Preparation method and application of desorption agent for promoting CO2 hydrogenation reaction

Abstract

The present application belongs to the field of coal chemical industry, and relates to a desorption agent for promoting CO2 hydrogenation reaction, which comprises Fe-based catalyst of component A and hydrophobic modified Silicalite-1 molecular sieve of component B through silanization reaction, and the mass ratio of component A to component B is 1:0.1-1:3, and a preparation method of the desorption agent is provided. The present application is scientifically and reasonably designed, mesoporous Silicalite-1 molecular sieve desorption agent modified by hydrophobic silanization method is physically incorporated on the basis of Fe-based catalyst, the desorption of water on the surface of Fe-based catalyst is accelerated, the active phase of the catalyst is protected from being oxidized by water, the mass transfer rate is improved, the olefin selectivity is improved, and the purpose of pulling the reaction equilibrium, improving the CO2 conversion rate is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of coal chemical industry, and relates to a preparation technology of a desorption agent, in particular to a preparation method and application of a desorption agent for promoting CO2 hydrogenation reaction. BACKGROUND

[0002] It is known that the surge in CO2 emissions not only causes a series of environmental problems, but also causes a large amount of carbon resources to be wasted. The resource utilization of CO2 can not only effectively slow down the greenhouse effect, but also achieve the purpose of recycling carbon resources. The hydrogenation of renewable H2 and CO2 into high-value chemicals and liquid fuels is a CO2 conversion route with great development potential.

[0003] Due to the chemical inertness of CO2 molecules and the kinetic barrier of C-C bond formation, it is difficult to activate CO2 and grow carbon chains. Therefore, developing a catalyst with high activity and high stability is a research hotspot in the industry and academia. Fe-based catalysts have strong reverse water gas shift (RWGS) activity, and have high olefin selectivity and chain growth ability in CO hydrogenation (Fischer-Tropsch synthesis, FTS), and can selectively produce liquid fuels and high-value chemicals such as high-quality gasoline, aromatic hydrocarbons and olefins. Therefore, Fe-based catalysts are widely concerned for the preparation of olefins by the RWGS-FTS route of CO2 hydrogenation.

[0004] In the preparation of high-value olefins by the RWGS-FTS route of CO2 hydrogenation, a large amount of by-product (water) will be generated in the reaction. The water partial pressure in the reaction system is too high, which will limit the equilibrium conversion rate of CO2, and the presence of water will also oxidize the active phase (Fe5C2) of the FTS reaction, resulting in catalyst deactivation. The addition of a hydrophobic promoter accelerates the desorption of water on the catalyst surface, which on the one hand reduces the water partial pressure in the reaction system, and according to the Le Chatelier principle, the reduction of the water partial pressure in the system will promote the forward reaction, pull the reaction equilibrium, and improve the CO2 conversion rate; on the other hand, the water is timely separated from the reaction system, which protects the active phase (Fe5C2) of the FTS reaction from being oxidized, and improves the service life of the catalyst. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a desorption agent for promoting CO2 hydrogenation reaction, which can rapidly desorb the by-product H2O from the catalyst surface and improve the CO2 conversion rate and olefin selectivity.

[0006] The technical problem of the present application is solved by adopting the following technical scheme:

[0007] A kind of desorption agent for promoting CO2 hydrogenation reaction, including A component Fe-based catalyst, B component silicalite-1 molecular sieve by silanization reaction hydrophobic modification, the mass ratio of A component Fe-based catalyst and B component silicalite-1 molecular sieve by silanization reaction hydrophobic modification is 1:0.1-1:3.

[0008] A component Fe-based catalyst includes Fe3O4 and Fe5C2, the mass ratio of Fe3O4 and Fe5C2 is 1:0.5-1:2, and A component iron-based catalyst is prepared by precise combination. The preparation method of A component Fe-based catalyst is as follows:

[0009] ①Preparation of Fe3O4: the preparation method of Fe3O4 includes: first, 2.4g sodium acetate, 0.35g sodium citrate and 2.16g Fe salt are dissolved in 300mL ethylene glycol, stirring until completely dissolved, the obtained mixed solution is moved to the hydrothermal synthesis reaction kettle with polytetrafluoroethylene lining, the conditions of solvent thermal synthesis process are 200 DEG C, 12h, the product is repeatedly washed with anhydrous ethanol several times, centrifuged to neutral solution, finally dried at 60-80 DEG C for more than 10h, the dried powder is placed in a tube furnace and calcined at a heating rate of 2 DEG C / min under nitrogen atmosphere for more than 3h, then Fe3O4 is obtained.

