Pt-based crystalline-amorphous heterostructure catalyst, and preparation method and application thereof

Abstract

This invention discloses a Pt-based crystalline-amorphous heterostructure catalyst, its preparation method, and its applications. The invention involves depositing Mo into ZIF-67 followed by calcination to obtain a solid product consisting of a porous framework formed by the accumulation of crystalline Co3O4 nanoparticles and a surface cobalt-molybdenum oxide precursor. Subsequent liquid-phase reduction transforms the cobalt-molybdenum oxide precursor into amorphous sheet-like CoMo material, which grows in situ and adheres to the surface of the porous framework, forming a crystalline-amorphous heterostructure interface. Simultaneously, Pt nanoparticles are reduced and loaded onto this interface. The resulting catalyst possesses a crystalline-amorphous composite heterostructure, with Pt highly dispersed at the heterostructure interface and strong metal-support interaction. This catalyst exhibits excellent performance in catalyzing the hydrolysis of ammonia borane to produce hydrogen at room temperature and pressure, achieving complete hydrogen release within 1.05 minutes. Furthermore, it requires low Pt dosage, has a simple preparation method, and is suitable for industrial applications.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation and hydrogen energy application, specifically relating to a Pt-based crystalline-amorphous heterostructure catalyst, its preparation method, and its application. Background Technology

[0002] Rapid societal development and sustained economic growth have led to a dramatic increase in energy demand. In the traditional energy structure, fossil fuels such as coal, oil, and natural gas dominate, but their resources are finite and non-renewable, prompting the continuous search for new, sustainable, and clean energy sources. Clean energy takes many forms, such as wind power, tidal power, and hydrogen energy. Among these, hydrogen energy boasts advantages such as high energy density, combustion byproducts consisting only of water, and widespread availability, making it one of the most ideal energy sources. However, developing a hydrogen economy requires addressing the crucial issues of safe hydrogen storage and transportation, which are key bottlenecks restricting the large-scale application of hydrogen energy.

[0003] Ammonia borane, with its high hydrogen storage content of 19.6 wt%, stability at room temperature, non-toxicity, and ease of transportation, shows great promise for chemical hydrogen storage. Producing clean and renewable hydrogen through the hydrolysis of ammonia borane is one of the effective ways to conveniently utilize hydrogen energy. Ammonia borane can undergo hydrolysis at room temperature and pressure under the action of a catalyst, efficiently and stably releasing hydrogen.

[0004] Noble metal catalysts exhibit excellent catalytic performance in the hydrolysis of ammonia borane, with Pt-based catalysts being particularly outstanding. However, the high price and scarcity of noble metals severely hinder their large-scale industrial application. To reduce the amount of noble metals used while maintaining catalytic activity, researchers have attempted to develop supported catalysts, utilizing the interaction between the metal and the support to enhance catalytic performance.

[0005] Li et al. (ACS Applied Materials & Interfaces, 2021, 13 (48), 57362-57371) reported a Pt / Co3O4 nanocage catalyst. This catalyst maximizes the metal-support interface by embedding Pt clusters into high specific surface area Co3O4 nanocages. The metal-support interaction in the catalyst can simultaneously accelerate hydrogen generation and improve catalyst stability. The conversion frequency of this Pt / Co3O4 catalyst is approximately nine times that of commercial Pt / C catalysts. However, the support of this catalyst is only a single crystalline Co3O4, and there is still room for improvement in the interaction between it and Pt nanoparticles. The catalytic activity and stability are not yet sufficient for practical applications.

[0006] Non-precious metals such as Co, Mo, Ni, and Fe can also be used to prepare cost-effective and efficient catalysts, but their catalytic activity and stability are far inferior to those of precious metal catalysts. Therefore, how to enhance the interaction between the metal and the support and improve catalytic activity and stability by constructing catalysts with special structures while reducing the amount of precious metals used is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a Pt-based crystalline-amorphous heterostructure catalyst, its preparation method, and its applications, to address the technical problems of existing noble metal catalysts, such as high Pt content, limited metal-support interaction, and insufficient catalytic activity and stability. Specifically, this invention aims to achieve high dispersion and stable anchoring of Pt nanoparticles by constructing a crystalline-amorphous heterostructure support, thereby obtaining a highly efficient and stable catalyst for hydrogen production from ammonia borane hydrolysis while significantly reducing Pt content. Furthermore, this invention provides a preparation method for this catalyst that is simple, operates under mild conditions, is easy to scale up, and has good prospects for industrial application.

[0008] Another objective is to provide the application of the above-mentioned Pt-based crystalline-amorphous heterostructure catalysts in the catalytic hydrogen decomposition of ammonia borane, thereby providing an efficient and economical catalyst solution for the convenient utilization of hydrogen energy.

