Preparation method of supported iron-based catalyst for catalyzing carbon dioxide hydrogenation

Abstract

The invention 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, the catalyst takes one of TiO2, SiO2, HZSM-5 molecular sieve and gamma-Al2O3 as a carrier and is loaded with three elements of Fe, Zr and K. The preparation method comprises the following steps: S1, respectively drying, crushing and screening the TiO2, SiO2, HZSM-5 molecular sieve and gamma-Al2O3 carrier; four carriers are obtained; s2, mixing an iron-containing metal salt, a zirconium-containing metal salt and an alkali metal auxiliary agent, dissolving in deionized water, and stirring; s3, respectively adding the mixed solution into each carrier, and stirring in a constant-temperature water bath kettle; and S4, drying, grinding and roasting the uniformly stirred solution. The catalyst has the advantages that CO2 hydrogenation reaction can be efficiently catalyzed, and hydrocarbon mixtures with components similar to those of commercial diesel oil can be synthesized.

Description

Technical Field

[0001] The invention belongs to the technical field of catalytic hydrogenation of carbon dioxide, and in particular relates to a method for preparing a supported iron-based catalyst for catalytic hydrogenation of carbon dioxide. Background Art

[0002] Carbon dioxide (CO2), a major greenhouse gas, has a profound impact on global climate change 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 has attracted widespread attention.

[0003] Supported catalysts, owing to their high activity, selectivity, and excellent stability, have become a crucial component of industrial catalysis. Iron-based catalysts, in particular, are considered an ideal candidate due to their abundant resources, low cost, and excellent performance in heterogeneous catalysis. In CO2 hydrogenation reactions, supported iron-based catalysts can effectively convert CO2 into a variety of high-value-added chemicals, such as light olefins, alcohols, and jet fuel.

[0004] However, traditional iron-based catalysts still have shortcomings in terms of activity, selectivity and stability. To overcome these problems, researchers have developed a variety of modification strategies, including the addition of metal additives, optimization of supports and innovation of preparation methods. Among them, the selection of supports is crucial for optimizing catalyst performance. Commonly used supports include alumina, silica, zirconia, activated carbon, molecular sieves, etc., which not only provide the necessary mechanical strength and thermal stability, but also affect the efficiency of the catalytic reaction by regulating the pore structure and surface properties of the catalyst.

[0005] By precisely controlling reaction conditions such as temperature, pressure, and gas flow ratio, product distribution can be precisely controlled. Furthermore, catalyst recyclability and regeneration are crucial considerations for industrial applications. Optimizing catalyst stability and resistance to poisoning can significantly improve the feasibility and economic viability of industrial applications.

[0006] In the prior art, patent application number CN202410162447.2 discloses an Fe-based catalyst for CO2 hydrogenation to prepare mixed alcohols, its preparation method and application. The molecular formula of the Fe-based catalyst is Fe x M-yA; where M is a metal promoter; A is an alkali metal promoter; where x is the molar ratio of Fe to M, ranging from 0.5 to 7; and y is the mass fraction of A in the Fe-based catalyst, ranging from 0.5% to 5%. This Fe catalyst has excellent CO2 conversion and C2 +Mixed alcohol selectivity, very low C1 product selectivity (CO, CH4, methanol), its preparation method is simple, easy to operate, easy to repeat and scale up production, and has potential industrial application prospects, but the method's precise control of the reaction products needs to be improved. Patent application number CN202311399953.5 discloses a method for preparing an Fe-based catalyst for CO2 hydrogenation to light olefins. FeMnKBr / Y is prepared by melt infiltration with molecular sieves. meso -Na. The Fe-based catalyst prepared by this invention has a better product distribution. The bromine element can control the electron density around the active center of the catalyst through its own electronegativity and ability to gain electrons, thereby changing the catalyst's hydrogenation ability in a hydrogen-rich atmosphere. Its preparation method reduces the degree of sintering and agglomeration of the catalyst during calcination and reaction, which is beneficial to improving the catalytic performance. However, the preparation process of the catalyst is relatively cumbersome and not conducive to repeated and scaled-up production. Patent application number CN202311370616.3 discloses a preparation method and application of a catalyst for the catalytic conversion of CO2 to long-chain hydrocarbons. The Fe-based catalyst is prepared using iron salts, iron ion precipitants and metal additives. The catalyst prepared by this invention is used for CO2 hydrogenation reaction and has very high selectivity for hydrocarbons with a carbon number of more than 5, and the selectivity of the by-products CO and CH4 is extremely low, and the product has a high olefin ratio. This method is simple in process, low in cost, can be prepared on a large scale and in large quantities, and has good industrial application prospects, but the method is not precise in regulating the metal molar ratio. Patent application number: CN202311328994.5, discloses a modified calcium iron ore catalyst and its preparation method and application, and uses the calcium iron ore catalyst Ca2Fe2O5 for CO2 hydrogenation to produce light olefins. The results show that the calcium iron ore catalyst Ca2Fe2O5 can promote the RWGS reaction, has excellent CO2 adsorption and activation ability, and has excellent CO2 conversion rate; the modified calcium iron ore catalyst Ca x K 2-x Fe2O5 promotes the RWGS reaction, which in turn enhances the FTS reaction, resulting in not only excellent CO2 conversion but also high light olefin selectivity, with CO2 conversion reaching up to 46.33% and light olefin selectivity up to 34.59%. However, the catalyst preparation process is relatively complex, making it difficult to replicate and scale up production.

