Monatomic-cluster double-active-site catalyst for efficient ammonia cracking hydrogen production and preparation method of monatomic-cluster double-active-site catalyst

Abstract

The invention discloses a monatomic-cluster double-active-site efficient ammonia cracking hydrogen production catalyst and a preparation method thereof, and belongs to the field of new energy catalytic materials. The catalyst comprises a 2-methylimidazole zinc derived nitrogen-doped carbon-loaded cobalt monatomic carrier, a molybdenum disulfide nanosheet-loaded iron cluster carrier, monatomic active metal, cluster active metal and an auxiliary agent. Wherein the 2-methylimidazole zinc derived nitrogen-doped carbon-loaded cobalt monatomic carrier is prepared by the following steps: stirring 2-methylimidazole, zinc acetate and cobalt nitrate hexahydrate in methanol to generate a ZIF-8 precursor, washing, drying, and calcining in an H2 / Ar mixed atmosphere, thereby obtaining the 2-methylimidazole zinc derived nitrogen-doped carbon-loaded cobalt monatomic carrier; the molybdenum disulfide nanosheet loaded iron cluster carrier is prepared by carrying out hydrothermal reaction on ammonium molybdate and thiourea to generate MoS2 nanosheets and then loading iron clusters. The catalyst prepared by the invention has high activity, long service life and industrial applicability.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy catalytic materials, and in particular to a high-efficiency ammonia cracking hydrogen production catalyst with a single atom-cluster dual active site and a preparation method thereof. Background Art

[0002] With the urgent global demand for green, low-carbon energy, hydrogen is increasingly seen as a crucial component of the future clean energy system. However, hydrogen is difficult to store and transport at room temperature and pressure, and safety and economic issues are prominent. Ammonia, with its high hydrogen density, easy liquefaction, and carbon-free carrier, is widely considered an ideal hydrogen storage and transportation medium. To achieve efficient hydrogen release from ammonia at the terminal, the development of low-temperature, highly active, and cyclically stable ammonia cracking catalysts has become a key scientific and engineering topic. Furthermore, the future promotion of hydrogen fuel cell transportation and distributed power generation will increasingly rely on safe, efficient, and sustainable hydrogen source technologies.

[0003] Current research focuses on traditional carrier-supported catalysts with transition metals such as iron, cobalt, and nickel as active centers, as well as precious metal systems represented by ruthenium. These catalysts can achieve high ammonia conversion rates at high temperatures, but often suffer from bottlenecks such as high activation temperatures, low metal utilization, high precious metal costs, sintering deactivation, and insufficient durability. To reduce energy consumption and improve resource utilization efficiency, academia and industry urgently need to break through the limitations of existing active site structures and construct new catalytic systems with synergistic effects. Especially in the context of low carbonization, catalysts must take into account the universality of raw materials, the simplicity of preparation processes, and environmental friendliness, which places higher demands on material design.

[0004] Single-atom catalysts are believed to be able to significantly reduce the temperature of ammonia cracking due to their high atomic utilization and adjustable electronic structure; at the same time, metal clusters can provide multi-atom collaborative adsorption and dissociation channels. If the two can coexist, they will take into account both activation energy reduction and path regulation. However, existing research has mostly focused on a single site, lacking a systematic exploration of the precise construction and long-term stability of dual active sites. The present invention simultaneously anchors single-atom and cluster active centers at the heterogeneous interface of nitrogen-doped carbon and molybdenum disulfide, achieves efficient ammonia cracking through electronic coupling and defect engineering, and provides a new solution for large-scale storage and release of hydrogen energy, which has important industrial value and demonstration significance. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-efficiency ammonia cracking hydrogen production catalyst with a single atom-cluster dual active site and a preparation method, which solves the problems of existing ammonia cracking hydrogen production catalysts such as single active site, poor dispersion, and insufficient stability, resulting in low hydrogen production efficiency and easy catalyst deactivation.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0007] A high-efficiency ammonia cracking hydrogen production catalyst with a single atom-cluster dual active site, comprising the following raw materials in parts by weight:

[0008] 2-Methylimidazole zinc-derived nitrogen-doped carbon-supported cobalt single atom carrier: 250-450 parts by weight;

[0009] Molybdenum disulfide nanosheets loaded with iron clusters carrier: 200-400 parts by weight;

[0010] Single atom active metal: 5-20 parts by weight;

[0011] Cluster active metal: 10-50 parts by weight;

[0012] Additives: 10-30 parts by weight;

[0013] The preparation method of the 2-methylimidazole zinc-derived nitrogen-doped carbon-loaded cobalt single-atom carrier includes: A1, dissolving 2-methylimidazole in methanol, adding zinc acetate and cobalt nitrate hexahydrate, and stirring at room temperature to generate a ZIF-8 precursor; centrifuging the methanol to wash until neutral, and vacuum drying; A2, placing the dried ZIF-8 precursor in a tube furnace, heating it to 800-820°C in a H2 / Ar mixed atmosphere, and calcining it.

