Iron-based catalyst as well as preparation method and application thereof
By preparing the carbon support by the solvothermal method and using H2O2 to modify the surface groups of the Fe-based catalyst, the problem of high selectivity of C1 by-products in Fischer-Tropsch synthesis was solved, the olefin selectivity was improved and the catalyst stability was improved, breaking through the ASF distribution limitation.
Patent Information
- Application Number
- CN202511038219.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-28
- Publication Date
- 2025-10-17
AI Technical Summary
Existing Fischer-Tropsch synthesis catalysts have the problem of high selectivity for C1 by-products and low selectivity for target products. Traditional modification methods lead to decreased catalyst stability, and the interaction between the metal and the carrier affects the dispersion of the Fe active phase.
Anhydrous glucose was used as the carbon source to prepare the carbon support by a solvothermal method, and the surface of the carbon support was modified by H2O2 to construct an Fe-based catalyst with rich surface groups. The preparation process was mild and did not affect the intrinsic performance of the catalyst.
It improves olefin selectivity, inhibits the formation of C1 by-products, improves the distribution of Fischer-Tropsch synthesis products, enhances catalyst activity and stability, and breaks through the ASF distribution limitation.
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Figure CN120790152A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application relates to the technical field of catalyst preparation, in particular to an iron-based catalyst and a preparation method and application thereof. BACKGROUND
[0002] Energy, as the core material basis for national development, runs through multiple fields such as economic policy, politics and military security, and a continuous and stable energy supply is a basic prerequisite for ensuring long-term peace and stability in the country. China's energy resources are characterized by 'rich coal, poor oil and little gas', and the coal industry has thus become an important pillar of the national economy. Although a large amount of resources have been invested in the research and application of new energy sources such as nuclear energy, wind energy and solar energy, limited by cost and technical bottlenecks, coal resources still dominate the energy consumption structure in China.
[0003] Fischer-Tropsch synthesis (FTS) was proposed by German chemists Franz Fischer and Hans Tropsch in 1923, and is a key technical path for converting synthesis gas of raw materials such as coal, natural gas, biomass and shale gas into low-carbon olefins, diesel, gasoline and other fuels and bulk chemicals. Through this technology, high-value-added products can be prepared to a certain extent to alleviate the pressure of oil resource depletion. Under the background of increasingly serious energy and environmental problems, the research value of Fischer-Tropsch synthesis is becoming increasingly prominent.
[0004] Designing efficient catalysts to regulate product distribution is the core research goal in this field, and exploring the construction strategy of new Fischer-Tropsch catalysts and its mechanism is of great significance to optimize product distribution, improve carbon utilization efficiency and product added value. However, the product distribution of the Fischer-Tropsch synthesis catalyst system is limited by the ASF (Anderson-Schulz-Flory) law, and there is a problem of high selectivity of C1 by-products and low selectivity of target products. Therefore, modification of the Fischer-Tropsch catalyst is the key to improving the reaction performance.
[0005] Traditional modification methods are mostly achieved by introducing K, Na, Mg and other additives. These additives can transfer electrons through electron donation and active phase to reduce methane selectivity, increase olefin selectivity and catalyst activity, but the addition of additives often leads to a decrease in catalyst stability, and easy sintering and carbon deposition deactivation. To solve this problem, oxides such as Al2O3 and SiO2 are usually used as carriers to enhance stability, but the strong interaction between the metal and the carrier may hinder the conversion of metal sites to active phase and inhibit the dispersion of Fe active phase.
[0006] In contrast, most carbon materials have regular structure, considerable specific surface area and controllable pore structure, and weak interaction with Fe, which does not affect the intrinsic catalytic performance of Fe-based catalysts. In addition, when using glucose, sucrose and the like as carbon precursors, the mild preparation conditions can retain part of the groups on the surface of the carbon carrier when the carbon carrier is prepared by a solvothermal carbonization method. These surface groups (especially carbon-oxygen groups, surface hydroxyl groups and nitrogen-containing groups) are closely related to the distribution of Fischer-Tropsch synthesis products. Related studies have shown that the surface groups of the catalyst can improve the Fischer-Tropsch reaction activity, increase the olefin selectivity and inhibit the generation of C1 by-products. The physical and chemical properties of the carrier affect its interaction with the catalyst, and after surface treatment, the dispersion and activation of the active component can be promoted, and the service life of the catalyst can be prolonged.
