A metal atomically dispersed catalyst grown directionally confined within a micropore and a method of preparing the same

Abstract

The application discloses a kind of metal atom dispersion catalyst materials of directional limited growth in micropore and preparation method thereof.The catalyst material uses carbon nanofiber with micropore / mesopore hierarchical pore structure as carrier, and metal atoms exist in the form of atomic dispersion in the pore of carbon carrier.This structure helps to improve catalytic efficiency and stability.The method has simple preparation process, controllable technology, good stability, can produce in batches, and is suitable for macro-preparation.

Description

Technical Field

[0001] This invention belongs to the field of nanocatalyst preparation technology, and relates to a single-atom catalyst, its preparation method and application, specifically to a metal atom-level dispersed catalyst grown in a directional confined environment within micropores and its preparation method. Background Technology

[0002] With the depletion of traditional fossil fuels and the emission of greenhouse gases (such as CO2 and N2O) causing serious environmental problems, the development and utilization of efficient and clean energy (wind and solar power) has become a commanding height of next-generation energy technology and a new field of economic development. In recent years, metal-air fuel cells and water electrolysis hydrogen production systems based on electrocatalytic reactions such as oxygen reduction reaction (ORR), oxygen oxidation reaction (OER), and hydrogen evolution reaction (HER) have attracted attention. These systems can serve as complementary energy storage for electrochemical energy storage power stations to achieve stable grid connection, and can also utilize clean energy to electrolyze water to produce hydrogen for periodic storage and distributed power generation. Among these, catalysts, as "accelerators" of catalytic reactions, can not only effectively reduce the activation energy of the reaction, making the reaction easier to carry out, but also greatly reduce reaction energy consumption and improve energy conversion efficiency.

[0003] Currently, commercial catalysts still heavily rely on the precious metal platinum (Pt). However, the scarcity of Pt not only leads to its high price and long-term dependence on imports, but also causes it to account for up to 36% of the cost of fuel cells (stacks), limiting the large-scale application of such fuel cell stacks. To address the challenges of resource scarcity and cost reduction and efficiency improvement, there is an urgent need to develop high-performance non-platinum catalysts. However, non-platinum catalysts often exhibit low activity and poor stability under actual operating conditions. Therefore, developing highly active and stable non-platinum catalysts is a key focus in both research and practical applications.

[0004] Constructing atomically dispersed materials, with their fully exposed active metal atoms, not only achieves maximum atom utilization efficiency, improving catalytic efficiency and selectivity, but also effectively reduces costs due to low metal content, making them highly valuable for applications. However, due to the high surface energy of isolated atoms, atomically dispersed catalysts are prone to agglomeration into nanoparticles under pyrolysis and electrochemical processes, resulting in poor stability. Furthermore, the preparation conditions for most atomically dispersed materials are demanding, requiring careful consideration of the coordination effects between the support and the metal.

[0005] A search of existing patent literature revealed that CN 117996096 A discloses the synthesis of a support with a three-dimensional network structure of mesoporous carbon fibers@carbon nanolayers using electrospinning-chemical vapor deposition as a polymer precursor, and the application of this support to load single-atom metals in the oxygen reduction reaction and carbon dioxide reduction reaction of fuel cell cathodes. The formation of this single-atom metal catalyst relies on the strong interaction between nitrogen atoms and metal atoms in the support; this interaction is called metal-support electronic interaction. Therefore, in the preparation of mesoporous carbon fibers, a nitrogen source (dicyandiamide) needs to be introduced. The nitrogen source undergoes pyrolysis to grow nitrogen-containing nanosheets in situ, thereby anchoring iron metal atoms and forming iron single-atom materials. That is, the single atom is anchored by the metal-support electronic interaction between nitrogen and metal atoms. However, this interaction may limit the choice of metal type and the optimization of catalyst performance. Furthermore, the process of preparing the mesoporous carbon fiber@carbon nanolayer network supported single-atom iron catalyst involves multiple steps, including controlling the mass ratio of mesoporous PAN fibers adsorbing iron salts to dicyandiamide and heat treatment under a N2 atmosphere. This complex preparation process may result in lower yields and higher energy consumption.