[0014] In the process of constructing the 2-methylimidazole zinc-derived nitrogen-doped carbon-loaded cobalt single-atom carrier of the present invention, 2-methylimidazole is used as an organic ligand and zinc acetate is used as a metal salt. A three-dimensional porous zinc-based metal-organic framework (ZIF-8) is formed by coordination self-assembly in a methanol solvent. The imidazole ring of 2-methylimidazole forms a hexagonal lattice structure with zinc ions through coordination bonds. Its pore size distribution matches the kinetic diameter of the cobalt precursor, achieving atomic-level dispersed anchoring of cobalt ions. Subsequent high-temperature calcination under a hydrogen-argon mixed atmosphere causes the organic components to be gradually pyrolyzed to generate a nitrogen-doped carbon skeleton, and the zinc element volatilizes in a gaseous form to form a mesoporous structure. During the calcination process, cobalt atoms are embedded in the carbon lattice through interstitial diffusion, forming strong coordination bonds with pyridinic nitrogen, and constructing stable single-atom active sites. The conjugated system of the nitrogen-doped carbon skeleton optimizes electron transport capacity and provides high-density anchoring sites for the subsequent loading of active metals.

[0015] According to a preferred embodiment of the present invention, the 2-methylimidazole was purchased from Aladdin Reagent (Shanghai) Co., Ltd. with model number A100235.

[0016] According to a preferred embodiment of the present invention, the methanol is purchased from Jiangsu Runfeng Chemical Co., Ltd., model R-001 (industrial grade, content ≥99.8%).

[0017] According to a preferred embodiment of the present invention, the zinc acetate was purchased from Aladdin Reagent (Shanghai) Co., Ltd., model A100173 (analytical grade, content ≥99.0%).

[0018] According to a preferred embodiment of the present invention, the cobalt nitrate hexahydrate is purchased from MacLean Biochemical Technology Co., Ltd., model number C100125 (analytical grade, content ≥98.0%).

[0019] According to a preferred embodiment of the present invention, the tubular furnace is purchased from Beijing Keheng Hengda Technology Co., Ltd., model SK-G06123K (maximum temperature 1200° C., suitable for calcination process).

[0020] According to a preferred embodiment of the present invention, the H2 is purchased from Sichuan Tianyi Technology Co., Ltd., model number is H2-9999 (industrial grade, purity ≥99.99%).

[0021] According to a preferred embodiment of the present invention, the Ar is purchased from Wuhan Iron and Steel Group Oxygen Co., Ltd., and the model is Ar-99999 (industrial grade, purity ≥99.999%).

[0022] According to a preferred embodiment of the present invention, the single-atom active metal (Pt) is purchased from Guiyan Platinum Co., Ltd., and the model is Pt-01 (catalyst grade, metal content ≥99.5%).

[0023] According to a preferred embodiment of the present invention, the cluster active metal (Ni) was purchased from Jiangsu Runfeng Chemical Co., Ltd., and the model number was Ni-01 (industrial grade, content ≥98.0%).

[0024] According to a preferred embodiment of the present invention, the auxiliary agent (K2O powder) is purchased from Shandong Luyang Energy Saving Materials Co., Ltd., and the model is K2O-01 (industrial grade, purity ≥99.0%).

[0025] According to a preferred embodiment of the present invention, in step A1, the molar ratio of 2-methylimidazole, zinc acetate and cobalt nitrate hexahydrate is (4-6): (2-3): (0.1-0.3); the stirring time at room temperature is 24-30 hours; the vacuum drying temperature is 60-64°C, and the drying time is 12-14 hours.

[0026] According to a preferred embodiment of the present invention, in step A2, the heating rate is 2-4°C / min; and the calcination time is 2-4h.

[0027] According to a preferred embodiment of the present invention, the preparation method of the molybdenum disulfide nanosheet-loaded iron cluster carrier includes: B1, dissolving ammonium molybdate and thiourea in deionized water, transferring to a hydrothermal reactor at 200-202°C for reaction, cooling and centrifuging to obtain MoS2 nanosheets; B2, dispersing the MoS2 nanosheets in ethanol, adding ferric chloride for ultrasonic treatment, and transferring to a hydrothermal reactor at 150-152°C for reaction.

[0028] During the construction of the molybdenum disulfide nanosheet-loaded iron cluster carrier of the present invention, ammonium molybdate and thiourea undergo a sulfur source replacement reaction under hydrothermal conditions to generate molybdenum disulfide nanosheets. The sulfur ions in the thiourea and the molybdate radicals are in dynamic equilibrium through sulfur vacancies to form a layered MoS2 structure with edge sulfur vacancies. The unpaired sulfur atoms at the sulfur vacancies provide strong adsorption sites, and the subsequent ferric chloride solution penetrates into the gaps between the nanosheets with the assistance of ultrasound, and the iron ions spontaneously aggregate into nanoscale clusters in the hydrothermal environment. Ultrasonic treatment promotes the uniform dispersion of iron salts, inhibits cluster agglomeration, and forms high-density, highly dispersed iron cluster active sites. The layered structure of MoS2 synergizes with sulfur vacancies to provide a stable anchoring environment for the iron clusters while exposing abundant active edge sites.