[0009] To achieve the above objectives, the specific solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a Pt-based crystalline-amorphous heterostructure catalyst, comprising the following steps: Step (1): Dissolve the Mo source in a solvent, add ZIF-67, mix well, and then evaporate the solvent to obtain the Mo-deposited ZIF-67. Step (2): The ZIF-67 deposited with Mo is calcined in an air atmosphere to transform ZIF-67 into a porous framework formed by the stacking of crystalline Co3O4 nanoparticles. At the same time, a cobalt-molybdenum oxide precursor containing Mo and Co is formed on the surface of the porous framework to obtain a solid product. Step (3): Disperse the solid product obtained in step (2) in water, add Pt source and sodium borohydride for liquid phase reduction. During this process, the cobalt molybdenum oxide precursor is converted into amorphous sheet-like CoMo material and grows in situ on the surface of the porous framework to form a crystalline-amorphous heterostructure interface. At the same time, Pt nanoparticles are reduced and loaded on the crystalline-amorphous heterostructure interface to obtain the catalyst.

[0010] Further, the preparation method of ZIF-67 used in step (1) is as follows: cobalt nitrate is dissolved in methanol to obtain solution A, 2-methylimidazole is dissolved in methanol to obtain solution B, solution A is quickly added to solution B under stirring conditions, and stirring is continued at 20-35℃ for 12-48h. After centrifugation, washing and drying, ZIF-67 is obtained.

[0011] Furthermore, in the preparation of solution A, the ratio of cobalt nitrate to methanol is 1 mol: 12-20 L; In the preparation of solution B, the ratio of 2-methylimidazole to methanol is 1 mol: 1-2 L; The molar ratio of cobalt nitrate in solution A to 2-methylimidazole in solution B is 1:4-5.

[0012] Further, in step (2), the Mo source is any one of molybdenum chloride, molybdenum nitrate, or molybdenum acetylacetonate; the mass ratio of Mo atoms to ZIF-67 is 1:1 to 1:100.

[0013] Further, the solvent in step (2) is methanol or ethanol, and the ratio of solvent volume to ZIF-67 mass is 0.3-0.5 mL: 1 mg.

[0014] Furthermore, in step (3), the heating rate during calcination is 1-5℃ / min.

[0015] Further, in step (3), the Pt source is any one of chloroplatinic acid, platinum hexahydroxide, dinitrosodiamineplatinum, or platinum nitrate; the molar ratio of the platinum source to sodium borohydride is 1:5 to 1:20.

[0016] Secondly, the present invention provides a Pt-based crystalline-amorphous heterostructure catalyst, which is prepared by the method described above.

[0017] Furthermore, the catalyst has a crystalline-amorphous composite heterostructure, comprising: A porous framework formed by the stacking of crystalline Co3O4 nanoparticles; An amorphous sheet-like CoMo material is grown in situ and attached to the surface of the porous framework, wherein a crystalline-amorphous heterostructure interface is formed between the crystalline Co3O4 nanoparticles and the amorphous sheet-like CoMo material. And Pt nanoparticles loaded on the crystalline-amorphous heterostructure interface.

[0018] Thirdly, the present invention provides the application of the above-mentioned Pt-based crystalline-amorphous heterostructure catalyst in the catalytic hydrolysis of ammonia borane to produce hydrogen.

[0019] The functions of each raw material are explained below.

[0020] Cobalt nitrate: provides cobalt ions (Co) 2+ As a metal node of ZIF-67, it is eventually transformed into the active component of the catalyst, Co3O4.

[0021] 2-Methylimidazole: As an organic ligand, it coordinates with cobalt ions to form the framework structure of ZIF-67. Its unique molecular structure determines the pore size and morphology of ZIF-67.

[0022] Methanol: As a solvent, it also participates in the formation reaction of ZIF-67. The polarity of methanol is suitable for the dissolution of cobalt nitrate and 2-methylimidazole, and its rapid evaporation facilitates subsequent drying.

[0023] Mo source (molybdenum chloride, molybdenum nitrate, or molybdenum acetylacetonate): The introduction of Mo is crucial for the formation of crystalline-amorphous heterostructures. During liquid-phase reduction, the presence of Mo promotes the transformation of the cobalt-molybdenum oxide precursor into amorphous plate-like CoMo material. The formation of amorphous material is beneficial for increasing the interfacial area and charge transfer.

[0024] Pt source (chloroplatinic acid, etc.): provides Pt ions, which are reduced to form Pt nanoparticles. Pt is the active center for catalyzing the hydrolysis of ammonia borane.

[0025] Sodium borohydride: a reducing agent that reduces Pt ions to Pt nanoparticles. Sodium borohydride has a strong reducing power and can rapidly reduce Pt ions at room temperature. Its alkaline environment also favors the hydrolysis reaction of ammonia borane.

[0026] Deionized water: the reaction medium used to disperse cobalt-molybdenum oxide precursors and dissolve Pt sources and sodium borohydride.

[0027] Ethanol: A washing solvent used to remove organic impurities from the catalyst surface. Also, due to its low surface tension, ethanol helps maintain the catalyst morphology during the drying process.