[0007] At present, the researches at home and abroad use carbon materials as Fischer-Tropsch synthesis carriers, mainly based on the advantages that the high specific surface area and controllable pore structure can effectively anchor Fe-based catalysts and inhibit sintering, but the research on how the surface groups of the carbon carrier affect the reaction mechanism and product distribution is still relatively weak.
[0008] Therefore, how to develop an iron-based catalyst is a problem that those skilled in the art need to solve. SUMMARY
[0009] Therefore, the purpose of the present application is to provide an iron-based catalyst and its preparation method and application to solve the problems in the prior art.
[0010] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:
[0011] A preparation method of an iron-based catalyst, specifically comprising the following steps:
[0012] (1) Dissolve anhydrous glucose in ethylene glycol, magnetically stir, carbonize, cool, centrifuge, wash, dry, calcine, and obtain a carbon carrier CS;
[0013] (2) Add H2O2 to the carbon carrier CS, ultrasonically stir, wash, dry, and obtain CS-H2O2;
[0014] (3) Dissolve CS-H2O2 in an iron nitrate solution, magnetically stir, dry, and calcine to obtain a Fe / CS-H2O2 iron-based catalyst.
[0015] Further, in the above step (1), the amount ratio of anhydrous glucose to ethylene glycol is (10-20) g:(15-30) mL, preferably 20 g:30 mL.
[0016] Further, in the step (1), the temperature of magnetic stirring is room temperature, and the time is 4 h; the equipment for carbonization is a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene lining, the temperature is 190℃, and the time is 4 h; the speed of centrifugation is 3500 r / min, and the time is 7 min; the temperature of drying is 80℃, and the time is 6 h; the equipment for calcination is a tube furnace, the atmosphere is N2, the heating rate is 2℃ / min, the temperature is 500℃, and the time is 4 h.
[0017] The further beneficial effect is that the carbon carrier is prepared by the ethylene glycol solvothermal method with anhydrous glucose as a carbon source, the branched structures such as C-C bonds and C-O bonds are reserved on the surface of the carbon carrier due to the mild preparation conditions, these surface groups can improve the Fischer-Tropsch synthesis activity, improve the olefin selectivity, and inhibit the generation of C1 by-products; at the same time, the inertness of the carbon carrier surface makes the interaction between the carbon carrier and the Fe-based catalyst weak, which is beneficial to the reduction of the catalyst and does not affect the intrinsic catalytic performance.
[0018] Further, in the step (2), the mass fraction of H2O2 is 30%; the ratio of the amount of the carbon carrier CS to the amount of H2O2 is (1-4) g:(2.5-50) mL, preferably 4 g:50 mL.
[0019] Further, in the step (2), the temperature of ultrasonic stirring is 60℃, and the time is 4 h.
[0020] The further beneficial effect is that the surface of the carbon carrier is modified by H2O2 to generate oxygen-containing groups such as -OH and C-O on the surface of the carrier, these surface groups not only affect the texture properties of the catalyst, but also change the product distribution by regulating the dispersion, reduction and activation process of the Fe active phase, thereby inhibiting the generation of C1 by-products and the secondary hydrogenation of olefins, improving the selectivity of low-carbon olefins, improving the activity and stability of the catalyst, and improving the product distribution of the Fischer-Tropsch synthesis.
[0021] Further, in the step (3), the concentration of the iron nitrate solution is 0.125 mol / L; the ratio of the amount of CS-H2O2 to the amount of the iron nitrate solution is (1-2) g:(10-20) mL, preferably 2 g:10 mL.
[0022] Further, in the step (3), the time of magnetic stirring is 1 h; the temperature of drying is 80℃, and the time is 6 h; the equipment for calcination is a tube furnace, the atmosphere is N2, the heating rate is 2℃ / min, the temperature is 500℃, and the time is 4 h.