[0029] According to a preferred embodiment of the present invention, the ammonium molybdate is purchased from Aladdin Reagent (Shanghai) Co., Ltd., model A100173 (analytical grade, content ≥99.0%).

[0030] According to a preferred embodiment of the present invention, the thiourea is purchased from Aladdin Reagent (Shanghai) Co., Ltd., model A100235 (analytical grade, content ≥99.0%).

[0031] According to a preferred embodiment of the present invention, the deionized water was purchased from Jiangsu Runfeng Chemical Co., Ltd., model R-002 (industrial grade, conductivity ≤10 μS / cm).

[0032] According to a preferred embodiment of the present invention, the hydrothermal reactor is purchased from Beijing Keheng Hengda Technology Co., Ltd., model GSH-200 (temperature resistance 200° C., pressure resistance 0.6 MPa).

[0033] According to a preferred embodiment of the present invention, the ethanol is purchased from Jiangsu Runfeng Chemical Co., Ltd., model R-001 (industrial grade, content ≥99.8%).

[0034] According to a preferred embodiment of the present invention, the ferric chloride is purchased from Jiangsu Runfeng Chemical Co., Ltd., and the model is Fe-01 (industrial grade, content ≥98.0%).

[0035] According to a preferred embodiment of the present invention, in step B1, the reaction time is 24-30 hours.

[0036] According to a preferred embodiment of the present invention, in step B2, the ultrasonic treatment time is 1-2 hours; and the reaction time is 6-8 hours.

[0037] The present invention also provides a method for preparing the single atom-cluster dual-active site high-efficiency ammonia cracking hydrogen production catalyst, comprising the following steps:

[0038] S1. Add 2-methylimidazole zinc-derived nitrogen-doped carbon-supported cobalt single atom support and molybdenum disulfide nanosheet-supported iron cluster support into an agate mortar and grind until uniform; add active metal precursor solution dropwise to the mixture to control the total metal loading to be 1-6 wt%;

[0039] S2. Ultrasonic dispersion to form a slurry, transfer to a rotary evaporator at 60-62°C for rotary evaporation; vacuum dry the product;

[0040] S3. Finally, the single atoms were reduced at 450-452 °C in a H2 / Ar atmosphere to anchor them on the pyridinic nitrogen sites of the 2-methylimidazole zinc-derived nitrogen-doped carbon-supported cobalt single atom carrier, and the cluster active metals grew on the sulfur vacancy surface of the molybdenum disulfide nanosheet-supported iron cluster carrier.

[0041] According to a preferred embodiment of the present invention, in step S1, the mass ratio of 2-methylimidazole zinc-derived nitrogen-doped carbon-loaded cobalt single atom carrier and molybdenum disulfide nanosheet-loaded iron cluster carrier is (1-3):1; the grinding time is 10-20 min; the raw materials for preparing the active metal precursor solution include: Pt(NH3)4Cl2 and Ni(NO3)2.

[0042] According to a preferred embodiment of the present invention, the Pt(NH3)4Cl2 was purchased from Shanghai Jiuling Chemical Co., Ltd., model A100235 (analytical grade, metal platinum content ≥38.5%).

[0043] According to a preferred embodiment of the present invention, the Ni(NO3)2 is purchased from Shanghai Jiuling Chemical Co., Ltd., model A100123 (analytical grade, nickel content ≥22.5%).

[0044] According to a preferred embodiment of the present invention, in step S2, the ultrasonic dispersion time is 30-40 minutes; the vacuum drying temperature is 60-62° C., and the time is 12-14 hours.

[0045] In the present invention, the platinum precursor solution is ultrasonically assisted to penetrate into the porous structure of the nitrogen-doped carbon support, and the platinum ions are preferentially adsorbed on the pyridinic nitrogen sites. During the rotary evaporation process, the solvent evaporates to concentrate the platinum precursor, and the low-temperature reduction under the hydrogen and argon atmosphere causes the platinum ions to dissociate into single atoms, forming MN with the nitrogen-doped carbon. xCoordination structure (x≈4). The defect sites of nitrogen-doped carbon and the lone pair electrons of pyridinic nitrogen stabilize the single atoms through coordination, inhibiting their agglomeration and forming highly dispersed platinum single atom active sites. The nickel precursor solution undergoes a coordination reaction with the sulfur vacancies of MoS2 under acidic conditions. Nickel ions preferentially occupy the sulfur vacancies and form nickel oxide cores through hydrolysis. In a hydrothermal environment, the strong interaction between sulfur vacancies and nickel ions promotes the reduction of nickel oxide to metallic nickel and spontaneous aggregation into nanoclusters. The sulfur vacancies of MoS2 act as nucleation sites, limiting the size of nickel clusters and forming iron-nickel alloy clusters with uniform particle size. The charge transfer between sulfur vacancies and metal clusters optimizes the electronic structure and enhances the adsorption capacity for reaction intermediates.

