Preparation method and application of Fe metal catalyst encapsulated by ZSM-5 with carbon sphere as structural template

Abstract

The application discloses a preparation method of a Fe metal catalyst encapsulated by ZSM-5 with carbon spheres as a structural template and application thereof. The metal iron can be better impregnated on the carbon sphere template through ultrasonic immersion, and then is placed into a ZSM-5 precursor solution for hydrothermal synthesis, and the template is removed through high-temperature calcination in a muffle furnace, so that the active metal iron is retained in the molecular sieve to obtain the target catalyst. The iron-based catalyst is an ideal choice for CO2 conversion through a modified Fischer-Tropsch synthesis process, has excellent catalytic performance and low cost. However, the iron-based catalyst is easy to sinter and form carbon deposition in a high-temperature environment, and thus the catalyst is deactivated. Therefore, the research focus is how to improve the utilization rate and stability of the metal Fe.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and specifically discloses a method for preparing an Fe metal catalyst using carbon spheres as a structural template and encapsulated in ZSM-5, as well as its application. Background Technology

[0002] With rapid economic growth, increasing CO2 emissions into the atmosphere have placed a huge burden on the environment, leading to issues such as global warming, ocean acidification, and climate change. Converting CO2 into high-value-added chemicals is a promising strategy that can not only reduce carbon emissions but also meet the needs of sustainable development. In recent years, with the development of CO2 capture technology and advancements in renewable energy-based hydrogen production technology, the heterogeneous catalytic hydrogenation of CO2 to produce high-value-added chemicals has become a new approach that can simultaneously utilize waste CO2 while producing high-value-added chemicals.

[0003] Unlike other molecular sieves, ZSM-5 molecular sieves encapsulate metals, preventing metal agglomeration through micropore confinement and providing additional strong acidic sites and pore selectivity, thus comprehensively improving catalytic performance. Due to the abundant porosity of ZSM-5 molecular sieves, a large amount of iron is confined within narrow channels, resulting in smaller iron species. Simultaneously, iron has more opportunities to interact with the framework aluminum, thereby enhancing the interaction between the metal and ZSM-5. ZSM-5 exhibits better stability at high temperatures, allowing it to catalyze reactions under high-temperature conditions, thus improving catalyst stability. Compared to other molecular sieves used as encapsulation shells, such as the S-1 all-silica molecular sieve (which has almost zero alumina content) and the SAPO-34 molecular sieve (a molecular sieve composed of silicon, aluminum, and phosphorus with extremely low acidity), the Fe metal catalyst encapsulated in ZSM-5 using carbon spheres as a structural template disclosed in this invention has a thinner ZSM-5 shell, smaller and more uniformly dispersed metal particles, and stronger interaction between metallic Fe and ZSM-5. Summary of the Invention

[0004] The purpose of this invention is to propose a method for preparing an Fe metal catalyst using carbon spheres as a structural template and encapsulated in ZSM-5, and to study its CO2 hydrogenation performance. Ultrasonic impregnation allows for better impregnation of metallic iron onto the carbon sphere template. Subsequently, the catalyst is hydrothermally synthesized in a ZSM-5 precursor solution, followed by high-temperature calcination in a muffle furnace to remove the template, retaining the active metallic iron within the molecular sieve to obtain the target catalyst. Iron-based catalysts are an ideal choice for CO2 conversion through modified Fischer-Tropsch synthesis processes, exhibiting excellent catalytic performance and low cost. However, they are prone to sintering and carbon deposition at high temperatures, leading to catalyst deactivation. Therefore, our research focuses on improving the utilization rate and stability of metallic Fe.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing an Fe metal catalyst using carbon spheres as structural templates and encapsulated in ZSM-5, comprising loading metallic iron and metallic Fe onto a carbon sphere template and encapsulating them in ZSM-5.

