Carbon-based monatomic dehydrogenation catalyst, preparation method thereof and method for producing low-carbon olefin

Abstract

The invention relates to a carbon-based monatomic dehydrogenation catalyst, a preparation method thereof and a method for producing low-carbon olefin, the dehydrogenation catalyst comprises a carbon-based monatomic catalyst and a molecular sieve catalyst, the carbon-based monatomic catalyst comprises a carbon-based carrier and a transition metal element active component loaded on the carbon-based carrier; the transition metal element active component is one or more of Fe, Cu, Co and Sn. The invention also relates to a preparation method of the dehydrogenation catalyst. The preparation method comprises the step of stirring and mixing the carbon-based monatomic catalyst and the molecular sieve catalyst. The invention also relates to a method for producing low-carbon olefins. The method comprises the step of contacting a light hydrocarbon raw material with the dehydrogenation catalyst under an oxidative dehydrogenation condition. According to the technical scheme, when the dehydrogenation catalyst is used for the oxidative dehydrogenation reaction of the light hydrocarbon raw material, the yield of ethylene and propylene is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical industry, in particular to a carbon-based single-atom dehydrogenation catalyst and a preparation method thereof and a method for producing light olefins. Background Art

[0002] Low-carbon olefins, such as ethylene and propylene, are important industrial raw materials and are widely used in important fields such as rubber, polymers, pesticides, medicines, and fine chemicals. With the development of the market economy, the demand for downstream products has grown rapidly, but the growth of olefin production capacity has lagged behind the growth of demand in downstream industries, and there is a huge gap between production and demand. In industrial production, low-carbon olefins are mainly derived from the steam cracking of naphtha, with a reaction temperature of about 800°C, high energy consumption, and a wide distribution of reaction products, requiring complex separation processes.

[0003] At present, the technology of catalytic dehydrogenation of low-carbon alkanes to produce olefins has attracted much attention. The existing industrial alkane dehydrogenation technologies are all oxygen-free dehydrogenation processes using platinum and chromium catalysts. Platinum catalysts are expensive, and chromium catalysts are harmful to the human body and the environment. From the perspective of process operation, the oxygen-free dehydrogenation process is limited by thermodynamic equilibrium and requires a high temperature and low pressure environment to achieve a good alkane conversion rate and olefin yield. The operation energy consumption is high and the catalyst needs to be regenerated frequently. Compared with oxygen-free dehydrogenation, the oxidative dehydrogenation reaction is an exothermic reaction that is not limited by thermodynamic equilibrium. It is easy to proceed in the positive reaction direction and can be carried out under low temperature conditions, which reduces energy consumption and side reactions. There is less carbon deposition on the catalyst, so that the catalyst can maintain a high activity for a long time. Therefore, oxidative dehydrogenation is an ideal process for the dehydrogenation of low-carbon alkanes to produce olefins.

[0004] In recent years, single-atom catalysts have attracted extensive attention due to their high metal atom utilization, variable adsorption selectivity, and high catalytic activity. Since small-sized metal particles at the atomic level are easily aggregated during the preparation and catalytic process, resulting in reduced catalytic activity, a support material with a high specific surface area that can form a strong interaction with metal atoms is required. Carbon materials have many excellent properties, such as large specific surface area, high thermal conductivity, good mechanical properties, and easy functionalization. These characteristics make carbon materials a good single-atom catalyst carrier. Due to the rarity and high price of precious metals, carbon-based non-precious metal single-atom catalysts are expected to become ideal catalysts with high activity and low cost.

