A carbon nitride-coated nickel-ruthenium alloy catalyst, a preparation method and application thereof

Abstract

The application relates to a carbon nitride-coated nickel-ruthenium alloy catalyst and a preparation method and application thereof, and belongs to the technical field of ammonia decomposition catalyst preparation. The method comprises the following steps: mixing a nickel source and a ruthenium source into a metal salt mixture according to the molar ratio of nickel to ruthenium being (7-9):(1-3); mixing a complexing agent, the metal salt mixture, a combustion-supporting agent and a solvent into a mixed solution according to the molar ratio of the complexing agent to the metal elements in the metal salt mixture being (1.0-1.5):1; removing a set amount of solvent in the mixed solution to obtain a first mixture; initiating a self-spread combustion reaction of the mixture under a first protective atmosphere at 200-350 DEG C to obtain a second mixture; and baking the second mixture under a second protective atmosphere to 600-750 DEG C for 1-3 hours to obtain the carbon nitride-coated nickel-ruthenium alloy catalyst. The complexing agent avoids particle aggregation caused by solute segregation in the drying and baking process of the traditional impregnation method, and the self-spread exothermic combustion reaction promotes complete mutual solubility of Ni-Ru to form an alloy structure with a crystal lattice match.

Description

Technical Field

[0001] This invention belongs to the field of ammonia decomposition catalyst preparation technology, specifically relating to a carbon nitride-coated nickel-ruthenium alloy catalyst, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Ammonia (NH3) has a high hydrogen storage density (liquid ammonia has a volumetric hydrogen storage density of 121 kg / m³). 3 With its advantages of easy liquefaction, safe storage and transportation, and zero carbon emissions, ammonia is a highly promising hydrogen energy carrier. However, it needs to be decomposed into hydrogen gas before it can be used as hydrogen energy. Efficient ammonia decomposition catalysts are the core technology for achieving efficient "ammonia-hydrogen" conversion at the end.

[0004] Ruthenium (Ru)-based catalysts exhibit the highest ammonia decomposition activity at low temperatures, but they are expensive. Doping with other metals to prepare bimetallic catalysts can effectively reduce costs. However, when preparing bimetallic catalysts using the impregnation method, the metal components undergo phase separation or uneven particle aggregation at the microscale, failing to form a fully alloyed active interface. Furthermore, in alkaline electrochemical reaction environments, non-noble metals are susceptible to the acidity / alkalinity of the catalyst surface and the influence of oxide interfaces, leading to slow electron kinetics. These factors affect the catalytic performance of bimetallic catalysts. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a carbon nitride-coated nickel-ruthenium alloy catalyst, its preparation method, and its application. The catalyst achieves rapid exothermic reaction in a short time through a self-propagating instantaneous combustion method, which promotes the complete alloying of Ni and Ru. The expanded gas is used to form a porous framework with a high specific surface area, resulting in a carbon nitride-coated Ni-Ru alloy catalyst with ultra-high dispersion and strong interfacial electronic effects.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, a method for preparing a carbon nitride-coated nickel-ruthenium alloy catalyst includes the following steps: Nickel nitrate and nitrite ruthenium nitrate were mixed into a metal salt mixture according to a molar ratio of nickel to ruthenium of (7~9):(1~3); According to the ratio of the molar ratio of metal elements in the complexing agent and metal salt mixture to (1.0~1.5):1, and the molar ratio of nitrate ions in the combustion accelerator and metal salt mixture to (0~0.75):1, the complexing agent, metal salt mixture, combustion accelerator and solvent are mixed to form a mixture. After removing a predetermined amount of solvent from the mixture, a first mixture is obtained. The mixture is then subjected to a self-propagating combustion reaction at 200-350°C under a first protective atmosphere to obtain a second mixture. The second mixture was heated to 600-750°C and calcined for 1-3 hours under a second protective atmosphere to obtain the carbon nitride-coated nickel-ruthenium alloy catalyst. The solvent includes water, anhydrous ethanol, methanol, or a mixture of anhydrous ethanol and water.

[0007] Secondly, the carbon nitride-coated nickel-ruthenium alloy catalyst prepared by the above-mentioned method is a carbon nitride-coated nickel-ruthenium alloy catalyst.

[0008] Thirdly, the applications of the aforementioned carbon nitride-coated nickel-ruthenium alloy catalysts include their use in hydrogen production from ammonia decomposition or in the electrocatalytic reaction of hydrogen oxidation (HOR) in alkaline media.

