A water-slag-based nitrate reduction catalyst and a method for preparing the same

Abstract

This invention discloses a water slag-based nitrate reduction catalyst and its preparation method, belonging to the field of ammonia synthesis technology. The catalyst preparation method includes pretreating water slag as a support, preparing a copper-cobalt mixed aqueous solution in a specific ratio, and preparing the water slag-based catalyst through co-precipitation, aging, and calcination. By utilizing inexpensive industrial waste residue to replace expensive support materials, combined with a simple co-precipitation process, low-cost and high-efficiency catalyst preparation is achieved, offering advantages such as low cost, simple process, environmental friendliness, and effective utilization of industrial waste residue. The synergistic effect among the components in the catalyst of this invention gives it high catalytic activity and stability, maintaining good catalytic performance under a wide range of reaction conditions.

Description

Technical Field

[0001] This application relates to the field of ammonia synthesis technology, and more specifically, to a water slag-based nitrate reduction catalyst and its preparation method. Background Technology

[0002] Ammonia, as a crucial raw material for modern agriculture and industry, plays an irreplaceable role in fertilizer production, chemical synthesis, and energy storage. While the Haber-Bosch process, widely used in industry, is mature and reliable, it suffers from significant drawbacks such as high energy consumption and severe pollution. This process requires high temperatures of 400-500°C and high pressures of 15-25 MPa, resulting in enormous energy consumption and the generation of large amounts of greenhouse gases. In recent years, nitrate (electro)catalytic reduction ammonia synthesis technology has attracted considerable attention due to its mild reaction conditions and the ability to utilize industrial wastewater or low-concentration nitrates as raw materials, and is considered a potential alternative for green ammonia synthesis.

[0003] However, existing nitrate reduction catalysts still face many challenges. On the one hand, while noble metal-based catalysts (such as Pt / C and Pd / C) exhibit excellent catalytic activity, their high cost severely restricts their industrial-scale application. On the other hand, although transition metal-based catalysts are relatively inexpensive, they typically rely on expensive support materials such as carbon nanotubes and graphene, or employ energy-intensive preparation processes, resulting in persistently high overall costs. Furthermore, while biomass-derived catalysts have low raw material costs, their catalytic activity and stability often fail to meet the demands of industrial applications.

[0004] Meanwhile, the large amount of slag generated by the steel industry also brings serious environmental problems. This waste not only occupies a large amount of land resources, but also generates significant dust pollution during storage, loading, unloading, and transportation. A large steel enterprise can generate thousands or even tens of thousands of tons of waste slag daily from ironmaking. This slag contains iron oxide and other iron-containing elements; ignoring it would be a huge waste, while effective utilization could reduce catalyst preparation costs and achieve resource utilization of industrial waste. However, there are currently no reports on highly efficient nitrate reduction catalysts using a combination of low-cost transition metal oxides and inexpensive supports.

[0005] To address the aforementioned technical bottlenecks, there is an urgent need to develop a water slag-based nitrate reduction catalyst that is readily available, has a simple preparation process, is low in cost, and exhibits stable performance, in order to promote the industrial application of green ammonia synthesis technology. Summary of the Invention

[0006] The purpose of this application is to provide a method for preparing a water slag-based nitrate reduction catalyst, which has the advantages of low cost, simple process, environmental friendliness, and effective utilization of industrial waste residue.

[0007] A method for preparing a water slag-based nitrate reduction catalyst includes the following steps: (a) Grinding to obtain water slag with a particle size of 50-200 μm; (b) Prepare an alcohol-water mixture with a volume ratio of ethanol to water of 1:2 to 1:4; (c) Add the water residue from step (a) to the alcohol-water mixture from step (b) and stir; the amount of alcohol-water mixture added per gram of water residue is 60-100 mL. (d) During the stirring process, hexadecyltrimethylammonium bromide is added to the alcohol-water mixture from step (c), with an addition amount of 0.1-0.6 g per gram of water residue; then ammonia is slowly added to the alcohol-water mixture, with an ammonia concentration of 5-30%, and an addition amount of 8-16 mL per gram of water residue. (e) After stirring, collect the sample by centrifugation and wash with deionized water; (f) After drying the sample washed in step (e), calcinate it in air to obtain the pretreated water slag-based carrier. (g) Dissolve the copper source and cobalt source in deionized water to prepare... and A copper-cobalt mixed aqueous solution with a mass ratio of 1:5-5:1 and a total metal ion concentration of 0.3 mol / L; (h) The pretreated water slag-based carrier obtained in step (f) is added to the copper-cobalt mixed aqueous solution obtained in step (g) for coprecipitation reaction; the amount of copper-cobalt mixed aqueous solution added per gram of water slag is 40-70 mL. (i) The mixture after the reaction in step (h) is subjected to aging treatment; (j) After filtering, washing and drying the aging product from step (i), it is calcined in air to obtain the catalyst.