[0028] The principle behind the superior catalytic performance of the catalyst in this invention is as follows: First, the ZIF-67 precursor, after high-temperature calcination, transforms into a porous framework formed by the accumulation of crystalline Co3O4 nanoparticles. This porous framework has a high specific surface area, providing abundant reaction sites for the catalytic reaction. Second, the introduction of Mo is crucial. During the liquid-phase reduction process, the presence of Mo promotes the transformation of the cobalt-molybdenum oxide precursor into amorphous plate-like CoMo material. This amorphous material has a disordered internal structure, exposing more active sites. Simultaneously, the amorphous plate-like CoMo material grows in situ and adheres to the surface of the porous framework, forming numerous crystalline-amorphous heterojunction interfaces between the crystalline Co3O4 nanoparticles and the amorphous plate-like CoMo material. The formation of crystalline-amorphous heterojunction interfaces is the core technical feature of this invention. The catalyst support, composed of the porous framework and the amorphous plate-like CoMo material, facilitates electron transfer between the metal and the support, significantly enhancing the interaction between the metal and the support. Electron transfer effects can modulate the electronic state of Pt nanoparticles, optimizing their adsorption and activation capabilities for ammonia borane molecules, thereby accelerating hydrogen generation. Furthermore, Pt nanoparticles supported on a crystalline-amorphous heterostructure interface exhibit enhanced metal-support interactions, resulting in robust anchoring of the nanoparticles at the interface and reduced agglomeration, thus improving catalyst stability. Simultaneously, the high dispersion of Pt nanoparticles at the interface exposes more Pt atoms, enhancing the utilization efficiency of the noble metal.

[0029] Beneficial effects: (1) The catalyst provided by this invention has a unique crystalline-amorphous composite heterostructure. Specifically, the catalyst comprises: a porous framework formed by the stacking of crystalline Co3O4 nanoparticles; an amorphous plate-like CoMo material grown in situ and attached to the surface of the porous framework, wherein the crystalline Co3O4 nanoparticles and the amorphous plate-like CoMo material form a crystalline-amorphous heterostructure interface; and Pt nanoparticles loaded on the crystalline-amorphous heterostructure interface. This structural feature has not been reported in the prior art and has significant structural innovation.

[0030] (2) In this invention, the introduction of Mo helps to change the structural composition of the catalyst during the preparation process, forming a crystalline-amorphous interface structure that combines crystalline Co3O4 nanoparticles with amorphous sheet-like CoMo material. This crystalline-amorphous heterostructure interface is more conducive to the transfer of electrons between the metal and the support, significantly improving the metal-support interaction between Pt and the support. This strong interaction can optimize the adsorption and activation ability of Pt nanoparticles for ammonia borane molecules, thereby accelerating the generation of hydrogen; on the other hand, it can stably anchor Pt nanoparticles on the interface, effectively preventing the aggregation of Pt particles during the reaction process.

[0031] (3) The catalyst prepared in this invention exhibits excellent catalytic activity in the hydrolysis of ammonia borane to produce hydrogen. Data from the examples show that the catalyst prepared in Example 1 can completely release hydrogen from ammonia borane in just 1.05 minutes, a significantly better catalytic rate than other catalysts in the comparative examples (Comparative Example 1: 2.2 minutes, Comparative Example 2: 1.5 minutes, Comparative Example 3: 7.3 minutes, Comparative Example 4: 21.5 minutes). Even when the amount of Pt is reduced to 1 / 8 of that in Example 1 (Example 3), complete hydrogen release from ammonia borane can still be achieved within 1.9 minutes.

[0032] (4) By constructing a crystalline-amorphous heterostructure, this invention significantly improves the dispersion of Pt nanoparticles on the support through the enhancement effect of metal-support interaction, thereby achieving excellent catalytic performance with a low Pt content. In this invention, the mass ratio of Pt atoms to ZIF-67 can reach 1:1000, realizing the efficient utilization of precious metals, effectively reducing catalyst costs, and facilitating large-scale industrial applications.

[0033] (5) The preparation method of the present invention has the following advantages: (1) The steps are simple, and only three steps, namely Mo deposition, calcination and liquid phase reduction, are required to obtain the target catalyst; (2) The conditions are mild, and the liquid phase reduction is carried out at room temperature without high temperature and high pressure; (3) The raw materials are readily available, and the cobalt nitrate, 2-methylimidazole, molybdenum source, platinum source and other materials used are all common chemical reagents; (4) The reproducibility is good, and the structure and performance of the catalyst can be controlled by controlling the amount of Mo and Pt; (5) It is easy to scale up production, without the need for complex equipment, and is suitable for industrial production.

[0034] (6) The Pt-based crystalline-amorphous heterostructure catalyst prepared by this invention can efficiently catalyze the hydrolysis of ammonia borane to produce hydrogen at room temperature and pressure, providing a new technical solution for the convenient utilization of hydrogen energy. Ammonia borane, as a chemical hydrogen storage material with high hydrogen storage density, combined with the efficient catalyst provided by this invention, is expected to be widely used in portable fuel cells, mobile hydrogen sources and other fields, with good economic and social benefits.