[0005] CN112996596A discloses a cobalt-based single-atom dehydrogenation catalyst and a method for preparing corresponding olefins from paraffin using the catalyst, wherein the dehydrogenation catalyst is loaded with single-atom cobalt on an inorganic oxide (specifically silicon dioxide) support of an alkali metal in single-atom form fixed by pretreatment of the alkali metal. The document (SCIENCE ADVANCES, 4Dec 2015, Vol 1, Issue 11) successfully prepared a carbon-based single-atom Fe catalyst by grinding graphene nanosheets and iron phthalocyanine powder with high-energy ball milling, and used the energy of high-energy ball milling in the grinding and impact process to create defects and vacancies on graphene, so that Fe-N4 type active centers are embedded in the graphene lattice, and further obtain a carbon-based single-atom Fe catalyst. However, when the current catalyst is used for oxidative dehydrogenation to produce light olefins, there are still problems of low conversion rate and low selectivity, and the yield of ethylene and propylene still needs to be further improved. Summary of the invention

[0006] The purpose of the present invention is to provide a carbon-based single-atom dehydrogenation catalyst and a preparation method thereof and a method for producing light olefins, so as to further improve the yield of light hydrocarbon oxidative dehydrogenation to produce ethylene and propylene.

[0007] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a carbon-based single-atom dehydrogenation catalyst, which dehydrogenation catalyst includes a carbon-based single-atom catalyst and a molecular sieve catalyst. The carbon-based single-atom catalyst includes a carbon-based carrier and an active component of a transition metal element loaded on the carbon-based carrier; the active component of the transition metal element is one or more of Fe, Cu, Co and Sn.

[0008] Optionally, the mass ratio of the carbon-based single-atom catalyst to the molecular sieve catalyst is 1:(0.1-12), preferably 1:(0.5-3); based on the total weight of the carbon-based single-atom catalyst, the content of the transition metal element active component is 0.05%-10%, preferably 1%-5%; the content of the carbon-based carrier is 90%-99.5%, preferably 95%-99%; the carbon-based carrier includes carbon-nitrogen material and / or carbon material.

[0009] Optionally, the specific surface area of ​​the carbon-based single-atom catalyst is 300-1000m 2 / g, preferably 550-800m 2 / g; pore diameter is 6-14nm, preferably 10-12nm; pore volume is 2-4cm 3 / g, preferably 2.5-3.5cm 3 / g.

[0010] Optionally, the specific surface area of ​​the molecular sieve catalyst is 30-250m 2 / g, a silicon-aluminum ratio of 12-100, and a pore size of 0.1-3nm; the molecular sieve component in the molecular sieve catalyst includes at least one of ZSM-5 molecular sieve, ZSM-11 molecular sieve, ZSM-22 molecular sieve and Y molecular sieve.

[0011] The second aspect of the present invention provides a method for preparing the dehydrogenation catalyst provided in the first aspect of the present invention, the preparation method comprising: stirring and mixing a carbon-based single-atom catalyst and a molecular sieve catalyst; the mass ratio of the carbon-based single-atom catalyst to the molecular sieve catalyst is 1: (0.1-12), preferably 1: (0.5-3).

[0012] Optionally, the preparation method further includes: mixing a nitrate containing a transition metal element, a carbon source and a ligand to obtain a mixed solution, heating the mixed solution to reflux, and then drying and pyrolyzing to prepare the carbon-based single-atom catalyst; the mass ratio of the nitrate containing a transition metal element, the carbon source and the ligand is 1: (80-300): (0.3-5), preferably 1: (120-200): (0.8-2); the transition metal element is one or more of Fe, Cu and Sn; the carbon source is one or more of methanol, glucose, trimesic acid, graphene oxide and carbon nanotubes; the ligand is one or more of 2-methylimidazole, ethylene glycol, o-phenanthroline and 2,2'-bipyridine; the heating temperature is 60-80°C, and the reflux time is 0.5-2h; the pyrolysis temperature is 800-1000°C, and the time is 2-6h.

