A single-atom porous material catalyst and a preparation method and application thereof in a methane aerobic conversion reaction

Abstract

The application belongs to the technical field of catalyst material preparation, and provides a single-atom porous material catalyst, a preparation method thereof and application of the single-atom porous material catalyst in a methane aerobic conversion reaction. The application introduces reaction gas containing a gaseous metal precursor, a carbon source and a nitrogen source into a plasma reaction chamber, and uses plasma for chemical vapor deposition to obtain the single-atom porous material catalyst. The preparation method provided by the application can select gaseous, liquid or solid raw materials as a source of the gaseous metal precursor. The application can prepare various types of single-atom porous material catalysts, and enriches the application range of the single-atom porous material catalysts. The application realizes control of the particle size, morphology and distribution of the single-atom porous material catalyst by adjusting reaction parameters, and the prepared single-atom porous material catalyst can be used in the methane aerobic conversion reaction. Therefore, the preparation method provided by the application is simple in operation, strong in universality and has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of catalyst material preparation technology, and specifically relates to a single-atom porous material catalyst and its preparation method, as well as its application in the oxygen-free conversion reaction of methane. Background Technology

[0002] Single-atom porous materials refer to materials in which metal elements are uniformly dispersed as individual atoms on a support, forming a "plum-bread" structure similar to the Thomson model. Due to their low-coordination metal centers and uniform active sites, catalysts prepared from single-atom porous materials exhibit excellent catalytic activity and selectivity in various catalytic reactions, such as CO2 reduction, redox reaction, hydrogen evolution, water-gas shift reaction, hydrogenation, dehydrogenation, electrocatalysis, and photocatalysis. Therefore, single-atom porous material catalysts have broad application prospects in energy, environment, and biology. However, preparing highly efficient, stable, and uniformly distributed single-atom porous material catalysts remains a challenge.

[0003] Currently, the main methods for preparing single-atom porous catalysts are: (1) wet precipitation method, in which a metal salt solution is mixed with a support and then dried and calcined to obtain a single-atom catalyst. (2) solution gel method, in which a metal salt solution is mixed with an organic precursor and then subjected to high-temperature hydrolysis, gelation, drying, and calcination to obtain a single-atom catalyst. (3) atomization method, in which a metal salt solution is atomized by ultrasound or compressed air and then subjected to high-temperature decomposition to obtain a single-atom catalyst. (4) zero-valent metal deposition method, in which a zero-valent metal or its alloy is contacted with a support and then subjected to acid washing or oxidation treatment to obtain a single-atom catalyst. (5) surface anchoring method, in which an organic ligand containing a specific coordinating group is combined with the surface of a support to capture the target metal element, and then subjected to acid washing and calcination to obtain a single-atom catalyst.

[0004] The above preparation methods have some common problems. They can only use organometallic compounds or metal salt solutions containing specific groups as reaction raw materials and are prepared under high temperature conditions. Due to the limited source of raw materials and the harsh preparation conditions, the types of single-atom material catalysts prepared by the above methods are limited, and their application range is also limited to a certain extent, that is, they have poor universality.

[0005] Guo Xiaoguang (Science, 344(6184), May 2014, pp. 616-619) disclosed a silicide lattice-confined single-center iron catalyst for the selective activation of methane under anaerobic conditions, which can efficiently produce ethylene, an important basic chemical raw material, as well as high-value chemicals such as aromatics and hydrogen in one step. The method disclosed in the paper is innovative, but it also has certain problems. The catalyst preparation process used in this method is complicated, which limits the wide application of the method. Moreover, the method uses SiO2 with extremely low specific surface area to confine the Fe centers, resulting in a very low content of exposed metal active centers, which to some extent limits the activity of the catalyst. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a single-atom porous material catalyst and its preparation method, as well as its application in the oxygen-free conversion of methane. The preparation method provided by this invention has the advantages of simple operation and wide applicability, and the single-atom porous material catalyst has high catalytic activity.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] A method for preparing a single-atom porous material catalyst includes the following steps:

[0009] The carrier material is placed in the plasma reaction chamber of the plasma device;

[0010] The raw material gas is introduced into the plasma reaction chamber, and chemical vapor deposition is performed using plasma to obtain the single-atom porous material catalyst.