[0009] The beneficial effects of this invention are as follows: The complexing agent used in this invention has extremely strong multidentate coordination ability, and can simultaneously and firmly complex Ni. 2+ and Ru 3+ This process creates a locked, atomically mixed state in solution. This effectively avoids particle aggregation caused by solute segregation during drying and calcination in traditional impregnation methods. Furthermore, the instantaneous high-temperature characteristics of the self-propagating exothermic combustion reaction overcome the thermodynamic barrier of bimetallic alloying, promoting complete Ni-Ru miscibility and forming an alloy structure with excellent lattice matching. Simultaneously, this interfacial effect induces high-valence / electron-deficient active sites at the microscopic level, generating a strong electronic synergistic effect within the catalyst. During the reaction, the nitrogen- and carbon-rich matrix is ​​in situ transformed into a nitrogen-doped carbon (NC) ultrathin layer, which coats the surface of the RuNi alloy nanoparticles, preventing high-temperature sintering through spatial confinement. In ammonia decomposition for hydrogen production: it significantly improves the interfacial charge transfer rate and reaction kinetics, resulting in excellent low-temperature catalytic activity and operational stability of the catalyst. In alkaline hydroxide (HOR) electrocatalysis: the ultrathin shell finely modulates the local electronic structure of the inner alloy, constructs an interfacial hydrogen overflow path, and effectively reduces the kinetic resistance of hydrogen desorption and hydroxyl adsorption in alkaline media, thereby exhibiting electrocatalytic HOR activity and antioxidant passivation ability that surpasses traditional pure nickel catalysts. Attached Figure Description

[0010] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0011] Figure 1The images show the transmission electron microscopy (TEM) results of the catalyst in Example 2, where A is a low-magnification TEM image of the catalyst and B is a high-resolution HRTEM image of a single nanoparticle.

[0012] Figure 2 The images show the microstructure and elemental distribution of the catalyst in Example 2. In the images, A is the superimposed image of each element, B is the HAADF-STEM image, C is the surface scan distribution of carbon, D is the surface scan distribution of nitrogen, E is the surface scan distribution of Ni, and F is the surface scan distribution of Ru.

[0013] Figure 3 for Figure 2 EDS energy spectrum of the region.

[0014] Figure 4 This is a temperature-conversion rate statistical chart for each catalyst in Example 3.

[0015] Figure 5 This is a time-conversion statistics chart of the catalyst in Example 2 of Example 3.

[0016] Figure 6 This is a statistical graph of the potential-current density of each catalyst in Example 4. Detailed Implementation

[0017] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0018] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0019] The substances involved in the following specific embodiments include: Nickel nitrate hexahydrate, Ni(NO3)2·6H2O, CAS number: 13478-00-7; Ruthenium nitrite nitrate, Ru(NO)(NO3) x (OH) y The CAS number is 34513-98-9, where x+y=3, and the ruthenium mass fraction is ≥31.3%. Ethylenediaminetetraacetic acid, abbreviated as EDTA, has the CAS number 60-00-4.

[0020] Disodium ethylenediaminetetraacetate, abbreviated as EDTA-2Na, has the CAS number 139-33-3; Urea, CH4N2O, CAS number 57-13-6; Glycine, NH2CH2COOH, CAS number 56-40-6; Melamine, C3H6N6, CAS number 108-78-1.

[0021] One or more embodiments of the present invention provide a method for preparing a carbon nitride-coated nickel-ruthenium alloy catalyst, comprising the following steps: Nickel nitrate and nitrite ruthenium nitrate were mixed into a metal salt mixture according to a molar ratio of nickel to ruthenium of (7~9):(1~3); The complexing agent, metal salt mixture, combustion accelerator and solvent are mixed into a mixture according to the following ratio: the molar ratio of metal elements in the complexing agent and metal salt mixture is (1.0~1.5):1, and the molar ratio of nitrate in the combustion accelerator and metal salt mixture is (0~0.75):1. After removing a predetermined amount of solvent from the mixture, a first mixture is obtained. The mixture is then subjected to a self-propagating combustion reaction at 200-350°C under a first protective atmosphere to obtain a second mixture. The second mixture is heated to 600-750°C and calcined for 1-3 hours under a second protective atmosphere to obtain the carbon nitride-coated nickel-ruthenium alloy catalyst.

[0022] In the above process, a nickel source is used to provide nickel in the bimetallic catalyst, and a ruthenium source is used to provide ruthenium in the bimetallic catalyst. The complexing agent has multidentate coordination ability and simultaneously complexes Ni. 2+ and Ru 3+ In solution, an atomic-level mixed state is formed, providing a basis for preventing segregation and preparing completely miscible bimetallic alloys. During the self-propagating combustion reaction, metal nitrates are used as oxidants and combustion promoters as reducing agents to initiate the self-propagating combustion reaction, providing phase transition energy in a very short time to promote the complete alloying of Ni and Ru, generating uniform nano-RuNi alloys. At the same time, the N2, CO2, and H2O gases generated instantaneously during the reaction cause the material to expand, forming a porous framework with a high specific surface area. During the subsequent calcination process, the porous framework undergoes pyrolysis with the highly cross-linked organic matrix (containing nitrogen and carbon), forming an ultrathin nitrogen-doped carbon (NC) layer in situ on the surface of the RuNi alloy nanoparticles.