[0006] The preparation method includes the following steps:

[0007] Step 1: The sugar carbon source is subjected to hydrothermal treatment at 150~200 ℃, followed by carbonization at 500~800 ℃ under an inert atmosphere, and then ground to obtain carbon ball templates;

[0008] Step 2: Load the metal onto the carbon ball template to obtain a carbon ball template containing metallic iron;

[0009] Step 3: Take a carbon ball template containing metallic iron, add it to the precursor solution and stir evenly. Then transfer it to a hydrothermal synthesis reactor and solvothermally synthesize it at 150~200 ℃ for 24~36 h. The obtained product is filtered with deionized water to clean the sample. Wash the sample with deionized water until it is odorless. After washing, put it in an oven to dry. Then calcine it in a muffle furnace at 500~800 ℃ to obtain an Fe metal catalyst with carbon balls as structural template and ZSM-5 encapsulation.

[0010] The precursor solution is an aqueous solution of tetrapropylammonium hydroxide, ethanol, aluminum nitrate hexahydrate, and tetraethyl silicate.

[0011] In step 1, the inert atmosphere is one or two of nitrogen, argon, and helium.

[0012] The carbohydrate carbon source can be one or both of sucrose and glucose.

[0013] The nitrate can be one or two of ferric nitrate, copper nitrate, and cobalt nitrate; the mass fraction of the metal relative to the carbon sphere template is 1-8%.

[0014] Step 2 involves loading the metal onto a carbon ball template using one or more of the following methods: physical grinding, equal volume impregnation, hydrothermal synthesis, and ultrasonic impregnation.

[0015] Step 2 uses ultrasonic impregnation.

[0016] When making carbon ball templates, the calcination temperature is 500~800 ℃, the holding time is 0.5~5 h, and the heating rate is 1~5℃ / min.

[0017] The method for loading active metal components onto carbon sphere templates is one or more of the following: physical grinding, equal volume impregnation, hydrothermal synthesis, and ultrasonic impregnation.

[0018] The catalyst prepared by the method is characterized in that it comprises carbon particles encapsulated by a molecular sieve ZSM, the carbon particles being loaded with Fe, the Fe mass content being 744.964ppm~3082.501ppm.

[0019] This invention employs a method for preparing Fe metal catalysts using carbon spheres as structural templates and encapsulated in ZSM-5, thereby improving CO2 hydrogenation performance and providing insights for the future rational design of catalysts with high thermal stability, high catalytic activity, and selectivity.

[0020] The advantages of this invention, which differ from existing technologies, are as follows:

[0021] This invention utilizes carbon spheres obtained through ultrasonic impregnation as a structural template, followed by hydrothermal synthesis to obtain a catalyst encapsulated in ZSM-5 with metallic Fe. This solves the problem that anchoring metal nanoparticles on a support surface cannot meet the stability requirements during catalysis. ZSM-5 molecular sieve is a zeolite molecular sieve with a ten-membered ring MFI topology, exhibiting excellent thermal stability and good selectivity. Therefore, compared to other porous materials, ZSM-5 molecular sieve demonstrates superior thermal and chemical stability even under harsh reaction conditions. The ZSM-5 molecular sieve-encapsulated metal nanoparticle catalyst exhibits excellent anti-sintering properties, and particle aggregation is not easily observed even under harsh catalytic conditions. The "molecular sieve encapsulating metal" method has unique advantages in regulating reaction selectivity and improving the stability of metal species. Iron-based catalysts are an ideal choice for CO2 conversion through modified Fischer-Tropsch synthesis. Under operating reaction conditions, the iron-based catalyst contains two active sites: Fe3O4 for generating CO intermediates and Fe5C2 for subsequent chain growth. The encapsulation of metal species in ZSM-5 molecular sieves combines the acidic sites, pore structure, and internal metal sites of the sieve, enhancing the interaction between the metal and the support. This results in high activity, unique selectivity, and excellent stability in CO2 catalytic hydrogenation. Molecular sieve-encapsulated catalysts utilize the confinement effect to isolate the active components from the external environment, thereby protecting the active components and maintaining the long-term stability of the catalyst. Attached Figure Description

[0022] Figure 1 The preparation process of the catalyst of this invention is as follows;

[0023] Figure 2 TEM image of the 2Fe-C@ZSM-5 catalyst prepared in this invention;

[0024] Figure 3 TEM image of ZSM-5 catalyst without encapsulated metallic iron;