[0007] Despite significant progress in CO2 hydrogenation technology using supported iron-based catalysts, challenges remain. These include improving catalyst selectivity while maintaining high activity, achieving long-term stable operation, and reducing catalyst preparation costs. By leveraging the synergistic effects of transition metal and alkali metal promoters, optimizing catalyst preparation methods, improving catalyst stability, and reducing preparation costs, the application prospects of supported iron-based catalysts in CO2 hydrogenation technology will be even broader. Summary of the Invention

[0008] To overcome the deficiencies of the prior art, the present invention aims to provide a method for preparing an efficient and low-cost supported iron-based catalyst for catalytic carbon dioxide hydrogenation, which has both RWGS reaction and FTS catalytic performance, and can hydrogenate CO2 to produce diesel fraction hydrocarbons, thereby reducing the preparation cost.

[0009] To achieve the above object, the present invention is implemented through the following technical solutions:

[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, and γ-Al2O3 as a carrier and is loaded with three elements: Fe, Zr, and K. The preparation method comprises the following steps:

[0011] S1. Dry and crush TiO2, SiO2, HZSM-5 molecular sieve and γ-Al2O3 carrier respectively, and sieve them into particles of 40-60 mesh;

[0012] S2, placing the four carriers in containers respectively;

[0013] S3, mixing an iron-containing metal salt, a zirconium-containing metal salt, and an alkali metal additive in a molar ratio of Fe:Zr:K=5:1:(1-1.5), dissolving the mixture in deionized water, and stirring for 10-20 minutes to obtain a mixed solution;

[0014] S4, adding the mixed solution prepared in step S3 to each carrier respectively, and placing them in a constant temperature water bath for stirring; the impregnation amount of the carrier is 90% to 100% of the saturated absorption solution amount;

[0015] S5. Drying, grinding and calcining the stirred solution to obtain four 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° C., and the stirring time is 3-6 hours.

[0020] The drying temperature is 80-120° C., and the drying time is 6-24 hours.

[0021] The calcination is carried out in a muffle furnace in a nitrogen atmosphere at normal pressure, and the temperature is raised to the calcination temperature at a heating rate of 2-10°C / min, the calcination temperature is 400-600°C, and the calcination time is 2-8h.

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

[0023] The preparation method of the present invention features a simple process, easy operation, low cost, and is readily applicable industrially. The prepared catalyst can efficiently catalyze the hydrogenation of CO2 to produce a hydrocarbon mixture with a composition similar to commercial diesel, providing a novel approach to diesel production with potential economic and environmental benefits.

[0024] The present invention loads three elements, Fe, Zr, and K, to stabilize the catalyst structure. Fe is the primary active ingredient; K acts as an additive to improve the catalyst surface pH and increase the CO2 adsorption rate; Zr generates ZrO2, which has oxygen storage capacity, stabilizes the catalyst structure, and optimizes the redox environment of Fe. Simultaneously, loading Fe, Zr, and K together maintains the reaction kinetic equilibrium.

[0025] The prepared catalyst successfully hydrogenated CO2 to generate components C 10 ~C 20 In the prepared catalyst, Fe is the main active ingredient. By combining the synergistic effect of Zr and K, it is loaded on a carrier with a high specific surface area, good pore structure and excellent thermal stability. This can effectively improve the structural strength of the catalyst and the dispersion of the active phase, thereby improving the catalyst performance. In the process of CO2 hydrogenation to diesel fraction hydrocarbons, the CO2 conversion rate of this catalyst can reach 41.1%, and C 10 -C 20 The hydrocarbon selectivity can reach 37.2%. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0027] The present invention will be further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby.