[0046] According to a preferred embodiment of the present invention, in step S3, the reduction time is 2-4 hours, and the heating rate is 2-4°C / min.

[0047] In the present invention, temperature-controlled reduction is performed in a hydrogen-argon mixed atmosphere, and hydrogen molecules are adsorbed on the surface of the carrier and dissociated into active hydrogen species. Single-atom platinum is preferentially reduced to form metallic platinum atoms, which form strong metal-carrier interactions with nitrogen-doped carbon, inhibiting agglomeration at high temperatures. Iron-nickel clusters are gradually reduced on the surface of sulfur vacancies, and the strong bonding between sulfur vacancies and metals inhibits cluster migration, forming a three-dimensional porous structure. During the reduction process, nitrogen and sulfur heteroatoms on the surface of the carrier optimize the electronic structure of the metal site through electron transfer, thereby reducing the reaction activation energy. The reduced catalyst is cooled in an inert atmosphere, and the conjugated system of the nitrogen-doped carbon skeleton forms a synergistically stable network with the layered structure of MoS2. Single platinum atoms are reduced by MN x The iron-nickel clusters are embedded in the carbon skeleton, and the sulfur vacancies anchor the iron-nickel clusters to the MoS2 surface. The strong interactions between the support and the active sites (such as covalent and coordination bonds) inhibit structural collapse at high temperatures. At the same time, the multi-level pore structure promotes reactant mass transfer, achieving a synergistic improvement in catalytic activity and stability.

[0048] The beneficial effects of the present invention are:

[0049] The single atom-cluster dual-active site high-efficiency ammonia cracking hydrogen production catalyst of the present invention shows significant advantages in low-temperature activity. Due to the single electronic structure, traditional single-atom catalysts are difficult to stabilize the reaction intermediates and efficiently activate chemical bonds at the same time, and high temperature conditions are required to achieve a high ammonia conversion rate; cluster catalysts are easy to migrate due to the low atomic coordination number, and the loss of active sites causes the efficiency to decrease significantly over time. The present invention constructs a "single atom-cluster" synergistic catalytic system, utilizing the strong ammonia adsorption ability of cobalt single atoms and the efficient chemical bond breaking characteristics of iron clusters to form a relay catalysis of the reaction path: the single atom preferentially adsorbs ammonia and weakens the first chemical bond, and the cluster then relays to break the remaining bonds and promote hydrogen desorption, and the interfacial electron transfer further reduces the reaction energy barrier. Experiments show that the catalyst can achieve efficient catalysis at a relatively low temperature, significantly improving the activity and stability compared to traditional single-atom or cluster catalysts, successfully breaking through the bottleneck of low-temperature activity.

[0050] The stability and anti-poisoning ability of the catalyst are the core indicators of its industrial application. Traditional single-atom catalysts have weak carrier confinement, and single atoms are easy to migrate and agglomerate, resulting in a significant attenuation of activity with running time; cluster catalysts are easily inactivated by sulfur-containing impurities occupying the active sites. The present invention uses two high-stability carriers for collaborative confinement: 2-methylimidazole zinc-derived nitrogen-doped carbon network anchors cobalt single atoms through strong coordination of pyridine nitrogen, effectively inhibiting their migration; the high specific surface area and sulfur vacancy structure of molybdenum disulfide nanosheets stabilize iron clusters and avoid agglomeration. At the same time, sulfur vacancies can preferentially adsorb sulfur-containing impurities in industrial crude ammonia, reducing their poisoning of active sites. Experimental verification shows that after the catalyst has been running continuously for a long time, the ammonia conversion rate only decays slightly, far exceeding the life decay threshold of industrial-grade catalysts, significantly improving the reliability of practical applications.

[0051] The present invention has outstanding performance in reducing costs and improving industrial applicability. Traditional precious metal catalysts rely on high-cost precious metals and are easy to sinter at high temperatures, while non-precious metal catalysts have poor active site dispersion and are easily poisoned. The present invention uses cheap and readily available 2-methylimidazole, zinc acetate, ammonium molybdate, etc. as carrier precursors, combined with low-load active metals, to greatly reduce raw material costs. At the same time, the dual confinement effect of the carrier (nitrogen-doped carbon-anchored single atoms, molybdenum disulfide confined clusters) and the anti-poisoning design reduce the regeneration frequency after catalyst deactivation and extend its service life. According to calculations, the preparation cost of the catalyst is significantly lower than that of traditional precious metal catalysts, and the industrial-grade continuous operation stability is excellent, providing an economically feasible technical path for the large-scale production of green hydrogen. DETAILED DESCRIPTION

[0052] The following specific implementation methods are only used to further illustrate the present application and should not be understood as limiting the scope of protection of the present application. Technicians in this field may make some non-essential improvements and adjustments to the present application based on the above application content.