[0010] ②Preparation of Fe5C2: the preparation method of Fe5C2 includes: first, ferrous oxalate dihydrate is prepared by solvothermal method, then ferrous oxalate dihydrate is placed in a carbonization furnace, CO is used as carbon source gas, the composition is CO:N2=10:90, the flow rate is 30mL / min, the temperature is raised to 350 DEG C at a heating rate of 0.5 DEG C / min and kept for 4h, finally the black solid powder is obtained, which is Fe5C2.

[0011] The preparation method of the ferrous oxalate dihydrate includes: first, 2.224g ferrous salt is dissolved in 16mL ethanol and 64mL water, stirred uniformly and marked as solution I, then 0.72g oxalic acid is dissolved in the same proportion of ethanol and water, stirred uniformly and marked as solution II, slowly mix solution I and II at room temperature to obtain a transparent mixture, the mixture is transferred to a reaction kettle with polytetrafluoroethylene, and the crystal is grown at 100 DEG C for 24h, the obtained solid is washed with ethanol and water for several times and dried to obtain ferrous oxalate dihydrate.

[0012] The B component is mesoporous Silicalite-1 molecular sieve which is hydrophobically modified by a silanization method, and the specific preparation method comprises the following steps: first, a silicon source, a template agent TPAOH, ammonia water and ethanol are added into deionized water in a proportion of 1:0.25:0.15:2 in terms of molar ratio, and stirring is carried out for 2 hours until a transparent sol is obtained, the obtained sol is moved to a crystallization reaction kettle with a polytetrafluoroethylene lining, the reaction kettle is sealed and transferred to a homogeneous reactor, crystallization is carried out at 180 DEG C for 72 hours, the product after crystallization is washed to be neutral, and drying is carried out at 60-80 DEG C for more than 12 hours, and finally, the product is calcined at 550 DEG C for 6 hours to obtain mesoporous Silicalite-1 molecular sieve, and then the hydrophobic Silicalite-1 molecular sieve is prepared by a silanization method, and the specific method is as follows: 1g of Silicalite-1 molecular sieve is dispersed in 20mL of anhydrous toluene by ultrasonic dispersion, then 1g of a hydrophobic coupling agent hexadecyl trimethoxysilane is dispersed in 40mL of anhydrous toluene, and finally, the two parts are mixed and stirred at room temperature for 24 hours, and the sample is washed by centrifugation with anhydrous ethanol for multiple times to obtain the hydrophobic Silicalite-1.

[0013] The prepared A component Fe-based catalyst and the B component hydrophobic Silicalite-1 molecular sieve are combined in a fixed bed reactor in a mass ratio of 1:0.1-1:3, and reduction is carried out, and the reduction conditions are as follows: high-purity H2, programmed reduction, 350 DEG C, 0.2MPa, 1000h –1 , 6h. After reduction, the temperature is lowered, and the raw material gas is switched to carry out reaction, the raw material gas composition is H2 / CO2=3:1, the space velocity is controlled to be 1000-4000h-1, the reaction temperature is 280-360 DEG C, and the reaction pressure is 2.5-3.5MPa.

[0014] The advantages and positive effects of the present application are as follows:

[0015] Due to the inertness of CO2 molecules and the kinetic barrier of C-C bond formation, the production of high-value chemicals by using CO2 is limited by low CO2 conversion rate and wide product distribution. The present application is designed scientifically and reasonably, and the hydrophobic desorption agent is physically doped on the basis of the Fe-based catalyst, on the one hand, the mesoporous Silicalite-1 molecular sieve desorption agent which is hydrophobically modified by a silanization method is doped to improve the mass transfer rate, and on the other hand, the desorption of water on the surface of the Fe-based catalyst is accelerated, the active phase of the catalyst is protected from being oxidized by water, the olefin selectivity is improved, and the purpose of pulling the reaction equilibrium to improve the CO2 conversion rate is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The figure is a structural schematic comparison diagram of the water contact angle of Silicalite-1 molecular sieve before and after hydrophobic modification. DETAILED DESCRIPTION

[0017] The application will be further described in detail below through specific examples, the following examples are only descriptive, not limiting, and cannot limit the protection scope of the application.

