FeZnC-coated Al2O3 catalyst with core-shell structure and application of FeZnC-coated Al2O3 catalyst in catalysis of CO2 hydrogenation for preparation of alpha-olefin

Abstract

The invention provides a FeZnC-coated Al2O3 catalyst with a core-shell structure and application of the FeZnC-coated Al2O3 catalyst in catalyzing CO2 hydrogenation to prepare alpha-olefin, and belongs to the technical field of catalyst preparation. The preparation method of the catalyst comprises the following steps: dissolving FeCl3. 6H2O, ZnCl2 and anhydrous glucose in a solvent for mixing, then dissolving gamma-Al2O3, sodium acetate and sodium citrate in the solution, then carrying out hydrothermal treatment, cooling and suction filtration to obtain a filter cake, carrying out dipping treatment on the filter cake, and finally roasting to obtain the FeZnC-coated Al2O3 catalyst with the core-shell structure. The catalyst is used for preparing alpha olefin through carbon dioxide hydrogenation, the conversion rate of CO2 and the selectivity of the target product alpha olefin are remarkably improved, the conversion rate of CO2 can reach 58%, and the selectivity of alpha olefin reaches 37.9%.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and in particular to a core-shell structure FeZnC@Al2O3 catalyst and its application in the catalytic hydrogenation of CO2 to α-olefins. Background Art

[0002] At present, the direct catalytic hydrogenation of CO2 to synthesize α-olefins mainly involves the conversion of CO2 to CO through the RWGS reaction first, and then the synthesis of α-olefins and other compounds through FTS. However, due to the stability of the raw material molecules in the CO2 hydrogenation process, the adsorption and desorption rates on the catalyst surface are slow, so it is very difficult to produce long-chain hydrocarbons, and the general products are concentrated in low-carbon hydrocarbons such as CH4 or C2-C4. According to literature reports, iron, cobalt, etc. are usually used as reaction catalysts for preparing hydrocarbons. Compared with Fe-based catalysts, Co-based catalysts are generally considered to be methanation catalysts, while Fe-based catalysts have higher activity and selectivity for both the RWGS reaction and the FTS synthesis reaction. Therefore, Fe-based catalysts are expected to obtain excellent catalytic performance in the reaction of CO2 hydrogenation to synthesize α-olefins. However, unmodified Fe-based catalysts are prone to secondary hydrogenation reactions, resulting in a higher selectivity for alkanes and a lower selectivity for α-olefins in the products. Therefore, during the preparation of iron-based catalysts, it is generally necessary to add promoters to adjust the hydrogenation ability of the catalysts to improve the selectivity of α-olefins in the products.

[0003] The application number is CN202211492721.X, and the publication name is: A modified iron-based catalyst for the hydrogenation of carbon dioxide to synthesize α-olefins and its preparation method. This patent reports the preparation of a promoter-modified Fe-based catalyst by the co-precipitation method, using one or more of transition metal elements and alkali metal elements as electronic promoters of the Fe-based catalyst. In the CO2 hydrogenation reaction, the CO2 conversion rate is relatively high, but the selectivity of α-olefins is relatively low. At the reaction conditions of 280 °C, 3.0 MPa, H2 / CO2 = 3, 1000 mL·gcat -1 ·h -1 Under the reaction conditions of, the conversion rate of CO2 is 45.3%, and the selectivity of α-olefins is 25.6%. However, the CO2 conversion rate of this patent is relatively low, and it is impossible to efficiently convert CO2.

[0004] The application number is CN202111553302.8, and the publication name is: Catalyst for the hydrogenation of CO2 to prepare high-carbon linear α-olefins and its preparation and application. This patent reports the use of a promoter-modified Fe-based catalyst, which can significantly improve the reaction activity of the Fe-based catalyst. At 330 °C, 1.0 MPa, H2 / CO2 = 3, 15000 mL·gcat -1 ·h -1Under the reaction conditions, the conversion rate of CO2 was 30.3%, and the selectivity of α-olefins was 33.8%. However, the selectivity of α-olefins in this patent was poor.

[0005] Based on this, it is of great practical significance to provide an Fe-based catalyst for α-olefin synthesis that can improve the conversion rate of CO2 and the selectivity of α-olefins. Summary of the Invention

[0006] The purpose of the present invention is to provide a core-shell structure FeZnC@Al2O3 catalyst and a method for catalytic hydrogenation of CO2 to α-olefins, aiming to solve the technical problem that the Fe-based catalyst used for α-olefin synthesis in the prior art cannot improve the conversion rate of CO2 and the selectivity of α-olefins.