[0023] The further beneficial effect is that the modified carrier is reacted with the iron nitrate solution to prepare the Fe-based catalyst with rich surface groups.
[0024] The application also claims an iron-based catalyst prepared by the above preparation method.
[0025] The application also claims an application of the iron-based catalyst prepared by the above preparation method in Fischer-Tropsch synthesis. Specifically, the iron-based catalyst is used in Fischer-Tropsch synthesis after being ground and sieved, and the reaction conditions are as follows: the iron-based catalyst addition amount is 0.5-5 mL, the reaction temperature is 280-500℃, the reaction pressure is 1.0-5 MPa, the synthesis gas H2 / CO = 2:1, and the gas space velocity is 500-10000 h-1. -1 ; preferably, the reaction conditions are as follows: the iron-based catalyst addition amount is 2 mL, the reaction temperature is 300℃, the reaction pressure is 1.5 MPa, the synthesis gas H2 / CO = 2:1, and the gas space velocity is 1000 h-1. -1 .
[0026] It can be known from the above technical solution that, compared with the prior art, the application has the following beneficial effects:
[0027] 1. The carbon carrier is prepared by a solvothermal method, and the Fe-based catalyst with rich surface groups is constructed through surface modification, so that the selectivity of olefins is improved, and a simple design idea and synthesis strategy are provided for low-cost and large-scale preparation of high-performance Fe-based catalysts.
[0028] 2. The surface groups of the iron-based catalyst are rich, which can effectively improve the problems of high methane selectivity and low olefin selectivity of traditional iron-based catalysts in Fischer-Tropsch synthesis, and realize the regulation of Fischer-Tropsch synthesis product distribution.
[0029] 3. In the Fischer-Tropsch synthesis reaction, the surface groups of the catalyst can promote the dispersion of Fe species, improve the activity and stability of the catalyst, and significantly promote the generation of low-carbon olefins. Under the condition of not adding alkali metal additives, the catalyst effectively breaks through the bottleneck that the product distribution of traditional Fe-based catalysts is limited by the ASF distribution. BRIEF DESCRIPTION OF DRAWINGS
[0030] Figure 1 XRD spectra of the iron-based catalysts of Example 1 and Comparative Examples 1-2;
[0031] Figure 2 FT-IR spectra of the iron-based catalysts of Example 1 and Comparative Examples 1-2. DETAILED DESCRIPTION
[0032] The technical solutions in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.
[0033] Example 1
[0034] The preparation method of the iron-based catalyst specifically comprises the following steps:
[0035] (1) 20 g of anhydrous glucose was weighed, 30 mL of ethylene glycol was measured, the weighed anhydrous glucose was dissolved in the ethylene glycol solution, and magnetic stirring was performed for 4 h to form a glucose solution; the glucose solution was transferred to a stainless steel high-pressure reaction kettle containing polytetrafluoroethylene, carbonization was performed at 190℃ for 4 h, and after the reaction was completed, natural cooling was performed to room temperature; the obtained precipitate was centrifuged at a speed of 3500 r / min for 7 min, washed three times, and then dried at 80℃ for 6 h to obtain a carbon precursor; the carbon precursor was placed in a tube furnace, heated to 500℃ at a heating rate of 2℃ / min, and kept under N2 atmosphere for 4 h to obtain a carbon carrier CS;
[0036] (2) 4 g of the carbon carrier CS was weighed, 50 mL of H2O2 solution with a concentration of 30% was measured, the H2O2 was poured into a beaker containing the carbon carrier CS and ultrasonically treated for 4 h, then washed and dried at 80℃ to obtain CS-H2O2;
[0037] (3) 2 g of CS-H2O2 was dissolved in 10 mL of iron nitrate solution with a concentration of 0.125 mol / L, magnetic stirring was performed for 1 h, and then dried at 80℃ to obtain a catalyst precursor, which was finally placed in a tube furnace, heated to 500℃ at a heating rate of 2℃ / min, and kept under N2 atmosphere for 4 h to obtain an Fe / CS-H2O2 iron-based catalyst with a loading of 5%.