[0006] Based on the above research, this invention proposes for the first time a method for preparing a metal atomic-level dispersed catalyst and its preparation by amplifying the capillary adsorption process to achieve confined growth within micropores. This method relies solely on the capillary forces between the support and the metal-organic groups for indiscriminate adsorption, directionally adsorbing the metal groups into the micropores and confining them to synthesize atomically dispersed materials. This effectively solves the technical difficulties of the demanding preparation conditions of traditional atomic-level materials. Furthermore, due to its unique high degree of directional confinement, the prepared atomic-level catalyst is not prone to aggregation during thermal treatment and electrochemical processes, exhibiting extremely high stability and activity. Summary of the Invention

[0007] The purpose of this invention is to provide a metal atomic-level dispersed catalyst material grown in a directional confined environment within micropores and its preparation method. The preparation method enables multi-dimensional control of highly active and stable single-atom, cluster, and particulate catalytic materials.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] This invention relates to a metal atomic-level dispersed catalyst material grown in a directional confinement within micropores. The carbon material is carbon nanofiber with a microporous / mesoporous hierarchical pore structure, and metal atoms exist in an atomically dispersed form within the pores of the carbon support. The atomic-level material prepared by this invention is grown in a directional confinement within micropores via capillary adsorption. This method of directional confinement growth within micropores helps achieve high dispersion of metal species, thereby improving catalytic efficiency and stability.

[0010] As one implementation, the atomic dispersion may be in the form of single-atom dispersion or dispersion in the form of atomic clusters; the particle size of the atomic clusters is 1-5 nm.

[0011] This invention also relates to a method for preparing a metal atomic-level dispersed catalyst material grown in a directional confined environment within micropores, the method comprising the following steps:

[0012] S1. Pretreatment: The polymer precursor and pore-forming agent are mixed, and a solvent is added to form a homogeneous solution. The polymer nanofibers are formed under the action of an electric field through electrospinning technology. Carbon nanofibers are obtained by high-temperature pyrolysis. The carbon nanofibers are subjected to gradient washing with water and organic solvent and vacuum drying. Excess pore-forming agent and impurities are removed by washing to obtain carbon nanofibers with a dry microporous / mesoporous hierarchical pore structure.

[0013] S2. Capillary adsorption process: The carbon nanofibers obtained in step S1 are mixed in a vacuum with solutions of different surface tensions. At the same time, metal-organic groups with a size smaller than the pore size of the carbon nanofibers are added as adsorbents. Under vacuum, the mixture is stirred thoroughly and the metal-organic groups are absorbed into the porous carbon fibers. After natural drying, a metal-carbon mixture is obtained.

[0014] S3. Pyrolysis process: The metal-carbon mixture material obtained in step S2 is placed in an inert atmosphere for pyrolysis treatment; the metal-organic groups are pyrolyzed and anchored on the carrier to form highly active and stable atomic-level dispersed materials such as single atoms and clusters.

[0015] This highly conductive and stable atomically dispersed catalyst material is prepared using a capillary adsorption-pyrolysis annealing process. The capillary adsorption process involves adding metal-organic groups and appropriately sized carbon materials in a specific ratio and mixing them uniformly with solvents of varying surface tensions under vacuum. The pyrolysis annealing process utilizes a tube furnace, heating the mixture in an inert atmosphere. The organic groups pyrolyze and anchor at different positions on the support, resulting in atomically dispersed materials such as single atoms and clusters.

[0016] As one implementation, in step S1, the polymer precursor is preferably polyacrylonitrile. The pore-forming agent is one or more of potassium hydroxide, potassium carbonate, ammonium chloride, and sodium chloride, which have small diameters and are easily decomposed.

[0017] As one implementation scheme, in step S1, the ratio of polymeric precursor, pore-forming agent, and solvent (DMF) is 2g:0.01-0.1g:20mL.

[0018] As one implementation scheme, in step S1, the temperature of the high-temperature pyrolysis is 800°C and the time is 1 to 2 hours.

[0019] As one implementation scheme, in step S1, the vacuum drying temperature is 110°C and the time is 24–36 h.

[0020] As one implementation, in step S1, the solvent includes N,N-dimethylformamide.