[0013] Optionally, the preparation method further comprises: mixing a nitrate containing a transition metal element, a complexing agent, a solvent and a carbon material to obtain a mixed solution, heating and stirring the mixed solution until the water is completely evaporated, and then pyrolyzing to prepare the carbon-based single-atom catalyst; the mass ratio of the nitrate containing a transition metal element, the complexing agent and the carbon material is 1: (0.5-10): (80-120), preferably 1: (1-3): (90-105); the transition metal element is Co; the complexing agent is one or more of EDTA-2Na, ethanolamine, triethylenetetramine and N,N-dimethylacetamide; the carbon material is one or more of activated carbon, graphene, silicon carbide and carbon nanotubes; The pyrolysis temperature is 800-1000° C. and the time is 2-6 hours.

[0014] The third aspect of the present invention provides a method for producing light olefins, which comprises: contacting a light hydrocarbon feedstock with the dehydrogenation catalyst provided by the first aspect of the present invention under oxidative dehydrogenation conditions.

[0015] Optionally, the final distillation point of the light hydrocarbon feedstock is any value between 20-350° C.; the total content of saturated paraffins and cycloalkanes in the light hydrocarbon feedstock is 30-100wt%.

[0016] Optionally, the conditions for the oxidative dehydrogenation include: a reaction temperature of 500-750° C., preferably 550-680° C.; a weight space velocity of 30-160 (g / hour) / g catalyst, preferably 50-70 (g / hour) / g catalyst.

[0017] Through the above technical scheme, the present invention combines a carbon-based single-atom catalyst with an oxidative dehydrogenation function with a molecular sieve catalyst with catalytic cracking activity to achieve simultaneous oxidative dehydrogenation reaction and catalytic cracking reaction, thereby obtaining a higher alkane conversion rate and olefin selectivity, and improving the yield of ethylene and propylene.

[0018] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings: Figure 1 is a spherical aberration-corrected scanning transmission electron micrograph of the carbon-based single-atom Cu catalyst prepared in Example 1 of the present invention; Figure 2 It is a stability diagram of a composite catalyst prepared from the carbon-based single-atom Cu catalyst and the ZSM-5 molecular sieve catalyst of the present invention. DETAILED DESCRIPTION

[0020] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0021] A first aspect of the present invention provides a carbon-based single-atom dehydrogenation catalyst, which includes a carbon-based single-atom catalyst and a molecular sieve catalyst. The carbon-based single-atom catalyst includes a carbon-based carrier and an active component of a transition metal element loaded on the carbon-based carrier; the active component of the transition metal element is one or more of Fe, Cu, Co and Sn.

[0022] The dehydrogenation catalyst in the present invention is a composite catalyst composed of a carbon-based transition metal single atom catalyst and a molecular sieve catalyst. The transition metal coordination introduced on the carbon-based carrier makes it difficult for the transition metal to aggregate due to the coordination environment and steric hindrance, which helps to load more highly dispersed transition metal species, is not easy to deactivate, and has good catalytic stability.

[0023] According to the present invention, optionally, the mass ratio of the carbon-based single-atom catalyst to the molecular sieve catalyst may be 1:(0.1-12), preferably 1:(0.5-3).

[0024] According to the present invention, optionally, based on the total weight of the carbon-based single-atom catalyst, the content of the transition metal element active component can be 0.05%-10%, preferably 1%-5%; the content of the carbon-based carrier can be 90%-99.5%, preferably 95%-99%; the carbon-based carrier includes carbon-nitrogen material and / or carbon material. The carbon material can be one or more of activated carbon, graphene, silicon carbide and carbon nanotubes; the carbon-nitrogen material can be at least one of nitrogen-doped carbon material and carbon nitride.

[0025] According to the present invention, optionally, the specific surface area of ​​the carbon-based single-atom catalyst can be 300-1000m 2 / g, preferably 550-800m 2 / g; the pore diameter can be 6-14nm, preferably 10-12nm; the pore volume can be 2-4cm 3 / g, preferably 2.5-3.5cm 3 / g.