[0008] Furthermore, in step (c), the stirring rate is 200-350 r / min, and the reaction time is 2-4 h.

[0009] Furthermore, in step (f), the calcination temperature is 400-600℃, and the holding time is 2-4h.

[0010] Further, in step (g), the copper source is a soluble copper salt such as copper nitrate, copper sulfate, or copper nitrate trihydrate, and the cobalt source is a soluble cobalt salt such as cobalt nitrate, cobalt sulfate, or cobalt nitrate hexahydrate.

[0011] Furthermore, in step (h), the stirring rate of the coprecipitation reaction is 200-350 r / min, the coprecipitation reaction temperature is 80-110℃, and the reaction time is 5-8 h.

[0012] Furthermore, in step (i), the aging temperature is 90-120℃ and the aging time is 1-3h.

[0013] Furthermore, in step (j), the calcination temperature is 400-600℃ and the holding time is 3-6h.

[0014] Another object of the present invention is to provide a water-slag-based nitrate reduction catalyst, which is obtained by the above preparation method.

[0015] As can be seen from the above, the preparation method of the water slag-based nitrate reduction catalyst provided in this application includes pretreating water slag as a carrier, preparing a copper-cobalt mixed aqueous solution in a specific ratio, and preparing the catalyst through co-precipitation, aging and calcination. By using inexpensive industrial waste residue to replace expensive carrier materials and combining a simple co-precipitation process, the catalyst can be prepared at low cost and high efficiency. It has the advantages of low cost, simple process, environmental friendliness and effective utilization of industrial waste residue.

[0016] Under alkaline reaction conditions, the catalyst of this invention exhibits high catalytic activity. At -0.8V vs. RHE... At that time, the ammonia yield can reach 108 mgh. -1 mg cat. -1 The Faraday efficiency can reach 87.56%. The synergistic effect among the components in the catalyst of this invention gives the catalyst high catalytic activity and stability, and it can maintain good catalytic effect under a wide range of reaction conditions, which is conducive to the widespread industrial application of nitrate reduction to ammonia synthesis technology. Attached Figure Description

[0017] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the catalyst prepared in Example 1. Figure 2 The impedance comparison diagram is shown for the catalyst prepared in Example 1 and the water slag-based support. Figure 3 The graph shows the ammonia yield and Faraday efficiency of the catalyst at different potentials in Example 1. Figure 4 The graph shows the ammonia production rate and Faraday efficiency of the catalyst in Application Example 1 after 12 cycles. Detailed Implementation

[0018] For ease of understanding, the following explains some key terms in this embodiment: Water slag-based carriers refer to pretreated water slag with particle size controlled within a specific range and porous characteristics. They serve as support materials for catalysts, providing a surface for loading active components and a source of iron.

[0019] Pore-forming treatment refers to a modification process that uses chemical methods to create a large number of interconnected or closed pore structures inside or on the surface of slag. This operation aims to significantly enhance the specific surface area, porosity, and other properties of slag.

[0020] A copper source refers to a compound that provides copper ions during the preparation of a copper-cobalt mixed aqueous solution; it can dissociate in aqueous solution to release copper ions. ion.

[0021] A cobalt source refers to a compound that provides cobalt ions during the preparation of a copper-cobalt mixed aqueous solution; this compound can dissociate in aqueous solution. ion.

[0022] Coprecipitation is a process in which two or more metal ions simultaneously precipitate from solution under specific conditions, forming a mixed precipitate. This process aims to uniformly load the active metal component onto a support.

[0023] Aging treatment refers to the process of maintaining the resulting mixture at a certain temperature for a period of time after the co-precipitation reaction is completed, in order to promote the growth of precipitate crystals and the stabilization of their structure.

[0024] Calcination is a process in which the dried product is heated to a certain temperature in air and held at that temperature, followed by slow cooling. This treatment aims to remove impurities, reconstruct crystals to generate the target product, and improve the activity and stability of the catalyst.

[0025] This application discloses a method for preparing a water slag-based nitrate reduction catalyst, comprising the following steps: (a) Grinding to obtain water slag with a particle size of 50-200 μm. This method first grinds the water slag to prepare a catalyst support. Specifically, the water slag can be collected and pulverized using mechanical grinding equipment, such as dry grinding with a ball mill, to reduce its particle size. The grinding process can be adjusted to obtain a water slag-based support with a particle size distribution in the range of 50-200 μm.

[0026] (b) Prepare an alcohol-water mixture with a volume ratio of ethanol to water of 1:2 to 1:4. This alcohol-water mixture is used to adjust the polarity of the system, control the reaction rate and product morphology, and avoid product agglomeration or uneven pore size caused by excessively fast reaction under a single solvent.

[0027] (c) Add the water residue from step (a) to the alcohol-water mixture from step (b) and stir. The amount of alcohol-water mixture added per gram of water residue is 60-100 mL. The stirring rate is controlled at 200-350 r / min and the reaction time is 2-4 h.