[0021] As one implementation, in step S1, the organic solvent used for gradient washing is an alcohol solvent, including methanol and ethanol.

[0022] As one implementation scheme, carbon nanofiber materials are subjected to gradient washing with water and organic solvents and vacuum drying to obtain carbon nanofiber materials with dried pores, the pore size of which needs to be controlled within 0.5 to 5 nm.

[0023] As one implementation, in step S2, the solutions with different surface tensions are one or more of water, methanol, ethanol, dimethylformamide, N-methyl-2-pyrrolidone, acetone, and cyclohexane.

[0024] As one implementation, in step S2, the organometallic group is an organic chelate molecular group containing noble metals and non-noble metals, including an organic chelate molecular group containing ruthenium, iron, cobalt or nickel.

[0025] As one implementation scheme, in step S2, the ratio of carbon nanofibers, solutions with different surface tensions, and organometallic compounds is 200 mg: 10 mL: 15–35 mg.

[0026] As one implementation, in step S3, the pyrolysis temperature is 700–800°C and the time is 0.5–2 hours.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) This invention amplifies the capillary adsorption process, relying on the capillary forces between the carrier and the metal-organic groups for indiscriminate adsorption, which simplifies the complex conditions in the traditional atomic-level material preparation process and reduces the preparation difficulty; by directionally adsorbing the metal groups into the micropores, it realizes the confined synthesis of atomic-level dispersed materials, and this high degree of orientation helps to improve the uniformity and consistency of the materials.

[0029] 2) Due to its unique high degree of orientation and confinement, the prepared atomic-level catalyst is not prone to agglomeration during pyrolysis and electrochemical processes, thus exhibiting extremely high stability, which is crucial for the long-term effective use of the catalyst.

[0030] 3) The simplified preparation process and reduced dependence on harsh conditions can lower production costs and improve efficiency and yield, making it possible to use atomically dispersed catalysts on a large scale.

[0031] 4) This invention prepares carbon nanofibers by electrospinning a polymer and pore-forming agent solution → preparing polymer fibers → high-temperature treatment to obtain microporous / mesoporous carbon fibers → gradient washing to obtain dried microporous / mesoporous hierarchical pore structure carbon nanofibers → precursor adsorption in a solvent with surface tension → pyrolysis to obtain atomic-level materials. This preparation process does not rely on metal-carrier electronic interactions between nitrogen in the carrier and metal atoms to anchor single atoms. Instead, it constructs microporous / mesoporous carbon materials, controls the differences in capillary adsorption forces of solvents with different surface tensions, and amplifies capillary adsorption, making the pores act as "straws" to uniformly disperse the precursor solution into the bulk phase. The pores provide confinement, preventing the aggregation of metal elements during pyrolysis. This simple atomic dispersion strategy achieves differential distribution of metal-organic molecular precursors during adsorption through differences in capillary adsorption forces, thereby synthesizing atomic-level materials such as single atoms and clusters, providing a wider range of metal selection and better performance regulation. Attached Figure Description

[0032] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0033] Figure 1 This is a flow chart of the capillary adsorption-pyrolysis annealing process;

[0034] Figure 2 SEM image of carbon nanofibers with hierarchical pore structure;

[0035] Figure 3 The pore size distribution of carbon nanofibers under the action of different pore-forming agents;

[0036] Figure 4 The image shows the aberration AC-TEM image of the Ru single-atom dispersed catalyst in Example 1.

[0037] Figure 5 SEM image of carbon nanofibers with hierarchical pore structure;

[0038] Figure 6 The image shows the aberration-corrected AC-TEM image of the Ru cluster-dispersed catalyst in Example 2.

[0039] Figure 7 The image shows the aberration-corrected AC-TEM image of the Ru cluster-dispersed catalyst in Example 3.

[0040] Figure 8 SEM image of carbon nanofibers with hierarchical pore structure;

[0041] Figure 9 The image shows the aberration AC-TEM image of the Fe single-atom dispersed catalyst in Example 4.

[0042] Figure 10 This is a spherical aberration diagram of the Fe cluster-dispersed catalyst in Example 5.