[0026] According to the present invention, optionally, the specific surface area of ​​the molecular sieve catalyst is 30-250m 2 / g, a silicon-aluminum ratio of 12-100, and a pore size of 0.1-3nm; the molecular sieve component in the molecular sieve catalyst includes at least one of ZSM-5 molecular sieve, ZSM-11 molecular sieve, ZSM-22 molecular sieve and Y molecular sieve.

[0027] The second aspect of the present invention provides a method for preparing the dehydrogenation catalyst provided in the first aspect of the present invention, the preparation method comprising: stirring and mixing a carbon-based single-atom catalyst and a molecular sieve catalyst; the mass ratio of the carbon-based single-atom catalyst to the molecular sieve catalyst is 1: (0.1-12), preferably 1: (0.5-3).

[0028] According to the present invention, optionally, the carbon-based single-atom catalyst synthesis method is one or more of an impregnation method, a coprecipitation method, a deposition precipitation method, a high-temperature pyrolysis method, and a ball milling method, preferably a high-temperature pyrolysis method or a coprecipitation method.

[0029] According to the present invention, optionally, the preparation method further comprises: mixing a nitrate containing a transition metal element, a carbon source and a ligand to obtain a mixed solution, heating the mixed solution to reflux, and then drying and pyrolyzing the mixed solution to prepare the carbon-based single-atom catalyst.

[0030] According to the present invention, optionally, the mass ratio of the nitrate containing a transition metal element, the carbon source and the ligand can be 1: (80-300): (0.3-5), preferably 1: (120-200): (0.8-2); the transition metal element can be one or more of Fe, Cu and Sn; the carbon source can be one or more of methanol, glucose, trimesic acid, graphene oxide and carbon nanotubes; the ligand can be one or more of 2-methylimidazole, ethylene glycol, o-phenanthroline and 2,2'-bipyridine.

[0031] According to the present invention, optionally, the heating temperature is 60-80°C, and the reflux time is 0.5-2h; the pyrolysis temperature is 800-1000°C, and the time is 2-6h.

[0032] According to the present invention, optionally, the preparation method further comprises: mixing a nitrate containing a transition metal element, a complexing agent, a solvent and a carbon material to obtain a mixed solution, heating and stirring the mixed solution until the water is completely evaporated, and then pyrolyzing the mixed solution to prepare the carbon-based single-atom catalyst.

[0033] According to the present invention, optionally, the mass ratio of the nitrate containing a transition metal element, the complexing agent and the carbon material can be 1: (0.5-10): (80-120), preferably 1: (1-3): (90-105); the transition metal element is Co; the complexing agent can be one or more of EDTA-2Na, ethanolamine, triethylenetetramine and N,N-dimethylacetamide; the carbon material can be one or more of activated carbon, graphene, silicon carbide and carbon nanotubes.

[0034] According to the present invention, optionally, the pyrolysis temperature is 800-1000° C. and the time is 2-6 hours.

[0035] The third aspect of the present invention provides a method for producing light olefins, which comprises: contacting a light hydrocarbon feedstock with the dehydrogenation catalyst provided by the first aspect of the present invention under oxidative dehydrogenation conditions.

[0036] In the present invention, a carbon-based single-atom catalyst having an oxidative dehydrogenation function is combined with a molecular sieve catalyst having a catalytic cracking activity to achieve simultaneous oxidative dehydrogenation reaction and catalytic cracking reaction, thereby obtaining a higher alkane conversion rate and olefin selectivity. When the composite catalyst of the present invention is used for the oxidative dehydrogenation of light hydrocarbons to produce ethylene and propylene, it can break the original chemical balance, reduce the energy consumption required for the reaction, and improve the conversion rate of alkanes and the selectivity of light olefins.

[0037] According to the present invention, optionally, the final distillation point of the light hydrocarbon feedstock is any value between 20-350° C.; and the total content of saturated paraffins and cycloalkanes in the light hydrocarbon feedstock is 30-100wt%.