[0035] (7) Compared with the Pt / Co3O4 nanocage catalyst reported by Li et al., this invention constructs a crystalline-amorphous heterostructure by introducing Mo and loading Pt nanoparticles onto the heterostructure interface, resulting in significantly better catalytic activity than existing technologies. Compared with Comparative Examples 1-2, which use Fe or Ni instead of Mo, the Mo system in this invention can more effectively form a crystalline-amorphous heterostructure and achieve higher catalytic activity. Compared with catalysts prepared by the equal-volume impregnation method (Comparative Example 3) and the hydrothermal method (Comparative Example 4), the liquid-phase reduction method of this invention can form an amorphous plate-like structure in situ and achieve Pt loading on the heterostructure interface, which has irreplaceable technical advantages. Attached Figure Description

[0036] Figure 1 It is the Pt2 / CoMo prepared in Example 1 of this invention. 0.1 SEM image of the -O catalyst.

[0037] Figure 2 It is the Pt2 / CoMo prepared in Example 1 of this invention. 0.1 TEM image of the -O catalyst.

[0038] Figure 3 It is the CoMo prepared in Example 1 of this invention. 0.1 SEM image of the -O solid product.

[0039] Figure 4 It is the Pt2 / CoMo prepared in Example 1 0.1 Selected area electron diffraction pattern of the lamellar structure in the -O catalyst.

[0040] Figure 5 It is the CoMo prepared in Example 1 of this invention. 0.1 -O solid products and Pt2 / CoMo 0.1 XRD pattern of the -O catalyst.

[0041] Figure 6 These are test graphs showing the performance of the catalysts prepared in Examples 1-3 of this invention in catalyzing the hydrolysis of ammonia borane at room temperature.

[0042] Figure 7 The graphs show the performance of the catalysts prepared in Example 1 and Comparative Examples 1-2 of this invention in catalyzing the hydrogen release from the hydrolysis of ammonia borane at room temperature.

[0043] Figure 8 The graphs show the performance of the catalysts prepared in Examples 1 and 3-4 of this invention in catalyzing the hydrogen release from the hydrolysis of ammonia borane at room temperature. Detailed Implementation

[0044] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0045] This invention provides a Pt-based crystalline-amorphous heterostructure catalyst, its preparation method, and its application. The preparation method of the catalyst of this invention is described in detail below: Step (1), Preparation of ZIF-67: Cobalt nitrate and methanol are dissolved in a ratio of 1 mol: 12-20 L to obtain a transparent solution A. 2-Methylimidazole and methanol are dissolved in a ratio of 1 mol: 1-2 L to obtain a transparent solution B. Solution A is rapidly added to solution B under stirring conditions, wherein the molar ratio of cobalt nitrate to 2-methylimidazole is 1:4-5. Stirring is continued in a water bath at 20-35℃ for 12-48 h. ZIF-67 crystals are formed through coordination (cobalt nitrate provides cobalt ions, and 2-methylimidazole acts as an organic ligand. The two react rapidly in methanol to form ZIF-67 metal-organic framework material with a regular morphology; too short a stirring time will lead to incomplete crystal growth, while too long a stirring time may cause excessive crystal growth or agglomeration). After the reaction is completed, the mixture is centrifuged, washed with methanol to remove unreacted raw materials, and then dried in a vacuum oven at 50-120℃. Vacuum drying can prevent material oxidation or structural collapse, thus obtaining ZIF-67. Step (2), Preparation of Mo-deposited ZIF-67: Add the Mo source (any one of molybdenum chloride, molybdenum nitrate, or molybdenum acetylacetonate) to a solvent (methanol or ethanol) and stir for 30-60 min to completely dissolve it. Then, add ZIF-67 under stirring at 20-30℃, mix evenly, and then heat to 60-80℃ and continue stirring until the solvent is completely evaporated to obtain Mo-deposited ZIF-67. This step ensures that Mo is uniformly deposited on the surface and in the channels of ZIF-67, wherein the mass ratio of Mo atoms to ZIF-67 is 1:1 to 1:100, and the ratio of solvent volume to ZIF-67 mass is 0.3-0.5 mL: 1 mg. Step (3), Preparation of solid product (cobalt-molybdenum oxide precursor / porous framework): Mo-deposited ZIF-67 is placed in a muffle furnace and calcined at 400-700℃ for 1-4 hours in air at a heating rate of 1-5℃ / min. This transforms ZIF-67 into a porous framework formed by the accumulation of crystalline Co3O4 nanoparticles, and a cobalt-molybdenum oxide precursor containing Mo and Co is formed on the surface of the framework, yielding a solid product. The air atmosphere ensures sufficient oxidation of the metal elements, and the heating rate is controlled at 1-5℃ / min to avoid structural damage or low efficiency. The solid product is essentially a composite material composed of a crystalline Co3O4 porous framework and a surface cobalt-molybdenum oxide precursor. Step (4), Preparation of Pt-based crystalline-amorphous heterostructure catalyst: The solid product obtained in step 3 is added to deionized water, sonicated for 10-20 min and stirred for 0.5-1 h to ensure complete dispersion; then, a Pt source (any one of chloroplatinic acid, platinum hexahydroxide, dinitrosodiammonium platinum, or platinum nitrate) is added, and stirred at room temperature for 1-3 h to allow Pt ions to be fully adsorbed on the surface of the solid product; next, sodium borohydride is added (the molar ratio of Pt source to sodium borohydride is 1:5~1:20), and stirred for another 0.5-1 h. During the liquid-phase reduction process, the cobalt-molybdenum oxide precursor on the surface of the solid product is transformed into amorphous sheet-like CoMo material and grows in situ on the porous framework surface, forming a crystalline-amorphous heterostructure interface. At the same time, Pt nanoparticles are reduced and loaded onto this interface. After the reaction is complete, the catalyst is washed three times by centrifugation with water and ethanol to remove unreacted reducing agent and impurities, and then vacuum dried at 50-80℃ for 6-15h to obtain the Pt-based crystalline-amorphous heterostructure catalyst.