[0043] Figure 11 The images show the spherical aberration AC-TEM and TEM images of the Ru particles in Comparative Example 1.

[0044] Figure 12 The UV spectra of the change in phenanthroline content in the solution before and after adsorption in water and propanol environments are shown.

[0045] Figure 13 The image shows the spherical aberration AC-TEM image of the Ru particles in Comparative Example 2.

[0046] Figure 14 The images show the spherical aberration AC-TEM and HRTEM images of the Ru particles in Comparative Example 3. Detailed Implementation

[0047] The present invention will be described in detail below with reference to embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0048] Example 1

[0049] A single-atom ruthenium catalyst material grown in a micropore with directional confinement; its preparation process is as follows: Figure 1 As shown, it includes:

[0050] (1) Pretreatment: 2g of polyacrylonitrile was mixed with 0.07g of pore-forming agent potassium hydroxide (KOH), and 20mL of N,N-dimethylformamide (DMF) was added. The mixture was stirred at 50℃ for 12h to form a homogeneous solution. The polymer solution was loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. As the applied electric field strength increased, the charged droplets were gradually elongated due to electrostatic force, eventually forming polymer nanofibers on the collecting device. After pyrolysis at 800℃ in an inert atmosphere for 1h, the obtained polymer nanofibers were carbonized, and their graphitization degree increased. At the same time, since KOH can react with carbon rings at high temperature, a large number of microporous / mesoporous hierarchical pore structures were formed in the fibers. The prepared carbon nanofibers were washed with 5mL of water, methanol, and ethanol in a gradient to remove excess pore-forming agent and impurities, and then vacuum dried at 110℃ for 36h to obtain carbon nanofibers with dry microporous / mesoporous hierarchical pore structures, such as Figure 2 As shown. The carbon nanofibers obtained at this time have a pore size distribution of 0.8–2.2 nm, as... Figure 3 As shown.

[0051] (2) Capillary adsorption process: 200 mg of porous carbon nanofibers and 10 mL of water were added to a vacuum mixer. Simultaneously, 15 mg of tris-(1,10-phenanthroline)ruthenium chloride was added as the adsorbent (the maximum diameter of this molecule is approximately ~1.2 nm). After addition, the adsorbent dissolved in the water, forming a mixed aqueous solution. Under vacuum, the material was thoroughly stirred for 12 h, and the organometallic groups were absorbed into the porous carbon fibers. After natural drying for 3 days, a metal-carbon mixture was obtained.

[0052] (3) Pyrolysis process: The obtained metal-carbon mixture material was placed in an inert atmosphere and pyrolyzed at 700℃ for 2 hours, with a heating rate of 5℃ / min. The organometallic groups were pyrolyzed and anchored on the support to form a highly active and stable Ru single-atom catalyst with directional confined growth in micropores. Figure 4 The image shows the aberration diagram of the Ru atomically dispersed catalyst in Example 1. The Ru metal is dispersed on the support in the form of single atoms, and the Ru content is 1.52 wt%.

[0053] Example 2

[0054] ruthenium cluster catalyst materials grown in micropores

[0055] (1) Pretreatment: 2g of polyacrylonitrile was mixed with 0.02g of pore-forming agent ammonium chloride (NH4Cl), and 20mL of N,N-dimethylformamide (DMF) was added. The mixture was stirred at 50℃ for 12h to form a homogeneous solution. The polymer solution was loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. As the applied electric field strength increased, the charged droplets were gradually elongated due to electrostatic force, eventually forming polymer nanofibers on the collecting device. After pyrolysis at 800℃ in an inert atmosphere for 1.5h, the obtained polymer nanofibers were carbonized, and their graphitization degree increased. At the same time, because NH4Cl melts and becomes molten, it penetrates into the carbon source, generating a large number of micropores / mesopore hierarchical channels in the carbon fibers. The prepared carbon nanofibers were washed with 10mL of water, methanol, and ethanol in a gradient to remove excess pore-forming agent and impurities, and then vacuum dried at 110℃ for 24h to obtain carbon nanofibers with a dry micropore / mesopore hierarchical channel structure, such as Figure 5 As shown. The carbon nanofibers obtained at this time have a pore size distribution of 0.4–2.5 nm, as... Figure 3 As shown.