[0038] According to the present invention, optionally, the conditions for the oxidative dehydrogenation include: the reaction temperature can be 500~750°C, preferably 550~680°C; the weight space velocity is 30~160 (g / hour) / g catalyst, preferably 50~70 (g / hour) / g catalyst.

[0039] The inventors of the present invention have found that the active transition metal elements on the single-atom catalyst exist in the form of single atoms. When applied to the dehydrogenation reaction of low-carbon hydrocarbons, the olefin selectivity can be improved, so that the yield of ethylene and propylene is increased. Specifically, the metal element has the highest atomic utilization rate when it exists in the form of single atoms, which can reduce the amount of metal used and select non-toxic metal elements to reduce costs and pollution; secondly, the monodispersed atoms have high surface energy, can show high catalytic performance at lower reaction temperatures, reduce energy consumption, and avoid the temperature range of carbon deposition; finally, the monodispersed atoms have a single active site, and there are no adjacent active sites, which can catalyze the activation of CH bonds with high selectivity without destroying CC bonds, avoid the formation of by-products and effectively inhibit the formation of carbon deposition.

[0040] According to the present invention, optionally, a fixed bed reaction system can be used when the light hydrocarbon feedstock contacts the dehydrogenation catalyst, and the oxidative dehydrogenation reaction and the oxidative regeneration reaction are respectively carried out simultaneously in two parallel fixed bed reactors, which are switched back and forth for continuous operation.

[0041] In the present invention, a fixed bed reaction system can be used. In the process of oxidative dehydrogenation reaction, the transition metal element active component serves as the dehydrogenation active center, on which the alkane dehydrogenation reaction to generate olefins and hydrogen occurs, and the catalytic cracking reaction occurs on the molecular sieve catalyst with catalytic cracking activity. The lattice oxygen carried by the transition metal element active component can selectively react with the hydrogen generated by the dehydrogenation reaction to oxidize it into water vapor, accompanied by the reduction of the lattice oxygen. After the reaction is completed, the transition metal element active component that has lost the lattice oxygen is oxidized and regenerated in the air at 150-220°C, the lattice oxygen is replenished, and the reaction activity is restored, thus completing a redox reaction regeneration cycle.

[0042] According to the present invention, optionally, a circulating fluidized bed reaction system can be used when the light hydrocarbon feedstock contacts the dehydrogenation catalyst, the catalyst is fluidized and circulated in the reactor and the oxidation regenerator, and the heat released by the oxidation and dehydrogenation of the catalyst is supplied to the reactor, thereby reducing the external heating of the reactor.

[0043] According to the present invention, optionally, a moving bed reaction system can be used when the light hydrocarbon feedstock contacts the dehydrogenation catalyst, the alkane is introduced from the top inlet of the reactor, and the dehydrogenation catalyst is continuously added from the top of the reactor. As the reaction proceeds, the dehydrogenation catalyst gradually moves downward by gravity, and is finally continuously unloaded from the bottom and lifted by gas to the regenerator for oxidation regeneration. The oxidation regeneration reaction temperature is 600-750°C, the reaction pressure is normal pressure, and the air flow rate is 30-80mL / min.

[0044] The present invention is further illustrated by the following examples, but the present invention is not limited thereto.

[0045] The present invention describes the preparation of a dehydrogenation catalyst and evaluates the catalytic performance of the catalyst. The dehydrogenation catalyst prepared in the embodiment is evaluated using a fixed bed reactor. A certain amount of catalyst is loaded into a fixed bed reactor, and n-octane is injected by an injection pump to perform a catalytic cracking reaction. The gas product is analyzed online using a gas chromatograph to obtain a detailed composition of the cracked gas.

[0046] The raw material n-octane (mass fraction greater than 99.0%) in the examples was analytically pure and was a product of Acros Organics Reagent Company.