[0053] 1. Implementation

[0054] Example 1

[0055] 2-Methylimidazole was dissolved in methanol, and zinc acetate and cobalt nitrate hexahydrate were added. The amounts of 2-methylimidazole, zinc acetate, and cobalt nitrate hexahydrate were 0.06 mol, 0.05 mol, and 0.004 mol, respectively. The following steps were performed: 200 mL of methanol was weighed into a 500 mL three-necked flask, and 4.93 g of 2-methylimidazole was added. Subsequently, 9.38 g of zinc acetate was dissolved in 20 mL of methanol and slowly added dropwise to the flask at a rate of 5 mL / min while a magnetic stirrer (IKA RCT Basic, 800 rpm) was turned on. 1.16 g of cobalt nitrate hexahydrate was dissolved in 10 mL of methanol and added dropwise at a rate of 0.5 mL / min while stirring. Stirring was continued at room temperature (25 ± 1°C) for 24 hours. The solution was inspected every 2 hours to ensure a uniform milky white suspension (without precipitation or separation). The suspension was transferred to a centrifuge tube (50 mL), centrifuged at 8000 rpm for 10 minutes, the supernatant was discarded, and the precipitate was washed with methanol three times (20 mL each time) until the pH of the washing solution was 7 (neutral with pH test paper). The washed precipitate was transferred to a vacuum drying oven (DZF-6050), set at 60°C, vacuum ≤10 Pa, and dried for 12 hours to constant weight (the difference between the two weighings was ≤0.01 g) to obtain ZIF-8 precursor powder.

[0056] The ZIF-8 precursor powder was spread on a quartz boat (made of high-purity quartz) and placed in the constant temperature zone of a tube furnace (temperature control accuracy ±1°C). The temperature was raised to 800°C at a rate of 2°C / min. A H2 / Ar mixed gas (volume ratio 1:99, flow rate 200mL / min) was introduced and maintained for 2 hours to complete calcination. The calcination process was monitored by thermogravimetric-differential thermal analysis (TG-DSC, NETZSCH STA449F3, heating rate 10°C / min). Heating was stopped when the mass loss was ≤5% (corresponding to complete decomposition of organic matter), and the mixture was naturally cooled to room temperature to obtain a nitrogen-doped carbon-supported cobalt single atom support.

[0057] Next, prepare the molybdenum disulfide nanosheet-loaded iron cluster carrier: weigh 0.8g ammonium molybdate and 0.16g thiourea and dissolve them in 50mL deionized water, transfer them to a high-pressure reactor, seal it and place it in an oven at 200℃ for 24 hours, keeping the internal pressure ≤2MPa (monitored in real time by a pressure gauge). After the reaction is completed, cool it naturally to room temperature (about 2 hours), transfer the reaction solution to a centrifuge tube (50mL), centrifuge it at 10000rpm for 15 minutes, collect the precipitate, wash it with deionized water and ethanol three times (20mL each time), and transfer the washed precipitate to a vacuum drying oven (60℃, 12 hours, vacuum ≤10Pa) to obtain MoS2 nanosheets.

[0058] 0.5g MoS2 nanosheets were dispersed in 50mL of ethanol (anhydrous grade) and ultrasonically treated (KQ-500DE ultrasonic cleaner, frequency 40kHz, power 300W) for 1h to form a uniform dispersion. 0.306g of ferric chloride (FeCl3·6H2O, molecular formula correct, molecular weight 270.30g / mol, purity ≥99.0%) was added and ultrasonication was continued for 1h (stirring every 15 minutes during the period). The dispersion was transferred to an autoclave and reacted at 150°C for 8 hours. After natural cooling, the mixture was centrifuged at 12000rpm for 20 minutes, the precipitate was collected, and washed with ethanol three times (20mL each time). The washed precipitate was transferred to a vacuum drying oven (60°C, 14 hours, vacuum ≤10Pa) to obtain a molybdenum disulfide nanosheet-loaded iron cluster carrier.

[0059] Finally, a single-atom-cluster dual-active-site catalyst was prepared: 300 g of 2-methylimidazole zinc-derived nitrogen-doped carbon-supported cobalt single atoms and 100 g of molybdenum disulfide nanosheet-supported iron clusters were placed in an agate mortar (100 mm diameter, lined with polytetrafluoroethylene, hardness ≥ 7 on the Mohs scale) and ground for 15 minutes (using an agate mortar, manual speed control, and uniform force) until the mixture formed a uniform dark gray powder with no apparent separation of support particles. An active metal precursor solution (containing 5 g of Pt(NH₃)₄Cl₂ and 10 g of Ni(NO₃)₂·6H₂O) was added dropwise to the mixture, and ultrasonic dispersion was performed for 30 minutes to form a homogeneous slurry (microscopic observation revealed no metal particle agglomeration). The slurry was transferred to a rotary evaporator (RE-52AA, 50 rpm, 60°C water bath) and evaporated for 1 hour to remove the solvent. The product was then transferred to a vacuum drying oven (60°C, 12 hours, vacuum ≤10 Pa) to obtain the metal-loaded precursor powder. Finally, the temperature was raised to 450°C in a H2 / Ar atmosphere (volume ratio 1:99, flow rate 100 mL / min) at a heating rate of 2°C / min, and reduced for 2 hours (during which the hydrogen concentration was monitored by a hydrogen concentration detector to ensure complete reduction), and then naturally cooled to room temperature to obtain the target catalyst.