[0056] (2) Capillary adsorption process: 200 mg of porous carbon nanofibers and 10 mL of water were added to a vacuum mixer, and at the same time, 15 mg of tris-(1,10-phenanthroline)ruthenium chloride (C) was added. 36 H 24Cl2N6Ru) was used as the adsorbent. After addition, the adsorbent dissolved in water to form a mixed aqueous solution. Under vacuum, the material was stirred thoroughly for 12 hours, and the metal-organic groups were absorbed into the porous carbon fibers. After natural drying for 3 days, a metal-carbon mixture was obtained.

[0057] (3) Pyrolysis process: The obtained metal-carbon mixture material was placed in an inert atmosphere and pyrolyzed at 700℃ for 2 hours, with a heating rate of 5℃ / min. The organometallic groups were pyrolyzed and anchored on the support to form a highly active and stable Ru cluster catalyst with directional confined growth in micropores. Figure 6 The image shows the aberration diagram of the Ru cluster-dispersed catalyst in Example 2. The Ru metal is dispersed on the support in the form of small clusters. The Ru content is 1.53 wt%.

[0058] Example 3

[0059] ruthenium cluster catalyst materials grown in micropores

[0060] (1) Pretreatment: 2g of polyacrylonitrile was mixed with 0.07g of pore-forming agent potassium hydroxide (KOH), and 20mL of N,N-dimethylformamide (DMF) was added. The mixture was stirred at 50℃ for 12h to form a homogeneous solution. The polymer solution was then loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. As the applied electric field strength increased, the charged droplets were gradually elongated due to electrostatic forces, eventually forming polymer nanofibers on the collecting device. After pyrolysis at 800℃ under an inert atmosphere for 1h, the prepared carbon nanofibers were washed sequentially with 5mL of water, methanol, and ethanol to remove excess pore-forming agent and impurities, and then vacuum dried at 110℃ for 36h to obtain carbon nanofibers with a dry microporous / mesoporous hierarchical pore structure. The pore size distribution of the carbon nanofibers obtained at this time was 0.8~2.2nm.

[0061] (2) Capillary adsorption process: 200 mg of porous carbon nanofibers and 10 mL of ethanol were added to a vacuum mixer, along with 15 mg of tris-(1,10-phenanthroline)ruthenium chloride as the adsorbent. After addition, the adsorbent dissolved in the ethanol, forming a mixed ethanol solution. Under vacuum, the material was stirred thoroughly for 12 h, and the organometallic groups were absorbed into the porous carbon fibers. After natural drying for 3 days, a metal-carbon mixture was obtained.

[0062] (3) Pyrolysis process: The obtained metal-carbon mixture material was placed in an inert atmosphere and pyrolyzed at 700℃ for 2 hours, with a heating rate of 5℃ / min. The organometallic groups were pyrolyzed and anchored on the support to form a highly active and stable Ru cluster catalyst with directional confined growth in micropores. Figure 7The image shows the aberration diagram of the Ru cluster-dispersed catalyst in Example 3. The Ru metal is dispersed on the support in the form of small clusters, and the Ru content is 1.53 wt%.

[0063] Example 4

[0064] Metallic iron single-atom catalyst materials grown in micropores

[0065] (1) Pretreatment: 2g of polyacrylonitrile was mixed with 0.04g of potassium carbonate (K2CO3) as a pore-forming agent, and 20mL of N,N-dimethylformamide (DMF) was added. The mixture was stirred at 50℃ for 12h to form a homogeneous solution. The polymer solution was loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. As the applied electric field strength increased, the charged droplets were gradually elongated due to electrostatic force, eventually forming polymer nanofibers on the collecting device. After pyrolysis at 800℃ in an inert atmosphere for 2h, the obtained polymer nanofibers were carbonized, and their graphitization degree increased. At the same time, due to the decomposition of potassium carbonate at high temperature to generate KOH and K2O, the carbon material was etched to form a well-developed pore structure. The prepared carbon nanofibers were washed with 10mL of water, methanol, and ethanol in a gradient to remove excess pore-forming agent and impurities, and then vacuum dried at 110℃ for 36h to obtain carbon nanofibers with a dry microporous / mesoporous hierarchical pore structure, such as Figure 8 As shown. The carbon nanofibers obtained at this time have a pore size distribution of 2–4 nm, as shown. Figure 3 As shown.