[0023] The molar ratio of nickel to ruthenium is (7~9):(1~3). This molar ratio is set based on the synergistic catalytic effect and the balance of active sites of the two. If the proportion of nickel is too high, the activation energy of the catalyst under low temperature conditions will be significantly increased, reducing the catalytic efficiency of the catalyst. If the proportion of nickel is too low and the proportion of ruthenium is too high, on the one hand, the manufacturing cost of the catalyst will be greatly increased, and on the other hand, ruthenium nanoparticles will easily sinter and aggregate during high temperature or long-term catalytic operation, reducing the structural stability of the catalyst.

[0024] The molar ratio of metal elements in the complexing agent and metal salt mixture is (1.0~1.5):1. The molar ratio of the complexing agent to the metal elements is set based on the complete coordination saturation of the metal ions and the uniformity of the precursor network. If the molar ratio is lower than 1.0, some metal ions in the system cannot be effectively complexed, and heterogeneous local segregation is prone to occur during solvent evaporation, resulting in the aggregation of unalloyed single phases in the final product. If the molar ratio is higher than 1.5, the excessive complexing agent not only increases the cost of raw materials, but also causes excessive carbon layers due to local carbon excess during subsequent self-propagation and calcination processes. This carbon layer can wrap and bury the active sites of the alloy, hindering the mass transfer and diffusion of reactants and reducing catalytic activity.

[0025] The self-propagating combustion reaction time is determined by the stoichiometry of the precursor itself, and can be indirectly controlled by adjusting the ratio of the combustion-supporting agent and the preheating temperature. The control time is 5~30s. If the reaction time is too long (>30s), it indicates that the reaction wave propagation dynamics are slow and the heat release intensity is insufficient, making it difficult to provide the instantaneous high energy to promote the complete mutual dissolution and alloying of Ni and Ru. If the reaction time is too short (<5s), it indicates that the reaction is too instantaneous and violently deflagration. The extremely high local instantaneous temperature can easily cause the generated nano-alloy grains to undergo violent sintering and agglomeration, resulting in a serious increase in particle size.

[0026] Optionally, the nickel nitrate can be added in the form of hydrated nickel nitrate. Both nickel nitrate and hydrated nickel nitrate are soluble in solvents such as water, and the nitrate ions contained therein can participate in the self-propagating reaction as oxidants.

[0027] Optionally, ruthenium nitrite with nitrosyl has excellent water solubility. Its molecular structure contains both nitrate (-NO3) and nitrosyl (-NO) groups, which are highly oxidizing. It can work synergistically with nickel nitrate as a composite oxidant in self-propagating combustion reactions and release a large amount of gas to form a porous framework structure when it is exothermically heated at high temperature.

[0028] Optionally, the complexing agent includes one or more of EDTA and EDTA-2Na, both of which are hexadectic ligands capable of binding metal ions and forming stable chelates in solution, thereby achieving an atomic-level mixed state of nickel and ruthenium in solution.

[0029] Optionally, the combustion aid includes one or more of urea, glycine, and melamine. These compounds are rich in carbon and nitrogen elements and can serve as high-quality carbon nitride precursors during high-temperature in-situ pyrolysis and polycondensation. This facilitates the in-situ construction of an ultrathin nitrogen-doped carbon (NC) layer with high conductivity and abundant active sites on the surface of alloy particles. These combustion aid molecules contain abundant amino (-NH2) and carboxyl (-COOH) groups, which themselves possess weak auxiliary coordination ability and can synergistically stabilize metal ions with the main complexing agent. At the same time, their redox reaction with metal nitrates has moderate exothermic reaction and large gas production, which can provide ideal self-propagating instantaneous phase transition energy and in-situ construct a porous framework structure.

[0030] Optionally, the solvent is deionized water; the reason for choosing deionized water as the solvent is that it has high solubility for metal nitrates and EDTA / EDTA-2Na, which can ensure that the components achieve the highest molecular and atomic level uniform mixing in the liquid phase, and deionized water is low in cost, non-toxic and environmentally friendly.

[0031] Optionally, during the process of adding a complexing agent, a mixture of metal salts, and a combustion accelerant to the solvent to obtain a mixture, ammonia is added to the mixture to adjust its pH to 7-10. The reason for adjusting the pH to this range is as follows: if pH < 5, EDTA and its sodium salt have extremely low solubility and are easily precipitated; if pH < 7, complexation is incomplete, easily leading to heterogeneous segregation; at pH 7-10, all carboxyl groups of the complexing agent are completely deprotonated, significantly enhancing the complexing ability and facilitating the formation of homogeneous and stable metal complexes; if pH > 10, metal ions readily react with OH-. - They combine to form an amorphous metal hydroxide precipitate.