[0011] The raw material gas includes a reaction gas;

[0012] The reactant gas includes a gaseous metal precursor, a carbon source, and a nitrogen source.

[0013] Preferably, the carrier material comprises one or more of carbon nanotubes, activated carbon, graphene, porous silica, molecular sieves, and porous boron nitride; the specific surface area of ​​the carrier material is ≥200 m². 2 / g.

[0014] Preferably, the active component of the gaseous metal precursor has the general formula MR. x M is a metallic element, including one or more of Fe, Co, Ni, Cu, Zn, Pd, Ag, Pt, Au, Ru, Rh, Ir, Ti, Al, and Mo; R is a ligand, including one or more of carbonyl*-C=O, halogen, carboxyl R'-CO-O-*, and acyl R'-CO-*, where R' is a H atom or a straight-chain alkane or olefin group with 1 to 4 carbon atoms, x represents the coordination number, and the * is connected to a metallic element.

[0015] Preferably, the carbon source is one or more of alkanes, alkenes, and alkynes having 1 to 4 carbon atoms;

[0016] The nitrogen source includes one or more of NH3, N2, N2O, NO, and NO2;

[0017] The raw material gas also includes a dilution gas, which is one or more of an inert gas and / or hydrogen.

[0018] Preferably, the volume ratio of the gaseous metal precursor, carbon source, nitrogen source and dilution gas in the raw material gas is 0.001~1:0.01~3:0.01~3:0~3.

[0019] Preferably, the total pressure of the raw material gas introduced into the plasma reaction chamber is 0.01 to 3 bar, and the flow rate of the raw material gas introduced into the plasma reaction chamber is 1 to 100 mL / min.

[0020] Preferably, the plasma generation method is dielectric barrier discharge, and the parameters of the dielectric barrier discharge include: voltage of 5-50kV, current of 10-100mA, and reaction time of 0.1-6h.

[0021] The present invention also provides a single-atom porous material catalyst prepared by the preparation method described above. The single-atom porous material catalyst is a metal-nitrogen-carbon MNC single-atom material, where M is a metal atom, N is a nitrogen atom, and C is a carbon atom. The metal atom includes one or more of Fe, Co, Ni, Cu, Zn, Pd, Ag, Pt, Au, Ru, Rh, Ir, Ti, Al, and Mo.

[0022] This invention also provides the application of the single-atom porous material catalyst described in the above-mentioned technical solution in the oxygen-free conversion reaction of methane, including the following steps:

[0023] The feed gas undergoes an oxygen-free conversion reaction of methane under the action of a single-atom porous material catalyst;

[0024] The temperature for the anaerobic conversion of methane is 750–1150 °C.

[0025] The space velocity of the anaerobic conversion of methane is 1000–50000 mL / gcat / h.

[0026] The feed gas includes methane;

[0027] The methane accounts for 1 to 100% of the volume of the feed gas.

[0028] Preferably, the raw material gas further includes an auxiliary gas;

[0029] The auxiliary gas includes chemically inert gases and / or chemically non-inert gases;

[0030] The chemical inert gas is one or more of nitrogen, helium, and argon; the volume fraction of the chemical inert gas in the raw material gas is ≤99%;

[0031] The non-inert chemical gas is one or more of carbon monoxide, hydrogen, carbon dioxide, water, C2-4 monohydric alcohols, C2-4 alkanes, and C2-4 olefins; the volume fraction of the non-inert chemical gas in the raw material gas is ≤10%.

[0032] This invention provides a method for preparing a single-atom porous material catalyst, comprising the following steps: placing a support material in a plasma reaction chamber of a plasma device; introducing a raw material gas into the plasma reaction chamber and performing chemical vapor deposition using plasma to obtain the single-atom porous material catalyst; wherein the raw material gas includes a reaction gas; and the reaction gas includes a gaseous metal precursor, a carbon source, and a nitrogen source.