[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] The preparation method of a supported iron-based catalyst for catalytic carbon dioxide hydrogenation comprises the following steps:

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

[0032] S2. Weigh 3 g of TiO2 carrier and add it to the metal precursor solution. Place it in a constant temperature water bath at 60°C and stir for 4 h to fully mix the TiO2 and metal precursor solution. Place the stirred solution in an electric blast drying oven at 120°C and dry it for 12 h, then cool it to room temperature.

[0033] S3. Grind the dried bulk catalyst into powder in a mortar and place it in a muffle furnace. Heat the temperature to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere and calcine for 5 h. After cooling to room temperature, grind the powder to obtain the catalyst, which is recorded as FeZrK / TiO2.

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

[0035] Weigh 1.0 g of catalyst and mix it with an equal amount of quartz sand, ensuring that the particle size of both materials is within the 40-60 mesh range. The mixture is evenly filled into the center of the reactor, and both ends are sealed with ceramic fiber to prevent gas short-circuiting when the reactor is horizontal. The catalyst is reduced and activated under atmospheric pressure. H2 (flow rate set at 50 mL / min) and N2 (flow rate set at 250 mL / min) are introduced into the reactor via a gas flowmeter. The catalyst bed temperature is raised from room temperature to 500°C at a rate of 10°C / min and maintained at this temperature for 1 hour. After reduction and activation, the CO2 valve is opened and the gas flowmeter is adjusted to produce a gas mixture 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 serves 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. The reaction continues for 4 hours. After the reaction, the reactor was cooled to room temperature and the reactor and wash bottle were thoroughly rinsed with n-hexane to collect the reaction products. The n-hexane-containing organic phases from the washes were combined to form the total product solution. The product was concentrated to a volume of approximately 1 mL using a nitrogen purge device. Finally, the concentrated organic phase was analyzed in detail using gas chromatography-mass spectrometry (GC-MS) to identify the types and relative amounts of organic compounds in the product. Detailed evaluation results of the catalyst performance are shown in Table 1.

[0036] Example 2:

[0037] The preparation method of a supported iron-based catalyst for catalytic carbon dioxide hydrogenation comprises the following steps:

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

[0039] S2. Weigh 3 g of SiO2 carrier and add it to the metal precursor solution. Place it in a constant temperature water bath at 60°C and stir for 4 h to fully mix the SiO2 and metal precursor solution. Place the stirred solution in an electric blast drying oven at 120°C and dry it for 12 h, then cool it to room temperature.

[0040] S3. Grind the dried bulk catalyst into powder in a mortar and place it in a muffle furnace. Heat the temperature to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere and calcine for 5 h. After cooling to room temperature, grind it to obtain the catalyst, which is recorded as FeZrK / SiO2.

[0041] The same method was used to evaluate the performance of the catalyst prepared in Example 2 in a fixed-bed stainless steel reactor for the synthesis of diesel fraction hydrocarbons by CO2 hydrogenation. The evaluation results of the catalyst are shown in Table 1.

[0042] Example 3:

[0043] The preparation method of a supported iron-based catalyst for catalytic carbon dioxide hydrogenation comprises the following steps:

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

[0045] S2. Weigh 3 g of HZSM-5 molecular sieve and add it to the metal precursor solution. Place it in a constant temperature water bath at 60°C and stir for 4 h to fully mix the HZSM-5 molecular sieve and the metal precursor solution. Place the stirred solution in an electric blast drying oven at 120°C and dry it for 12 h, then cool it to room temperature.

[0046] S3. The dried bulk catalyst was crushed into powder in a mortar and placed in a muffle furnace. The temperature was raised to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere and calcined for 5 h. After cooling to room temperature, the catalyst was ground to obtain FeZrK / HZSM-5.

[0047] The same method was used to evaluate the performance of the catalyst prepared in Example 3 in a fixed-bed stainless steel reactor for the synthesis of diesel fraction hydrocarbons by CO2 hydrogenation. The evaluation results of the catalyst are shown in Table 1. Figure 1 , based on the comparison of the retention time of the chromatographic peak with the mass spectrum, a supported iron-based catalyst was successfully prepared.

[0048] Example 4:

[0049] The preparation method of a supported iron-based catalyst for catalytic carbon dioxide hydrogenation comprises the following steps:

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

[0051] S2. Weigh 3 g of γ-Al2O3 carrier and add it to the metal precursor solution. Place it in a constant temperature water bath at 60°C and stir for 4 hours to fully mix the γ-Al2O3 and the metal precursor solution. Place the stirred solution in an electric blast drying oven at 120°C for 12 hours and then cool it to room temperature.