[0028] (d) During stirring, hexadecyltrimethylammonium bromide is added to the alcohol-water mixture from step (c); the amount of hexadecyltrimethylammonium bromide added is 0.1-0.6 g per gram of water slag. Then, ammonia water is slowly added to the alcohol-water mixture, with an ammonia concentration of 5-30%, and the amount of ammonia water added is 8-16 mL per gram of water slag. The water slag is treated with hexadecyltrimethylammonium bromide and ammonia water to create pores, thereby increasing its specific surface area. Hexadecyltrimethylammonium bromide is used to construct a large number of interconnected or closed pore structures inside or on the surface of the water slag, thereby significantly enhancing the specific surface area and porosity of the water slag. The addition of ammonia water is to provide an alkaline environment and regulate the rate of hydrolysis and condensation. When the concentration is appropriate, the size and morphology of the pores can be controlled, promoting the formation of a mesoporous water slag-based carrier with uniform pore size and regular morphology. Too high or too low a concentration may lead to the collapse of the pore structure or irregular morphology.

[0029] (e) After stirring, the sample is collected by centrifugation and washed with deionized water to remove excess ammonia, incompletely assembled hexadecyltrimethylammonium bromide and other soluble impurities remaining in the system.

[0030] (f) The sample washed in step (e) is calcined in air to obtain the pretreated water-slag-based support. The calcination equipment can be a box-type muffle furnace or a tube furnace, and the appropriate calcination equipment can be selected according to the temperature control requirements. The calcination temperature is controlled at 400-600℃, and the holding time is 2-4 hours. Calcination is performed to decompose the added hexadecyltrimethylammonium bromide, thereby preventing the introduction of other substances during catalyst preparation.

[0031] (g) Preparation of solutions for the active metal components: Dissolve the copper source and cobalt source in deionized water to prepare... A copper-cobalt mixed aqueous solution with a mass ratio of 1:5-5:1 and a total metal ion concentration of 0.3 mol / L is prepared. The copper and cobalt sources are weighed separately and added to deionized water, then stirred until fully dissolved to form a homogeneous copper-cobalt mixed aqueous solution. The copper source can be a soluble copper salt such as copper chloride or copper sulfate, and the cobalt source can be a soluble cobalt salt such as cobalt chloride or cobalt sulfate. Precise control of copper ion concentration is necessary during the preparation process. With cobalt ions The mass ratio was kept within the range of 1:5 to 5:1. Simultaneously, the total metal ion concentration in the mixed aqueous solution was ensured to reach 0.3 mol / L by adjusting the amount of metal salt added. In practice, there are many types of copper and cobalt sources, and their solubility, purity, and performance in coprecipitation reactions vary, affecting the preparation accuracy of the copper-cobalt mixed aqueous solution and the stability of the subsequent coprecipitation reaction, thus affecting the performance of the final catalyst. Therefore, copper nitrate trihydrate is more suitable as the copper source, and cobalt nitrate hexahydrate as the cobalt source. Specifically, copper nitrate trihydrate... As a common copper salt, it exhibits good water solubility and readily dissolves in deionized water to form a homogeneous copper ion solution. Its stable water of crystallization content facilitates accurate weighing and preparation of copper ion solutions at the desired concentration. In coprecipitation reactions, nitrate ions act as ligands, contributing to the uniform precipitation of copper ions under certain conditions, preventing localized excessively high or low concentrations, thereby promoting the uniform distribution of copper and cobalt components on the carrier. Simultaneously, cobalt nitrate hexahydrate... As another commonly used cobalt salt, it also exhibits excellent water solubility, rapidly dissolving in deionized water to form a stable cobalt ion solution. Its water of crystallization content is fixed, facilitating precise control of the cobalt ion dosage. During co-precipitation, nitrate ions also contribute to the uniform precipitation of cobalt ions, working synergistically with copper ions to ensure good dispersion of copper and cobalt components on the catalyst support.

[0032] Choosing copper nitrate trihydrate as the copper source and cobalt nitrate hexahydrate as the cobalt source ensures the rapid and complete dissolution of copper and cobalt ions in deionized water, forming a homogeneous and stable copper-cobalt mixed aqueous solution. These two salts have well-defined chemical formulas and stable water of crystallization content, facilitating accurate weighing and control of the mass ratio and total concentration of metal ions, thus guaranteeing the accuracy and repeatability of the copper-cobalt mixed aqueous solution preparation in step (b). In the subsequent coprecipitation reaction, due to the homogeneity of the precursor solution, copper and cobalt ions can be more uniformly coprecipitated onto the slag-based support, avoiding component segregation caused by impurities in raw materials or uneven dissolution. This helps to prepare a slag-based nitrate reduction catalyst with uniformly dispersed active components and stable performance, improving catalyst preparation efficiency and product consistency.