[0060] Example 2

[0061] The specific implementation method is the same as that of Example 1, except that the amounts of 2-methylimidazole, zinc acetate, and cobalt nitrate hexahydrate are 0.06 mol, 0.048 mol, and 0.0044 mol, respectively. The specific operation is as follows: 200 mL of methanol is measured and placed in a 500 mL three-necked flask, 4.93 g of 2-methylimidazole is added, and then 9.00 g of zinc acetate is weighed and dissolved in 20 mL of methanol; 1.20 g of cobalt nitrate hexahydrate is weighed and dissolved in 10 mL of methanol, and added dropwise at a rate of 0.5 mL / min while maintaining stirring. Stirring is continued at room temperature (25 ± 1 ° C) for 25 hours, during which the solution state is observed every 2 hours to ensure that a uniform milky white suspension is formed (no precipitation or stratification). The suspension is transferred to a centrifuge tube (50 mL), centrifuged at 8000 rpm for 10 minutes, the supernatant is discarded, and the precipitate is washed with methanol 3 times (20 mL each time) until the pH of the washing solution is neutral (detected with pH paper). The washed precipitate was transferred to a vacuum drying oven (DZF-6050) at 60°C and a vacuum level of ≤10 Pa. Dry for 12 hours to a constant weight (the difference between two weighings was ≤0.01 g) to obtain a ZIF-8 precursor powder. In subsequent steps, the Pt(NH3)4Cl2 content was adjusted to 6 g, the Ni(NO3)2·6H2O content to 12 g, and the additive K2CO3 content to obtain the target catalyst.

[0062] Example 3

[0063] The specific implementation method is the same as that of Example 1, except that 2-methylimidazole is dissolved in methanol, and the amounts of zinc acetate and cobalt nitrate hexahydrate are 0.06 mol, 0.048 mol, and 0.0044 mol, respectively. The specific operation is as follows: 200 mL of methanol is measured in a 500 mL three-necked flask, 4.93 g of 2-methylimidazole is added, and then 9.00 g of zinc acetate is weighed and dissolved in 20 mL of methanol, and slowly added dropwise to the three-necked flask at a rate of ≤ 5 mL / min, while turning on a magnetic stirrer (IKA RCT Basic, speed 800 rpm); 1.20 g of cobalt nitrate hexahydrate is continued to be weighed and dissolved in 10 mL of methanol, and added dropwise at a rate of 0.5 mL / min, maintaining a stirring state. Stirring is continued at room temperature (25 ± 1 ° C) for 26 hours, and the solution state is observed every 2 hours during the period to ensure the formation of a uniform milky white suspension (no precipitation or stratification). Suspension is transferred to centrifuge tube (50mL), centrifuged 10 minutes with 8000rpm, supernatant is discarded, precipitation is washed with methanol 3 times (each 20mL), until washings pH=7 (detected with pH test paper, neutral). The precipitation after washing is transferred to vacuum drying oven (DZF-6050), setting temperature 60 DEG C, vacuum degree≤10Pa, dry 12 hours, to constant weight (weighing difference≤0.01g before and after twice), obtain ZIF-8 precursor powder. In subsequent steps, the hydrothermal reaction temperature of molybdenum disulfide nanosheet loaded iron cluster carrier is adjusted to 201 DEG C, reaction time 25 hours, and other parameters (ammonium molybdate 0.8g, thiourea 0.16g, iron chloride 0.306g) are consistent with Example 1, finally obtain target catalyst.

[0064] Comparative Example 1

[0065] The specific implementation method is the same as that of Example 1, except that the amounts of 2-methylimidazole, zinc acetate, and cobalt nitrate hexahydrate are 0.07 mol, 0.06 mol, and 0.005 mol, respectively. The specific operation is as follows: 200 mL of methanol is measured and placed in a 500 mL three-necked flask, 5.74 g of 2-methylimidazole is added, 1.12 g of zinc acetate is then weighed and dissolved in 20 mL of methanol, and slowly added dropwise to the three-necked flask at a rate of ≤5 mL / min, while a magnetic stirrer (IKA RCT Basic, speed 800 rpm) is turned on; 1.46 g of cobalt nitrate hexahydrate is then weighed and dissolved in 10 mL of methanol, and added dropwise at a rate of 0.5 mL / min, maintaining stirring. Stirring is continued at room temperature (25 ± 1 ° C) for 24 hours, and the ZIF-8 precursor powder is obtained after centrifugation, washing, and drying.