[0033] Beneficial effects:

[0034] On the one hand, the preparation method provided by this invention offers greater flexibility in selecting raw materials for the gaseous metal precursor. It allows for the direct use of gaseous active components as the raw material, or the preparation of liquid or solid active components into a solution, which is then vaporized via an atomizer to become the gaseous metal precursor, thus expanding the sources of raw materials for gaseous metal precursors. On the other hand, the preparation method provided by this invention can modify the types of metal elements in the gaseous metal precursor to prepare various types of single-atom porous catalysts, enriching the application range of single-atom porous catalysts; that is, the preparation method provided by this invention has strong versatility. Furthermore, the preparation method provided by this invention is carried out in a plasma reaction chamber at room temperature, avoiding the drawback of traditional single-atom material preparation methods requiring additional high-temperature conditions. Moreover, the preparation method provided by this invention utilizes plasma excitation to generate a large number of free electrons that surround the fragments of the gaseous metal precursor, carbon source, and nitrogen source, preventing metal atom aggregation and allowing the fragments of the gaseous metal precursor, carbon source, and nitrogen source to directly deposit onto the surface of the carrier material to form single-atom materials. Furthermore, bombarding the surface of the support material with plasma and high-energy electrons facilitates the formation of microporous structures on the support material surface, which can increase the catalytic area and improve catalytic efficiency. Therefore, the preparation method provided by this invention is simple to operate, highly universal, and has good prospects for industrial application.

[0035] Furthermore, the preparation method provided by this invention controls the total pressure of the raw material gas introduced into the plasma reaction chamber to be 0.01–3 bar; the volume ratio of the gaseous metal precursor, carbon source, nitrogen source, and dilution gas in the raw material gas is 0.001–1:0.01–3:0.01–3:0–3; the plasma is generated by dielectric barrier discharge, and the parameters of the dielectric barrier discharge include: voltage of 5–50 kV, current of 10–100 mA, and reaction time of 0.1–6 h; by controlling the above parameters, precise control of the particle size, morphology, and distribution of the single-atom porous material catalyst can be achieved, thereby improving the activity and stability of the single-atom porous material catalyst; at the same time, the deposition amount and dispersion degree of single atoms on the surface of the support material can be controlled, thereby improving the catalytic efficiency and catalytic activity of the single-atom porous material catalyst.

[0036] This invention also provides the application of the single-atom porous material catalyst described in the above-mentioned technical solution in the oxygen-free conversion of methane. The single-atom porous material catalyst provided by this invention has the advantage of significantly increasing the specific surface area, exposing more active sites, improving catalytic activity, and thus increasing the conversion rate of methane. Simultaneously, the larger specific surface area leads to high dispersion, avoiding coupling between adjacent metal elements and improving the selectivity of the oxygen-free conversion of methane. Attached Figure Description

[0037] Figure 1 A schematic diagram of the apparatus and process flow of a plasma device;

[0038] Figure 2 The EXAFS fitted spectrum of the Fe-NC single-atom porous material of iron-nitrogen-carbon in Example 2 is shown.

[0039] Figure 3 The specific surface area diagram of the Fe-NC single-atom porous material of iron-nitrogen-carbon in Example 2 is shown.

[0040] Figure 4 The image shows a HAADF-STEM image of the platinum-nitrogen-carbon Pt-NC single-atom porous material in Example 6. Detailed Implementation

[0041] This invention provides a method for preparing a single-atom porous material catalyst, comprising the following steps:

[0042] The carrier material is placed in the plasma reaction chamber of the plasma device;

[0043] The raw material gas is introduced into the plasma reaction chamber, and chemical vapor deposition is performed using plasma to obtain the single-atom porous material catalyst.

[0044] The raw material gas includes a reaction gas;

[0045] The reactant gas includes a gaseous metal precursor, a carbon source, and a nitrogen source.

[0046] Unless otherwise specified, all raw materials used in this invention are preferably commercially available products.

[0047] In this invention, a carrier material is placed in the plasma reaction chamber of a plasma device. The carrier material includes one or more of carbon nanotubes, activated carbon, graphene, porous silica, molecular sieves, and porous boron nitride. The specific surface area of ​​the carrier material is preferably ≥200 m². 2 / g, more preferably ≥400m 2 / g.