[0033] (h) The pretreated slag-based support obtained in step (f) is added to the copper-cobalt mixed aqueous solution obtained in step (g). The amount of copper-cobalt mixed aqueous solution added is 40-70 mL per gram of slag, and a coprecipitation reaction is carried out to prepare the catalyst precursor. In this step, the slag-based support is slowly added to the copper-cobalt mixed aqueous solution while it is being stirred. The amount of mixed aqueous solution added needs to be calculated based on the amount of solid support per gram and controlled within the range of 40-70 mL. The coprecipitation reaction can be carried out under heating conditions. Through continuous stirring, copper and cobalt ions are precipitated on the surface or within the pores of the support. Improper control of the process parameters of the coprecipitation reaction (such as stirring rate, reaction temperature, and reaction time) may lead to uneven particle size of the precipitate, poor crystallinity, or even the formation of non-target phases, thereby affecting the activity, selectivity, and stability of the final catalyst. To address this, the stirring rate of the coprecipitation reaction is controlled at 200-350 r / min, the coprecipitation reaction temperature is controlled at 80-110℃, and the reaction time is controlled at 5-8 h. Stirring rate is one of the key parameters affecting the coprecipitation process. Its main function is to promote ion diffusion and mass transfer in the liquid phase, ensuring uniform mixing of components in the reaction system. When the stirring rate is set within the range of 200-350 r / min, it can effectively avoid non-uniform precipitation caused by excessively high local concentrations, while also preventing excessive shear forces that may be caused by excessively fast stirring, thus contributing to the formation of precipitates with uniform particle size distribution and regular morphology. Reaction temperature has a significant impact on the kinetics and thermodynamic properties of the coprecipitation reaction. It directly determines the reaction rate, the solubility of precursors, and the crystallization behavior of the precipitate. Controlling the coprecipitation reaction temperature within the range of 80-110℃ can provide suitable energy conditions for the coprecipitation of metal ions. For example, a constant-temperature water bath, oil bath, or a jacketed reactor with a temperature control system can be used to achieve precise maintenance of the reaction temperature. Reaction time is a key factor in ensuring that the coprecipitation reaction proceeds fully and reaches equilibrium. A reaction time of 5-8 hours ensures sufficient precipitation of metal ions. Shorter reaction times may lead to incomplete precipitation, while excessively long reaction times may cause excessive growth, aggregation, or phase transition of the precipitate, thus affecting its subsequent catalytic performance. Therefore, controlling the reaction time to 5-8 hours helps obtain catalyst precursors with good crystallinity and stable structure. For example, the start and end times of the reaction can be precisely controlled by setting a timer and using an automatic control system. Precise control of the stirring rate, reaction temperature, and reaction time in the coprecipitation reaction can effectively solve the problems of uneven precipitate morphology and poor crystallinity during coprecipitation. Specifically, an appropriate stirring rate ensures the homogeneity of the reaction system and avoids local supersaturation; precisely controlled reaction temperature optimizes reaction kinetics and thermodynamic conditions, allowing metal ions to coprecipitate with the desired crystal structure and particle size; and sufficient reaction time ensures the complete precipitation reaction and sufficient crystal growth.These synergistic effects result in catalyst precursors with superior uniformity, dispersibility, and crystallinity. Consequently, after subsequent calcination, these precursors can form catalysts with a more rational distribution of active sites and a more stable structure, significantly enhancing their catalytic activity, selectivity, and long-term stability in the nitrate reduction to ammonia synthesis reaction.

[0034] (i) The mixture after the reaction in step (h) is subjected to aging treatment; the aging treatment can be carried out directly in the reaction vessel or the mixture can be transferred to another vessel. During the aging process, the mixture is maintained at a relatively high temperature for a period of time. This treatment helps the rearrangement and growth of precipitate crystals, thereby improving the structural stability and homogeneity of the catalyst precursor. Improper control of aging conditions may lead to the catalyst precursor's crystal phase structure, grain size, and pore structure not reaching the optimal state, thus affecting the performance and stability of the final catalyst. To address this, the aging temperature is controlled at 90-120℃, and the aging time is controlled at 1-3h. Specifically, the aging temperature is a key parameter affecting the crystal growth kinetics of the catalyst precursor. Setting the aging temperature in the range of 90-120℃ can provide suitable thermodynamic conditions for the dissolution, recrystallization, and growth of precursor particles, thereby promoting the formation of uniform and appropriately sized grains. If the temperature is too low, the crystal growth rate is slow, which may lead to incomplete crystallization or small and uneven grains; if the temperature is too high, it may cause rapid and disordered grain growth, forming excessively large or agglomerated particles, reducing the specific surface area. Therefore, this temperature range helps balance crystal growth rate and particle uniformity. Meanwhile, aging time refers to the duration the mixture is held at a specific aging temperature. Controlling the aging time within the range of 1-3 hours ensures that the precursor has sufficient time to complete processes such as phase transformation, grain growth, and particle rearrangement, thereby forming a structurally stable catalyst precursor with good morphology. Insufficient aging time may result in incomplete crystallization and an unstable crystal structure; excessive aging time may lead to over-aging, forming excessively large grains and reducing the number of active sites on the catalyst. Therefore, this time range aims to optimize the structural integrity and chemical composition of the precursor.