[0018] The application provides a desorption agent for promoting CO2 hydrogenation reaction, which is a hydrophobic desorption agent physically doped in a Fe-based catalyst, and is composed of two different components A and B, which are respectively ground, pressed into tablets, and accurately combined according to different mass ratios. The component A is a Fe-based catalyst, and the component B is a Silicalite-1 molecular sieve modified by a silanization reaction. The reaction process is that the component A induces CO2 molecular activation and C-C occurrence, and the component B accelerates water desorption from a CO2-FTS reaction system.

[0019] The Fe-based catalyst of the component A is a mixture of metal oxides and iron carbides, which is prepared by a solvothermal method and a heat treatment method. The specific preparation method is as follows:

[0020] ①Preparation of Fe3O4: first, sodium acetate, sodium citrate and Fe salt are respectively dissolved in a certain amount of ethylene glycol, and stirred vigorously until completely dissolved. The obtained mixed solution is moved to a hydrothermal synthesis reaction kettle with a polytetrafluoroethylene liner, and the solvothermal synthesis process is carried out at 200℃ for 12h. The obtained product is repeatedly washed with anhydrous ethanol for several times, centrifuged until the solution is neutral. Finally, the dried powder is placed in a tube furnace and calcined at a certain heating rate under nitrogen atmosphere for more than 3h, and then Fe3O4 is obtained.

[0021] ②Preparation of Fe5C2: first, ferrous oxalate dihydrate is prepared by a solvothermal method, and then reduced-carburized at 350℃-400℃ by taking CO as a carbon source, and finally a black solid powder is obtained, which is Fe5C2. The mass ratio of Fe3O4 to Fe5C2 is 1:0.5-1:2, and the Fe-based catalyst of the component A is prepared by accurate combination.

[0022] The component B is a mesoporous Silicalite-1 molecular sieve modified by a silanization method, and the specific preparation method is as follows:

[0023] Firstly, the silicon source, template agent TPAOH, ammonia and ethanol were added into deionized water in turn, and stirred for 2 h to obtain a transparent sol. The sol was moved to a crystallization reactor with a polytetrafluoroethylene liner, the reactor was sealed and transferred to a homogeneous reactor, and crystallized at 180°C for 72 h. The product after crystallization was washed to neutral, dried at 60-80°C for more than 12 h, and finally calcined at 550°C for 6 h to obtain mesoporous Silicalite-1 molecular sieve. Then, hydrophobic Silicalite-1 was designed by silanization method: Silicalite-1 molecular sieve and hydrophobic coupling agent (hexadecyl trimethoxysilane) were dispersed in anhydrous toluene respectively, and then the two parts were mixed to design hydrophobic Silicalite-1 by precisely controlling the silanization reaction.

[0024] The prepared Fe-based catalyst of group A and hydrophobic Silicalite-1 molecular sieve of group B were precisely combined and loaded into a fixed bed reactor in a mass ratio of 1:0.1-1:3 for reduction. The reduction was carried out in high-purity H2 by programmed temperature reduction, and the reduction conditions were 350°C, 0.2 MPa, 1000 h –1 , 6 h. After reduction, the temperature was lowered and the raw gas was switched for reaction. The raw gas composition was H2 / CO2=3:1, the space velocity was controlled at 1000-4000 h-1, the reaction temperature was 280-360°C, and the reaction pressure was 2.5-3.5 MPa. The inorganic components in the gas phase product were analyzed by online gas chromatography with a TCD detector, and the light organic components (C1-C5) were analyzed by gas chromatography with an FID detector.

[0025] Example 1

[0026] According to the mass ratio of Fe-based catalyst (Fe3O4 and Fe5C2 were 1:1) and hydrophobic Silicalite-1 molecular sieve was 1:0.8, the above two components were granulated to 20-40 mesh, named "catalyst 1", and precisely combined and loaded into a fixed bed reactor. The reduction was carried out in high-purity H2 by programmed temperature reduction, and the reduction conditions were 350°C, 0.2 MPa, 1000 h –1 , 6 h. After reduction, the temperature was lowered and the raw gas was switched for reaction. The reaction conditions were 320°C, 3 MPa, 1000 h –1 , H2 / CO2=3:1. The reaction results are shown in Table 1.