[0032] Optionally, solvent removal methods include rotary evaporation or drying, reducing the mass of the first mixture to 15-25% of the total mass of the liquid mixture. Solvent removal does not involve completely removing water to an absolutely dry solid state, but rather removing the solvent until the system exhibits a viscous, semi-solid wet gel state. The purpose of removing the solvent to this gel state is twofold: firstly, to preserve the integrity of the complex network structure, constructing a three-dimensional porous framework and a uniform, ultrathin confined shell during the self-propagating reaction; secondly, to prevent excessive solvent absorption of the heat released by the self-propagating reaction, thus inhibiting the reaction. Specifically, this involves evaporation in an oven at 75-85 degrees Celsius for 4-6 hours, or evaporation at 80 degrees Celsius for 4-6 hours in a rotary evaporator.

[0033] Optionally, the first protective atmosphere includes either argon or nitrogen. The function of the first protective atmosphere is to provide a low-oxygen or oxygen-free local environment for the self-propagating combustion reaction, prevent the combustion accelerant from undergoing disordered and violent combustion with oxygen in the air, and ensure that the redox reaction is confined to the nitrate, nitrosyl group and combustion accelerant, thereby ensuring the controllability of heat release and gas-producing porous framework.

[0034] Optionally, the second mixture is ground; the loose porous powder obtained after self-propagation is ground to 100-200 mesh; the grinding fineness will significantly affect the uniformity of mass and heat transfer during subsequent high-temperature calcination; if the grinding particles are too coarse (not passing through 100 mesh), the internal heat and reducing atmosphere cannot penetrate evenly during tube furnace calcination, resulting in incomplete carbonization or uneven alloying of some organic matter; if the grinding is too fine (more than 300 mesh), the powder is too densely packed, and the small amount of gas released during calcination will cause the powder to be lifted and lost, and will also squeeze and destroy the original three-dimensional porous skeleton mass transfer channels formed by self-propagation.

[0035] Optionally, the second protective atmosphere includes one of argon, nitrogen, and ammonia. The function of the second protective atmosphere is to maintain a reducing or inert non-oxidizing environment during the high-temperature calcination stage, prevent the nano-RuNi alloy from being oxidized at high temperatures, and promote the graphitization of the carbon network and the doping of nitrogen atoms. Ammonia can be added at this time because the NH3 introduced during the high-temperature calcination stage will undergo weak dissociation to produce highly active nitrogen-containing free radicals and hydrogen. This can not only serve as a supplementary nitrogen source to significantly increase the doping concentration of active pyridine nitrogen and pyrrole nitrogen in the outer carbon layer (NC), but also provide a reducing environment to protect the alloy from oxidation. However, in the first stage (self-propagating stage), the system itself is a strong redox environment rich in nitrate. If flammable and explosive NH3 gas is introduced in advance, it will cause an uncontrollable and violent explosion with the high-valence nitrate in the system when it is ignited, posing a serious safety hazard and failing to play the regulatory role of in-situ coating.

[0036] Optionally, the calcination is carried out in a tube furnace; the second mixture is ground and spread evenly in a corundum boat, and then the corundum boat is placed in a tube furnace for calcination, with a spreading thickness of 5~10mm; the heating rate of the calcination process is 2~5℃ / min.

[0037] Optionally, the calcined product is washed sequentially with deionized water and ethanol, then vacuum dried; it is then tableted, crushed, and sieved to a set mesh size to obtain the catalyst product.

[0038] One or more embodiments of the present invention provide a carbon nitride-coated nickel-ruthenium alloy catalyst prepared by the above-mentioned method for preparing carbon nitride-coated nickel-ruthenium alloy catalyst.

[0039] The prepared catalyst consists of a porous framework and embedded RuNi alloy nanoparticles with a particle size of 10–50 nm, with a nitrogen-doped carbon (NC) layer of 5–15 nm thickness coating the surface of the alloy nanoparticles. A highly lattice-matched alloy structure is formed during the self-propagating combustion reaction. The interfacial effect of the alloy structure induces high-valence / electron-deficient active sites at the microscopic level, resulting in a strong electronic synergistic effect within the catalyst. The in-situ generated nitrogen-doped carbon (NC) layer provides spatial confinement for the internal RuNi alloy particles, preventing sintering and loss during high-temperature ammonia decomposition (>500℃) or long-term electrocatalytic operation. Furthermore, the highly conductive porous framework significantly enhances the charge transfer rate in the electrocatalytic HOR reaction; while the nitrogen atoms incorporated into the nitrogen-doped carbon (NC) ultrathin layer can modulate the local electronic structure of the carbon layer. In the alkaline HOR / HER reaction, the NC ultrathin layer effectively optimizes the surface acidity / alkalinity and enhances the resistance to OH-. - The adsorption kinetics, and as a medium for proton transfer.