[0038] Comparative Example 1
[0039] The preparation method of the iron-based catalyst is basically the same as that of Example 1, except that the H2O2 of Example 1 is changed to HNO3, and specifically comprises the following steps:
[0040] (1) 20 g of anhydrous glucose was weighed, 30 mL of ethylene glycol was measured, the weighed anhydrous glucose was dissolved in the ethylene glycol solution, and magnetic stirring was performed for 4 h to form a glucose solution; the glucose solution was transferred to a stainless steel high-pressure reaction kettle containing polytetrafluoroethylene, carbonization was performed at 190℃ for 4 h, and after the reaction was completed, natural cooling was performed to room temperature; the obtained precipitate was centrifuged at a speed of 3500 r / min for 7 min, washed three times, and then dried at 80℃ for 6 h to obtain a carbon precursor; the carbon precursor was placed in a tube furnace, heated to 500℃ at a heating rate of 2℃ / min, and kept under N2 atmosphere for 4 h to obtain a carbon carrier CS;
[0041] (2) 4 g of the carbon carrier CS was weighed, 50 mL of H2O2 solution with a concentration of 30% was measured, the H2O2 was poured into a beaker containing the carbon carrier CS and ultrasonically treated for 4 h, then washed and dried at 80℃ to obtain CS-H2O2;
[0042] (3) Weigh 2 g CS-HNO3 and dissolve it in 10 mL of iron nitrate solution with a concentration of 0.125 mol / L, and then magnetically stir for 1 h. After that, dry it at 80°C to obtain a catalyst precursor. Finally, put it into a tube furnace, and then heat it to 500°C at a heating rate of 2°C / min under N2 atmosphere for 4 h to obtain a Fe / CS-HNO3 iron-based catalyst with a loading of 5%.
[0043] Comparative Example 2
[0044] The preparation method of the iron-based catalyst is basically the same as that of Example 1, except that the surface modification step (2) of Example 1 is removed. Specifically, it comprises the following steps:
[0045] (1) Weigh 20 g of anhydrous glucose, and then measure 30 mL of ethylene glycol. Dissolve the weighed anhydrous glucose in the ethylene glycol solution, and then magnetically stir for 4 h to form a glucose solution. Then, transfer the glucose solution into a stainless steel high-pressure reaction kettle with polytetrafluoroethylene, and then carbonize it at 190°C for 4 h. After the reaction is completed, naturally cool it to room temperature. Then, centrifuge the obtained precipitate at a speed of 3500 r / min for 7 min, and then wash it three times. After that, dry it at 80°C for 6 h to obtain a carbon precursor. Then, put the carbon precursor into a tube furnace, and then heat it to 500°C at a heating rate of 2°C / min under N2 atmosphere for 4 h to obtain a carbon carrier CS.
[0046] (2) Weigh 2 g of CS and dissolve it in 10 mL of iron nitrate solution with a concentration of 0.125 mol / L, and then magnetically stir for 1 h. After that, dry it at 80°C to obtain a catalyst precursor. Finally, put it into a tube furnace, and then heat it to 500°C at a heating rate of 2°C / min under N2 atmosphere for 4 h to obtain a Fe / CS iron-based catalyst with a loading of 5%.
[0047] Performance test
[0048] 1. XRD analysis
[0049] The XRD spectra of the iron-based catalysts of Example 1 and Comparative Examples 1-2 are shown in Figure 1 .