[0027] Example 2

[0028] According to the Fe-based catalyst (mass ratio of Fe3O4 to Fe5C2 is 1:0.8) and the hydrophobic Silicalite-1 molecular sieve with a mass ratio of 1:0.5, the above two components are granulated to 20-40 mesh respectively, named as "catalyst 2", and precisely combined into a fixed bed reactor. The reduction is carried out in high-purity H2, and the reduction conditions are 350°C, 0.2 MPa, 1000 h –1 , 6 h. After reduction, the temperature is lowered and the raw gas is switched for reaction, and the reaction conditions are 320°C, 3 MPa, 1000 h –1 , H2 / CO2=3:1. The reaction results are shown in Table 1.

[0029] Example 3

[0030] According to the Fe-based catalyst (mass ratio of Fe3O4 to Fe5C2 is 1:0.6) and the hydrophobic Silicalite-1 molecular sieve with a mass ratio of 1:0.8, the above two components are granulated to 20-40 mesh respectively, named as "catalyst 3", and precisely combined into a fixed bed reactor. The reduction is carried out in high-purity H2, and the reduction conditions are 350°C, 0.2 MPa, 1000 h –1 , 6 h. After reduction, the temperature is lowered and the raw gas is switched for reaction, and the reaction conditions are 320°C, 3.5 MPa, 2000 h –1 , H2 / CO2=3:1. The reaction results are shown in Table 1.

[0031] Example 4

[0032] According to the Fe-based catalyst (mass ratio of Fe3O4 to Fe5C2 is 1:1.5) and the hydrophobic Silicalite-1 molecular sieve with a mass ratio of 1:1, the above two components are granulated to 20-40 mesh respectively, named as "catalyst 4", and precisely combined into a fixed bed reactor. The reduction is carried out in high-purity H2, and the reduction conditions are 350°C, 0.2 MPa, 1000 h –1 , 6 h. After reduction, the temperature is lowered and the raw gas is switched for reaction, and the reaction conditions are 300°C, 3 MPa, 2000 h –1 , H2 / CO2=3:1. The reaction results are shown in Table 1.

[0033] Example 5

[0034] According to the Fe-based catalyst (mass ratio of Fe3O4 to Fe5C2 is 1:1.2) and the hydrophobic Silicalite-1 molecular sieve with a mass ratio of 1:2, the above two components are granulated to 20-40 mesh respectively, named as "catalyst 5", and precisely combined into a fixed bed reactor. The reduction is carried out in high-purity H2, and the reduction conditions are 350°C, 0.2 MPa, 1000 h –1, 6h. After reduction, switch to feed gas for reaction, reaction conditions: 320℃, 3MPa, 1000h –1 , H2 / CO2=3:1. The reaction results are shown in Table 1.

[0035] Example 6

[0036] According to the Fe-based catalyst (mass ratio of Fe3O4 to Fe5C2 is 1:0.5) and the mass ratio of hydrophobic Silicalite-1 molecular sieve is 1:2.5, the above two components are granulated to 20-40 mesh respectively, named "catalyst 6", and precisely combined into a fixed bed reactor. Temperature programmed reduction in high purity H2, reduction conditions: 350℃, 0.2MPa, 1000h –1 , 6h. After reduction, switch to feed gas for reaction, reaction conditions: 320℃, 3MPa, 1000h –1 , H2 / CO2=3:1. The reaction results are shown in Table 1.

[0037] Example 7

[0038] According to the Fe-based catalyst (mass ratio of Fe3O4 to Fe5C2 is 1:1.8) and the mass ratio of hydrophobic Silicalite-1 molecular sieve is 1:3, the above two components are granulated to 20-40 mesh respectively, named "catalyst 7", and precisely combined into a fixed bed reactor. Temperature programmed reduction in high purity H2, reduction conditions: 350℃, 0.2MPa, 1000h –1 , 6h. After reduction, switch to feed gas for reaction, reaction conditions: 290℃, 3MPa, 1000h –1 , H2 / CO2=3:1. The reaction results are shown in Table 1.