[0035] By precisely controlling the aging temperature at 90-120℃ and the aging time at 1-3 hours using the above technical solutions, the crystal growth process and crystal phase structure evolution of the catalyst precursor can be effectively regulated. These optimized aging conditions help form a precursor with uniform grain size, stable crystal phase, and good porosity, avoiding crystal defects or particle agglomeration caused by improper aging conditions. Ultimately, the catalyst obtained after subsequent calcination will possess a higher specific surface area, more abundant active sites, and superior structural stability, thereby significantly improving its catalytic activity, selectivity, and long-term stability in the nitrate reduction to ammonia synthesis reaction.

[0036] (j) After filtering, washing, and drying the aging product from step (i), it is calcined in air to obtain a water-slag-based nitrate reduction catalyst. The aged mixture is first separated into solid and liquid phases by filtration equipment, such as a Buchner funnel or a filter press. The filtered solid product needs to be washed multiple times, for example, with deionized water, to remove surface-adsorbed impurity ions. The washed solid is then sent to a drying device, such as a vacuum oven or a forced-air drying oven, to remove residual moisture. The dried product is placed in a muffle furnace or a tube furnace and calcined in air. The calcination heating rate and calcination time can be adjusted according to the desired physicochemical properties of the catalyst to achieve oxidation and phase transformation of the active component. In the above method for preparing a water-slag-based nitrate reduction catalyst, after co-precipitation reaction and aging treatment, the product needs to be calcined to obtain the final catalyst. However, if the calcination conditions are not properly controlled, the crystal structure, porosity, and dispersion of the active component of the catalyst may be unsatisfactory, thereby affecting the final catalytic performance and stability of the catalyst. To address this, the roasting temperature is controlled at 400-600℃, and the holding time is controlled at 3-6 hours.

[0037] Specifically, calcination temperature refers to the highest temperature reached during the heat treatment of the aged product after filtration, washing, and drying in the catalyst preparation process. Calcination is a crucial heat treatment step aimed at promoting the decomposition of the catalyst precursor, phase transformation, oxidation or reduction of the active component, and the interaction between the active component and the support, thereby forming the final catalyst with a specific crystal structure, porosity characteristics, and active site distribution. Within the temperature range of 400-600℃, fine adjustments can be made according to the specific performance requirements of the target catalyst. Specific heating methods can employ equipment such as muffle furnaces and tube furnaces, using programmed temperature control to ensure temperature accuracy and uniformity.

[0038] The holding time refers to the length of time the preset calcination temperature is maintained. The length of the holding time directly affects the adequacy of the calcination process. A sufficiently long holding time ensures that the physicochemical changes within the catalyst (such as phase transformation, grain growth, defect repair, and diffusion of active components) proceed fully, thereby enabling the catalyst to achieve a stable structure and performance. The holding time, ranging from 3 to 6 hours, can be optimized based on the catalyst's composition, structure, and desired performance. For example, a longer holding time can be selected for systems requiring a longer period for phase transformation or component diffusion; a shorter holding time may be chosen for systems sensitive to thermal stability. The holding process should ensure uniform temperature within the furnace to avoid performance differences in different parts of the catalyst.

[0039] By precisely controlling the calcination temperature within the range of 400-600℃ and setting the holding time to 3-6 hours, this application effectively promotes the full interaction between the active components (copper and cobalt) of the catalyst and the water-slag-based support, forming a stable crystal phase structure and optimizing the pore structure and specific surface area of ​​the catalyst. Temperatures above 400℃ ensure the full decomposition of moisture and organic matter in the catalyst precursor and promote the oxidation or crystallization of the active components; while temperatures below 600℃ effectively inhibit excessive sintering and grain growth of the active components, thus maintaining a high density of active sites. Simultaneously, the 3-6 hour holding time ensures that these physicochemical changes can proceed fully, resulting in a more stable catalyst structure and uniform dispersion of the active components. Therefore, the above calcination conditions significantly improve the catalytic activity, selectivity, and long-term stability of the prepared catalyst in the nitrate reduction to ammonia synthesis, avoiding the performance degradation problem caused by improper calcination conditions.

[0040] This method effectively solves the technical problems of high cost and complex preparation of existing nitrate reduction catalysts by utilizing low-cost water slag as a catalyst support and iron source, combined with the co-precipitation of copper and cobalt active components. This method also makes rational use of water slag resources. Therefore, this method provides an economical and environmentally friendly catalyst preparation route, which helps promote the industrial application of green ammonia synthesis technology, while also achieving the effective conversion and utilization of industrial waste.