[0048] In this invention, after placing the carrier material in the plasma reaction chamber of the plasma device, the present invention introduces the raw material gas into the plasma reaction chamber and uses plasma to perform chemical vapor deposition to obtain the single-atom porous material catalyst.

[0049] In this invention, the raw material gas includes a reaction gas, which comprises a gaseous metal precursor, a carbon source, and a nitrogen source. In this invention, the preferred general formula for the active component of the gaseous metal precursor is MR. x M is a metallic element, preferably including one or more of Fe, Co, Ni, Cu, Zn, Pd, Ag, Pt, Au, Ru, Rh, Ir, Ti, Al, and Mo, and more preferably one or more of Fe, Co, Ni, Pt, and Au. In this invention, the MR... x R in the formula represents a ligand, preferably one or more of carbonyl*-C=O, halogen, carboxyl R'-CO-O-*, and acyl R'-CO-*, more preferably carbonyl*-C=O and halogen, wherein R' is a H atom or a straight-chain alkane or olefin group with 1 to 4 carbon atoms, x represents the coordination number, and * is connected to a metal element. In specific embodiments of the present invention, the active component of the gaseous metal precursor is preferably Fe(CO)5, Co2(CO)8, Ni(CO)4, PtCl4, or RuCl3.

[0050] In this invention, the carbon source is preferably one or more of alkanes, alkenes and alkynes having 1 to 4 carbon atoms, and more preferably one or more of methane, ethane and ethylene.

[0051] In this invention, the nitrogen source preferably includes one or more of NH3, N2, N2O, NO and NO2, and more preferably one or more of NH3, N2 and N2O.

[0052] In this invention, the raw material gas preferably also includes a diluting gas, which is preferably one or more of an inert gas and / or hydrogen, more preferably an inert gas, and even more preferably argon.

[0053] In this invention, the active component of the gaseous metal precursor is preferably gaseous and can be directly introduced into the plasma reaction chamber; when the active component of the gaseous metal precursor is liquid or solid, it is preferable to vaporize the active component or prepare it into a solution and then vaporize it through an atomizer to form a gaseous metal precursor, which is then introduced into the plasma reaction chamber.

[0054] In this invention, the preferred volume ratio of the gaseous metal precursor, carbon source, nitrogen source and dilution gas in the raw material gas is 0.001-1:0.01-3:0.01-3:0-3.

[0055] In this invention, the total pressure of the raw material gas introduced into the plasma reaction chamber is preferably 0.01 to 3 bar, more preferably 0.1 to 2 bar; the flow rate of the raw material gas introduced into the plasma reaction chamber is preferably 1 to 100 mL / min, more preferably 5 to 50 mL / min.

[0056] In this invention, the plasma generation method is preferably dielectric barrier discharge, and the parameters of the dielectric barrier discharge include: voltage preferably 5-50kV, more preferably 10-30kV, current preferably 10-100mA, more preferably 20-60mA, and reaction time preferably 0.1-6h, more preferably 1-4h.

[0057] In this invention, if it is not necessary to remove the support material, the single-atom porous material obtained by chemical vapor deposition using plasma can be used directly as a catalyst; if it is necessary to remove the support material according to actual requirements, the preferred method for removing the support material is acid washing.

[0058] In this invention, the pickling reagent is preferably an inorganic acid, and the concentration of the inorganic acid is preferably 0.01–20 mol / L, more preferably 0.1–10 mol / L; the inorganic acid preferably includes one or more of hydrofluoric acid, hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, acetic acid, hypochlorous acid, and phosphoric acid. When the carrier material is porous silica or a molecular sieve, hydrofluoric acid is preferred for pickling. After pickling, this invention further includes washing and drying the single-atom porous material from which the carrier material has been removed by pickling; the washing is preferably centrifugal washing, and the reagent for centrifugal washing is preferably water, preferably deionized water.