[0007] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0008] The present invention provides a preparation method of a core-shell structure FeZnC@Al2O3 catalyst, which is characterized by including the following steps:

[0009] Dissolve FeCl3·6H2O, ZnCl2 and anhydrous glucose in a solvent for mixing to obtain a first mixed solution;

[0010] Dissolve γ-Al2O3, sodium acetate and sodium citrate in the first mixed solution to obtain a second mixed solution;

[0011] Perform hydrothermal treatment on the second mixed solution, cool it and then perform suction filtration to obtain a filter cake;

[0012] Perform impregnation treatment on the filter cake and then perform calcination to obtain the core-shell structure FeZnC@Al2O3 catalyst.

[0013] Further, the molar ratio of FeCl3·6H2O to ZnCl2 is 1:0.1~1; the molar ratio of FeCl3·6H2O to anhydrous glucose is 24:1~24.

[0014] Further, the solvent is ethylene glycol.

[0015] Further, the molar ratio of γ-Al2O3, sodium acetate and sodium citrate is 15:132:5.

[0016] Further, the molar ratio of γ-Al2O3 to FeCl3·6H2O is 1:2~4:1.

[0017] Further, the temperature of the hydrothermal treatment is 200°C and the time is 10h;

[0018] Further, before the impregnation treatment, the filter cake is washed alternately with ethanol and water; the impregnation treatment is carried out with a 5 wt% sodium carbonate solution; the solvent of the sodium carbonate solution is water and ethanol; the mass ratio of water to ethanol is 1:1.

[0019] Further, the calcination temperature is 600 °C, the heating rate is 2 °C / min, and the time is 2 h.

[0020] The present invention also provides a core-shell structured FeZnC@Al2O3 catalyst obtained by the preparation method of the core-shell structured FeZnC@Al2O3 catalyst described in the above technical solution.

[0021] The present invention also provides an application of the core-shell structured FeZnC@Al2O3 catalyst described in the above technical solution in the catalytic hydrogenation of CO2 to α-olefins.

[0022] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0023] (1) In the present invention, γ-Al2O 3， As the introduction amount of γ-Al2O3 increases, the specific surface area increases from 31.8 m 2 / g to 193.1 m 2 / g; the grain size decreases from 25.5 nm to 15.8 nm, which is beneficial to the exposure of the active phase, promotes the dispersion of the catalyst, and improves the reaction activity. Al2O3 has a supporting and protecting effect around the iron carbide active phase to improve the stability and selectivity of the catalyst. By adjusting the Fe / Al molar ratio, the important role of alumina in improving the reducibility of the catalyst, stabilizing the iron phase structure, and regulating the electronic structure is systematically revealed; the introduction of an appropriate amount of Al not only enhances the CO2 adsorption capacity and the dispersion and stability of the active phase, but also is beneficial to the generation of oxygen vacancies, thereby synergistically improving the reaction activity and product distribution selectivity of the catalyst;

[0024] (2) When the catalyst of the present invention is used for the hydrogenation of carbon dioxide to α-olefins, the conversion rate of CO2 and the selectivity of the target product α-olefins are significantly improved. The conversion rate of CO2 can reach 58%, and the selectivity of α-olefins reaches 37.9%;

[0025] (3) The catalyst provided by the present invention has stable properties after 50 h of continuous reaction and no obvious deactivation, which is beneficial to improving the service life of the catalyst;

[0026] (4) The catalyst provided by the present invention has cheap and easily available raw materials and a simple preparation method, which is beneficial to realizing mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the reaction system of Application Example 1 of the present invention;

[0028] Among them, 1 - gas purifier, 2 - mass flowmeter, 3 - gas mixing tank, 4 - reactor, 5 - heating furnace, 6 - cold trap, 7 - low-temperature cooling circulation pump, 8 - back pressure valve. Specific implementation mode

[0029] The present invention provides a preparation method of a core-shell structure FeZnC@Al2O3 catalyst, which is characterized by including the following steps:

[0030] Dissolve FeCl3·6H2O, ZnCl2 and anhydrous glucose in a solvent and mix them to obtain a first mixed solution;

[0031] Dissolve γ-Al2O3, sodium acetate and sodium citrate in the first mixed solution to obtain a second mixed solution;

[0032] Perform hydrothermal treatment on the second mixed solution, cool it and then perform suction filtration to obtain a filter cake;

[0033] Perform impregnation treatment on the filter cake, and then perform calcination to obtain the core-shell structure FeZnC@Al2O3 catalyst.