[0041] The following examples will provide a more in-depth explanation of the above technical solutions: Example 1 Weigh 5g of water sludge with a particle size of 150μm and add it to 300mL of an alcohol-water mixture prepared by mixing ethanol and water in a volume ratio of 1:3; add 1.5g of hexadecyltrimethylammonium bromide (CTAB) and dropwise add 60mL of 25% ammonia water to the alcohol-water mixture, and stir at 300r / min for 3h. After centrifugation and washing, the sample was dried and calcined at 500°C for 3 hours in air to obtain the pretreated water slag-based carrier. Weigh out cobalt nitrate hexahydrate 1.6g, copper nitrate trihydrate 0.8 g was dissolved in deionized water to prepare a 0.3 mol / L copper-cobalt mixed aqueous solution.

[0042] 1.0 g of water-based slag carrier was added to a copper-cobalt mixed aqueous solution. The amount of copper-cobalt mixed aqueous solution added was 60 mL. The co-precipitation reaction was carried out at 300 r / min and 70 °C for 7 h. The mixture after the coprecipitation reaction was aged at 100℃ for 2 hours; After filtering, washing, and drying the aging products, they were calcined at 550°C for 5 hours in air to obtain a water-slag-based catalyst.

[0043] Weigh 3 mg of the prepared catalyst powder, add 1 mL of isopropanol and 20 μL of Nafion (5 wt%) solution, mix, and sonicate at room temperature for 20-40 minutes to obtain a mixed solution. Next, drop-coat the mixed solution onto a glassy carbon sheet to prepare a working electrode, ensuring that the catalyst loading per unit area of ​​the glassy carbon sheet is 0.1 mg. Place the above-prepared working electrode and reference electrode (Hg / HgO electrode) in a cathode electrolyte, which is a mixed solution of 1 mol / L potassium hydroxide and 0.1 mol / L potassium nitrate; place the counter electrode (Pt sheet electrode) in an anolyte, which is 1 mol / L potassium hydroxide; and maintain the temperature between 0.01 and 10 °C. 6 Impedance tests were performed on the catalyst and water slag-based support at a frequency of Hz.

[0044] like Figure 1 As shown, the structure of the catalyst was characterized by X-ray diffraction (XRD), indicating that it belongs to CuO and... The relevant diffraction peaks prove that the metal oxides copper oxide and cobalt tetroxide were successfully loaded onto the slag-based carrier.

[0045] like Figure 2 As shown, the impedance comparison between the catalyst and the water slag-based support reveals that after loading copper-cobalt bimetallic oxide, due to the synergistic effect of Fe, Cu, and Co, the catalyst exhibits higher electron transfer efficiency and lower interfacial charge transport resistance, thus possessing superior catalytic reaction kinetics.

[0046] Example 2 Weigh 5g of water sludge with a particle size of 50μm and add it to 300mL of an alcohol-water mixture prepared by mixing ethanol and water in a volume ratio of 1:2; add 0.5g of hexadecyltrimethylammonium bromide (CTAB) and dropwise add 40mL of 20% ammonia water to the alcohol-water mixture, and stir at 250r / min for 2h. After centrifugation and washing, the sample was dried and calcined at 400°C in air for 2 hours to obtain the pretreated water slag-based carrier. Weigh out cobalt nitrate hexahydrate 1.0g, copper nitrate trihydrate 1.2g was dissolved in deionized water to prepare a 0.3mol / L copper-cobalt mixed aqueous solution.

[0047] 1.0 g of water-based slag carrier was added to a copper-cobalt mixed aqueous solution of 50 mL, and the co-precipitation reaction was carried out at 250 r / min and 60 °C for 6 h. The mixture after the coprecipitation reaction was aged at 90°C for 1 hour; After filtering, washing, and drying the aging products, they were calcined at 450°C for 4 hours in air to obtain a water-slag-based catalyst.

[0048] Example 3 Weigh 5g of water sludge with a particle size of 200μm and add it to 300mL of alcohol-water mixed solution prepared by ethanol and water in a volume ratio of 1:4; then add 2.5g of hexadecyltrimethylammonium bromide (CTAB) and dropwise add 75mL of 30% ammonia water, and stir at 350r / min for 4h. After centrifugation and washing, the sample was dried and calcined at 600°C in air for 4 hours to obtain the pretreated water slag-based carrier. Weigh out cobalt nitrate hexahydrate 1.6g, copper nitrate trihydrate 1.6 g was dissolved in deionized water to prepare a 0.3 mol / L copper-cobalt mixed aqueous solution.

[0049] 1.0 g of water-based slag carrier was added to a copper-cobalt mixed aqueous solution of 70 mL, and the co-precipitation reaction was carried out at 350 r / min and 80 °C for 8 h. The mixture after the coprecipitation reaction was aged at 110℃ for 3 hours; After filtering, washing, and drying the aging products, they were calcined at 600°C for 6 hours in air to obtain a water-slag-based catalyst.