[0046] The Pt-based crystalline-amorphous heterostructure catalysts prepared by the above method have unique microstructures, specifically including: A porous framework formed by the stacking of crystalline Co3O4 nanoparticles. These Co3O4 nanoparticles stack together to form a porous structure with a large specific surface area, providing abundant reaction sites for catalytic reactions.

[0047] An amorphous sheet-like CoMo material is grown in situ and attached to the surface of a porous framework. This amorphous sheet-like CoMo material is transformed from a cobalt-molybdenum oxide precursor during liquid-phase reduction and is grown in situ and attached to the surface of a porous framework. A crystalline-amorphous heterogeneous interface is formed between the crystalline Co3O4 nanoparticles and the amorphous sheet-like CoMo material.

[0048] Pt nanoparticles are loaded onto the crystalline-amorphous heterostructure interface. The Pt nanoparticles are reduced and loaded onto the crystalline-amorphous heterostructure interface by liquid-phase reduction. Due to the introduction of Mo into the support, the structural composition of the catalyst changes during the preparation process, which is more conducive to the transfer of electrons between the metal and the support, improves the interaction between the metal and the support, and thus improves the dispersion of Pt nanoparticles.

[0049] The technical solution of the present invention will be further described below with reference to specific embodiments and comparative examples.

[0050] Example 1

[0051] This embodiment provides a method for preparing a Pt-based crystalline-amorphous heterostructure catalyst, comprising the following steps: Step (1): Dissolve 12 mmol of cobalt nitrate in 120 mL of methanol to obtain a clear solution A, and dissolve 48 mmol of 2-methylimidazole in 40 mL of methanol to obtain a clear solution B; under stirring conditions, quickly add solution A to solution B and continue stirring at 25 °C for 24 hours; after centrifugation, wash three times with methanol and dry at 100 °C in a vacuum oven for 12 hours to obtain ZIF-67; Step (2): Dissolve 0.1 mmol of molybdenum acetylacetonate in 30 mL of methanol, and sonicate for 10 min to completely dissolve the molybdenum acetylacetonate to obtain solution C. Under stirring, rapidly add 100 mg of ZIF-67 to solution C, and continue stirring at 25 °C for 0.5 hours until fully mixed and dispersed. Heat to 65 °C and continue stirring until the solvent is completely evaporated to obtain Mo-deposited ZIF-67. Place it in a muffle furnace and heat to 450 °C at a rate of 2 °C / min under air atmosphere, hold for 2 hours, cool to room temperature, and remove to obtain CoMo. 0.1 -O solid products; Step (3): 50 mg of the prepared CoMo 0.1 The -O solid product was dispersed in 50 mL of deionized water and sonicated for 10 min to ensure uniform dispersion. The mixture was then stirred at room temperature for 1 h. 2 mL of a 0.0001 g / mL chloroplatinic acid aqueous solution was added, and stirring continued at room temperature for 3 h. Then, 10 times the molar amount of sodium borohydride aqueous solution (e.g., Pt) was added, and stirring continued for another 0.5 h. The product was washed three times by centrifugation with water and ethanol, and then vacuum dried at 60 °C for 12 h to obtain Pt2 / CoMo. 0.1 -O catalyst.