[0059] In this invention, the apparatus and process diagram of the plasma device are as follows: Figure 1 As shown below, in conjunction with Figure 1The preparation method of the single-atom porous material catalyst provided by the present invention is described as follows: The support material is placed in the heating and plasma excitation area of ​​the plasma device, and the flow rate of the raw material gas is controlled by a gas flow meter. After the raw material gas is introduced into the plasma reaction chamber, the plasma decomposes the raw material gas into free radical fragments and free electrons. The free radical fragments of the carbon source and nitrogen source combine in situ with the free radical fragments of the metal precursor to directly form a metal-nitrogen-carbon MNC single-atom material, which is then deposited on the surface of the support material to obtain the single-atom porous material catalyst.

[0060] This invention also provides a single-atom porous material catalyst prepared by the preparation method described in the above technical solution. In this invention, the single-atom porous material catalyst is a metal-nitrogen-carbon MNC single-atom material, where M is a metal atom, N is a nitrogen atom, and C is a carbon atom. The metal atom includes one or more of Fe, Co, Ni, Cu, Zn, Pd, Ag, Pt, Au, Ru, Rh, Ir, Ti, Al, and Mo.

[0061] This invention also provides the application of the single-atom porous material catalyst described in the above technical solution in the oxygen-free conversion reaction of methane.

[0062] In this invention, when the single-atom porous material catalyst is applied to the oxygen-free conversion reaction of methane, the preferred method includes the following steps:

[0063] The feed gas undergoes an oxygen-free conversion reaction of methane under the action of a single-atom porous material catalyst.

[0064] In this invention, the temperature of the anaerobic methane conversion reaction is 750–1150°C, preferably 800–1100°C; the space velocity of the anaerobic methane conversion reaction is 1000–50000 mL / gcat / h, preferably 2500–20000 mL / gcat / h. In this invention, the feed gas includes methane. In this invention, the volume fraction of methane in the feed gas is 1–100%. In this invention, the feed gas preferably also includes an auxiliary gas. In this invention, the auxiliary gas preferably includes a chemically inert gas and / or a chemically non-inert gas; the chemically inert gas is preferably one or more of nitrogen, helium, and argon; the volume fraction of the chemically inert gas in the feed gas is preferably ≤99%; the chemically non-inert gas is preferably one or more of carbon monoxide, hydrogen, carbon dioxide, water, C2–4 monohydric alcohols, C2–4 alkanes, and C2–4 olefins; the volume fraction of the chemically non-inert gas in the feed gas is preferably ≤10%.

[0065] In this invention, the products obtained after the anaerobic conversion of methane preferably include: ethylene + acetylene, propylene, benzene, toluene, and naphthalene.

[0066] To further illustrate the present invention, the single-atom porous material catalyst and its preparation method provided by the present invention, as well as their application in the oxygen-free conversion reaction of methane, are described in detail below with reference to embodiments. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0067] Example 1

[0068] Commercial porous silica (specific surface area ≥200 m²) 2 / g) is placed in the plasma reaction chamber as a carrier material.

[0069] A raw material gas, consisting of a gaseous metal precursor Fe(CO)5, a carbon source methane, and a nitrogen source NH3 in a volume ratio of 0.06:1:1, is introduced into the plasma reaction chamber at a flow rate of 10 mL / min. The total pressure of the raw material gas is 0.1 bar.

[0070] The plasma equipment was turned on at room temperature, and the voltage was adjusted to 20kV and the current to 30mA to start generating plasma, which excited the gaseous metal precursor, carbon source and nitrogen source to react and be directly deposited on the porous silica surface. After 4 hours of reaction, the equipment was turned off and the reaction was terminated to obtain the iron-nitrogen-carbon Fe-NC single-atom porous material.

[0071] Example 2

[0072] Commercial porous silica was placed in a plasma reaction chamber as a carrier material.

[0073] A raw material gas, composed of a gaseous metal precursor Fe(CO)5, a carbon source ethane, and a nitrogen source N2O in a volume ratio of 0.02:1:1, is introduced into the plasma reaction chamber at a flow rate of 10 mL / min. The total pressure of the raw material gas is 0.1 bar.

[0074] The plasma equipment was turned on at room temperature, and the voltage was adjusted to 10kV and the current to 50mA to start generating plasma, which excited the metal precursor, carbon source and nitrogen source to react and be directly deposited on the porous silica surface. After 4 hours of reaction, the equipment was turned off and the reaction ended.