[0052] S3. The dried bulk catalyst was crushed into powder in a mortar and placed in a muffle furnace. The temperature was raised to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere and calcined for 5 h. After cooling to room temperature, the catalyst was ground to obtain FeZrK / γ-Al2O3.

[0053] The same method was used to evaluate the performance of the catalyst prepared in Example 4 in a fixed-bed stainless steel reactor for the synthesis of diesel fraction hydrocarbons by CO2 hydrogenation. The evaluation results of the catalyst are shown in Table 1.

[0054] Comparative Example 1:

[0055] This comparative example provides a method for preparing a non-supported 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 evenly. The stirred solution was placed in an electric blast 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. The powder was calcined at 500° C. for 5 h under a nitrogen atmosphere. After cooling to room temperature, the catalyst was ground to obtain a catalyst, which was recorded as FeZrK.

[0056] Comparative Example 2:

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

[0058] Comparative Example 3:

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

[0060] Comparative Example 4:

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

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

[0063] Table 1 Activity evaluation results of catalysts prepared in Examples 1-4 and Comparative Examples

[0064]

[0065] As shown in Table 1, at a temperature of 300°C and a pressure of 2 MPa, the prepared catalyst exhibits excellent CO2 hydrogenation to diesel fraction hydrocarbon reaction performance. As can be seen from Table 1, γ-Al2O3 is the best carrier. When γ-Al2O3 is used as a carrier, the CO2 conversion rate can reach 41.1%, and the C 10 -C 20 The hydrocarbon selectivity can reach 37.2%.

[0066] The preparation method of the present invention has a simple process, is easy to operate, has low cost, and is easy to industrially apply. The prepared catalyst can efficiently catalyze the CO2 hydrogenation reaction to synthesize a hydrocarbon mixture with a composition similar to that of commercial diesel, providing a new approach for diesel production with potential economic and environmental benefits. The prepared catalyst successfully hydrogenates CO2 to generate components C 10 ~C 20 In the prepared catalyst, Fe is the main active ingredient. By combining the synergistic effect of Zr and K, it is loaded on a carrier with a high specific surface area, good pore structure and excellent thermal stability. This can effectively improve the structural strength of the catalyst and the dispersion of the active phase. The mesoporous structure on the carrier surface can provide more active sites, promote the diffusion of reactants, and thus improve the catalyst performance. In the process of CO2 hydrogenation to diesel fraction hydrocarbons, the CO2 conversion rate of this catalyst can reach 41.1%, and C 10 -C 20 The hydrocarbon selectivity can reach 37.2%.

Claims

1. A method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation, characterized in that: The catalyst uses one of TiO2, SiO2, HZSM-5 molecular sieve, and γ-Al2O3 as a carrier and is loaded with three elements: Fe, Zr, and K. The preparation method thereof comprises the following steps: S1. Dry and crush TiO2, SiO2, HZSM-5 molecular sieve and γ-Al2O3 carrier respectively, and sieve them into particles of 40-60 mesh; S2, placing the four carriers in containers respectively; S3, mixing an iron-containing metal salt, a zirconium-containing metal salt, and an alkali metal additive in a molar ratio of Fe:Zr:K=5:1:(1-1.5), dissolving the mixture in deionized water, and stirring for 10-20 minutes to obtain a mixed solution; S4, adding the mixed solution prepared in step S3 to each carrier respectively, and placing them in a constant temperature water bath for stirring; the impregnation amount of the carrier is 90% to 100% of the saturated absorption solution amount; S5. Drying, grinding and calcining the stirred solution to obtain four supported iron-based catalysts.

2. The method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation according to claim 1, wherein: The iron-containing metal salt is ferric nitrate nonahydrate.

3. The method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation according to claim 1, characterized in that: The zirconium-containing metal salt is zirconium nitrate pentahydrate.

4. The method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation according to claim 1, wherein: The alkali metal auxiliary agent is potassium nitrate.

5. The method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation according to claim 1, characterized in that: In step S4, the water bath temperature is 50-80° C., and the stirring time is 3-6 hours.

6. The method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation according to claim 1, characterized in that: The drying temperature of S1 is 80-120° C., and the drying time is 6-24 hours.

7. The method for preparing a supported iron-based catalyst for catalytic carbon dioxide hydrogenation according to claim 1, characterized in that: The calcination is carried out in a muffle furnace in a nitrogen atmosphere at normal pressure, and the temperature is raised to the calcination temperature at a heating rate of 2-10°C / min, the calcination temperature is 400-600°C, and the calcination time is 2-8h.

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