[0047] Example 1 In this example, the carbon-based single-atom Cu catalyst was synthesized according to the following steps: 300 g methanol, 2 g 2-methylimidazole and 2 g Cu(NO 3 ) 2 9H 2 O was prepared into a solution, stirred and heated under reflux at 70°C in an oil bath for 2h to generate a skeleton structure material containing the Cu element, which was then ultrasonically cleaned and dried at 120°C for 3h, and pyrolyzed at 900°C for 2h under a reducing atmosphere of hydrogen to obtain a carbon-based single-atom Cu catalyst. The content of the active component of the Cu element in the carbon-based single-atom Cu catalyst is 2%, and the content of the carbon-based carrier is 98%; the specific surface area of ​​the carbon-based single-atom Cu catalyst is 800m 2 / g, pore diameter is 12nm, pore volume is 3.5cm 3 / g.

[0048] The carbon-based single-atom Cu catalyst and the ZSM-5 molecular sieve catalyst (specific surface area of ​​200 m 2 / g, silicon-aluminum ratio of 30, pore size of 2nm) were stirred and mixed in a mass ratio of 5:3 to prepare a composite dehydrogenation catalyst.

[0049] With n-octane as the raw material, at a reaction temperature of 550°C, a pressure of 1 MPa, and a weight space velocity of 60 (g / h) / g catalyst, the yields of ethylene and propylene in one pass are 11.5% and 14.0%. At a reaction temperature of 600°C, a pressure of 1 MPa, and a weight space velocity of 60 (g / h) / g catalyst, the yields of ethylene and propylene in one pass are 17.6% and 22.3%.

[0050] Example 2 In this example, the carbon-based single-atom Fe catalyst was synthesized according to the following steps: 320 g methanol, 2.5 g 2-methylimidazole and 2 g Fe(NO 3 ) 3 9H 2 O was prepared into a solution, stirred and heated under reflux at 70°C in an oil bath for 2h to generate a skeleton structure material containing the Fe element, which was then ultrasonically cleaned and dried at 120°C for 2h, and pyrolyzed at 900°C for 2h under a reducing atmosphere of hydrogen to obtain a carbon-based single-atom Fe catalyst. The content of the active component of the Fe element in the carbon-based single-atom Fe catalyst is 1%, and the content of the carbon-based carrier is 99%; the specific surface area of ​​the carbon-based single-atom Fe catalyst is 600m 2 / g, pore diameter is 10nm, pore volume is 2.5cm 3 / g.

[0051] The prepared carbon-based single-atom Fe catalyst and ZSM-5 molecular sieve catalyst (specific surface area of ​​200m 2 / g, silicon-aluminum ratio of 30, pore size of 2nm) were ground and mixed in a mass ratio of 5:3 to prepare a composite dehydrogenation catalyst.

[0052] With n-octane as the raw material, at a reaction temperature of 550°C, a pressure of 1 MPa, and a weight space velocity of 60 (g / h) / g catalyst, the yields of ethylene and propylene in one pass were 12.2% and 15.3%. At a reaction temperature of 600°C, a pressure of 1 MPa, and a weight space velocity of 60 (g / h) / g catalyst, the yields of ethylene and propylene in one pass were 13.7% and 16.5%.

[0053] Example 3 In this example, the carbon-based single-atom Co catalyst was synthesized according to the following steps: 3 g Co(NO 3 ) 2 6H 2O and 9g EDTA-2Na are dissolved in water to prepare a Cu-EDTA solution of a certain concentration. Then 300g activated carbon powder is added to the Co-EDTA solution, heated and stirred until the water is completely evaporated. The obtained mixture powder is placed in a nitrogen atmosphere, heated from room temperature to 900℃ at a heating rate of 5℃ / min and maintained for 2h, and then naturally cooled to room temperature to obtain a carbon-based single-atom Co catalyst. The content of Co element active components in the carbon-based single-atom Co catalyst is 3%, and the content of carbon-based carrier is 97%; the specific surface area of ​​the carbon-based single-atom Co catalyst is 700m 2 / g, pore diameter is 11nm, pore volume is 3.0cm 3 / g.