[0050] Example 4 Weigh 5g of water sludge with a particle size of 150μm and add it to 300mL of alcohol-water mixed solution prepared by ethanol and water in a volume ratio of 1:3; then add 2.0g of hexadecyltrimethylammonium bromide (CTAB) and dropwise add 75mL of 15% ammonia water, and stir at 350r / min for 4h. After centrifugation and washing, the sample was dried and calcined at 500°C in air for 4 hours to obtain the pretreated water slag-based carrier. Weigh out cobalt nitrate hexahydrate 1.6g, copper nitrate trihydrate 1.6 g was dissolved in deionized water to prepare a 0.3 mol / L copper-cobalt mixed aqueous solution.

[0051] 1.0 g of water-based slag carrier was added to a copper-cobalt mixed aqueous solution of 70 mL, and the co-precipitation reaction was carried out at 350 r / min and 80 °C for 7 h. The mixture after the coprecipitation reaction was aged at 110℃ for 4 hours; After filtering, washing, and drying the aging products, they were calcined at 600°C for 5 hours in air to obtain a water-slag-based catalyst.

[0052] Example 5 Weigh 5g of water sludge with a particle size of 150μm and add it to 300mL of alcohol-water mixed solution prepared by ethanol and water in a volume ratio of 1:4; then add 1.0g of hexadecyltrimethylammonium bromide (CTAB) and dropwise add 60mL of 10% ammonia water, and stir at 300r / min for 4h. After centrifugation and washing, the sample was dried and calcined at 500°C for 3 hours in air to obtain the pretreated water slag-based carrier. Weigh out cobalt nitrate hexahydrate 1.6g, copper nitrate trihydrate 1.6 g was dissolved in deionized water to prepare a 0.3 mol / L copper-cobalt mixed aqueous solution.

[0053] 1.0 g of water-based slag carrier was added to a copper-cobalt mixed aqueous solution. The amount of copper-cobalt mixed aqueous solution added was 60 mL. The co-precipitation reaction was carried out at 300 r / min and 80 °C for 7 h. The mixture after the coprecipitation reaction was aged at 100℃ for 3 hours; After filtering, washing, and drying the aging products, they were calcined at 500°C for 5 hours in air to obtain a water-slag-based catalyst.

[0054] Example 6 Weigh 5g of water sludge with a particle size of 150μm and add it to 300mL of alcohol-water mixed solution prepared by ethanol and water in a volume ratio of 1:2; then add 1.0g of hexadecyltrimethylammonium bromide (CTAB) and dropwise add 60mL of 5% ammonia water, and stir at 300r / min for 4h. After centrifugation and washing, the sample was dried and calcined at 500°C for 3 hours in air to obtain the pretreated water slag-based carrier. Weigh out cobalt nitrate hexahydrate 1.6g, copper nitrate trihydrate 1.6 g was dissolved in deionized water to prepare a 0.3 mol / L copper-cobalt mixed aqueous solution.

[0055] 1.0 g of water-based slag carrier was added to a copper-cobalt mixed aqueous solution of 70 mL, and the co-precipitation reaction was carried out at 300 r / min and 80 °C for 8 h. The mixture after the coprecipitation reaction was aged at 110℃ for 3 hours; After filtering, washing, and drying the aging products, they were calcined at 500°C for 5 hours in air to obtain a water-slag-based catalyst.

[0056] Application Example 1 Weigh 3 mg of the catalyst powder prepared in Example 1, add 1 mL of isopropanol and 20 μL of Nafion (5 wt%) solution, mix, and sonicate at room temperature for 20-40 minutes to obtain a mixed solution. Next, drop-coat the mixed solution onto a glassy carbon sheet to prepare a working electrode, ensuring that the catalyst loading per unit area of ​​the glassy carbon sheet is 0.1 mg. Place the above-prepared working electrode and reference electrode (Hg / HgO electrode) in a cathode electrolyte, which is a mixed solution of 1 mol / L potassium hydroxide and 0.1 mol / L potassium nitrate; place the counter electrode (Pt sheet electrode) in an anolyte, which is 1 mol / L potassium hydroxide. Perform iterative tests at -0.4 V, -0.5 V, -0.6 V, -0.7 V, and -0.8 V vs. RHE potentials, respectively, for 600 s, with each experiment repeated three times. Perform a performance cycle test on the catalyst at -0.8 V vs. RHE potential for 12 cycles. Subsequently, the concentration of ammonia was determined by the indophenol blue colorimetric method, and the concentration of nitrite was determined by the Griess method. Figure 3 The Faraday efficiency of each product at different potentials in Application Example 1 is shown. Figure 4 The ammonia production rate and Faraday efficiency for 12 cycles of the catalyst in Application Example 1 are shown.