[0066] Comparative Example 2

[0067] The specific implementation method is the same as Example 1, except that the single-atom active metal loading amount Pt is adjusted to 2g, the cluster active metal loading amount Ni is adjusted to 20g, and the auxiliary agent K2CO3 is adjusted to 2g, and finally the target catalyst is obtained.

[0068] Comparative Example 3

[0069] The specific implementation method is the same as that of Example 1, except that, in the subsequent steps, the auxiliary agent K2CO3 is omitted and the catalyst is directly assembled.

[0070] 2. Performance Testing

[0071] The insulating materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the following method:

[0072] 1. The test equipment includes a fixed-bed microreactor (8mm inner diameter, 500mm length, 316L stainless steel), a gas chromatograph (Agilent 7890B, TCD detector), high-purity nitrogen (99.999%), high-purity hydrogen (99.999%), argon (99.999%), and ammonia (99.99%). The test steps are as follows: 50mg of catalyst sample is placed in the constant temperature zone of the reactor and purged with 100mL / min Ar for 30 minutes to remove moisture and impurities; the reaction conditions are set at 450℃, and a mixture of ammonia and Ar (volume ratio 1:99) is introduced at a flow rate of 50mL / min, with a space velocity (GHSV) of 50,000mL / (g·h); the tail gas is condensed and dehydrated before entering the gas chromatograph (TCD detector, column temperature 100℃, carrier gas He, flow rate 30mL / min), and samples are collected every 30 minutes, and the peak areas of H2, N2, and unreacted NH3 are recorded; The data calculation includes the ammonia conversion rate (X(NH3) = [n0(NH3)-n(t)(NH3)] / n0(NH3)×100%, n0 is the amount of initial NH3 substance, n(t) is the amount of remaining NH3 substance at time t) and the hydrogen production rate (r(H2) = [n(t)(H2)×2] / (m(catalyst)×Δt), m(catalyst) is 50 mg, Δt is the sampling time interval, and 2 is the stoichiometric ratio of NH3 cracking to produce H2).

[0073] 2. The test equipment is the same as the ammonia cracking hydrogen production activity test reactor and gas chromatograph. The test steps are as follows: catalyst pretreatment is the same as in step 1 of the activity test; continuous reaction conditions are 450°C, GHSV = 50,000 mL / (g·h), ammonia / Ar = 1:99, and continuous operation for 200 hours; activity monitoring involves sampling every 50 hours to analyze ammonia conversion and hydrogen production rate, and recording activity trends over 200 hours.

[0074] 3. The test instrument is Micromeritics ASAP 2460 surface area analyzer. The test steps are as follows: the catalyst is vacuum degassed at 300°C for 3 hours (pressure ≤ 10Pa); adsorption-desorption test is performed at 77K using high-purity nitrogen (99.999%) as the adsorbent; the specific surface area (S αβt ), BJH model analysis of pore size distribution (D p ).

[0075] 4. The test instrument is a Netzsch STA 449F3 thermogravimetric-differential thermal analyzer. The test steps are as follows: 5-10 mg of catalyst is placed in an alumina crucible; under a nitrogen atmosphere (flow rate of 50 mL / min), the temperature is increased at a rate of 10°C / min to 800°C; the mass loss (TG curve) and heat flow change (DSC curve) are recorded to analyze the decomposition temperature and thermal stability of the organic matter.

[0076] 5. Performance test results:

[0077] Table 1: Performance test results of various embodiments and comparative examples

[0078]

[0079] As can be seen from Table 1, the present invention effectively solves the problems of single active site, poor dispersion and insufficient stability of traditional ammonia cracking hydrogen production catalysts by constructing a single atom-cluster dual active site structure and combining the synergistic effect of dual carriers. Specifically: Single active site problem: Traditional catalysts mostly rely on a single active site (such as a single atom or cluster), and the reaction path is limited. In the embodiment, Pt single atom (to adsorb and activate NH3) and Ni cluster (to promote H + The dual-active site design (with catalytic activity dissociation) forms a multi-center reaction network, which significantly improves the catalytic activity. The ammonia conversion rate (90.1%-92.3%) and hydrogen production rate (11.8-12.5 mmol / (g·h)) of Examples 1-3 are higher than those of the comparative example (82.7%-88.3%), indicating that the dual sites synergistically reduce the reaction activation energy and broaden the reaction path.

[0080] Poor dispersion problem: Traditional carriers (such as ordinary carbon-based materials) have uneven pores, which easily lead to agglomeration of active sites. In the embodiment, 2-methylimidazole zinc-derived nitrogen-doped carbon (uniform mesoporous structure) and molybdenum disulfide nanosheets (rich in sulfur vacancies) are selected as dual carriers: nitrogen-doped carbon uniformly disperses Pt single atoms (particle size 2.8-3.2nm), and the sulfur vacancies of molybdenum disulfide anchor Ni clusters (particle size 3.1-3.5nm) through strong metal-carrier interactions, preventing them from agglomerating, which is 20%-30% higher than the comparative example.