[0075] After the reaction was completed, the material after chemical vapor deposition was treated with 2 mol / L hydrofluoric acid. After centrifugation, washing and drying, iron-nitrogen-carbon Fe-NC single-atom porous material with the support material removed was obtained.

[0076] Example 3

[0077] Commercial activated carbon was placed in the plasma reaction chamber as a carrier material.

[0078] A raw material gas, consisting of a gaseous metal precursor Co2(CO)8, a carbon source ethane, and a nitrogen source NH3 in a volume ratio of 0.09:2:1, is introduced into the plasma reaction chamber at a flow rate of 10 mL / min. The total pressure of the raw material gas is 1.2 bar.

[0079] The plasma equipment was turned on at room temperature, and the voltage was adjusted to 20kV and the current to 30mA to start generating plasma, which excited the metal precursor, carbon source and nitrogen source to react and be directly deposited on the surface of activated carbon. After 4 hours of reaction, the equipment was turned off and the reaction was terminated to obtain cobalt-nitrogen-carbon Co-NC single-atom porous material.

[0080] Example 4

[0081] Commercial ZSM-5 molecular sieve (pre-burned in air at 600℃ to remove the template agent) was placed as a carrier material in the plasma reaction chamber.

[0082] A raw material gas, consisting of a gaseous metal precursor Ni(CO)4, a carbon source ethylene, a nitrogen source NH3, and a dilution gas argon in a volume ratio of 0.12:2:1:1, is introduced into the plasma reaction chamber at a flow rate of 20 mL / min. The total pressure of the raw material gas is 0.5 bar.

[0083] The plasma equipment was turned on at room temperature, and the voltage was adjusted to 20kV and the current to 30mA to start generating plasma, which excited the metal precursor, carbon source and nitrogen source to react and directly deposit on the surface of ZSM-5 molecular sieve. After 4 hours of reaction, the equipment was turned off and the reaction ended.

[0084] After the reaction was completed, the material after chemical vapor deposition was treated with 1 mol / L hydrofluoric acid. After centrifugation, washing and drying, a nickel-nitrogen-carbon Ni-NC single-atom porous material with the support material removed was obtained.

[0085] Example 5

[0086] Commercial ZSM-5 molecular sieve (pre-burned in air at 600℃ to remove the template agent) was placed as a carrier material in the plasma reaction chamber.

[0087] The raw material gas, composed of gaseous metal precursors Ni(CO)4 and Fe(CO)5, carbon source ethylene, nitrogen source NH3, and dilution gas argon in a volume ratio of 0.02:0.02:2:1:1, is introduced into the plasma reaction chamber at a flow rate of 20 mL / min. The total pressure of the raw material gas is 0.5 bar.

[0088] The plasma equipment was turned on at room temperature, and the voltage was adjusted to 20kV and the current to 30mA to start generating plasma, which excited the metal precursor, carbon source and nitrogen source to react and directly deposit on the surface of ZSM-5 molecular sieve. After 4 hours of reaction, the equipment was turned off and the reaction ended.

[0089] After the reaction was completed, the material after chemical vapor deposition was treated with 1 mol / L hydrofluoric acid. After centrifugation, washing and drying, a nickel-iron-nitrogen-carbon Ni-Fe-NC bimetallic single-atom porous material with the support material removed was obtained.

[0090] Example 6

[0091] Commercial graphene (GR) was placed as a carrier material in a plasma reaction chamber.

[0092] Solid metal salt PtCl4 was dissolved in water to obtain a 0.001 mol / L solution. The PtCl4 solution was then vaporized through an atomizer at a flow rate of 0.02 mL / min to obtain the gaseous metal precursor PtCl4.

[0093] A raw material gas, consisting of a gaseous metal precursor PtCl4, a carbon source ethane, and a nitrogen source NH3 in a volume ratio of 0.06:2:1, is introduced into the plasma reaction chamber at a flow rate of 10 mL / min. The total pressure of the raw material gas is 1.2 bar.

