A method for preparing a supported iron-based catalyst for catalyzing carbon dioxide hydrogenation

Abstract

The present application belongs to the technical field of carbon dioxide catalytic hydrogenation, and particularly relates to a preparation method of a supported iron-based catalyst for catalyzing carbon dioxide hydrogenation, which takes one of TiO2, SiO2, HZSM-5 molecular sieve and gamma-Al2O3 as a carrier, and is loaded with Fe, Zr and K elements, and comprises the following steps: S1, drying, crushing and screening the TiO2, SiO2, HZSM-5 molecular sieve and gamma-Al2O3 carrier respectively; obtaining four carriers; S2, mixing iron-containing metal salt, zirconium-containing metal salt and alkali metal additives, and dissolving them in deionized water for stirring; S3, adding the mixed solution into each carrier respectively, and stirring in a constant-temperature water bath; S4, drying, grinding and calcining the well-stirred solution. The advantage is that the catalyst can efficiently catalyze CO2 hydrogenation reaction, and synthesize a hydrocarbon mixture similar to the components of commercial diesel.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide catalytic hydrogenation technology, and particularly relates to a method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation. Background Technology

[0002] Carbon dioxide (CO2), a major greenhouse gas, has a profound impact on global climate due to its excessive emissions. Therefore, converting CO2 into useful chemicals and fuels not only helps mitigate climate change but also enables the recycling of carbon resources. Against this backdrop, the application of supported iron-based catalysts in catalytic CO2 hydrogenation technology has attracted widespread attention.

[0003] Supported catalysts have become an important component of industrial catalysis due to their high activity, high selectivity, and good stability. Iron-based catalysts, in particular, are considered ideal catalyst candidates due to their abundant resources, low cost, and excellent performance in heterogeneous catalysis. In the CO2 hydrogenation reaction, supported iron-based catalysts can effectively convert CO2 into various high-value-added chemicals, such as low-carbon olefins, alcohols, and jet fuels.

[0004] However, traditional iron-based catalysts still have shortcomings in terms of activity, selectivity, and stability. To overcome these problems, researchers have developed various modification strategies, including the addition of metal promoters, optimization of supports, and innovation in preparation methods. Among these, the choice of support is crucial for optimizing catalyst performance. Commonly used supports include alumina, silica, zirconium oxide, activated carbon, and molecular sieves, which not only provide the necessary mechanical strength and thermal stability but also influence the efficiency of catalytic reactions by adjusting the pore structure and surface properties of the catalyst.

[0005] Precise control of reaction conditions, such as temperature, pressure, and gas flow ratio, allows for precise regulation of product distribution. Furthermore, the recyclability and regeneration capacity of the catalyst are also crucial considerations for its industrial application. Optimizing the catalyst's stability and resistance to poisoning can significantly improve the feasibility and economic viability of its industrial applications.

[0006] In the prior art, patent application number CN202410162447.2 discloses an Fe-based catalyst for the preparation of mixed alcohols by CO2 hydrogenation, its preparation method, and its application. The general molecular formula of the Fe-based catalyst is Fe. x M-yA; where M is a metal promoter; A is an alkali metal promoter; x is the molar ratio of Fe to M, ranging from 0.5 to 7; y is the mass fraction of A in the Fe-based catalyst, ranging from 0.5% to 5%. This Fe catalyst exhibits excellent CO2 conversion and C2... +The method exhibits mixed alcohol selectivity and extremely low C1 product selectivity (CO, CH4, methanol). Its preparation method is simple, easy to operate, and readily reproducible and scaled up, showing potential for industrial applications. However, the precise control of reaction products requires further improvement. Patent application CN202311399953.5 discloses a method for preparing a Fe-based catalyst for CO2 hydrogenation to low-carbon olefins, using a melt permeation method with added molecular sieves to obtain FeMnKBr / Y. meso -Na. The Fe-based catalyst prepared by this invention has better product distribution. Bromine, through its electronegativity and electron-gaining ability, can control the electron density around the active center of the catalyst, thereby changing the catalyst's hydrogenation capacity in a hydrogen-rich atmosphere. The preparation method reduces sintering and agglomeration during calcination and reaction, which is beneficial for improving catalytic performance. However, the catalyst preparation process is relatively cumbersome, which is not conducive to reproducibility and scale-up production. Patent application number CN202311370616.3 discloses a method for preparing a catalyst for the catalytic conversion of CO2 hydrogenation to long-chain hydrocarbons and its application. The Fe-based catalyst is prepared using iron salts, iron ion precipitants, and metal promoters. The catalyst prepared by this invention exhibits very high selectivity for hydrocarbons with more than 5 carbon atoms in the CO2 hydrogenation reaction, with extremely low selectivity for byproducts CO and CH4, and a high alkene-to-alkane ratio in the products. This method is simple, low-cost, and can be prepared on a large scale, showing good prospects for industrial application. However, this method is not precise in controlling the metal molar ratio. Patent application number CN202311328994.5 discloses a modified calcium-iron-stone catalyst, its preparation method, and its application. The calcium-iron-stone catalyst Ca2Fe2O5 is used for CO2 hydrogenation to produce low-carbon olefins. Results show that the calcium-iron-stone catalyst Ca2Fe2O5 can promote the RWGS reaction, exhibits excellent CO2 adsorption and activation capabilities, and demonstrates excellent CO2 conversion rate. The modified calcium-iron-stone catalyst Ca2Fe2O5... x K 2-x Fe2O5 promotes the RWGS reaction and enhances the FTS reaction, exhibiting not only excellent carbon dioxide conversion but also high selectivity for low-carbon olefins, with a maximum CO2 conversion of 46.33% and a maximum low-carbon olefin selectivity of 34.59%. However, the catalyst preparation process is relatively complicated, which is not conducive to reproducible and scale-up production.