[0066] (2) Capillary adsorption process: 200 mg of porous carbon nanofibers and 10 mL of water were added to a vacuum mixer. Simultaneously, 35 mg of o-phenanthroline iron complex (the maximum diameter of this molecule is approximately ~1.2 nm) was added as the adsorbent. After addition, the adsorbent dissolved in the water, forming a mixed aqueous solution. Under vacuum, the material was thoroughly stirred for 12 h, and the organometallic groups were absorbed into the porous carbon fibers. After natural drying for 3 days, a metal-carbon mixture was obtained.

[0067] (3) Pyrolysis process: The obtained metal-carbon mixture material was placed in an inert atmosphere and pyrolyzed at 800℃ for 1 hour, with a heating rate of 5℃ / min. The Fe-containing organometallic groups were pyrolyzed and anchored on the support to form Fe single-atom catalysts with directional confined growth in micropores. Figure 9 The image shows the aberration diagram of the Fe single-atom dispersed catalyst in Example 4. The Fe metal is dispersed on the support in the form of single atoms, and the Fe content is 4.92 wt%.

[0068] Example 5

[0069] Metallic iron cluster catalyst materials

[0070] (1) Pretreatment: 2g of polyacrylonitrile was mixed with 0.04g of potassium carbonate (K2CO3) as a pore-forming agent, and 20mL of N,N-dimethylformamide (DMF) was added. The mixture was stirred at 50℃ for 12h to form a homogeneous solution. The polymer solution was then loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. Under the action of the electric field, polymer nanofibers were finally formed on the collecting device. After pyrolysis at 800℃ in an inert atmosphere for 2h, carbon fibers with well-developed porous structures were obtained. The prepared carbon nanofibers were washed sequentially with 10mL of water, methanol, and ethanol to remove excess pore-forming agent and impurities, and then dried under vacuum at 110℃ to obtain carbon nanofibers with a dry microporous / mesoporous hierarchical pore structure. The pore size distribution of the carbon nanofibers obtained at this time was 2-4nm.

[0071] (2) Capillary adsorption process: 200 mg of porous carbon nanofibers and 10 mL of acetone were added to a vacuum mixer, along with 35 mg of 1,000 phenanthroline iron complex as the adsorbent. After addition, the adsorbent dissolved in the acetone, forming a mixed acetone solution. The surface tension and dielectric constant of acetone are much lower than those of water, resulting in a lower capillary adsorption force. The material was thoroughly stirred for 12 hours under vacuum. After natural drying for 3 days, a metallic carbon mixture was obtained.

[0072] (3) Pyrolysis process: The obtained metal-carbon mixture material was placed in an inert atmosphere and pyrolyzed at 800℃ for 1 hour, with a heating rate of 5℃ / min. The Fe-containing organometallic groups were pyrolyzed to form Fe cluster catalysts that grow in a directional confined environment within micropores. Figure 10 The image shows the aberration diagram of the Fe cluster-dispersed catalyst in Example 5, where Fe metal is anchored in clusters on a carbon support, and the Fe content is 4.95 wt%.

[0073] Comparative Example 1

[0074] Ruthenium metal particle catalyst material

[0075] (1) Pretreatment: 2g of polyacrylonitrile was added to 20mL of N,N-dimethylformamide (DMF) and stirred at 50℃ for 12h to dissolve and form a solution. The polymer solution was loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. Under the action of the electric field, polymer nanofibers were finally formed on the collecting device. After pyrolysis at 800℃ in an inert atmosphere for 1h, the obtained polymer nanofibers were carbonized. The prepared carbon nanofibers were washed sequentially with 5mL of water, methanol, and ethanol, and then vacuum dried at 110℃ for 36h to obtain carbon nanofibers without micropores / mesopores. The pore size distribution is as follows. Figure 3 As shown.