[0034] Dissolve FeCl3·6H2O, ZnCl2 and anhydrous glucose in a solvent and mix them to obtain a first mixed solution;

[0035] First, dissolve FeCl3·6H2O, ZnCl2 and anhydrous glucose in a solvent according to a ratio, stir and mix them, and there is no special limitation on the mixing time, until all the solids are dissolved.

[0036] In the present invention, the molar ratio of FeCl3·6H2O to ZnCl2 is preferably 1:0.1 - 1, and more preferably 1:0.1 - 0.5; the molar ratio of FeCl3·6H2O to anhydrous glucose is preferably 24:1 - 24, and more preferably 24:1 - 12.

[0037] In the present invention, the solvent is preferably ethylene glycol.

[0038] The present invention does not have special limitations on the amount of the solvent, and it can completely dissolve all the raw material components.

[0039] Dissolve γ-Al2O3, sodium acetate and sodium citrate in the first mixed solution to obtain a second mixed solution;

[0040] In the present invention, the molar ratio of γ-Al2O3, sodium acetate and sodium citrate is preferably 15:132:5.

[0041] In the present invention, the molar ratio of the γ-Al2O3 to FeCl3·6H2O is preferably 1:2 to 4:1; more preferably 1:2 to 2:1.

[0042] γ-Al2O is added in the present invention 3， As the introduction amount of γ-Al2O3 increases, the specific surface area increases from 31.8 m 2 / g to 193.1 m 2 / g; the grain size decreases from 25.5 nm to 15.8 nm, which is beneficial to the exposure of the active phase, promotes the dispersion of the catalyst, improves the reaction activity, and Al2O3 has a supporting and protecting effect around the iron carbide active phase to improve the stability and selectivity of the catalyst; by adjusting the Fe / Al molar ratio, the important role of alumina in improving the reducibility of the catalyst, stabilizing the iron phase structure and regulating the electronic structure is systematically revealed; the introduction of an appropriate amount of Al not only enhances the CO2 adsorption capacity and the dispersion and stability of the active phase, but also is beneficial to the generation of oxygen vacancies, thereby synergistically improving the reaction activity and product distribution selectivity of the catalyst.

[0043] The second mixed solution is subjected to hydrothermal treatment, cooled and then filtered by suction to obtain a filter cake;

[0044] In the present invention, the temperature of the hydrothermal treatment is preferably 200 °C and the time is preferably 10 h;

[0045] The filter cake is subjected to impregnation treatment and then calcined to obtain the core-shell structured FeZnC@Al2O3 catalyst.

[0046] Before impregnation, the filter cake is dried overnight for 12 h in a vacuum drying oven, ground and then impregnated, and dried for another 12 h after impregnation is completed. Then it is calcined, and the calcination is carried out in an argon atmosphere.

[0047] In the present invention, before the impregnation treatment, the filter cake is alternately washed with ethanol and water; the impregnation treatment is carried out with a 5 wt% sodium carbonate solution; the solvent of the sodium carbonate solution is preferably water and ethanol; the mass ratio of water to ethanol is preferably 1:1.

[0048] In the present invention, the temperature of the calcination is preferably 600 °C, the heating rate is preferably 2 °C / min, and the time is preferably 2 h.

[0049] The present invention also provides a core-shell structured FeZnC@Al2O3 catalyst obtained by the preparation method of the core-shell structured FeZnC@Al2O3 catalyst described in the above technical solution.

[0050] The catalyst of the present invention is used for the hydrogenation of carbon dioxide to produce α-olefins, significantly improving the conversion rate of CO2 and the selectivity of the target product α-olefins. The conversion rate of CO2 can reach 58%, and the selectivity of α-olefins reaches 37.9%. The catalyst provided by the present invention has stable properties after 50 hours of continuous reaction and does not show obvious deactivation, which is beneficial to improving the service life of the catalyst.

[0051] The present invention also provides an application of the core-shell structure FeZnC@Al2O3 catalyst described in the above technical solution in the catalytic hydrogenation of CO2 to produce α-olefins.

[0052] In the present invention, unless otherwise specified, the required preparation raw materials are all commercially available products well-known to those skilled in the art.

[0053] The technical solutions provided by the present invention will be described in detail below with reference to the examples, but they should not be construed as limiting the protection scope of the present invention.