[0007] Despite significant progress made in CO2 hydrogenation technology using supported iron-based catalysts, several challenges remain. These include improving selectivity while maintaining high activity, ensuring long-term stable operation, and reducing preparation costs. By combining the synergistic effects of transition metal and alkali metal promoters, optimizing catalyst preparation methods, enhancing stability, and reducing costs, supported iron-based catalysts hold even greater promise for application in CO2 hydrogenation technology. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, the purpose of this invention is to provide a high-efficiency and low-cost method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation, which combines the performance of RWGS reaction and FTS catalysis, and hydrogenates CO2 to produce diesel fraction hydrocarbons, thereby reducing the preparation cost.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation, wherein the catalyst uses one of TiO2, SiO2, HZSM-5 molecular sieve, or γ-Al2O3 as a support and is loaded with three elements: Fe, Zr, and K. The preparation method includes the following steps:

[0011] S1. TiO2, SiO2, HZSM-5 molecular sieve, and γ-Al2O3 support are dried, pulverized, and sieved into 40-60 mesh particles respectively.

[0012] S2. Place the four carriers into separate containers;

[0013] S3. Mix the iron-containing metal salt, the zirconium-containing metal salt, and the alkali metal additive in a molar ratio of Fe:Zr:K=5:1:(1~1.5), dissolve them in deionized water, and stir for 10~20 minutes to obtain a mixed solution.

[0014] S4. Add the mixed solution obtained in step S3 to each carrier and place them in a constant temperature water bath for stirring; the impregnation amount of the carrier is 90%~100% of the saturated absorbent solution volume;

[0015] S5. The stirred solution was dried, ground, and calcined to obtain four types of supported iron-based catalysts.

[0016] The iron-containing metal salt is ferric nitrate nonahydrate.

[0017] The zirconium-containing metal salt is zirconium nitrate pentahydrate.

[0018] The alkali metal auxiliary agent is potassium nitrate.

[0019] In step S4, the water bath temperature is 50~80℃ and the stirring time is 3~6h.

[0020] The drying temperature is 80~120℃, and the drying time is 6~24h.

[0021] The calcination is carried out in a muffle furnace under atmospheric pressure and nitrogen atmosphere, with the temperature increased to the calcination temperature at a rate of 2~10℃ / min, the calcination temperature being 400~600℃, and the calcination time being 2~8h.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] The preparation method of this invention is simple, easy to operate, and low in cost, making it easy to apply industrially. The prepared catalyst can efficiently catalyze the hydrogenation reaction of CO2 to synthesize a hydrocarbon mixture with a composition similar to commercial diesel fuel, providing a completely new route for diesel production with potential economic and environmental benefits.

[0024] This invention loads Fe, Zr, and K to stabilize the catalyst structure. Fe is the main active component; K acts as a promoter to improve the pH of the catalyst surface and increase the CO2 adsorption rate; Zr can generate ZrO2, which has oxygen storage capacity, stabilizes the catalyst structure, and optimizes the redox environment of Fe. At the same time, loading Fe, Zr, and K can jointly maintain the reaction kinetic equilibrium.