[0039] Example 8

[0040] According to the Fe-based catalyst (mass ratio of Fe3O4 to Fe5C2 is 1:1.2) and the mass ratio of hydrophobic Silicalite-1 molecular sieve is 1:0.6, the above two components are granulated to 20-40 mesh respectively, named "catalyst 8", and precisely combined into a fixed bed reactor. Temperature programmed reduction in high purity H2, reduction conditions: 350℃, 0.2MPa, 1000h –1 , 6h. After reduction, switch to feed gas for reaction, reaction conditions: 360℃, 2.5MPa, 1000h –1 , H2 / CO2=3:1. The reaction results are shown in Table 1.

[0041] Example 9

[0042] Fe-based catalyst (Fe3C04 and Fe5C2 mass ratio of 1:2) and hydrophobic Silicalite-1 molecular sieve with a mass ratio of 1:0.7, the above two components were granulated to 20-40 mesh, named "catalyst 9", and precisely combined into a fixed bed reactor. Reduction in high-purity H2, reduction conditions: 350℃, 0.2MPa, 1000h –1 , 6h. After reduction, switch to raw gas for reaction, reaction conditions: 320℃, 2MPa, 1000h –1 , H2 / CO2=3:1. The reaction results are shown in Table 1.

[0043] Example 10

[0044] Fe-based catalyst (Fe3C04 and Fe5C2 mass ratio of 1:1) and hydrophobic Silicalite-1 molecular sieve with a mass ratio of 1:0.8, the above two components were granulated to 20-40 mesh, named "catalyst 10", and precisely combined into a fixed bed reactor. Reduction in high-purity H2, reduction conditions: 350℃, 0.2MPa, 1000h –1 , 6h. After reduction, switch to raw gas for reaction, reaction conditions: 300℃, 3MPa, 4000h –1 , H2 / CO2=3:1. The reaction results are shown in Table 1.

[0045] Comparative Example 1

[0046] Fe-based catalyst (Fe3C04 and Fe5C2 mass ratio of 1:1) was granulated to 20-40 mesh, named "comparative catalyst 1", and precisely combined into a fixed bed reactor. Reduction in high-purity H2, reduction conditions: 350℃, 0.2MPa, 1000h –1 , 6h. After reduction, switch to raw gas for reaction, reaction conditions: 320℃, 3MPa, 1000h –1 , H2 / CO2=3:1. The reaction results are shown in Table 1.

[0047] Comparative Example 2

[0048] Fe-based catalyst (Fe3C04 and Fe5C2 mass ratio of 1:1) and hydrophobic Silicalite-1 molecular sieve with a mass ratio of 1:0.8, the above two components were granulated to 20-40 mesh, named "comparative catalyst 2", and combined into a fixed bed reactor with the Fe-based catalyst on top and the hydrophobic Silicalite-1 molecular sieve on the bottom with quartz wool in between. Reduction in high-purity H2, reduction conditions: 350℃, 0.2MPa, 1000h –1, 6h. After reduction, switch to raw gas for reaction, reaction conditions: 320℃, 3MPa, 1000h –1 , H2 / CO2=3:1. Reaction results are shown in Table 1.

[0049] Comparative Example 3

[0050] According to the Fe-based catalyst (mass ratio of Fe3O4 to Fe5C2 is 1:1.2) and the mass ratio of hydrophobic modified SiO2 is 1:0.8, the above two components are granulated to 20-40 mesh respectively, named as "Comparative Catalyst 3", and then precisely combined and loaded into a fixed bed reactor. Reduction in high-purity H2, reduction conditions: 350℃, 0.2MPa, 1000h –1 , 6h. After reduction, switch to raw gas for reaction, reaction conditions: 320℃, 3MPa, 1000h –1 , H2 / CO2=3:1. Reaction results are shown in Table 1.

[0051] Comparative Example 4

[0052] According to the Fe-based catalyst (mass ratio of Fe3O4 to Fe5C2 is 1:1) and the mass ratio of activated carbon is 1:0.8, the above two components are granulated to 20-40 mesh respectively, named as "Comparative Catalyst 4", and then precisely combined and loaded into a fixed bed reactor. Reduction in high-purity H2, reduction conditions: 350℃, 0.2MPa, 1000h –1 , 6h. After reduction, switch to raw gas for reaction, reaction conditions: 320℃, 3MPa, 1000h –1 , H2 / CO2=3:1. Reaction results are shown in Table 1.