[0040] The present invention provides one or more embodiments that provide the application of the above-mentioned carbon nitride-coated nickel-ruthenium alloy catalyst, including its application in ammonia decomposition for hydrogen production or alkaline hydrogen oxidation reaction; in different reactions, it can significantly accelerate the reaction from the perspective of reaction kinetics through the "hydrogen spillover" effect.

[0041] In the ammonia decomposition reaction for hydrogen production, the Ru sites exhibit extremely high initial activity for breaking the NH bond, efficiently catalyzing the stepwise dehydrogenation of NH3 molecules. However, the Ru sites alone have excessively strong adsorption of conventional hydrogen atoms, easily leading to hydrogen poisoning. In this scheme, after Ru forms an alloy with Ni, the intermediate hydrogen atoms (H2O) generated... * It can rapidly undergo "hydrogen spillover" through strong interfaces, migrating to Ni sites or alloy interfaces with better hydrogen adsorption energy for complex desorption (2H). * → H2); This effectively releases the active sites of Ru and significantly reduces the low-temperature activation energy of ammonia decomposition.

[0042] In the alkaline hydroxide reaction (HOR), the RuNi alloy interface exhibits excellent non-noble metal bifunctional synergistic effect: the Ru sites have excellent oxyphilicity and can adsorb OH in situ from the alkaline electrolyte. - And form Ru-OH ads Simultaneously, the connected Ni sites or alloy interfaces efficiently chemisorb H2 and dissociate it into H2. * Subsequently, the adsorbed H * Hydrogen rapidly migrates to the alloy interface via "hydrogen spillover" and interacts with OH groups at the Ru sites. ads Interfacial nucleophilic reaction (H) occurs * + OH ads→ H2O + e - This dual-site synergistic mechanism perfectly overcomes the bottleneck of slow hydrogen desorption and hydroxide kinetics on a single metal.

[0043] The present invention will be further described below with reference to specific embodiments.

[0044] Example 1 A carbon nitride-coated nickel-ruthenium alloy catalyst is prepared from raw materials including 2.61 g of nickel nitrate hexahydrate (approximately 9 mmol, containing 18 mmol of nitrate), 0.32 g of ruthenium nitrite nitrate (approximately 1 mmol, containing 3 mmol of nitrate), and 4.36 g of EDTA-2Na (approximately 13 mmol). The calculated molar ratio of Ni to Ru is 9:1, and the molar ratio of complexing agent to metal ions (the sum of nickel and ruthenium elements) is 1.3:1. In this embodiment, no additional combustion improver is added.

[0045] The preparation process includes: dissolving nickel nitrate hexahydrate and ruthenium nitrite nitrate in 50 mL of deionized water and stirring until completely dissolved, then adding EDTA-2Na and stirring until completely dissolved and clear, and adding ammonia water dropwise to adjust the pH of the system to 8 during the dissolution and stirring process to obtain a mixed solution.

[0046] After stirring the mixture at room temperature for 1 hour, it was transferred to an 80°C oven to evaporate the solvent for 5 hours, yielding a dark green, transparent, viscous gel (i.e., the first mixture, at which point the gel mass was approximately 20% of the original mixture mass). The dark green, transparent, viscous gel was transferred to a quartz boat and placed on a preheated 350°C heating platform in a fume hood to initiate self-propagating combustion. High-purity nitrogen was used as the primary protective atmosphere. Due to the absence of a combustion accelerant for rapid deflagration, the reaction was relatively mild, with a self-propagating combustion time of 20 seconds. After the reaction, a black, fluffy solid was obtained (i.e., the second mixture).

[0047] The black, fluffy solid was ground to a fineness of 200 mesh and then spread evenly in a corundum boat to a thickness of 5 mm. The corundum boat was placed in a tube furnace and calcined at 750 °C for 2 hours under an argon atmosphere at a heating rate of 2 °C / min. The calcined product was then cooled to room temperature. The product was washed several times with deionized water and anhydrous ethanol, dried overnight in a vacuum oven at 60 °C, pressed into tablets, crushed, and sieved to 50 ± 10 mesh to obtain Ni. 0.9 Ru 0.1 @NC catalyst.