[0081] Insufficient stability: Traditional catalysts are prone to deactivation due to support sintering or active site shedding. In the examples, dual supports synergistically enhance thermal stability: the additive K2CO3 (added in Examples 1-3) decomposes into K2O during calcination, forming chemical bonds with the hydroxyl groups on the support surface, further inhibiting sintering. In summary, the collaborative design of dual active sites and dual supports breaks through the bottlenecks of traditional catalysts in terms of active site diversity, dispersion, and thermal stability, achieving efficient ammonia cracking to produce hydrogen.

[0082] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A high-efficiency single-atom-cluster dual-active-site ammonia cracking catalyst for hydrogen production, characterized in that: The composition comprises the following raw materials in parts by weight: 2-Methylimidazole zinc-derived nitrogen-doped carbon-supported cobalt single atom carrier: 250-450 parts by weight; Molybdenum disulfide nanosheets loaded with iron clusters carrier: 200-400 parts by weight; Single atom active metal: 5-20 parts by weight; Cluster active metal: 10-50 parts by weight; Additives: 10-30 parts by weight; The preparation method of the 2-methylimidazole zinc-derived nitrogen-doped carbon-loaded cobalt single-atom carrier includes: A1, dissolving 2-methylimidazole in methanol, adding zinc acetate and cobalt nitrate hexahydrate, and stirring at room temperature to generate a ZIF-8 precursor; centrifuging the methanol to wash until neutral, and vacuum drying; A2, placing the dried ZIF-8 precursor in a tube furnace, heating it to 800-820°C in a H2 / Ar mixed atmosphere, and calcining it.

2. The high-efficiency single-atom-cluster dual-active-site ammonia cracking catalyst for hydrogen production according to claim 1, characterized in that: In step A1, the molar ratio of 2-methylimidazole, zinc acetate and cobalt nitrate hexahydrate is (4-6): (2-3): (0.1-0.3); the stirring time at room temperature is 24-30 hours; the vacuum drying temperature is 60-64° C., and the drying time is 12-14 hours.

3. The high-efficiency single-atom-cluster dual-active-site ammonia cracking catalyst for hydrogen production according to claim 1, characterized in that: In step A2, the heating rate is 2-4°C / min; and the calcination time is 2-4h.

4. The single atom-cluster dual-active site high-efficiency ammonia cracking hydrogen production catalyst according to claim 1, characterized in that: The preparation method of the molybdenum disulfide nanosheet-loaded iron cluster carrier includes: B1, dissolving ammonium molybdate and thiourea in deionized water, transferring the solution to a hydrothermal reactor at 200-202°C for reaction, cooling, and then centrifuging and washing to obtain MoS2 nanosheets; B2, dispersing the MoS2 nanosheets in ethanol, adding ferric chloride for ultrasonic treatment, and transferring the solution to a hydrothermal reactor at 150-152°C for reaction.

5. The high-efficiency single-atom-cluster dual-active-site ammonia cracking catalyst for hydrogen production according to claim 4, characterized in that: In step B1, the reaction time is 24-30 hours.

6. The high-efficiency single-atom-cluster dual-active-site ammonia cracking catalyst for hydrogen production according to claim 4, characterized in that: In step B2, the ultrasonic treatment time is 1-2 hours; and the reaction time is 6-8 hours.

7. A method for preparing a high-efficiency ammonia cracking hydrogen production catalyst with a single atom-cluster dual active site according to any one of claims 1 to 6, characterized in that the steps include: S1. Add 2-methylimidazole zinc-derived nitrogen-doped carbon-supported cobalt single atom support and molybdenum disulfide nanosheet-supported iron cluster support into an agate mortar and grind until uniform; Add active metal precursor solution dropwise to the mixture to control the total metal loading to be 1-6 wt%; S2. Ultrasonic dispersion to form a slurry, transfer to a rotary evaporator at 60-62°C for rotary evaporation; vacuum dry the product; S3. Finally, the single atoms were reduced at 450-452 °C in a H2 / Ar atmosphere to anchor them on the pyridinic nitrogen sites of the 2-methylimidazole zinc-derived nitrogen-doped carbon-supported cobalt single atom carrier, and the cluster active metals grew on the sulfur vacancy surface of the molybdenum disulfide nanosheet-supported iron cluster carrier.

8. The preparation method according to claim 7, characterized in that In step S1, the mass ratio of the 2-methylimidazole zinc-derived nitrogen-doped carbon-supported cobalt single atom support to the molybdenum disulfide nanosheet-supported iron cluster support is (1-3):1; the grinding time is 10-20 min; The raw materials for preparing the active metal precursor solution include: Pt(NH3)4Cl2 and Ni(NO3)2.

9. The preparation method according to claim 7, characterized in that In step S2, the ultrasonic dispersion time is 30-40 minutes; the vacuum drying temperature is 60-62° C., and the time is 12-14 hours.

10. The preparation method according to claim 7, characterized in that In step S3, the reduction time is 2-4 hours, and the heating rate is 2-4°C / min.

Images