[0076] (2) Capillary adsorption process: 200 mg of carbon nanofibers and 10 mL of water were added to a vacuum mixer, along with 15 mg of tris-(1,10-phenanthroline)ruthenium chloride as the adsorbent. After addition, the adsorbent dissolved in the water, forming a mixed aqueous solution. The material was thoroughly stirred for 12 h under vacuum and then naturally dried for 3 days. The metal-organic groups simply adhered to the surface of the carbon fibers, resulting in a metal-carbon mixture.

[0077] (3) Pyrolysis process: The obtained metal-carbon mixture material was placed under an inert atmosphere and pyrolyzed at 700℃ for 2 hours, with a heating rate of 5℃ / min. The organometallic groups pyrolyzed to form a catalyst with Ru particles. Figure 11 The images show the spherical aberration and TEM images of the Ru particles in Comparative Example 1. During the pyrolysis process, Ru metal migrated and agglomerated severely, forming Ru particles. At this point, the Ru content was 1.50 wt%.

[0078] Comparative Example 2

[0079] Ruthenium metal particle catalyst material

[0080] (1) Pretreatment: 2g of polyacrylonitrile was mixed with 0.07g of pore-forming agent potassium hydroxide (KOH), and 20mL of N,N-dimethylformamide (DMF) was added. The mixture was stirred at 50℃ for 12h to form a homogeneous solution. The polymer solution was loaded into a syringe, and a voltage of 25kV was applied at a flow rate of 0.8mL / h. After the electric field was applied, polymer nanofibers were finally formed on the collecting device. After pyrolysis at 800℃ under an inert atmosphere, a large number of carbon nanofibers with microporous / mesoporous hierarchical pore structures were obtained. The prepared carbon nanofibers were washed sequentially with 5mL of water, methanol, and ethanol to remove excess pore-forming agent and impurities, and then vacuum dried at 110℃ for 36h to obtain carbon nanofibers with dry microporous / mesoporous hierarchical pore structures. The pore size distribution of the carbon nanofibers obtained at this time was 0.8~2.2nm.

[0081] (2) Capillary Adsorption Process: 200 mg of porous carbon nanofibers and 10 mL of propanol were added to a vacuum mixer, along with 15 mg of tris-(1,10-phenanthroline)ruthenium chloride as the adsorbent. After addition, the adsorbent dissolved in the propanol, forming a mixed propanol solution. The material was stirred thoroughly for 12 h under vacuum. The surface tension and dielectric constant of propanol are much lower than those of water, resulting in a lower capillary adsorption force. Therefore, the organometallic groups were not absorbed into the pores of the porous carbon fibers, but rather adhered to the fiber surface through π-π adsorption. After natural drying for 3 days, a metal-carbon mixture was obtained. The changes in the phenanthroline content in the solution before and after adsorption are shown in the figure. Figure 12 As shown, in the aqueous mixed solution, the phenanthroline content in the solution completely disappeared after the capillary adsorption process, while in the propanol mixed solution, the phenanthroline content in the solution remained in large quantities after the capillary adsorption process.

[0082] (3) Pyrolysis process: The obtained metal-carbon mixture material was placed under an inert atmosphere and pyrolyzed at 700℃ for 2 hours, with a heating rate of 5℃ / min. The organometallic groups pyrolyzed to form a catalyst with Ru particles. Figure 13 The image shows the aberration diagram of Ru particles in Comparative Example 2. During the pyrolysis process, Ru metal migrates and agglomerates severely, forming Ru particles. At this time, the Ru content is 1.52 wt%.

[0083] Comparative Example 3

[0084] Ruthenium metal particle catalyst material

[0085] (1) Pretreatment: Commercial carbon nanotubes were selected as the carbon source and washed sequentially with 5 mL of water, methanol and ethanol, and then vacuum dried at 110 °C for 24 h to obtain dried carbon nanotubes with a diameter distribution of 8-10 nm.

[0086] (2) Capillary adsorption process: 200 mg of carbon nanotubes and 10 mL of water were added to a vacuum mixer, and 15 mg of tris-(1,10-phenanthroline)ruthenium chloride was added as the adsorbent. After addition, the adsorbent dissolved in the water to form a mixed aqueous solution. The material was thoroughly stirred in a vacuum environment for 12 h and then naturally dried for 3 days.