[0048] Example 2 A carbon nitride-coated nickel-ruthenium alloy catalyst is prepared from raw materials including 2.04 g of nickel nitrate hexahydrate (approximately 7 mmol, containing 14 mmol of nitrate), 0.97 g of ruthenium nitrite nitrate (approximately 3 mmol, containing 9 mmol of nitrate), 4.36 g of EDTA-2Na (approximately 13 mmol), and a composite combustion improver (approximately 17.3 mmol) composed of 0.80 g of urea and 0.30 g of glycine. The calculated molar ratio of Ni to Ru is 7:3, the molar ratio of the complexing agent to metal ions (the sum of nickel and ruthenium elements) is 1.3:1, and the molar ratio of the combustion improver to the total metal salt nitrate is approximately 0.75:1.

[0049] The preparation process includes: dissolving nickel nitrate hexahydrate and ruthenium nitrite nitrate in 50 mL of deionized water and stirring until completely dissolved, then adding EDTA-2Na and stirring until completely dissolved and clear, then adding urea and glycine and stirring until evenly mixed, and adding ammonia water dropwise to adjust the pH of the system to 8 during the dissolution and stirring process to obtain a mixed solution.

[0050] After stirring the mixture at room temperature for 1 hour, it was transferred to a rotary evaporator and the solvent was evaporated at 80°C for 5 hours to obtain a dark green, transparent, viscous gel (i.e., the first mixture, at which point the gel mass was approximately 20% of the original mixture mass). The dark green, transparent, viscous gel was transferred to a quartz boat and placed on a preheated heating platform at 220°C in a fume hood to initiate self-propagating combustion. High-purity argon was used as the first protective atmosphere during the process. Due to the rapid ignition effect of the combustion accelerant, the self-propagating combustion time was only 8 seconds, and a black, fluffy solid (i.e., the second mixture) was obtained after the reaction.

[0051] The black, fluffy solid was ground to a fineness of 150 mesh and then spread evenly in a corundum boat to a thickness of 5 mm. The corundum boat was placed in a tube furnace and calcined at 700 °C for 2 hours under an argon atmosphere at a heating rate of 2 °C / min. The calcined product was then cooled to room temperature. The product was washed several times with deionized water and anhydrous ethanol, dried overnight in a vacuum oven at 60 °C, pressed into tablets, crushed, and sieved to 50 ± 10 mesh to obtain Ni0.7Ru. 0.3 @NC catalyst.

[0052] Comparative Example 1 This comparative example provides a carbon nitride-coated nickel catalyst, prepared from 2.91 g of nickel nitrate hexahydrate (approximately 10 mmol, containing 20 mmol of nitrate), 3.70 g of EDTA-2Na (approximately 11 mmol), and 1.40 g of urea (approximately 23.3 mmol). The molar ratio of the complexing agent to the metal ions (the sum of nickel and ruthenium) is 1.1:1, and the molar ratio of the combustion improver to the total metal salt nitrate is approximately 1.17:1.

[0053] The preparation process includes: dissolving nickel nitrate hexahydrate in 50 mL of deionized water and stirring until completely dissolved, then adding EDTA-2Na and stirring until completely dissolved and clear, then adding urea and stirring until evenly mixed, and adding ammonia dropwise to adjust the pH of the system to 8 during the dissolution and stirring process to obtain a mixed solution.

[0054] After stirring the mixture at room temperature for 1 hour, it was transferred to an 80°C oven to evaporate the solvent for 5 hours, resulting in a blue transparent viscous gel (i.e., the first mixture, at which point the gel mass was approximately 20% of the original mixture mass). The blue transparent viscous gel was then transferred to a quartz boat and placed on a preheated heating platform at 220°C in a fume hood to initiate self-propagating combustion. High-purity argon was used as the first protective atmosphere during the process. Due to the rapid ignition effect of the combustion aid, the self-propagating combustion time was only 8 seconds, resulting in a black fluffy solid (i.e., the second mixture).

[0055] The black, fluffy solid was ground to a fineness of 150 mesh and spread evenly in a corundum boat with a thickness of 5 mm. The corundum boat was placed in a tube furnace and calcined at 700 °C for 2 h under an argon atmosphere at a heating rate of 2 °C / min. The calcined product was then cooled to room temperature. The calcined product was washed several times with deionized water and anhydrous ethanol, dried overnight in a vacuum oven at 60 °C, and then pressed, crushed, and sieved to 50 ± 10 mesh to obtain the Ni@NC catalyst.

[0056] Detection example For Ni0.7Ru in Example 2 0.3 The NC catalyst was analyzed to obtain transmission electron microscopy (TEM) scans and EDS (electron spectroscopy) surface scans of each element.

[0057] Transmission electron microscopy scanning image as shown Figure 1 As shown, Figure 1 A in the image is a low-magnification TEM image of the catalyst. It can be seen that the catalyst as a whole presents a continuous three-dimensional porous framework support structure, and the metal nanoparticles are highly dispersed and embedded in the framework with an average particle size of 20~50 nm. No grain sintering or severe agglomeration was observed. Figure 1 B in the image is a high-resolution HRTEM image of a single nanoparticle, which shows that the metal nanoparticle has extremely high crystallinity and is coated with a nitrogen-doped carbon (NC) layer with a thickness of 5~10 nm on its surface.