[0050] From the XRD spectra of the iron-based catalysts of Example 1 and Comparative Examples 1-2, it can be seen that the catalysts of Example 1 and Comparative Examples 1-2 are all iron-based catalysts. Figure 1It can be seen that the diffraction peaks at 2θ of 43.12° and 24.38° correspond to carbon; the broadened diffraction peaks reflect the typical characteristics of amorphous materials. The diffraction peaks at 2θ of 30.12° (220), 35.48° (311), 43.01° (400), 57.02° (511) and 62.62° (440) all correspond to the characteristic diffraction peaks of Fe3O4. According to the Scherrer formula, the grain sizes of Fe / CS, Fe / CS-H2O2, and Fe / CS-HNO3 are 60.3nm, 59.6nm, and 48.69nm, respectively. After surface modification, the grain size of the catalysts decreased, indicating that surface modification can promote the dispersion of the Fe active phase on the support. In addition, the diffraction peaks in the XRD spectrum are sharp and free of impurity peaks, indicating that the synthesized catalysts have high crystallinity and relatively complete crystal shape.
[0051] 2. FT-IR analysis
[0052] The FT-IR spectra of the iron-based catalysts of Example 1 and Comparative Examples 1-2 are as follows: Figure 2 shown.
[0053] Depend on Figure 2 It can be seen that the figure reflects the types of surface functional groups and surface chemical structures of the catalyst before and after modification. -1 、1630cm -1 The broad peak at 3440 cm corresponds to the vibration peak of -OH on the catalyst surface. -1 The broad peak originates from the hydroxyl groups of adsorbed water. After modification, the intensity of the broad peak increases, indicating that the number of -OH groups on the catalyst surface increases. -1 、2850cm -1 The vibration peaks at 1460 cm are the -CH and -CH2 stretching vibration peaks remaining on the surface of the carbon support after carbonization of anhydrous glucose. After loading the Fe active phase, the vibration peak intensity weakens, which is due to the removal of some surface groups by high-temperature calcination in a N2 atmosphere. -1 The peak at 1390 cm is attributed to the deformation vibration of the OH bond on the carboxyl group. -1 The peak at 870 cm corresponds to the carboxyl carbonate structure on the catalyst surface. -1 The peak at 566cm is the characteristic peak of CH bond. -1 The Fe-O stretching vibration peak at confirms the presence of an Fe active phase in all three catalysts, which is consistent with the aforementioned XRD analysis results. In summary, the FT-IR analysis results indicate that the catalysts surface-modified with different reagents contain a variety of oxygen-containing functional groups.
[0054] 3. Fischer-Tropsch synthesis reaction
[0055] (1) The iron-based catalysts of Example 1 and Comparative Examples 1-2 were ground and sieved, and then used for Fischer-Tropsch synthesis reaction evaluation.
[0056] A micro fixed-bed reactor was used, 2 mL of the catalyst was loaded into the reaction tube constant temperature zone, and a raw material gas of H2 / CO = 2:1 was introduced, under the conditions of a reaction temperature of 300°C, a pressure of 1.5 MPa, a gas space velocity (GHSV) of 1000 h-1. After the system reached a steady state, sampling and analysis were started, with a sampling interval of 2 h. Gas chromatography was used for qualitative and quantitative analysis of the raw material gas and the products, and the CO conversion rate and the selectivity of each product component were calculated by the methane correlation method. The results are shown in Table 1. -1
[0057] Table 1 Process parameters and performance test results of Fischer-Tropsch synthesis reaction of iron-based catalysts of Examples 1-3
[0058]
[0059] As can be seen from Table 1, the selectivity of CH4 and CO2 was significantly reduced in the Fischer-Tropsch synthesis of the Fe-based catalysts after surface modification, and the CO conversion rate was significantly improved compared with the unmodified catalyst. The hydrocarbon product changed significantly, among which the Fischer-Tropsch synthesis performance of the Fe / CS-H2O2 iron-based catalyst prepared in Example 1 was the best, with a low-carbon olefin selectivity of 43.57% and an olefin / alkane ratio (O / P) of 2.04.
[0060] (2) The iron-based catalyst prepared in Example 1 was used for multiple Fischer-Tropsch synthesis reaction tests. The results are shown in Table 2.
[0061] Table 2 Process parameters and performance test results of multiple Fischer-Tropsch synthesis reactions of the iron-based catalyst of Example 1
[0062]
[0063] As can be seen from Table 2, after the performance evaluation of the Fe / CS-H2O2 iron-based catalyst prepared in Example 1 for multiple reactions, it was found that the product distribution was uniform, the test result error was small, indicating that the catalyst had good evaluation effect reproducibility and high stability.