[0057] Table 1 shows the ammonia yield and Faraday efficiency of each product at different potentials during the nitrate reduction ammonia synthesis process using water slag-based catalysts. From Table 1, Figure 3 , Figure 4 It can be seen that the catalyst exhibits high ammonia yield and Faraday efficiency, and low byproduct (NO2) at potentials of -0.4V to -0.8V versus RHE during the ammonia synthesis process from nitrate reduction. - The catalyst exhibited excellent Faradaic efficiency and ammonia yield in the potential range of -0.4 to -0.8 V vs. RHE, with optimal performance at -0.8 V vs. RHE, achieving an ammonia yield of 108528 μg h⁻¹. -1 mg cat. -1 The Faraday efficiency reached 87.56%. Potential byproducts (NO2) were assessed. - The catalyst exhibits a Faraday efficiency over a wide potential range. Faraday efficiency can be maintained above 80%, demonstrating its effectiveness. High selectivity. During 12 cycles, no significant decrease was observed in the ammonia yield and Faraday efficiency of this catalyst, indicating good stability.

[0058] Application Example 2 Weigh 3 mg of the catalyst powder prepared in Example 1, add 1 mL of isopropanol and 20 μL of Nafion (5 wt%) solution, mix, and sonicate at room temperature for 20-40 minutes to obtain a mixed solution. Next, drop-coat the mixed solution onto a glassy carbon sheet to prepare a working electrode, ensuring that the catalyst loading per unit area of ​​the glassy carbon sheet is 0.2 mg. Place the above-prepared working electrode and reference electrode (Hg / HgO electrode) in a cathode electrolyte, which is industrial wastewater with added potassium hydroxide; place the counter electrode (Pt sheet electrode) in an anolyte, which is 1 mol / L potassium hydroxide. Tests were conducted at -0.8 V vs. RHE potential. The original nitrate concentration in the wastewater was 538.97 μg / mL. As shown in Table 2, after 4 hours of electrolysis, the nitrate concentration became 83.92 μg / mL, and the nitrate reduction rate reached 84.45%.

[0059] Table 2 shows the nitrate concentration and nitrate reduction rate of the catalyst after different reaction times at -0.8V vs. RHE potential; In summary, this invention uses water slag as a catalyst support, which not only conforms to sustainable development but also produces a high-performance and low-cost catalyst. When used in the nitrate reduction reaction to synthesize ammonia, it can achieve a high ammonia yield and Faraday efficiency.

Claims

1. A method for preparing a water slag-based nitrate reduction catalyst, characterized in that, Includes the following steps: (a) Grinding to obtain water slag with a particle size of 50-200 μm; (b) Prepare an alcohol-water mixture with a volume ratio of ethanol to water of 1:2 to 1:4; (c) Add the water residue from step (a) to the alcohol-water mixture from step (b) and stir; the amount of alcohol-water mixture added per gram of water residue is 60-100 mL. (d) During the stirring process, hexadecyltrimethylammonium bromide is added to the alcohol-water mixture from step (c), with an addition amount of 0.1-0.6 g per gram of water residue; then ammonia is slowly added to the alcohol-water mixture, with an ammonia concentration of 5-30%, and an addition amount of 8-16 mL per gram of water residue. (e) After stirring, collect the sample by centrifugation and wash with deionized water; (f) After drying the sample washed in step (e), calcin it in an air atmosphere to obtain the pretreated water slag-based carrier. (g) Dissolve the copper source and cobalt source in deionized water to prepare... and A copper-cobalt mixed aqueous solution with a mass ratio of 1:5-5:1 and a total metal ion concentration of 0.3 mol / L; (h) The pretreated water slag-based carrier obtained in step (f) is added to the copper-cobalt mixed aqueous solution obtained in step (g) for coprecipitation reaction; the amount of copper-cobalt mixed aqueous solution added per gram of water slag is 40-70 mL. (i) The mixture after the reaction in step (h) is subjected to aging treatment; (j) After filtering, washing and drying the aging product from step (i), it is calcined in air to obtain the catalyst.

2. The preparation method according to claim 1, characterized in that: In step (c), the stirring rate is 200-350 r / min and the reaction time is 2-4 h.

3. The preparation method according to claim 1, characterized in that: In step (f), the calcination temperature is 400-600℃ and the holding time is 2-4h.

4. The preparation method according to claim 1, characterized in that: In step (g), the copper source is a soluble copper salt such as copper nitrate, copper sulfate, or copper nitrate trihydrate, and the cobalt source is a soluble cobalt salt such as cobalt nitrate, cobalt sulfate, or cobalt nitrate hexahydrate.

5. The preparation method according to claim 1, characterized in that: In step (h), the stirring rate of the coprecipitation reaction is 200-350 r / min, the coprecipitation reaction temperature is 80-110℃, and the reaction time is 5-8 h.

6. The preparation method according to claim 1, characterized in that: In step (i), the aging temperature is 90-120℃ and the aging time is 1-3h.

7. The preparation method according to claim 1, characterized in that: In step (j), the calcination temperature is 400-600℃ and the holding time is 3-6h.

8. A water slag-based nitrate reduction catalyst, characterized in that, It is obtained by the preparation method described in any one of claims 1-7.

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