[0058] EDS surface scan distribution maps of each element are as follows Figure 2 As shown, where, Figure 2 In this diagram, A represents the superimposed image of all elements. Figure 2 B in the image represents the HAADF-STEM image. Figure 2 In the diagram, C represents the monochromatic mapping distribution of carbon. Figure 2 In the diagram, D represents the monochromatic mapping distribution of nitrogen. Figure 2In the diagram, E represents the monochromatic mapping distribution of the Ni element. Figure 2 In this diagram, F represents the monochromatic mapping distribution of the Ru element. Figure 2 The corresponding EDS spectrum in the middle is as follows Figure 3 As shown in the figure, the results indicate that, on the one hand, the signals of Ni (red) and Ru (green) are completely coincident and highly dispersed at the single-particle scale, confirming the efficient alloying of the bimetallic alloy and the formation of a uniform nanostructure; on the other hand, C (cyan) and N (blue) are distributed in a large-area continuous network substrate, achieving effective confined encapsulation of the alloy particles. The high degree of agreement between the integral area ratio of the metal elements and the stoichiometric ratio of the raw materials confirms the successful construction of a high-purity, accurately proportioned carbon nitride-coated nickel-ruthenium alloy confined catalyst.

[0059] Example 3 The catalytic performance test of the catalysts obtained in Examples 1, 2 and Comparative Example 1 for hydrogen production by ammonia decomposition includes the following steps.

[0060] Weigh 200 mg of catalyst (selected from one of Example 1, Example 2 and Comparative Example 1), mix it with 600 mg (3 times the mass) of the same mesh size of quartz sand, and then load it into a quartz fixed bed reactor with an inner diameter of 10 mm.

[0061] Before the reaction, the reactor was heated to 500℃ for 1 h under a pure NH3 atmosphere (20 mL / min) for reduction. Then, the temperature was increased to 450℃, 475℃, 500℃, 525℃, 550℃, 575℃, 600℃, or 625℃, and the NH3 flow rate was adjusted to a space velocity (GHSV) of 15,000 mL / g. cat In a quartz fixed-bed reactor (hereinafter referred to as the reactor), the untreated feed gas and the treated product gas are detected in real time by online gas chromatography at the inlet and outlet. The detected substances include the concentrations of N2, H2 and unreacted NH3, and the ammonia decomposition rate (also known as the conversion rate) is calculated based on this. The conversion rate is the ratio of the difference between the ammonia molar flow rate at the reactor inlet and the ammonia molar flow rate at the reactor outlet to the ammonia molar flow rate at the reactor inlet.

[0062] After stabilizing at each temperature point for 0.5 hours to ensure the catalytic state reaches steady state, samples were taken for testing, and the results are as follows: Figure 4 As shown, Ni 0.7 Ru 0.3 The @NC catalyst achieves a conversion rate of 80.3% at 550°C and 99% at 625°C; Ni prepared in Example 1 0.9 Ru 0.1The Ni@NC catalyst exhibited a nitrogen decomposition rate of 72.3% at 550℃ and 85.5% at 625℃. In contrast, the Ni@NC catalyst prepared in Comparative Example 1 showed the worst catalytic performance, with a conversion rate of only 27.1% at 550℃ and only 66.4% even at 625℃. These results indicate that the bimetallic alloy structure (especially when the Ni:Ru ratio is 7:3) has a significant electron-synergistic catalytic enhancement effect on the nitrogen decomposition reaction.

[0063] Maintaining a temperature of 625℃ continuously on N i0.7 Ru 0.3 The conversion rate of the @NC catalyst was detected, and the results are as follows: Figure 5 As shown, N i0.7 Ru 0.3 The @NC catalyst maintained a conversion rate of over 95% after 100 hours of continuous operation at 625°C, meaning its catalytic activity decreased by less than 5%, demonstrating exceptional high-temperature thermal stability and resistance to sintering loss. This is primarily attributed to the in-situ generated nitrogen-doped carbon (NC) ultrathin layer acting as a barrier, which creates a strong spatial confinement effect on the internal RuNi alloy particles, preventing thermal agglomeration of metal grains at high temperatures.

[0064] Example 4 The alkaline hydroxide reaction (HOR) performance tests of the catalysts obtained in Examples 1, 2 and Comparative Example 1 included the following steps.

