. After the reaction, cool the mixture, collect the solid by filtration, and wash it three times each with DMF and ethanol. Dry the solid in an 80 °C vacuum drying oven for 12 hours to obtain a light brown Ni-MOF-74 precursor powder.

[0064] S2. Take 2.0 g of the dried Ni-MOF-74 precursor powder and spread it evenly in an alumina boat, then place it in a tube furnace. Under a nitrogen atmosphere (flow rate 50 mL / min), heat to 550 °C at a rate of 5 °C / min, and calcine at this temperature for 4 hours. After the process is complete, allow it to cool naturally to room temperature under nitrogen protection to obtain a black Ni@C intermediate.

[0065] S3. Take about 1.5g of Ni@C intermediate and place it in a quartz tube reactor, then place it in another tube furnace. Purge with a hydrogen / argon mixture (5% H2 / Ar, flow rate 40 mL / min), and heat to 400℃ at a rate of 5℃ / min. Maintain this temperature at 400℃ for 2 hours. After reduction, continue cooling to room temperature under a hydrogen / argon mixture atmosphere to obtain reduced Ni@C-400.

[0066] S4. Weigh 1.0 g of reduced Ni@C-400 and disperse it in 50 mL of 50 wt% ethanol aqueous solution. After ultrasonic dispersion for 10 minutes, add 0.04 g of vinyltriethoxysilane dropwise and react at 40 °C for 4 h. Filter, collect the solid, wash and dry to obtain porous carbon-supported nickel catalyst.

[0067] Performance testing

[0068] The catalytic degradation of nitrate in water was carried out in a batch reactor. 150 mL of NO3- (with an initial concentration of 100 mg / L) was added to a 250 mL three-necked flask. - Simulated sodium nitrate wastewater (based on N) was initially pHed to 7.0. 0.1 g of the catalysts prepared in Examples 1-4 and Comparative Examples 1-3 were added, and pure H2 (flow rate 90 mL / min) was continuously bubbled through while stirring. The mixture was reacted in a 25°C water bath for 5 hours. Samples were taken periodically, and the NO3 content in the filtrate was determined by ultraviolet spectrophotometry after filtration. - NO2 - and NH4 + The concentrations and test results are shown in Table 1:

[0069]

[0070] The XRD patterns of the reduced Ni@C obtained in Examples 1-4 and Comparative Example 2 of this invention are shown in Table 1. The porous carbon-supported nickel catalysts (reduced Ni@C-300 / 350 / 400 / 450) prepared by pyrolysis-reduction of Ni-MOF-74 precursor all show characteristic diffraction peaks of metallic nickel (Ni) in their XRD patterns (such as 2θ=44.5º and 51.8º corresponding to Ni(111) and Ni(200) crystal planes). As the reduction temperature increases (300→450℃), the peak intensity gradually increases and the half-peak width decreases, indicating that the crystallinity of nickel particles increases and the particle size increases. However, the catalyst obtained by direct pyrolysis of nickel acetate in Comparative Example 1 may be due to the lack of confinement effect of MOF-derived carbon, and the nickel particles are prone to agglomeration, resulting in different trends in peak broadening or intensity change.

[0071] The FT-IR spectra of the reduced Ni@C materials obtained in Examples 1-4 and Comparative Example 2 of this invention are as follows: Figure 2 As shown in the figure, the precursor Ni-MOF-74 has a growth rate of 1600-1400 cm⁻¹. -1 The carboxylate vibration peak and 3400 cm -1 The hydroxyl peaks around 1500-1300 cm⁻¹ disappeared after pyrolysis, indicating complete decomposition of the organic ligands; the catalyst after reduction showed peaks at 1500-1300 cm⁻¹. -1 The presence of carbon skeleton vibration peaks, coupled with a decrease in the intensity of characteristic peaks of surface functional groups (such as CO and C=O) with increasing reduction temperature, may be attributed to further graphitization of the carbon material and decomposition of oxygen-containing groups on the surface at high temperatures. Comparative Example 2, which did not undergo pyrolysis-reduction, retained the characteristic peaks of the organic ligands in the MOF in its FTIR spectrum, but lacked metallic nickel diffraction peaks, confirming that only the MOF precursor lacks the metal active sites required for catalytic activity. In summary, the porous structure of MOF-derived carbon can effectively disperse nickel particles. The reduction temperature, by controlling the nickel particle size and carbon surface properties, affects the microstructure of the catalyst. Direct pyrolysis of metal salts or unconverted MOFs cannot form high-performance supported nickel catalysts.

[0072] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A method for preparing a porous carbon-supported nickel catalyst, characterized in that, Includes the following steps: S1. The nickel source and the organic ligand 2,5-dihydroxyterephthalic acid are dissolved in a mixed solvent composed of N,N-dimethylformamide, ethanol and deionized water to obtain a mixture. The mixture is then transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction is completed, the solid product is collected by cooling. The solid product is washed and dried to obtain Ni-MOF-74 precursor powder. S2. Ni-MOF-74 precursor powder was pyrolyzed under an inert atmosphere to obtain Ni@C intermediate; S3. The Ni@C intermediate is transferred to the reactor and reduced under a reducing gas atmosphere by programmed temperature increase to obtain reduced Ni@C; S4. Reduced Ni@C was dispersed in an aqueous ethanol solution, vinylsilane coupling agent was added, the mixture was stirred and reacted, the solid was collected by filtration, washed and dried, and then added to N,N-dimethylformamide, 2-vinylimidazole and azobisisobutyronitrile were added, and the mixture was heated under a nitrogen atmosphere. After the reaction was completed, the solid was collected by filtration, washed and dried to obtain a porous carbon-supported nickel catalyst.

2. The preparation method according to claim 1, characterized in that: In step S1, the nickel source is at least one of Ni(CH3COO)2·4H2O, Ni(NO3)2·6H2O, and NiCl2·6H2O.

3. The preparation method according to claim 1, characterized in that: The molar ratio of the nickel source to 2,5-dihydroxyterephthalic acid is 1:0.28-0.

32.

4. The preparation method according to claim 1, characterized in that: In step S2, the flow rate of the inert gas is controlled at 30-100 mL / min.

5. The preparation method according to claim 1, characterized in that: In step S2, the pyrolysis process involves heating the temperature to 500-650℃ at a rate of 2-5℃ / min and holding it at that temperature for 2-6 hours.

6. The preparation method according to claim 1, characterized in that: In step S3, the reducing gas is one of hydrogen or a mixture of hydrogen and an inert gas.

7. The preparation method according to claim 1, characterized in that: In step S3, the reduction process involves heating the temperature to 320-440℃ at a rate of 2-10℃ / min, with a reduction time of 1-4 hours.

8. The preparation method according to claim 1, characterized in that: In step S4, the mass ratio of reduced Ni@C, vinylsilane coupling agent, 2-vinylimidazolium, and azobisisobutyronitrile is 10:0.3-0.5:5-8:0.05-0.

1.

9. A porous carbon-supported nickel catalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of the porous carbon-supported nickel catalyst of claim 9 in wastewater treatment.

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