[0052] Example 2

[0053] This embodiment provides a method for preparing a Pt-based crystalline-amorphous heterostructure catalyst, comprising the following steps: Step (1): Prepare ZIF-67 according to the method in Example 1; Step (2): Dissolve 0.4 mmol of molybdenum acetylacetonate in 30 mL of methanol, and sonicate for 10 min to completely dissolve the molybdenum acetylacetonate, obtaining solution C. Add 100 mg of ZIF-67 rapidly to solution C under stirring, and continue stirring at 25 °C for 0.5 hours until fully mixed and dispersed. Increase the temperature to 65 °C and continue stirring until the solvent is completely evaporated, obtaining Mo-deposited ZIF-67. Place it in a muffle furnace and heat to 450 °C at a rate of 2 °C / min under air atmosphere, hold for 2 hours, cool to room temperature, and remove to obtain CoMo. 0.4 -O solid products; Step (3): 50 mg of the prepared CoMo 0.4The -O solid product was dispersed in 50 mL of deionized water and sonicated for 10 min to ensure uniform dispersion. The mixture was then stirred at room temperature for 1 h. 2 mL of a 0.0001 g / mL chloroplatinic acid aqueous solution was added, and stirring continued at room temperature for 3 h. Then, 10 times the molar amount of sodium borohydride aqueous solution (e.g., Pt) was added, and stirring continued for another 0.5 h. The product was washed three times by centrifugation with water and ethanol, and then vacuum dried at 60 °C for 12 h to obtain Pt2 / CoMo. 0.4 -O catalyst.

[0054] Example 3

[0055] This embodiment provides a method for preparing a Pt-based crystalline-amorphous heterostructure catalyst, comprising the following steps: Step (1): Prepare ZIF-67 according to the method in Example 1; Step (2): Dissolve 0.1 mmol of molybdenum acetylacetonate in 30 mL of methanol, and sonicate for 10 min to completely dissolve the molybdenum acetylacetonate to obtain solution C. Under stirring, rapidly add 100 mg of ZIF-67 to solution C, and continue stirring at 25 °C for 0.5 hours until fully mixed and dispersed. Heat to 65 °C and continue stirring until the solvent is completely evaporated to obtain Mo-deposited ZIF-67. Place it in a muffle furnace and heat to 450 °C at a rate of 2 °C / min under air atmosphere, hold for 2 hours, cool to room temperature, and remove to obtain CoMo. 0.1 -O solid products; Step (3): 50 mg of the prepared CoMo 0.1 The -O solid product was dispersed in 50 mL of deionized water and sonicated for 10 min to ensure uniform dispersion. The mixture was then stirred at room temperature for 1 h. 0.25 mL of a 0.0001 g / mL chloroplatinic acid aqueous solution was added, and stirring continued at room temperature for 3 h. Then, 10 times the molar amount of sodium borohydride aqueous solution (e.g., Pt) was added, and stirring continued for another 0.5 h. The product was washed three times by centrifugation with water and ethanol, and then vacuum dried at 60 °C for 12 h to obtain Pt. 0.25 / CoMo 0.1 -O catalyst.

[0056] Comparative Example 1 The specific steps for this comparative example are as follows: Step (1): Prepare ZIF-67 according to the method in Example 1; Step (2): Dissolve 0.1 mmol of ferric acetylacetone in 30 mL of methanol, and sonicate for 10 min to completely dissolve the ferric acetylacetone to obtain solution C. Add 100 mg of ZIF-67 rapidly to solution C under stirring, and continue stirring at 25 °C for 0.5 hours until fully mixed and dispersed. Increase the temperature to 65 °C and continue stirring until the solvent is completely evaporated to obtain Fe-deposited ZIF-67. Place it in a muffle furnace and heat to 450 °C at a rate of 2 °C / min under air atmosphere, hold for 2 hours, cool to room temperature, and remove to obtain CoFe. 0.1 -O solid products; Step (3): 50 mg of the prepared CoFe 0.1 The -O solid product was dispersed in 50 mL of deionized water and sonicated for 10 min to ensure uniform dispersion. The mixture was then stirred at room temperature for 1 h. 2 mL of a 0.0001 g / mL chloroplatinic acid aqueous solution was added, and stirring continued at room temperature for 3 h. Then, 10 times the molar amount of sodium borohydride aqueous solution (e.g., Pt) was added, and stirring continued for another 0.5 h. The product was washed three times by centrifugation with water and ethanol, and then vacuum dried at 60 °C for 12 h to obtain Pt2 / CoFe. 0.1 -O catalyst.

[0057] Comparative Example 2 The specific steps for this comparative example are as follows: Step (1): Prepare ZIF-67 according to the method in Example 1; Step (2): Dissolve 0.1 mmol of nickel acetylacetone in 30 mL of methanol, and sonicate for 10 min to completely dissolve the nickel acetylacetone to obtain solution C. Add 100 mg of ZIF-67 rapidly to solution C under stirring, and continue stirring at 25 °C for 0.5 hours until fully mixed and dispersed. Increase the temperature to 65 °C and continue stirring until the solvent is completely evaporated to obtain Ni-deposited ZIF-67. Place it in a muffle furnace and heat to 450 °C at a rate of 2 °C / min under air atmosphere, hold for 2 hours, cool to room temperature, and remove to obtain CoNi. 0.1 -O solid products; Step (3): Disperse 50 mg of the prepared CoNi0.1-O sample into 50 mL of deionized water, sonicate for 10 min to ensure uniform dispersion, and stir at room temperature for 1 h. Add 2 mL of 0.0001 g / mL chloroplatinic acid aqueous solution, continue stirring at room temperature for 3 h, then add 10 times the molar amount of sodium borohydride aqueous solution equal to the amount of Pt, and continue stirring for another 0.5 h. Wash three times with water and ethanol by centrifugation, and vacuum dry at 60 °C for 12 h to obtain Pt2 / CoNi. 0.1 -O catalyst.