[0025] The prepared catalyst successfully hydrogenated CO2 to produce C. 10 ~C 20 Diesel fraction hydrocarbons were produced. In the prepared catalyst, Fe was used as the main active component. Through the synergistic effect of Zr and K, Fe was supported on a support with high specific surface area, good pore structure, and excellent thermal stability, which effectively improved the structural strength and dispersion of the active phase of the catalyst, thereby improving the catalyst performance. In the process of CO2 hydrogenation to diesel fraction hydrocarbons, this catalyst can achieve a CO2 conversion rate of 41.1% and a C2 conversion rate of 41.1%. 10 -C 20 Hydrocarbon selectivity can reach 37.2%. Attached Figure Description

[0026] Figure 1 This is a chromatogram obtained by catalyzing the hydrogenation of CO2 using the catalyst in Example 3. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0028] The materials and instruments used in the following examples are all commercially available, and the raw materials are of analytical grade.

[0029] Example 1:

[0030] A method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation includes the following steps:

[0031] S1. Weigh 2.020g of ferric nitrate nonahydrate, 0.429g of zirconium nitrate pentahydrate, and 0.101g of potassium nitrate, dissolve them in 40mL of deionized water, and stir until homogeneous to obtain a metal precursor solution.

[0032] S2. Weigh 3g of TiO2 support and add it to the metal precursor solution. Place it in a constant temperature water bath at 60℃ and stir for 4h to ensure that TiO2 and the metal precursor solution are fully mixed. Place the stirred solution in an electric heating drying oven and dry it at 120℃ for 12h until it cools to room temperature.

[0033] S3. The dried block catalyst is crushed into powder in a mortar and placed in a muffle furnace. Under a nitrogen atmosphere, the temperature is increased to 500℃ at a heating rate of 5℃ / min and calcined for 5h. After cooling to room temperature, it is ground to obtain the catalyst, denoted as FeZrK / TiO2.

[0034] The performance of the above catalyst in CO2 hydrogenation to synthesize diesel fraction hydrocarbons in a fixed-bed reactor was evaluated.

[0035] Weigh 1.0 g of catalyst and mix it with an equal amount of quartz sand, ensuring that the particle size of both is within the range of 40-60 mesh. The mixture is uniformly filled into the middle of the reactor, and both ends are sealed with ceramic fiber to prevent short circuits when the reactor is placed horizontally. The catalyst is then reduced and activated under atmospheric pressure. H2 (flow rate set to 50 mL / min) and N2 (flow rate set to 250 mL / min) are introduced into the reactor under controlled flow meter conditions. The catalyst bed temperature is increased from room temperature to 500 °C at a rate of 10 °C / min and maintained at this temperature for 1 h. After reduction and activation, the CO2 valve is activated, and the flow meter is adjusted to form a mixed gas consisting of H2 (440 mL / min), CO2 (130 mL / min), and N2 (10 mL / min) in a ratio of H2:CO2:N2 = 3:1:0.3. This mixture is used as the feed gas for the CO2 hydrogenation reaction. The reactor temperature is set to 300 °C, and the pressure is maintained at 2 MPa for 4 h. After the reaction was complete, the reactor was cooled to room temperature, and the reactor and gas washing bottle were thoroughly cleaned with n-hexane to collect the reaction products. The hexane-containing organic phases obtained from the cleaning were combined to form the total product liquid. The product was concentrated to approximately 1 mL using a nitrogen blowing device. Finally, the concentrated organic phase was analyzed in detail using gas chromatography-mass spectrometry (GC-MS) to identify the types and relative contents of organic compounds in the product. Detailed evaluation results of the catalyst performance are shown in Table 1.

[0036] Example 2:

[0037] A method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation includes the following steps:

[0038] S1. Weigh 2.020g of ferric nitrate nonahydrate, 0.429g of zirconium nitrate pentahydrate, and 0.101g of potassium nitrate, dissolve them in 40mL of deionized water, and stir until homogeneous to obtain a metal precursor solution.

[0039] S2. Weigh 3g of SiO2 support and add it to the metal precursor solution. Place it in a constant temperature water bath at 60℃ and stir for 4h to ensure that SiO2 and the metal precursor solution are fully mixed. Place the stirred solution in an electric heating drying oven and dry it at 120℃ for 12h until it cools to room temperature.