[0054] The carbon-based single-atom Co catalyst and the ZSM-5 molecular sieve catalyst (specific surface area of ​​200 m 2 / g, silicon-aluminum ratio of 30, pore size of 2nm) were stirred and mixed in a mass ratio of 5:3 to prepare a composite dehydrogenation catalyst.

[0055] With n-octane as the raw material, at a reaction temperature of 550°C, a pressure of 1 MPa, and a weight space velocity of 50 (g / h) / g catalyst, the yields of ethylene and propylene in one pass were 10.2% and 13.6%. At a reaction temperature of 600°C, a pressure of 1 MPa, and a weight space velocity of 50 (g / h) / g catalyst, the yields of ethylene and propylene in one pass were 15.5% and 17.9%.

[0056] Comparative Example 1 The carbon-based single-atom Cu catalyst prepared in Example 1 was used alone as a dehydrogenation catalyst, with n-octane as a raw material, and the yields of ethylene and propylene in a single pass were 3.2% and 6.5% under the conditions of a reaction temperature of 550°C, a pressure of 1 MPa, and a weight space velocity of 60 (g / hour) / g catalyst. Under the conditions of a reaction temperature of 600°C, a pressure of 1 MPa, and a weight space velocity of 60 (g / hour) / g catalyst, the yields of ethylene and propylene in a single pass were 4.6% and 7.9%.

[0057] Comparative Example 2 When using a molecular sieve catalyst with a ZSM-5 molecular sieve content of 30% and n-octane as raw material, the yields of ethylene and propylene in one pass are 7.3% and 11.8% under the conditions of reaction temperature of 550°C, pressure of 1MPa, and weight space velocity of 60 (g / hour) / g catalyst; the yields of ethylene and propylene in one pass are 13.8% and 15.2% under the conditions of reaction temperature of 600°C, pressure of 1MPa, and weight space velocity of 60 (g / hour) / g catalyst.

[0058] Comparative Example 3 The carbon-based single-atom Co catalyst prepared in Example 3 was used alone as a dehydrogenation catalyst, with n-octane as a raw material, and the yields of ethylene and propylene in a single pass were 3.0% and 6.1% under the conditions of a reaction temperature of 550°C, a pressure of 1 MPa, and a weight space velocity of 50 (g / hour) / g catalyst. Under the conditions of a reaction temperature of 600°C, a pressure of 1 MPa, and a weight space velocity of 50 (g / hour) / g catalyst, the yields of ethylene and propylene in a single pass were 4.3% and 7.2%.

[0059] Test Case The composite dehydrogenation catalyst prepared in Example 1 was used as a catalyst to investigate its catalytic performance stability. With n-octane as the raw material, under the conditions of a reaction temperature of 650°C, a pressure of 1 MPa, and a weight space velocity of 60 (g / h) / g catalyst, the yields of ethylene and propylene in the first, fifth, tenth, and twentieth reactions were as follows: Figure 2 As shown in Figure 2, after 20 regenerations, the dehydrogenation catalyst still maintains a stable catalytic activity.

[0060] Table 1 Comparison of ethylene and propylene yields of dehydrogenation catalysts in comparative examples and examples The above examples and comparative examples show that the composite dehydrogenation catalyst synthesized by the present invention has good catalytic activity when used for oxidative dehydrogenation to produce light olefins, thereby obtaining a higher alkane conversion rate and olefin selectivity, and can increase the yield of ethylene and propylene.

[0061] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0062] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0063] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A carbon-based single-atom dehydrogenation catalyst, characterized in that: The dehydrogenation catalyst comprises a carbon-based single-atom catalyst and a molecular sieve catalyst. The carbon-based single-atom catalyst comprises a carbon-based carrier and a transition metal element active component loaded on the carbon-based carrier; the transition metal element active component is one or more of Fe, Cu, Co and Sn.