[0054] Example 1

[0055] (1) Weigh a certain amount of FeCl3·6H2O, ZnCl2 and anhydrous glucose, and dissolve them in 150 mL of ethylene glycol according to the molar ratio of Fe:Zn:C of 1:0.25:0.75, and stir at room temperature until all the solids are dissolved;

[0056] (2) Then, weigh 1.52 g of γ-Al2O3 (10 nm), 10.8 g of sodium acetate and 1.3 g of sodium citrate according to the molar ratio of Fe:Al of 1:1, dissolve them in the above-prepared metal salt solution, and continue to stir for 30 min;

[0057] (3) Transfer the above solution to a 200 mL hydrothermal autoclave, and perform hydrothermal treatment at 200 °C for 10 h; after the hydrothermal autoclave cools down, filter the sample, and alternately wash the filter cake with ethanol and deionized water;

[0058] (4) Finally, dry the filter cake in a vacuum drying oven overnight for 12 h, grind it, impregnate it with a 5 wt% sodium carbonate solution (the solvent of the sodium carbonate solution is water and ethanol; the mass ratio of water and ethanol is 1:1), and continue to dry for 12 h. Grind it and put it into a tubular furnace with continuous argon flow, and calcine it at 600 °C for 2 h at a heating rate of 2 °C / min. After cooling, press and granulate it into 40-60 mesh to obtain the core-shell structure FeZnC@Al2O3 catalyst.

[0059] Example 2

[0060] (1) Weigh a certain amount of FeCl3·6H2O, ZnCl2 and anhydrous glucose, and dissolve them in 150 mL of ethylene glycol according to the molar ratio of Fe:Zn:C of 1:0.25:0.75, and stir at room temperature until all the solids are dissolved;

[0061] (2) Then, according to the molar ratio of Fe:Al being 1:2 and the molar ratio of γ-Al2O3, sodium acetate, and sodium citrate being 15:132:5, weigh γ-Al2O3 (10 nm), sodium acetate, and sodium citrate and dissolve them in the above-prepared metal salt solution, and continue stirring for 30 min;

[0062] (3) Transfer the above solution to a 200 mL hydrothermal autoclave and perform hydrothermal treatment at 200 °C for 10 h; after the hydrothermal autoclave cools down, perform suction filtration on the sample, and alternately wash the filter cake with ethanol and deionized water;

[0063] (4) Finally, dry the filter cake in a vacuum drying oven overnight for 12 h, grind it, impregnate it with a 5 wt% sodium carbonate solution (the solvent of the sodium carbonate solution is water and ethanol; the mass ratio of water and ethanol is 1:1), and continue drying for 12 h. Grind it and put it into a tubular furnace with continuous argon flow. Calcinate it at a heating rate of 2 °C / min at 600 °C for 2 h. After cooling, press and granulate it into 40-60 mesh to obtain the core-shell structure FeZnC@Al2O3 catalyst.

[0064] Example 3

[0065] (1) Weigh a certain amount of FeCl3·6H2O, ZnCl2, and anhydrous glucose and dissolve them in ethylene glycol according to the molar ratio of Fe:Zn:C being 1:0.25:0.75, and stir at room temperature until all the solids are dissolved;

[0066] (2) Then, according to the molar ratio of Fe:Al being 4:1 and the molar ratio of γ-Al2O3, sodium acetate, and sodium citrate being 15:132:5, weigh γ-Al2O3 (10 nm), sodium acetate, and sodium citrate and dissolve them in the above-prepared metal salt solution, and continue stirring for 30 min;

[0067] (3) Transfer the above solution to a 200 mL hydrothermal autoclave and perform hydrothermal treatment at 200 °C for 10 h; after the hydrothermal autoclave cools down, perform suction filtration on the sample, and alternately wash the filter cake with ethanol and deionized water;

[0068] (4) Finally, dry the filter cake in a vacuum drying oven overnight for 12 h, grind it, impregnate it with a 5 wt% sodium carbonate solution (the solvent of the sodium carbonate solution is water and ethanol; the mass ratio of water and ethanol is 1:1), and continue drying for 12 h. Grind it and put it into a tubular furnace with continuous argon flow. Calcinate it at a heating rate of 2 °C / min at 600 °C for 2 h. After cooling, press and granulate it into 40-60 mesh to obtain the core-shell structure FeZnC@Al2O3 catalyst.

