A core-shell structured FeZnC@Al2O3 catalyst and its application in catalytic CO2 hydrogenation to α-olefins

Abstract

The present invention provides a core-shell structure FeZnC@Al2O3 catalyst and its application in catalytic CO2 hydrogenation to alpha-olefins, belonging to the field of catalyst preparation technology. The preparation method of the catalyst of the present invention is: FeCl3·6H2O, ZnCl2 and anhydrous glucose are dissolved in a solvent and mixed, and then γ-Al2O3, sodium acetate and sodium citrate are dissolved in the above solution, followed by hydrothermal treatment, cooling and suction filtration to obtain a filter cake, which is impregnated and finally calcined to obtain the core-shell structure FeZnC@Al2O3 catalyst. The catalyst of the present invention is used for carbon dioxide hydrogenation to produce alpha-olefins, significantly improving the conversion rate of CO2 and the selectivity of target product alpha-olefins, with a CO2 conversion rate of up to 58% and an alpha-olefin selectivity of 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 catalytic CO2 hydrogenation to alpha-olefins. Background Art

[0002] Currently, direct catalytic hydrogenation of CO2 to α-olefins primarily involves converting CO2 to CO via the RWGS reaction, followed by FTS synthesis to produce α-olefins and other compounds. However, due to the stability of the feedstock molecules and their slow adsorption and desorption rates on the catalyst surface, the CO2 hydrogenation process is difficult to produce long-chain hydrocarbons, with the products generally concentrated in CH4 or C2-C4 low-carbon hydrocarbons. Literature reports indicate that iron, cobalt, and other catalysts are commonly used to prepare hydrocarbons. Compared to Fe-based catalysts, Co-based catalysts are generally considered methanation catalysts, while Fe-based catalysts exhibit high activity and selectivity for both the RWGS and FTS reactions. Therefore, Fe-based catalysts hold promise for achieving excellent catalytic performance in CO2 hydrogenation to α-olefins. However, unmodified Fe-based catalysts are prone to secondary hydrogenation reactions, resulting in higher selectivity for alkanes and lower selectivity for α-olefins. Therefore, during the preparation of Fe-based catalysts, additives are often added to adjust the catalyst's hydrogenation capacity to improve the selectivity for α-olefins in the product.

[0003] The application number is CN202211492721.X, and the public name is: A modified iron-based catalyst for carbon dioxide hydrogenation to α-olefins and its preparation method. The patent reports the preparation of an additive-modified Fe-based catalyst by coprecipitation, using one or more transition metal elements and alkali metal elements as electronic additives for the Fe-based catalyst. In the CO2 hydrogenation reaction, the CO2 conversion rate is high, but the selectivity for α-olefins is low. At 280°C, 3.0MPa, H2 / CO2=3, 1000mL·gcat -1 ·h -1 Under the reaction conditions, the CO2 conversion rate is 45.3% and the α-olefin selectivity is 25.6%. However, the CO2 conversion rate of this patent is low and CO2 cannot be converted efficiently.

[0004] The application number is CN202111553302.8, and the public name is: Catalyst for the preparation of high-carbon linear α-olefins by CO2 hydrogenation and its preparation and application. The patent reports that the Fe-based catalyst modified with an additive can significantly improve the reaction activity of the Fe-based catalyst at 330°C, 1.0MPa, H2 / CO2=3, 15000mL·gcat -1 ·h -1Under the reaction conditions, the CO2 conversion rate is 30.3% and the α-olefin selectivity is 33.8%, but the α-olefin selectivity of this patent is 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-olefin. 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 catalyzing CO2 hydrogenation to produce α-olefins, aiming to solve the technical problem that Fe-based catalysts used for α-olefin synthesis in the prior art cannot improve the CO2 conversion rate and α-olefin selectivity.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing a core-shell structured FeZnC@Al2O3 catalyst, which is characterized by comprising the following steps:

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

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

[0011] hydrothermally treating the second mixed solution, cooling it, and then filtering it to obtain a filter cake;

[0012] The filter cake is impregnated and then calcined to obtain the core-shell structure FeZnC@Al2O3 catalyst.

[0013] Furthermore, 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.

[0014] Furthermore, the solvent is ethylene glycol.

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

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

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

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

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

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

[0021] The present invention also provides the use of the core-shell structure FeZnC@Al2O3 catalyst described in the above technical solution in catalyzing CO2 hydrogenation to produce α-olefins.