[0094] The plasma equipment was turned on at room temperature, and the voltage was adjusted to 30 kV and the current to 30 mA to start generating plasma, which excited the metal precursor, carbon source and nitrogen source to react and be directly deposited on the graphene (GR) surface. After 4 hours of reaction, the equipment was turned off to end the reaction and obtain a platinum-nitrogen-carbon Pt-NC single-atom porous material.

[0095] Example 7

[0096] Commercial porous alumina was placed in a plasma reaction chamber as a carrier material.

[0097] Solid metal salt RuCl3 was dissolved in water to obtain a 0.002 mol / L solution. The RuCl3 solution was then vaporized through an atomizer at a flow rate of 0.02 mL / min to obtain the gaseous metal precursor RuCl3.

[0098] A raw material gas, consisting of a gaseous metal precursor RuCl3, a carbon source methane, and a nitrogen source N2 in a volume ratio of 0.16:1:1, is introduced into the plasma reaction chamber at a flow rate of 10 mL / min. The total pressure of the raw material gas is 1.5 bar.

[0099] The plasma equipment was turned on at room temperature, and the voltage was adjusted to 20kV and the current to 40mA to start generating plasma, which excited the metal precursor, carbon source and nitrogen source to react and be directly deposited on the porous alumina surface. After 4 hours of reaction, the equipment was turned off and the reaction ended.

[0100] After the reaction was completed, the material after chemical vapor deposition was treated with 1 mol / L nitric acid, and after centrifugation, washing and drying, a ruthenium-nitrogen-carbon Ru-NC single-atom porous material with the support material removed was obtained.

[0101] Figure 2 This is the EXAFS fitted spectrum of the iron-nitrogen-carbon Fe-NC single-atom porous material in Example 2. From... Figure 2 It can be seen that the chemical environment surrounding the Fe atom is mainly composed of Fe-nitrogen Fe-N single atoms. The strength of the Fe-Fe-Fe aggregate particles is negligible compared to the Fe-nitrogen Fe-N single atoms, indicating that there are no Fe agglomerates, proving that the Fe in this material is in a single-atom state.

[0102] Figure 3 The image shows the specific surface area of ​​the Fe-NC single-atom porous material of iron-nitrogen-carbon in Example 2. Figure 3 As can be seen from this, the specific surface area of ​​the iron-nitrogen-carbon Fe-NC single-atom porous material is 527 m². 2 / g indicates that the material has a rich microporous structure.

[0103] Figure 4 The image shown is a HAADF-STEM image of the platinum-nitrogen-carbon Pt-NC single-atom porous material in Example 6. Figure 4 As can be seen from the image, the white bright spots are metal atoms. This image visually demonstrates that the prepared platinum-nitrogen-carbon Pt-NC single-atom porous material is a single-atom material.

[0104] Application Example 1

[0105] The single-atom porous material catalysts obtained in Examples 1 to 7 were used to carry out the anaerobic conversion of methane. The composition of the feed gas in the anaerobic conversion of methane was: 10% N2 volume fraction and 90% methane volume fraction. The specific conditions and products of the anaerobic conversion of methane are shown in Table 1.

[0106] Table 1 shows the conditions and products of the oxygen-free conversion of methane in Application Example 1.

[0107]

[0108] Application Example 2

[0109] The single-atom porous material catalysts obtained in Examples 1 to 7 were used to carry out the anaerobic conversion of methane. The composition of the feed gas in the anaerobic conversion of methane was: 90% N2 volume fraction and 10% methane volume fraction. The specific conditions and products of the anaerobic conversion of methane are shown in Table 2.

[0110] Table 2 shows the conditions and products of the oxygen-free conversion of methane in Application Example 2.

[0111]

[0112] As shown in Tables 1 and 2, the single-atom porous material catalyst prepared by the method provided in this invention exhibits excellent catalytic performance for the anaerobic conversion of methane. The results of Application Examples 1 and 2 demonstrate that the single-atom porous material catalyst prepared by the method provided in this invention can carry out the anaerobic conversion of methane with feed gases containing 90% and 10% methane, indicating that the single-atom porous material catalyst prepared in this application can perform anaerobic conversion of methane at different concentrations to prepare olefins, alkynes, and aromatics. The results of Examples 1 and 2 show that the catalytic efficiency and methane conversion rate of the single-atom material without the support material are higher.