[0069] Application Example 1

[0070] Adopt as Figure 1The reaction system shown is used to apply the catalyst obtained in Example 1

[0071] (1) Using quartz wool as the bottom layer for isolation, the catalyst and quartz sand are filled in the middle constant temperature zone of the reaction tube at a mass ratio of 1:1. The top and bottom are filled with quartz sand, and then it is sealed and fixed to the tubular furnace reactor through a flange. Before the reaction, first adjust the back pressure valve, introduce nitrogen with a pressure 0.5 MPa higher than the reaction pressure, and keep it for 4 h to check the airtightness of the device. After ensuring good airtightness, vent the N2, introduce H2 and keep the total space velocity at 5 SL gcat-1 h-1 (S: standard condition, 0 °C, 101.325 kPa), and adjust the back pressure valve to make the pressure in the reaction tube 0.1 MPa for reduction. The reduction process uses programmed temperature increase, with a heating rate of 2 °C / min to 350 °C and kept for 10 h. After the reduction is completed, wait for the reactor to cool to room temperature, introduce the feed gas according to the required space velocity, and adjust the back pressure valve to the reaction required pressure. After the pressure rises to the set value, start the heating furnace to the reaction temperature and then start the reaction.

[0072] (2) When the reaction temperature reaches the set value and stabilizes, start using a gas chromatograph equipped with an FID detector and a TCD to analyze the tail gas. The FID detector is used to detect low-boiling organic compounds such as C1-C4 hydrocarbons in the tail gas; the TCD detector is used to detect gases such as H2, CO, CO2, N2, and CH4 in the tail gas, and analyze and record the tail gas every 2 h. After the reaction is completed, the liquid-phase product is analyzed offline using a gas chromatograph equipped with an FID detector.

[0073] The present invention uses the catalyst obtained in Example 1 for application. As shown in Application Example 1, it significantly improves the conversion rate of CO2 and the selectivity of the target product α-olefin. The conversion rate of CO2 can reach 58%, and the selectivity of α-olefin reaches 37.9%.

[0074] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a core-shell structured FeZnC@Al2O3 catalyst, characterized in that: The steps include: Dissolving FeCl3·6H2O, ZnCl2 and anhydrous glucose in a solvent and mixing them to obtain a first mixed solution; Dissolving γ-Al2O3, sodium acetate and sodium citrate in the first mixed solution to obtain a second mixed solution; The second mixed solution is subjected to hydrothermal treatment, cooled, and then filtered to obtain a filter cake; The filter cake is impregnated and then calcined to obtain the core-shell structure FeZnC@Al2O3 catalyst.

2. The method for preparing the core-shell structure FeZnC@Al2O3 catalyst according to claim 1, characterized in that: The molar ratio of the FeCl3·6H2O to ZnCl2 is 1:0.1~1; the molar ratio of the FeCl3·6H2O to anhydrous glucose is 24:1~24.

3. The method for preparing the core-shell structure FeZnC@Al2O3 catalyst according to claim 1, characterized in that: The solvent is ethylene glycol.

4. The method for preparing the core-shell structure FeZnC@Al2O3 catalyst according to claim 1, characterized in that: The molar ratio of the γ-Al2O3, sodium acetate and sodium citrate is 15:132:

5.

5. The method for preparing the core-shell structure FeZnC@Al2O3 catalyst according to claim 1, characterized in that: The molar ratio of γ-Al2O3 to FeCl3·6H2O is 1:2-4:

1.

6. The method for preparing the core-shell structure FeZnC@Al2O3 catalyst according to claim 1, characterized in that: The temperature of the hydrothermal treatment is 200° C. and the time is 10 h.

7. The method for preparing the core-shell structure FeZnC@Al2O3 catalyst according to claim 1, characterized in that: Before the impregnation treatment, the filter cake is alternately washed with ethanol and water; the impregnation treatment uses a 5wt% sodium carbonate solution; the solvent of the sodium carbonate solution is water and ethanol; the mass ratio of water to ethanol is 1:

1.

8. The method for preparing the core-shell structure FeZnC@Al2O3 catalyst according to claim 1, characterized in that: The calcination temperature is 600° C., the heating rate is 2° C. / min, and the calcination time is 2 h.

9. A core-shell structure FeZnC@Al2O3 catalyst obtained by the preparation method of the core-shell structure FeZnC@Al2O3 catalyst according to any one of claims 1 to 8.

10. Use of the core-shell structure FeZnC@Al2O3 catalyst according to claim 9 in catalytic CO2 hydrogenation to α-olefins.

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