2. The dehydrogenation catalyst according to claim 1, wherein The mass ratio of the carbon-based single-atom catalyst to the molecular sieve catalyst is 1:(0.1-12), preferably 1:(0.5-3); Based on the total weight of the carbon-based single-atom catalyst, the content of the transition metal element active component is 0.05%-10%, preferably 1%-5%; the content of the carbon-based carrier is 90%-99.5%, preferably 95%-99%; The carbon-based carrier includes carbon-nitrogen material and / or carbon material.

3. The dehydrogenation catalyst according to claim 1, wherein The specific surface area of ​​the carbon-based single-atom catalyst is 300-1000m 2 / g, preferably 550-800m 2 / g; pore diameter is 6-14nm, preferably 10-12nm; pore volume is 2-4cm 3 / g, preferably 2.5-3.5cm 3 / g.

4. The dehydrogenation catalyst according to claim 1, wherein The specific surface area of ​​the molecular sieve catalyst is 30-250m 2 / g, silicon-aluminum ratio of 12-100, pore size of 0.1-3nm; The molecular sieve component in the molecular sieve catalyst includes at least one of ZSM-5 molecular sieve, ZSM-11 molecular sieve, ZSM-22 molecular sieve and Y molecular sieve.

5. The method for preparing the dehydrogenation catalyst according to any one of claims 1 to 4, characterized in that: The preparation method comprises: stirring and mixing a carbon-based single-atom catalyst and a molecular sieve catalyst; The mass ratio of the carbon-based single-atom catalyst to the molecular sieve catalyst is 1:(0.1-12), preferably 1:(0.5-3).

6. The preparation method according to claim 5, wherein: The preparation method further comprises: mixing a nitrate containing a transition metal element, a carbon source and a ligand to obtain a mixed solution, heating the mixed solution to reflux, and then drying and pyrolyzing the mixed solution to prepare the carbon-based single-atom catalyst; The mass ratio of the nitrate containing transition metal elements, the carbon source and the ligand is 1: (80-300): (0.3-5), preferably 1: (120-200): (0.8-2); The transition metal element is one or more of Fe, Cu and Sn; the carbon source is one or more of methanol, glucose, trimesic acid, graphene oxide and carbon nanotubes; the ligand is one or more of 2-methylimidazole, ethylene glycol, o-phenanthroline and 2,2'-bipyridine; The heating temperature is 60-80°C, and the reflux time is 0.5-2h; the pyrolysis temperature is 800-1000°C, and the time is 2-6h.

7. The preparation method according to claim 5, wherein: The preparation method further comprises: mixing a nitrate containing a transition metal element, a complexing agent, a solvent and a carbon material to obtain a mixed solution, heating and stirring the mixed solution until the water is completely evaporated, and then pyrolyzing the mixed solution to prepare the carbon-based single-atom catalyst; The mass ratio of the nitrate containing transition metal elements, the complexing agent and the carbon material is 1: (0.5-10): (80-120), preferably 1: (1-3): (90-105); The transition metal element is Co; the complexing agent is one or more of EDTA-2Na, ethanolamine, triethylenetetramine and N,N-dimethylacetamide; the carbon material is one or more of activated carbon, graphene, silicon carbide and carbon nanotubes; The pyrolysis temperature is 800-1000° C. and the time is 2-6 hours.

8. A method for producing light olefins, characterized in that: The method comprises: contacting a light hydrocarbon feedstock with the dehydrogenation catalyst described in any one of claims 1 to 4 under oxidative dehydrogenation conditions.

9. The method according to claim 8, wherein: The final distillation point of the light hydrocarbon feedstock is any value between 20-350° C.; the total content of saturated paraffins and cycloparaffins in the light hydrocarbon feedstock is 30-100wt%.

10. The method according to claim 8, wherein: The conditions for the oxidative dehydrogenation include: a reaction temperature of 500-750° C., preferably 550-680° C.; a weight space velocity of 30-160 (g / h) / g catalyst, preferably 50-70 (g / h) / g catalyst.

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