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

[0023] (1) The present invention adds γ-Al2O 3， With the increase of the amount of γ-Al2O3 introduced, the specific surface area increased from 31.8m 2 / g increased to 193.1m 2 / g; the grain size is reduced from 25.5nm to 15.8nm, which is beneficial to the exposure of the active phase, promotes catalyst dispersion, and improves reaction activity. Al2O3 supports and protects the active phase iron carbide, thereby improving its stability and selectivity. 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 promotes the generation of oxygen vacancies, thereby synergistically improving the reaction activity and product distribution selectivity of the catalyst;

[0024] (2) The catalyst of the present invention is used for the hydrogenation of carbon dioxide to produce α-olefins, which significantly improves 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 can reach 37.9%;

[0025] (3) The catalyst provided by the present invention has been reacted for 50 hours and has stable properties without obvious deactivation, which is beneficial to prolonging the life of the catalyst;

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

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

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

[0029] The present invention provides a method for preparing a core-shell structured FeZnC@Al2O3 catalyst, which is characterized by comprising the following steps:

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

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

[0032] hydrothermally treating the second mixed solution, cooling it, and then filtering it to obtain a filter cake;

[0033] The filter cake is impregnated and then calcined to obtain the core-shell structure FeZnC@Al2O3 catalyst.

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

[0035] First, FeCl3·6H2O, ZnCl2 and anhydrous glucose are dissolved in a solvent in proportion and stirred and mixed. There is no particular limit to the mixing time, and the mixture can be continued 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, more preferably 1:0.1~0.5; the molar ratio of FeCl3·6H2O to anhydrous glucose is preferably 24:1~24, more preferably 24:1~12.

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

[0038] The present invention does not impose any particular limitation on the amount of solvent used, as long as it can completely dissolve all raw material components.

[0039] dissolving 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 γ-Al2O3 to FeCl3·6H2O is preferably 1:2~4:1; more preferably 1:2~2:1.

[0042] The present invention adds γ-Al2O 3， With the increase of the amount of γ-Al2O3 introduced, the specific surface area increased from 31.8m 2 / g increased to 193.1m 2 / g; the grain size is reduced from 25.5nm to 15.8nm, which is beneficial to the exposure of the active phase, promotes catalyst dispersion, and improves the reaction activity. Al2O3 has a supporting and protective stabilizing effect around the active phase iron carbide, thereby improving 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 promotes the generation of oxygen vacancies, thereby synergistically improving the reaction activity and product distribution selectivity of the catalyst.

[0043] hydrothermally treating the second mixed solution, cooling it, and then filtering it 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 hours;

[0045] The filter cake is impregnated and then calcined to obtain the core-shell structure FeZnC@Al2O3 catalyst.

[0046] Before impregnation, the filter cake was dried overnight in a vacuum drying oven for 12 hours, ground and then impregnated, and dried for another 12 hours after impregnation. Calcination was then performed under 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 performed using 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 calcination temperature is preferably 600° C., the heating rate is preferably 2° C. / min, and the calcination time is preferably 2 h.

[0049] The present invention also provides a core-shell structure FeZnC@Al2O3 catalyst obtained by the preparation method of the core-shell structure 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 alpha olefins, significantly improving the CO2 conversion rate and the selectivity of the target product alpha olefins. The CO2 conversion rate can reach 58%, and the alpha olefin selectivity can reach 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 life of the catalyst.

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

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

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

[0054] Example 1

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

[0056] (2) Then, 1.52 g of γ-Al2O3 (10 nm), 10.8 g of sodium acetate, and 1.3 g of sodium citrate were weighed and dissolved in the above-prepared metal salt solution at a Fe:Al molar ratio of 1:1, and stirred for 30 min.

[0057] (3) The above solution was transferred to a 200 mL hydrothermal kettle and hydrothermally treated at 200 °C for 10 h. After the hydrothermal kettle cooled, the sample was filtered and the filter cake was washed alternately with ethanol and deionized water.

[0058] (4) Finally, the filter cake was dried overnight in a vacuum drying oven for 12 hours, ground, immersed in 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) and continued to dry for 12 hours. After grinding, it was placed in a tubular furnace with continuous argon flow and calcined at 600 °C for 2 hours at a heating rate of 2 °C / min. After cooling, it was pressed into tablets and granulated 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 in a molar ratio of Fe:Zn:C of 1:0.25:0.75 and dissolve them in 150 mL of ethylene glycol. Stir at room temperature until all the solids are dissolved.