[0058] Comparative Example 3 The specific steps for this comparative example are as follows: Step (1): Prepare CoMo according to the method in Example 1. 0.1 -O solid products; Step (2), using the prepared CoMo 0.1 Pt2 / CoMo was prepared from the -O solid product by an equal-volume impregnation method. 0.1 -OI catalyst, the specific method is: to use CoMo 0.1 The -O solid product and chloroplatinic acid solution were mixed and stirred evenly, then allowed to stand at room temperature for 8 hours, dried overnight at 60°C in an oven, and then calcined at 450°C for 2 hours in a tube furnace under a nitrogen atmosphere to obtain Pt2 / CoMo. 0.1 -OI catalyst.

[0059] Comparative Example 4 The specific steps of this comparative example are as follows: 4 mmol CoCl2·6H2O and 4 mmol Na2MoO4·2H2O were dissolved in 35 mL of deionized water and magnetically stirred for 1 h. The solution was then transferred to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and heated at 150 °C for 6 h. After natural cooling and washing three times with deionized water, the product was dried overnight in a 60 °C oven. The resulting powder was calcined at 450 °C for 1 h in air to finally obtain a solid CoMoO4 product. Using the prepared solid CoMoO4 product, a Pt / CoMoO4 catalyst was prepared using the same method as step (3) in Example 1.

[0060] Performance testing and results analysis (1) Microstructure characterization analysis Figure 1 and Figure 2 Pt2 / CoMo prepared in Example 1 of this invention 0.1 SEM and TEM images of the -O catalyst. Figure 1 and Figure 2 It can be seen that the catalyst possesses a porous framework formed by the stacking of crystalline Co3O4 nanoparticles, and the surface of the porous framework is attached with a plate-like structure; while Figure 3 The solid product CoMo shown after calcination 0.1 -O represents only a porous framework, with no sheet-like structures observed. This indicates that the sheet-like structures grow in situ and attach to the surface of the porous framework during the liquid-phase reduction process.

[0061] Figure 4 It is Pt2 / CoMo 0.1 The selected area electron diffraction pattern of the plate-like structure in the -O catalyst shows diffuse halos without obvious diffraction spots, proving that the plate-like structure is amorphous.

[0062] Figure 5 It is CoMo in Example 1 0.1-O solid products and Pt2 / CoMo 0.1 XRD pattern of the -O catalyst. The figure shows that after Pt loading, the diffraction peaks of the CoMoO4 crystalline phase disappear, transforming into an amorphous CoMo material. Combined with... Figure 4 and Figure 5 The results prove that the obtained catalyst is a Pt-based crystalline-amorphous heterostructure catalyst.

[0063] (2) Catalytic performance analysis The hydrogen expulsion performance of the catalysts prepared in the above examples and comparative examples was tested using the water displacement method. The test conditions were as follows: the reaction was carried out under constant temperature magnetic stirring at 25°C. 10 mg of catalyst dispersed in 5 mL of deionized water was added to a round-bottom flask, followed by the rapid addition of 10 mL of 0.1 mol / L aqueous solution of ammonia borane. The reaction system was sealed, and the change in hydrogen production volume over time was recorded until the reaction was complete (no more hydrogen was produced).

[0064] Figure 6-8 The catalytic performance of each catalyst at room temperature is demonstrated. According to... Figure 6-8 The test results and the complete hydrogen release time of each catalyst are shown in Table 1.

[0065] Table 1 Test results of Examples 1-3 and Comparative Examples 1-4 As shown in Table 1: (1) Example 1 (Pt2 / CoMo) 0.1 The complete hydrogen release time of Pt-O was the shortest, only 1.05 minutes, indicating that an optimal crystalline-amorphous heterostructure interface could be formed at a Mo dosage of 0.1 mmol, which is beneficial for Pt dispersion and electron transfer. Example 2 (Pt2 / CoMo) 0.4 The complete hydrogen release time of Pt-O was 5.6 minutes, significantly longer than in Example 1, indicating that excessive Mo dosage (0.4 mmol) may have affected the formation quality of the crystalline-amorphous heterostructure interface or the dispersion effect of Pt, leading to a decrease in catalytic activity. Example 3 (Pt-O) 0.25 / CoMo 0.1The complete hydrogen release time of (-O) was 1.9 minutes, which was longer than that of Example 1, but its Pt content was only 1 / 8 of that of Example 1. This shows that the catalyst of the present invention can still maintain high catalytic activity with extremely low Pt content, realizing the efficient utilization of precious metals. (2) Comparative Example 1 used Fe instead of Mo, and the complete hydrogen release time was 2.2 minutes; Comparative Example 2 used Ni instead of Mo, and the complete hydrogen release time was 1.5 minutes. Both were longer than the 1.05 minutes of Example 1, indicating that the introduction of Mo is more conducive to the formation of crystalline-amorphous heterostructure than Fe and Ni, thereby obtaining higher catalytic activity. (3) Comparative Example 3 used the equal volume impregnation method (not the liquid phase reduction method of the present invention) to prepare the catalyst, and the complete hydrogen release time was 7.3 minutes, which was much longer than the 1.05 minutes of Example 1. This proves that the liquid phase reduction process of the present invention is crucial: only in this process can the cobalt-molybdenum oxide precursor be transformed into amorphous plate-like CoMo material and grow in situ attached to the surface of the porous framework to form a crystalline-amorphous heterostructure interface. Comparative Example 4 uses a hydrothermal method to prepare a solid CoMoO4 product, which is then loaded with Pt via liquid-phase reduction, resulting in a complete hydrogen release time of up to 21.5 minutes. This demonstrates that the catalyst prepared in this invention possesses unique structural advantages, enabling the formation of a crystalline-amorphous heterogeneous interface, a structure that cannot be achieved by catalysts prepared using traditional hydrothermal methods.