[0064] In summary, the catalyst of the present application can promote the dissociative adsorption of CO, which is helpful to form hydrocarbon species involved in hydrogenation reaction. After treatment by H2O2 oxidizing agent, the dispersion of Fe active phase on carbon support is improved, thereby improving the CO conversion rate and the selectivity of low-carbon olefins. There are abundant oxygen-containing groups on the surface of the catalyst of the present application, which not only affect the texture properties of the catalyst, but also affect the dispersion, reduction and activation of the active phase, thereby affecting the product distribution. In FTS, it can inhibit the generation of C1 by-products, regulate chain growth, reduce the secondary hydrogenation ability of olefins, thereby improving the selectivity of low-carbon olefins. Without adding alkali metal additives, the catalyst of the present application effectively improves the problem that the product distribution of traditional Fe-based catalyst is limited by ASF distribution.
[0065] The above description of disclosed embodiments enables one of ordinary skill in the art to make and use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A method for preparing an iron-based catalyst, characterized in that: The specific steps include: (1) Anhydrous glucose was dissolved in ethylene glycol, subjected to magnetic stirring, carbonized, cooled, centrifuged, washed, dried, and calcined to obtain a carbon support CS; (2) adding H2O2 to the carbon support CS, ultrasonically stirring, washing, and drying to obtain CS-H2O2; (3) dissolving CS-H2O2 in ferric nitrate solution, stirring with magnetic force, drying, and calcining to obtain the Fe / CS-H2O2 iron-based catalyst.
2. The method for preparing an iron-based catalyst according to claim 1, wherein In step (1), the usage ratio of anhydrous glucose and ethylene glycol is (10-20) g: (15-30) mL.
3. The method for preparing an iron-based catalyst according to claim 1, wherein: In step (1), the temperature of the magnetic stirring is room temperature and the time is 4 hours; the carbonization equipment is a stainless steel high-pressure reactor lined with polytetrafluoroethylene, the temperature is 190°C, and the time is 4 hours; the centrifugal rate is 3500r / min, and the time is 7 minutes; the drying temperature is 80°C, and the time is 6 hours; the calcination equipment is a tubular furnace, the atmosphere is N2, the heating rate is 2°C / min, the temperature is 500°C, and the time is 4 hours.
4. The method for preparing an iron-based catalyst according to claim 1, wherein In step (2), the mass fraction of H2O2 is 30%; the usage ratio of the carbon support CS and H2O2 is (1-4) g: (2.5-50) mL.
5. The method for preparing an iron-based catalyst according to claim 1, wherein: In step (2), the temperature of the ultrasonic stirring is 60° C. and the time is 4 h.
6. The method for preparing an iron-based catalyst according to claim 1, characterized in that: In step (3), the concentration of the ferric nitrate solution is 0.125 mol / L; the usage ratio of the CS-H2O2 and the ferric nitrate solution is (1-2) g: (10-20) mL.
7. The method for preparing an iron-based catalyst according to claim 1, characterized in that: In step (3), the magnetic stirring time is 1 hour; the drying temperature is 80°C and the time is 6 hours; the calcination equipment is a tubular furnace, the atmosphere is N2, the heating rate is 2°C / min, the temperature is 500°C, and the time is 4 hours.
8. An iron-based catalyst prepared by the preparation method according to any one of claims 1 to 7.
9. Use of the iron-based catalyst prepared by the preparation method according to any one of claims 1 to 7 in Fischer-Tropsch synthesis.
10. The use according to claim 9, characterized in that The iron-based catalyst was ground and sieved and then used for Fischer-Tropsch synthesis. The reaction conditions were as follows: 0.5-5 mL of iron-based catalyst was added, the reaction temperature was 280-500°C, the reaction pressure was 1.0-5 MPa, the synthesis gas H2 / CO was 2:1, and the gas space velocity was 500-10000 h -1 .