[0061] (2) γ-Al2O3 (10 nm), sodium acetate and sodium citrate were weighed and dissolved in the above-prepared metal salt solution at a molar ratio of Fe:Al of 1:2 and a molar ratio of γ-Al2O3, sodium acetate and sodium citrate of 15:13:2:5, and the mixture was stirred for 30 min.

[0062] (3) The above solution was transferred to a 200 mL hydrothermal kettle and hydrothermally treated at 200 °C for 10 h. After the hydrothermal kettle cooled, the sample was filtered and the filter cake was washed alternately with ethanol and deionized water.

[0063] (4) Finally, the filter cake was dried overnight in a vacuum drying oven for 12 hours, ground, immersed in 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) and continued to dry for 12 hours. After grinding, it was placed in a tubular furnace with continuous argon flow and calcined at 600 °C for 2 hours at a heating rate of 2 °C / min. After cooling, it was pressed into tablets and granulated 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 in ethylene glycol at a molar ratio of Fe:Zn:C of 1:0.25:0.75 and stir at room temperature until all the solids are dissolved;

[0066] (2) γ-Al2O3 (10 nm), sodium acetate and sodium citrate were weighed and dissolved in the prepared metal salt solution at a molar ratio of Fe:Al of 4:1 and a molar ratio of γ-Al2O3, sodium acetate and sodium citrate of 15:132:5, and the mixture was stirred for 30 min.

[0067] (3) The above solution was transferred to a 200 mL hydrothermal kettle and hydrothermally treated at 200 °C for 10 h. After the hydrothermal kettle cooled, the sample was filtered and the filter cake was washed alternately with ethanol and deionized water.

[0068] (4) Finally, the filter cake was dried overnight in a vacuum drying oven for 12 hours, ground, immersed in 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) and continued to dry for 12 hours. After grinding, it was placed in a tubular furnace with continuous argon flow and calcined at 600 °C for 2 hours at a heating rate of 2 °C / min. After cooling, it was pressed into tablets and granulated into 40-60 mesh to obtain the core-shell structure FeZnC@Al2O3 catalyst.

[0069] Application Example 1

[0070] Use Figure 1The reaction system shown in FIG. 1 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 were loaded into the middle constant temperature zone of the reaction tube in a mass ratio of 1:1. The top and bottom were filled with quartz sand, and then fixed to the tubular furnace reactor through flange sealing. Before the reaction, the back pressure valve was adjusted and nitrogen was introduced at a pressure 0.5 MPa higher than the reaction pressure. The pressure was maintained for 4 h, and the air tightness of the device was checked. After ensuring good air tightness, N2 was vented and H2 was introduced with a total air velocity of 5 SL gcat-1 h-1 (S: standard conditions, 0℃, 101.325 kPa). The back pressure valve was adjusted so that the pressure in the reaction tube was 0.1 MPa for reduction. The reduction process was programmed to heat up at a rate of 2℃ / min to 350℃ and maintained for 10 h. After the reduction was completed, the reactor was cooled to room temperature, the raw gas was introduced at the required air velocity, and the back pressure valve was adjusted to the pressure required for the reaction. After the pressure rose to the set value, the heating furnace temperature was started to the reaction temperature and the reaction was started.

[0072] (2) When the reaction temperature reaches the set value and stabilizes, the tail gas is analyzed using a gas chromatograph equipped with an FID detector and a TCD detector. The FID detector is used to detect low-boiling point 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. The tail gas analysis is recorded every 2 hours. After the reaction is completed, the liquid 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, the conversion rate of CO2 and the selectivity of the target product α-olefin are significantly improved. The conversion rate of CO2 can reach 58%, and the selectivity of α-olefin can reach 37.9%.

[0074] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a core-shell structure 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; hydrothermally treating the second mixed solution, cooling it, and then filtering it 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 the 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 immersion treatment, the filter cake is alternately washed with ethanol and water; the immersion treatment uses a 5wt% sodium carbonate solution; the solvent of the sodium carbonate solution is water and ethanol; the mass ratio of the 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 structured FeZnC@Al2O3 catalyst according to claim 9 in catalytic CO2 hydrogenation to α-olefins.

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