[0113] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a single-atom porous material catalyst, characterized in that, Includes the following steps: The carrier material is placed in the plasma reaction chamber of the plasma device; The raw material gas is introduced into the plasma reaction chamber, and chemical vapor deposition is performed using plasma to obtain the single-atom porous material catalyst. The raw material gas includes a reaction gas; The reactant gas includes a gaseous metal precursor, a carbon source, and a nitrogen source; After the raw gas is introduced into the plasma reaction chamber, the plasma decomposes the raw gas into free radical fragments and free electrons. The free radical fragments of the carbon source and nitrogen source combine in situ with the free radical fragments of the metal precursor to directly form metal-nitrogen-carbon MNC single-atom materials, which are then deposited on the surface of the support material to obtain single-atom porous material catalysts. The carrier material includes one or more of carbon nanotubes, activated carbon, graphene, porous silica, molecular sieves, and porous boron nitride. The raw material gas also includes a diluent gas, which is one or more of an inert gas and / or hydrogen. In the raw material gas, the volume ratio of gaseous metal precursor, carbon source, nitrogen source and dilution gas is 0.001~1:0.01~3:0.01~3:0~3; The total pressure of the raw material gas introduced into the plasma reaction chamber is 0.01~3 bar; The plasma is generated by dielectric barrier discharge, and the parameters of the dielectric barrier discharge include: voltage of 5~50kV, current of 10~100mA, and reaction time of 0.1~6h.

2. The preparation method according to claim 1, characterized in that, The specific surface area of ​​the carrier material is ≥200m². 2 / g.

3. The preparation method according to claim 1, wherein the general formula of the active component of the gaseous metal precursor is MR x M is a metallic element, including one or more of Fe, Co, Ni, Cu, Zn, Pd, Ag, Pt, Au, Ru, Rh, Ir, Ti, Al, and Mo; R is a ligand, including a carbonyl group. -C=O, halogen, carboxyl group R'-CO-O- and acyl R'-CO- One or more of the following, where R' is a H atom or a straight-chain alkane or olefin group with 1 to 4 carbon atoms, and x represents the coordination number. Connecting to the metal element.

4. The preparation method according to claim 1, characterized in that, The carbon source is one or more of alkanes, alkenes, and alkynes with 1 to 4 carbon atoms; The nitrogen source includes one or more of NH3, N2, N2O, NO, and NO2.

5. The preparation method according to claim 1, characterized in that, The flow rate of the raw material gas introduced into the plasma reaction chamber is 1~100 mL / min.

6. The single-atom porous catalyst prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The single-atom porous material catalyst is a metal-nitrogen-carbon MNC single-atom material, where M is a metal atom, N is a nitrogen atom, and C is a carbon atom. The metal atom includes one or more of Fe, Co, Ni, Cu, Zn, Pd, Ag, Pt, Au, Ru, Rh, Ir, Ti, Al, and Mo.

7. The application of the single-atom porous material catalyst according to claim 6 in the oxygen-free conversion reaction of methane, characterized in that, Includes the following steps: The feed gas undergoes an oxygen-free conversion reaction of methane under the action of a single-atom porous material catalyst; The temperature for the anaerobic conversion of methane is 750~1150℃; The space velocity of the anaerobic conversion of methane is 1000~50000 mL / gcat / h; The raw material gas includes methane; The volume fraction of methane in the feed gas is 1-100%.

8. The application according to claim 7, characterized in that, The raw material gas also includes auxiliary gas; The auxiliary gas includes chemically inert gases and / or chemically non-inert gases; The chemical inert gas is one or more of nitrogen, helium, and argon; the volume fraction of the chemical inert gas in the raw material gas is ≤99%. The non-inert chemical gas is one or more of carbon monoxide, hydrogen, carbon dioxide, water, C2-4 monohydric alcohol, C2-4 alkane, and C2-4 olefin; the volume fraction of the non-inert chemical gas in the raw material gas is ≤10%.

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