[0025] Figure 4This is a TEM surface scan image of the 6Fe-C@ZSM-5 catalyst prepared in this invention. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0027] Weigh 5-10 g of glucose and dissolve it in 50-100 mL of deionized water. Stir until homogeneous, then transfer the solution to a hydrothermal synthesis reactor. Synthesize at 150-200 °C for 5-10 h using a solvothermal method. Wash the product several times with deionized water, then calcine at 500-800 °C under an inert atmosphere. Grind and dry to obtain a carbon sphere template. Dissolve appropriate amounts of tetrapropylammonium hydroxide, ethanol, aluminum nitrate hexahydrate, and tetraethyl silicate in 50-100 mL of deionized water. Stir for several hours until a colorless and transparent solution is obtained, which will be used as a precursor solution. Weigh an appropriate amount of ferric nitrate and dissolve it in 5-10 mL of deionized water. Sonicate until homogeneous. Weigh 1 g of the pre-prepared carbon sphere template and add it to the solution. Sonicate for 1-2 h, age for 12-24 h, then dry in an oven at 50-100 °C. Take 0.5-1 g of the carbon sphere template impregnated with metallic iron and add it to the pre-prepared precursor solution. Stir for 5-10 h. The sample was then transferred to a hydrothermal synthesis reactor and solvothermally synthesized at 150-200 °C for 24-36 h. The obtained product was filtered with deionized water to clean the sample. The sample was washed with deionized water until it was odorless. After washing, it was placed in an oven to dry and then calcined in a muffle furnace at 500-800 °C. The sample was observed to change from black to white.

[0028] Particle size and elemental distribution were observed using a transmission electron microscope (JEM-2100).

[0029] ICP-OES (Thermo Fisher iCAP 7400; ICP-MS: Agilent 7800) was used to measure the Fe content of the catalyst.

[0030] The present application will be described in detail below with reference to various embodiments. However, these embodiments do not limit the present application, and structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are all included within the protection scope of the present application.

[0031] Example 1

[0032] (1) Weigh 5.0 g of glucose and dissolve it in 50 mL of deionized water. Stir for 1 h and then transfer it to a 100 mL hydrothermal synthesis vessel. After sealing, it is solvothermal synthesized at 180 °C for 8 h. The product is washed with 500 mL of deionized water until the washing liquid is colorless. The resulting solid is then carbonized under a nitrogen atmosphere with a heating rate of 5 °C / min to 550 °C and a holding time of 4 h. After grinding, carbon ball templates are obtained.

[0033] (2) Mix 60 mL of deionized water, 15.6 g of tetrapropylammonium hydroxide, 14.6 g of anhydrous ethanol, 0.6 g of aluminum nitrate hexahydrate and 16.6 g of tetraethyl silicate and stir for 4 h until the solution is colorless and transparent. Use this solution as a precursor solution.

[0034] (3) Weigh ferric nitrate nonahydrate containing 0.02 g of metallic iron, dissolve it in 5 mL of deionized water, and sonicate to dissolve. Weigh 1 g of the pre-prepared carbon ball template, add it to the above ferric nitrate solution, sonicate for 1 h, age at room temperature for 12 h, and then dry it in a 60 ℃ oven for 48 h to obtain the carbon ball template impregnated with metallic iron, named 2Fe-C.

[0035] (4) Take 0.5 g of carbon ball template that has been pre-impregnated with metallic iron, add it to the precursor solution and stir for 6 h. Then transfer it to a hydrothermal annealing tank.

[0036] The product was sealed in a reactor and then solvothermal synthesized at 180 °C and 5 r / min for 24 h. The product was washed with deionized water by filtration until it was odorless. It was then washed once with anhydrous ethanol and then once with water. The resulting solid was heated to 600 °C in a muffle furnace at a heating rate of 5 °C / min and held for 4 h until the sample turned from black to white. This yielded the desired Fe metal catalyst encapsulated in ZSM-5 with carbon spheres as the structural template. The target catalyst was named 2Fe-C@ZSM-5.

[0037] Example 2

[0038] The Fe metal catalyst encapsulated in ZSM-5 with carbon spheres as the structural template was prepared according to the steps of Example 1. The difference was that in step (3), the mass of metallic iron was 0.04 g, and all other steps were the same. The catalyst was named 4Fe-C@ZSM-5.