[0040] S3. The dried block catalyst is crushed into powder in a mortar and placed in a muffle furnace. Under a nitrogen atmosphere, the temperature is increased to 500℃ at a heating rate of 5℃ / min and calcined for 5h. After cooling to room temperature, it is ground to obtain the catalyst, denoted as FeZrK / SiO2.

[0041] The catalyst prepared in Example 2 was subjected to CO2 hydrogenation to synthesize diesel fraction hydrocarbons in a fixed-bed stainless steel reactor using the same method. The evaluation results of the catalyst are shown in Table 1.

[0042] Example 3:

[0043] A method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation includes the following steps:

[0044] S1. Weigh 2.020g of ferric nitrate nonahydrate, 0.429g of zirconium nitrate pentahydrate, and 0.101g of potassium nitrate, dissolve them in 40mL of deionized water, and stir until homogeneous to obtain a metal precursor solution.

[0045] S2. Weigh 3g of HZSM-5 molecular sieve and add it to the metal precursor solution. Place it in a constant temperature water bath at 60℃ and stir for 4h to ensure that the HZSM-5 molecular sieve and the metal precursor solution are fully mixed. Place the stirred solution in an electric heating drying oven and dry it at 120℃ for 12h until it cools to room temperature.

[0046] S3. The dried block catalyst is crushed into powder in a mortar and placed in a muffle furnace. Under a nitrogen atmosphere, the temperature is increased to 500°C at a heating rate of 5°C / min and calcined for 5 hours. After cooling to room temperature, it is ground to obtain the catalyst, which is denoted as FeZrK / HZSM-5.

[0047] The catalyst prepared in Example 3 was evaluated for its performance in CO2 hydrogenation to synthesize diesel fraction hydrocarbons in a fixed-bed stainless steel reactor using the same method. The evaluation results are shown in Table 1. Figure 1 By comparing the retention times of chromatographic peaks with those of mass spectrometry, a supported iron-based catalyst was successfully prepared.

[0048] Example 4:

[0049] A method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation includes the following steps:

[0050] S1. Weigh 2.020g of ferric nitrate nonahydrate, 0.429g of zirconium nitrate pentahydrate, and 0.101g of potassium nitrate, dissolve them in 40mL of deionized water, and stir until homogeneous to obtain a metal precursor solution.

[0051] S2. Weigh 3g of γ-Al2O3 support and add it to the metal precursor solution. Place it in a constant temperature water bath at 60℃ and stir for 4h to make γ-Al2O3 and metal precursor solution fully mixed. Place the stirred solution in an electric heating drying oven and dry at 120℃ for 12h, then cool it to room temperature.

[0052] S3. The dried block catalyst is crushed into powder in a mortar and placed in a muffle furnace. Under a nitrogen atmosphere, the temperature is increased to 500℃ at a heating rate of 5℃ / min and calcined for 5h. After cooling to room temperature, it is ground to obtain the catalyst, which is denoted as FeZrK / γ-Al2O3.

[0053] The catalyst prepared in Example 4 was subjected to CO2 hydrogenation to synthesize diesel fraction hydrocarbons in a fixed-bed stainless steel reactor using the same method. The evaluation results of the catalyst are shown in Table 1.

[0054] Comparative Example 1:

[0055] This comparative example provides a method for preparing an unsupported iron-based catalyst. 2.020 g of ferric nitrate nonahydrate, 0.429 g of zirconium nitrate pentahydrate, and 0.101 g of potassium nitrate were weighed and dissolved in 40 mL of deionized water and stirred until homogeneous. The solution was then placed in an electric heating drying oven and dried at 120 °C for 12 h. After cooling to room temperature, the dried block catalyst was crushed into powder in a mortar and placed in a muffle furnace. Calcination was carried out at 500 °C for 5 h under a nitrogen atmosphere. After cooling to room temperature, the catalyst was ground to obtain the catalyst, denoted as FeZrK.

[0056] Comparative Example 2:

[0057] The difference from Example 4 is that the amount of potassium nitrate used is 0.152g, while the other operation steps are exactly the same as in Example 4, and the corresponding catalyst is prepared.

[0058] Comparative Example 3:

[0059] The difference from Example 4 is that the calcination temperature is 400°C, while the other operating steps are exactly the same as in Example 4, and the corresponding catalyst is prepared.

[0060] Comparative Example 4:

[0061] The difference from Example 4 is that the calcination temperature is 600°C, while the other operating steps are exactly the same as in Example 4, and the corresponding catalyst is prepared.