[0087] (3) Pyrolysis process: The obtained metal-carbon mixture material was placed under an inert atmosphere and pyrolyzed at 700℃ for 2 hours, with a heating rate of 5℃ / min. The organometallic groups pyrolyzed to form a catalyst with Ru particles. Figure 14 The images show the spherical aberration and HRTEM images of the Ru particles in Comparative Example 3. The Ru metal migrated and agglomerated severely during the pyrolysis process, forming Ru particles. At this time, the Ru content was 1.53 wt%.

[0088] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a metal atomic-level dispersed catalyst material grown in a directional confined environment within micropores, characterized in that, The carbon material in the metal atomically dispersed catalyst material is carbon nanofiber with a microporous / mesoporous hierarchical pore structure, and the metal atoms exist in an atomically dispersed form within the pores of the carbon support; the pore size of the carbon nanofiber is controlled at 0.5~5nm; the atomic dispersion includes single-atom dispersion or dispersion in the form of atomic clusters, and the particle size of the atomic clusters is 1~5nm. The method specifically includes the following steps: S1. Pretreatment: The polymer precursor and pore-forming agent are mixed, and a solvent is added to dissolve and stir to form a homogeneous solution. The polymer nanofibers are formed under the action of an electric field through electrospinning technology. Carbon nanofibers are obtained by high-temperature pyrolysis. The carbon nanofibers are subjected to gradient washing with water and organic solvent and vacuum drying to remove excess pore-forming agent and impurities, thereby obtaining carbon nanofibers with a dry microporous / mesoporous hierarchical pore structure. S2. Capillary adsorption process: The carbon nanofibers obtained in step S1 are mixed in a vacuum with solutions of different surface tensions. At the same time, metal-organic groups with a size smaller than the pore size of the carbon nanofibers are added as adsorbents. Under vacuum, the mixture is stirred thoroughly and the metal-organic groups are absorbed into the porous carbon fibers. After natural drying, a metal-carbon mixture is obtained. The solutions with different surface tensions are one or more of water, methanol, ethanol, acetone, dimethylformamide, N-methyl-2-pyrrolidone, and cyclohexane; the organometallic groups are organic chelate molecular groups containing ruthenium, iron, cobalt, or nickel. S3. Pyrolysis process: The metal-carbon mixture material obtained in S2 is placed in an inert atmosphere for pyrolysis treatment; the metal-organic groups are pyrolyzed and anchored on the carrier to form single-atom and cluster atomic-level dispersed materials.

2. The method for preparing a microporous, directionally confined, metal atomic-level dispersed catalyst material according to claim 1, characterized in that, The polymer precursor is polyacrylonitrile; the pore-forming agent is one or more of potassium hydroxide, potassium carbonate, ammonium chloride, and sodium chloride.

3. The method for preparing a microporous, directionally confined, metal atomic-level dispersed catalyst material according to claim 1, characterized in that, In step S1, the ratio of polymer precursor, pore-forming agent, and solvent is 2 g: 0.01-0.1 g: 20 mL.

4. The method for preparing a metal atomic-level dispersed catalyst material with directional confined growth within micropores according to claim 1, characterized in that, In step S1, the high-temperature pyrolysis temperature is 800℃ and the time is 1-2 h; the vacuum drying temperature is 110℃ and the time is 24-36 h; the solvent includes N,N-dimethylformamide; and the organic solvent is an alcohol solvent.

5. The method for preparing a microporous, directionally confined, metal atomic-level dispersed catalyst material according to claim 4, characterized in that, The alcohol solvents include methanol and ethanol.

6. The method for preparing a microporous, directionally confined, metal atomic-level dispersed catalyst material according to claim 1, characterized in that, In step S2, the ratio of carbon nanofibers, solutions with different surface tensions, and organometallic compounds is 200 mg: 10 mL: 15–35 mg.

7. The method for preparing a microporous, directionally confined, metal atomic-level dispersed catalyst material according to claim 1, characterized in that, The pyrolysis treatment is performed at a temperature of 700~800℃ for a time of 0.5~2 h.

Images