[0039] Example 3

[0040] The Fe metal catalyst encapsulated in ZSM-5 with carbon spheres as the structural template was prepared according to the steps of Example 1. The difference was that in step (3), the mass of metallic iron was 0.06 g, and all other steps were the same. The catalyst was named 6Fe-C@ZSM-5.

[0041] The catalyst evaluation process used in this invention is as follows:

[0042] The catalytic performance of the catalyst was investigated in a fixed-bed reactor. Before the reaction, the catalyst was reduced with pure H2 at 400 °C for 4 h. After reduction, the temperature was lowered to 280 °C. Subsequently, a reaction gas with an H2 / CO2 ratio of 3 was introduced into the reactor, and the system was gradually pressurized to 2.0 MPa and the temperature increased to 320 °C. The W / F value was defined as the ratio of catalyst weight to flow rate, and in the experiment, it was controlled at 5 g. cat ·h·mol -1 To collect heavy hydrocarbons and remove water produced in the reaction, a cold trap is placed between the reactor and the back pressure valve. Octane is added to the cold trap as a solvent to collect the heavy hydrocarbon components. The CO, CO2, and CH4 components in the gaseous products are analyzed by an online gas chromatograph equipped with a TCD detector, while the content of light hydrocarbon components (C1-C7) is analyzed by another online gas chromatograph equipped with an FID detector. After the reaction, the heavy hydrocarbon components in the octane cold trap are collected, and n-dodecane is added as an internal standard. The resulting liquid components are analyzed by an offline gas chromatograph equipped with an FID detector. The results from the analysis of the gas and liquid products are standardized to obtain the selectivity of various components and the CO2 conversion rate.

[0043] Table 1 Catalytic performance of 2Fe-C@ZSM-5 catalyst for carbon dioxide hydrogenation

[0044] Reaction conditions: 320 ℃, 2.0 MPa, W / F = 5 g·h·mol −1

[0045] Table 2 Catalytic performance of common Fe-based catalysts for carbon dioxide hydrogenation

[0046] [1]Kuei, CK; Lee, M. Hydrogenation of carbon dioxide by hybridcatalysts, direct synthesis of aromatics from carbon dioxide and hydrogen.Can. J. Chem. Eng. 1991, 69 (1), 347-354.

[0047] [2]Xu, Y. B.; Shi, C. M.; Liu, B.; Wang, T.; Zheng, J.; Li, W. P.;Liu, D. P.; Liu, X. H. Selective production of aromatics from CO2. Catal.Sci. Technol. 2019, 9 (3), 593-610.

[0048] [3]Gao, W.; Guo, L.; Wu, Q.; Wang, C.; Guo, X.; He, Y.; Zhang, P.;Yang, G.; Liu, G.; Wu, J. Capsule-like zeolite catalyst fabricated bysolvent-free strategy for para-Xylene formation from CO2 hydrogenation. Appl.Catal. B-Environ. 2022, 303, 120906.

[0049] [4]Xu, Y.; Wang, T.; Shi, C.; Liu, B.; Jiang, F.; Liu, X.Experimental Investigation on the Two-Sided Effect of Acidic HZSM-5 on theCatalytic Performance of Composite Fe Based Fischer–Tropsch Catalysts andHZSM-5 Zeolite in the Production of Aromatics from CO2 / H2. Ind. Eng. Chem.Res. 2020, 59 (18), 8581-8591.

[0050] [5] Ramirez, A.; Chowdhury, AD; Dokania, A.; Cnudde, P.; Caglapn, M.; Yarulina, I.; Abou-Hamad, E.; Gevers, L.; Ould-Chikh, S.; Catal. 2019, 9 (7), 6320-6334.

[0051] In reference [1], Fused-Fe / HZSM-5 is a complex of iron (Fe) and HZSM-5 molecular sieve. First, HZSM-5 molecular sieve is synthesized, and iron is introduced into the molecular sieve by impregnation. Then, the impregnated catalyst is calcined at high temperature to remove template agent and organic impurities, while promoting the binding of iron with molecular sieve. The iron phase is reduced by reduction step.