[0062] The catalyst prepared in the comparative example was evaluated using the same method in a fixed-bed stainless steel reactor for the CO2 hydrogenation synthesis of diesel fraction hydrocarbons. The evaluation results of the catalyst are shown in Table 1.

[0063] Table 1. Activity evaluation results of the catalysts prepared in Examples 1-4 and the comparative examples.

[0064]

[0065] As shown in Table 1, the catalyst prepared at 300℃ and 2MPa pressure exhibited excellent performance in the CO2 hydrogenation to diesel fraction hydrocarbon reaction. Table 1 shows that γ-Al2O3 is the optimal support; when γ-Al2O3 is used as the support, the CO2 conversion rate can reach 41.1%, and the C... 10 -C 20 Hydrocarbon selectivity can reach 37.2%.

[0066] The preparation method of this invention is simple, easy to operate, and low in cost, making it easy to apply industrially. The prepared catalyst can efficiently catalyze the hydrogenation reaction of CO2 to synthesize a hydrocarbon mixture similar in composition to commercial diesel fuel, providing a novel route for diesel production with potential economic and environmental benefits. The obtained catalyst successfully hydrogenates CO2 to produce a C24-based product. 10 ~C 20 Diesel fraction hydrocarbons were produced. In the prepared catalyst, Fe was used as the main active component. Through the synergistic effect of Zr and K, Fe was supported on a support with high specific surface area, good pore structure, and excellent thermal stability, which effectively improved the structural strength and dispersion of the active phase of the catalyst. The mesoporous structure on the support surface provided more active sites, promoted reactant diffusion, and thus improved catalyst performance. In the process of CO2 hydrogenation to diesel fraction hydrocarbons, this catalyst achieved a CO2 conversion rate of 41.1% and a C2 conversion rate of 10.5%. 10 -C 20 Hydrocarbon selectivity can reach 37.2%.

Claims

1. A supported iron-based catalyst for catalytically generating a component C 10 ~C 20 The application of diesel distillate hydrocarbons, characterized in that, The catalyst uses one of TiO2, SiO2, HZSM-5 molecular sieve, or γ-Al2O3 as a support and is loaded with three elements: Fe, Zr, and K. Its preparation method includes the following steps: S1. TiO2, SiO2, HZSM-5 molecular sieve, and γ-Al2O3 support are dried, pulverized, and sieved into 40-60 mesh particles respectively. S2. Place the four carriers into separate containers; S3. Mix the iron-containing metal salt, the zirconium-containing metal salt, and the alkali metal additive in a molar ratio of Fe:Zr:K=5:1:(1~1.5), dissolve them in deionized water, and stir for 10~20 minutes to obtain a mixed solution. S4. Add the mixed solution obtained in step S3 to each carrier and place them in a constant temperature water bath for stirring; the impregnation amount of the carrier is 90%~100% of the saturated absorbent solution volume; S5. The stirred solution was dried, ground, and calcined to obtain four types of supported iron-based catalysts. The calcination is carried out in a muffle furnace under atmospheric pressure and nitrogen atmosphere, with the temperature increased to the calcination temperature at a rate of 2~10℃ / min, the calcination temperature being 400~600℃, and the calcination time being 2~8h. This catalyst hydrogenates CO2 to produce component C. 10 ~C 20 Diesel fraction hydrocarbons.

2. The supported iron-based catalyst according to claim 1 is used to catalyze the generation of a component C. 10 ~C 20 The application of diesel distillate hydrocarbons, characterized in that, The iron-containing metal salt is ferric nitrate nonahydrate.

3. The supported iron-based catalyst according to claim 1 is used to catalyze the generation of a component C. 10 ~C 20 The application of diesel distillate hydrocarbons, characterized in that, The zirconium-containing metal salt is zirconium nitrate pentahydrate.

4. The supported iron-based catalyst according to claim 1 is used to catalyze the generation of a component C. 10 ~C 20 The application of diesel distillate hydrocarbons, characterized in that, The alkali metal auxiliary agent is potassium nitrate.

5. The supported iron-based catalyst according to claim 1 is used to catalyze the generation of a component C. 10 ~C 20 The application of diesel distillate hydrocarbons, characterized in that, In step S4, the water bath temperature is 50~80℃ and the stirring time is 3~6h.

6. The supported iron-based catalyst according to claim 1 is used to catalyze the generation of a component C. 10 ~C 20 The application of diesel distillate hydrocarbons, characterized in that, The drying temperature of S1 is 80~120℃, and the drying time is 6~24h.

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