[0053] Comparative Example 5

[0054] According to the Fe-based catalyst (mass ratio of Fe3O4 to Fe5C2 is 1:1) and the mass ratio of hydrophobic modified activated carbon is 1:0.8, the above two components are granulated to 20-40 mesh respectively, named as "Comparative Catalyst 6", and then precisely combined and loaded into a fixed bed reactor. Reduction in high-purity H2, reduction conditions: 350℃, 0.2MPa, 1000h –1 , 6h. After reduction, switch to raw gas for reaction, reaction conditions: 320℃, 3MPa, 1000h –1 , H2 / CO2=3:1. Reaction results are shown in Table 1.

[0055] Table 1 Comparison of catalytic effects of each example and comparative example

[0056]

[0057]

[0058] From the above table, it can be concluded that Examples 1-10 are specific implementation cases under the defined conditions according to the application, respectively, different mass ratios of Fe3O4 and Fe5C2 coupled with different masses of hydrophobic Silicalite-1 molecular sieves are used for catalyst evaluation under common CO2 hydrogenation reaction conditions. Comparative Example 1 is a combination of Fe catalyst and hydrophobic Silicalite-1 molecular sieve in a top-bottom layered manner filled into the reactor, and Comparative Examples 2-5 are Fe-based catalyst coupling with other materials.

[0059] By comparing Example 1 and Comparative Example 1, it is found that after coupling the Fe-based catalyst with the hydrophobic Silicalite-1 molecular sieve, the CO2 conversion rate is increased from 28.8% to 46.7%, and the olefin selectivity is increased from 6.5% to 40.5%. The increase in CO2 conversion rate indicates that the hydrophobic Silicalite-1 molecular sieve accelerates the desorption of H2O from the catalyst surface during the reaction, promoting the forward progress of the reaction; at the same time, the increase in olefin selectivity indicates that the hydrophobic Silicalite-1 molecular sieve protects the stability of the active phase of carbonized iron in the reaction.

[0060] In addition, the combination mode of Fe-based catalyst and hydrophobic Silicalite-1 molecular sieve also has a great influence on the performance of CO2 hydrogenation reaction. By comparing Example 1 and Comparative Example 2, it is found that compared with the double bed, the CO2 conversion rate is increased from 29.7% to 46.7% after mixing after granulation, which indicates that appropriate contact distance between Fe-based catalyst and hydrophobic Silicalite-1 molecular sieve is beneficial to the desorption of H2O from the catalyst system by hydrophobic Silicalite-1 molecular sieve, thereby achieving the purpose of promoting the forward progress of the reaction.

[0061] As Figure 1 is a schematic comparison diagram of the water contact angle structure of Silicalite-1 molecular sieve before and after hydrophobic modification, Figure 1 In the figure, a is Silicalite-1 molecular sieve without hydrophobic modification, and b is Silicalite-1 molecular sieve after hydrophobic modification. The greater the contact angle of Silicalite-1 molecular sieve with water, the stronger its hydrophobicity, and the stronger its H2O desorption capacity.

[0062] Although the embodiments of the present application are disclosed for illustrative purposes, those skilled in the art can understand that various alternatives, changes and modifications are possible without departing from the spirit and scope of the present application and the appended claims, therefore, the scope of the present application is not limited to the disclosed content of the embodiments.