[0052] The catalyst Na / Fe / H-ZSM-5 in reference [2] is a composite HZSM-5 molecular sieve containing alkali metals (such as sodium Na) and transition metals (such as iron Fe), and its preparation method is similar to that of Fused-Fe / HZSM-5.

[0053] In reference [3], 2.83Na-FeMn / HZSM-5@S1-S is a capsule-shaped zeolite catalyst. It mixes raw materials such as silicon source, aluminum source, sodium source, iron source and manganese source, and may also include template agent. The mixed raw materials are heated under specific conditions to crystallize and form a zeolite structure. The synthesized zeolite is filtered and washed to remove unreacted raw materials and template agent in the reaction. The washed zeolite is dried, then calcined at high temperature, and finally reduced in a hydrogen atmosphere.

[0054] The preparation process of Na / Fe / H-ZSM-5 in reference [4] includes: firstly, synthesizing HZSM-5 molecular sieve, then exchanging the synthesized HZSM-5 molecular sieve with a solution containing sodium ions to introduce sodium (Na). Iron (Fe) is introduced into the molecular sieve by impregnation, followed by drying and calcination. Finally, the calcined catalyst is reduced in a hydrogen atmosphere.

[0055] In reference [5], Fe2O3@K2O / HZSM-5 is a composite catalyst in which Fe2O3 is the active component, K2O is the promoter, and HZSM-5 is the support. First, HZSM-5 molecular sieve is synthesized. The synthesized HZSM-5 molecular sieve is impregnated with a solution containing iron salt to introduce an iron source. K2O is introduced by impregnation. The impregnated catalyst is dried at an appropriate temperature to remove the solvent. The dried catalyst is calcined at high temperature to fix iron and potassium and improve the structural stability of the catalyst. The calcined catalyst is reduced in hydrogen or inert gas to form active Fe2O3.

[0056] Use this formula to calculate the TOF value:

[0057] The prepared 2Fe-C@ZSM-5 catalyst, calculated to have a TOF value as high as 286 h⁻¹, exhibits an efficiency of up to 286 h⁻¹. -1 Compared to other iron-based catalysts and catalysts that encapsulate metallic iron within molecular sieves using other methods, the TOF value is higher. This indicates that the Fe metal catalyst encapsulated in ZSM-5 using carbon spheres as a template, as invented in this patent, exhibits excellent catalytic hydrogenation performance for carbon dioxide.

[0058] Table 3. Fe content values ​​of different catalysts determined by ICP

[0059]

[0060] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. The application of Fe metal catalyst encapsulated in ZSM-5 using carbon spheres as structural templates in the catalytic hydrogenation of CO2, characterized in that, The catalyst comprises carbon particles encapsulated by ZSM-5 molecular sieve, with Fe loaded on the carbon particles, and the Fe content in the catalyst is 744.964 ppm by mass. The preparation method of the catalyst includes the following steps: Step 1: The sugar carbon source is subjected to hydrothermal treatment at 150~200 ℃, followed by carbonization at 500~800 ℃ under an inert atmosphere, and then ground to obtain carbon ball templates; Step 2: The metal is loaded onto the carbon ball template using the ultrasonic impregnation method to obtain a carbon ball template containing metallic iron; Step 3: Take a carbon ball template containing metallic iron, add it to the precursor solution and stir evenly. Then transfer it to a hydrothermal synthesis reactor and solvothermally synthesize it at 150~200 ℃ for 24~36 h. The obtained product is filtered with deionized water to clean the sample. Wash the sample with deionized water until it is odorless. After washing, put it in an oven to dry. Then calcine it in a muffle furnace at 500~800 ℃ to obtain an Fe metal catalyst with carbon balls as structural template and ZSM-5 encapsulation. The precursor solution is an aqueous solution of tetrapropylammonium hydroxide, ethanol, aluminum nitrate hexahydrate, and tetraethyl silicate.

2. The application according to claim 1, characterized in that: In step 1, the inert atmosphere is one or two of nitrogen, argon, and helium.

3. The application according to claim 1, characterized in that: The carbohydrate carbon source is one or both of sucrose and glucose.

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