[0065] Weigh 5 mg of catalyst (selected from one of Example 1, Example 2 and Comparative Example 1) and add it to a mixed solvent consisting of 480 μL isopropanol, 500 μL deionized water and 20 μL Nafion 5%. Disperse the catalyst by ultrasonication for 30 min to obtain a uniform catalyst slurry. Use a micropipette to pick up 5 μL of the slurry and drop it onto the surface of a glassy carbon electrode. Let it air dry at room temperature to obtain the working electrode.

[0066] A standard three-electrode system was used, with a high-purity graphite rod as the counter electrode and a saturated calomel electrode as the reference electrode. Electrochemical tests were performed in an electrolyte of 0.1 MkOH saturated with H2. Linear sweep voltammetry (LSV) curves were measured at a scan rate of 5 mV / s.

[0067] Test results are as follows Figure 6 As shown in the figure, the polarization curves show that the HOR polarization current density of the catalyst in Comparative Example 1 (Ni@NC) is almost zero, and its current density is 0.005 mA / cm² at an overpotential of 0.1 V vs. RHE. 2 This demonstrates the extremely slow HOR reaction kinetics of conventional pure nickel-based catalysts in alkaline media; while for Example 1 (Ni...) with the introduction of a small amount of the noble metal ruthenium... 0.9 Ru 0.1@NC), although the slope of its polarization curve and current density are slightly improved compared to Comparative Example 1, the overall improvement in reaction kinetics is still limited; in contrast, the Ni prepared in Example 2 of this invention 0.7 Ru 0.3 The slope and current density of the polarization curve of the @NC catalyst are significantly improved compared to Comparative Example 1, exhibiting extremely high exchange current density, reaching approximately 0.46 mA / cm² at an overpotential of approximately 0.15 V vs. RHE. 2 The maximum limiting saturation current density. The above results strongly demonstrate that when the Ni:Ru molar ratio is within the optimal synergistic range of 7:3, the carbon nitride-coated bimetallic alloy constructed by the complexation self-propagating method can induce highly active interfacial electronic effects.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the 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 scope of protection of the present invention.

Claims

1. A method for preparing a carbon nitride-coated nickel-ruthenium alloy catalyst, characterized in that, Includes the following steps: Nickel nitrate and nitrite ruthenium nitrate were mixed into a metal salt mixture according to a molar ratio of nickel to ruthenium of (7~9):(1~3); According to the ratio of the molar ratio of metal elements in the complexing agent and the metal salt mixture being (1.0~1.5):1, and the molar ratio of nitrate ions in the combustion accelerator and the metal salt mixture being 0.75:1, the complexing agent, the metal salt mixture, the combustion accelerator and the solvent are mixed to form a mixture. After removing a predetermined amount of solvent from the mixture, a first mixture is obtained. The mixture is then subjected to a self-propagating combustion reaction at 200-350°C under a first protective atmosphere to obtain a second mixture. The second mixture was heated to 600-750°C and calcined for 1-3 hours under a second protective atmosphere to obtain the carbon nitride-coated nickel-ruthenium alloy catalyst. The solvent includes water or anhydrous ethanol; The complexing agent includes one or more of EDTA and EDTA-2Na; The combustion aid includes one or more of urea, glycine, and melamine; In the process of adding a complexing agent, a mixture of metal salts and a combustion accelerant to a solvent to obtain a mixture, ammonia water is added to the mixture to adjust the pH of the mixture to 7-10.

2. The method for preparing the carbon nitride-coated nickel-ruthenium alloy catalyst as described in claim 1, characterized in that, The first protective atmosphere includes either argon or nitrogen. The second protective atmosphere includes one of argon, nitrogen, and ammonia.

3. The method for preparing the carbon nitride-coated nickel-ruthenium alloy catalyst as described in claim 1, characterized in that, The calcination is carried out in a tube furnace; the second mixture is ground and spread evenly in a corundum boat, and then the corundum boat is placed in the tube furnace for calcination, with a spreading thickness of 5~10mm; the heating rate of the calcination process is 2~5℃ / min.

4. The method for preparing the carbon nitride-coated nickel-ruthenium alloy catalyst as described in claim 1, characterized in that, The calcined product was washed sequentially with deionized water and ethanol, then vacuum dried; it was then tableted, crushed, and sieved to a set mesh size to obtain the catalyst product.

5. The method for preparing the carbon nitride-coated nickel-ruthenium alloy catalyst as described in claim 1, characterized in that, Methods for removing solvent include rotary evaporation or drying, so that the mass of the first mixture is 15-25% of the mass of the liquid mixture.

6. A carbon nitride-coated nickel-ruthenium alloy catalyst prepared according to the preparation method of the carbon nitride-coated nickel-ruthenium alloy catalyst as described in any one of claims 1-5.

7. The application of the carbon nitride-coated nickel-ruthenium alloy catalyst as described in claim 6, characterized in that, This includes applications in ammonia decomposition for hydrogen production or alkaline hydroxide reactions.

Images