Claims

1. A desorbent to promote CO2 hydrogenation reactions, characterized in that: The A component is a Fe-based catalyst, the B component is a Silicalite-1 molecular sieve hydrophobically modified by a silanization reaction, and the mass ratio of the A component Fe-based catalyst to the B component Silicalite-1 molecular sieve hydrophobically modified by a silanization reaction is 1:0.1-1:3, the A component Fe-based catalyst comprises Fe3O4 and Fe5C 2， The mass ratio of Fe3O4 to Fe5C2 is 1:0.5-1:2, the preparation method of the desorption agent for promoting the CO2 hydrogenation reaction comprises the following steps: physically mixing the A component Fe-based catalyst and the B component Silicalite-1 molecular sieve hydrophobically modified by a silanization reaction in a mass ratio of 1:0.1-1:3 to obtain the desorption agent for promoting the CO2 hydrogenation reaction, and the A component Fe-based catalyst comprises Fe3O4 and Fe5C in a mass ratio of 1:0.5-1:2 2， The B component is a mesoporous Silicalite-1 molecular sieve hydrophobically modified by a silanization method, and the specific preparation method comprises the following steps: first, a silica source, a template agent TPAOH, ammonia water and ethanol are sequentially added to deionized water in a molar ratio of 1:0.25:0.15:2, and stirring is performed for 2 hours until a transparent sol is obtained, the obtained sol is transferred to a crystallization reaction kettle with a polytetrafluoroethylene lining, the reaction kettle is sealed and transferred to a homogeneous reactor, crystallization is performed at 180 DEG C for 72 hours, the product after crystallization is washed to neutral, drying is performed at 60-80 DEG C for more than 12 hours, and finally calcination is performed at 550 DEG C for 6 hours to obtain a mesoporous Silicalite-1 molecular sieve, then a hydrophobic Silicalite-1 molecular sieve is prepared by a silanization method, and the specific method is as follows: 1g of Silicalite-1 molecular sieve is ultrasonically dispersed in 20mL of anhydrous toluene, then 1g of a hydrophobic coupling agent hexadecyltrimethoxysilane is dispersed in 40mL of anhydrous toluene, finally, the two parts are mixed and stirred at room temperature for 24 hours, and the sample is washed by centrifugation with anhydrous ethanol for multiple times to obtain a hydrophobic Silicalite-1 molecular sieve.

2. The desorption agent for promoting CO2 hydrogenation reaction according to claim 1, characterized in that: The preparation method of Fe3O4 includes: first, 2.4 g of sodium acetate, 0.35 g of sodium citrate and 2.16 g of Fe salt are dissolved in 300 mL of ethylene glycol, and stirred until completely dissolved, and the obtained mixed solution is transferred to a hydrothermal synthesis reactor with a polytetrafluoroethylene liner, and the conditions of the solvothermal synthesis process are 200℃ and 12 h, the obtained product is repeatedly washed with anhydrous ethanol several times, centrifuged until the solution is neutral, and finally dried at 60-80℃ for more than 10 h, the dried powder is placed in a tube furnace and calcined at a heating rate of 2℃ / min under nitrogen atmosphere for more than 3 h, and then Fe3O4 is obtained.

3. The desorption agent for promoting CO2 hydrogenation reaction according to claim 1, characterized in that: The preparation method of Fe5C2 includes: first, preparing ferrous oxalate dihydrate by solvothermal method, then placing the ferrous oxalate dihydrate in a carbonization furnace, using CO as carbon source gas with a composition of CO:N2=10:90, a flow rate of 30 mL / min, and a heating rate of 0.5℃ / min to 350℃ and keeping for 4 h, and finally obtaining black solid powder which is Fe5C2.

4. The desorbent for promoting CO2 hydrogenation reaction according to claim 3, characterized in that: The preparation method of the ferrous oxalate dihydrate includes: first, dissolving 2.224 g of ferrous salt in 16 mL of ethanol and 64 mL of water, stirring uniformly to obtain solution I, then dissolving 0.72 g of oxalic acid in the same proportion of ethanol and water, stirring uniformly to record as solution II, slowly mixing solution I and II at room temperature to obtain a transparent mixture, transferring the mixture to a reaction kettle with polytetrafluoroethylene, crystallizing at 100℃ for 24 h, washing the obtained solid with ethanol and water several times and drying to obtain ferrous oxalate dihydrate.

5. The application of the desorption agent for promoting CO2 hydrogenation reaction according to claim 1, characterized in that: The prepared Fe-based catalyst of Group A and the hydrophobic Silicalite-1 molecular sieve of Group B were combined in a fixed bed reactor in a mass ratio of 1:0.1-1:3, and were reduced in high-purity H2 by programmed temperature reduction, with the reduction conditions being 350°C, 0.2 MPa, and 1000 h –1 , 6 h. After the reduction was completed, the temperature was lowered and the raw gas was switched to perform the reaction, the raw gas composition was H2 / CO2=3:1, the space velocity was controlled at 1000-4000 h –1 , the reaction temperature was 280-360°C, and the reaction pressure was 2.5-3.5 MPa.

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