[0066] Based on the above results, this invention successfully constructed a heterogeneous interface between a crystalline porous Co3O4 framework and an amorphous lamellar CoMo material through a Mo-introduced liquid-phase reduction method, and then loaded Pt nanoparticles onto this interface. This structure significantly enhances the metal-support interaction, improves the dispersibility and catalytic activity of Pt, thereby achieving efficient and rapid hydrogen production from ammonia borane hydrolysis with low Pt content.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a Pt-based crystalline-amorphous heterostructure catalyst, characterized in that, Includes the following steps: Step (1): Dissolve the Mo source in a solvent, add ZIF-67, mix well, and then evaporate the solvent to obtain the Mo-deposited ZIF-67. Step (2): The ZIF-67 deposited with Mo is calcined in an air atmosphere to transform ZIF-67 into a porous framework formed by the stacking of crystalline Co3O4 nanoparticles. At the same time, a cobalt-molybdenum oxide precursor containing Mo and Co is formed on the surface of the porous framework to obtain a solid product. Step (3): Disperse the solid product obtained in step (2) in water, add Pt source and sodium borohydride for liquid phase reduction. During this process, the cobalt molybdenum oxide precursor is converted into amorphous sheet-like CoMo material and grows in situ on the surface of the porous framework to form a crystalline-amorphous heterostructure interface. At the same time, Pt nanoparticles are reduced and loaded on the crystalline-amorphous heterostructure interface to obtain the catalyst.

2. The method according to claim 1, characterized in that, The preparation method of ZIF-67 used in step (1) is as follows: Cobalt nitrate is dissolved in methanol to obtain solution A, 2-methylimidazole is dissolved in methanol to obtain solution B, solution A is quickly added to solution B under stirring conditions, and stirring is continued at 20-35℃ for 12-48h. After centrifugation, washing and drying, ZIF-67 is obtained.

3. The method according to claim 2, characterized in that, In the preparation of solution A, the ratio of cobalt nitrate to methanol is 1 mol: 12-20 L; In the preparation of solution B, the ratio of 2-methylimidazole to methanol is 1 mol: 1-2 L; The molar ratio of cobalt nitrate in solution A to 2-methylimidazole in solution B is 1:4-5.

4. The method according to claim 1, characterized in that, In step (2), the Mo source is any one of molybdenum chloride, molybdenum nitrate, or molybdenum acetylacetonate; the mass ratio of Mo atoms to ZIF-67 is 1:1 to 1:

100.

5. The method according to claim 1, characterized in that, The solvent mentioned in step (2) is methanol or ethanol, and the ratio of solvent volume to ZIF-67 mass is 0.3-0.5 mL: 1 mg.

6. The method according to claim 1, characterized in that, In step (3), the heating rate during calcination is 1-5℃ / min.

7. The method according to claim 1, characterized in that, In step (3), the Pt source is any one of chloroplatinic acid, platinum hexahydroxide, dinitrosodiamineplatinum, or platinum nitrate; the molar ratio of the platinum source to sodium borohydride is 1:5 to 1:

20.

8. A Pt-based crystalline-amorphous heterostructure catalyst, characterized in that, Prepared by the method described in any one of claims 1-7.

9. The catalyst according to claim 8, characterized in that, The catalyst has a crystalline-amorphous composite heterostructure, including: A porous framework formed by the stacking of crystalline Co3O4 nanoparticles; An amorphous sheet-like CoMo material is grown in situ and attached to the surface of the porous framework, wherein a crystalline-amorphous heterostructure interface is formed between the crystalline Co3O4 nanoparticles and the amorphous sheet-like CoMo material. And Pt nanoparticles loaded on the crystalline-amorphous heterostructure interface.

10. The application of the Pt-based crystalline-amorphous heterostructure catalyst as described in any one of claims 8-9 in the catalytic hydrolysis of ammonia borane to produce hydrogen.

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