Hollow ceramic fibrous iron-based catalyst for the production of biofuel from syngas and its preparation method and application

Abstract

The present application belongs to the field of heterogeneous catalysis and material synthesis, and relates to a hollow ceramic fibrous iron-based catalyst for preparing biofuel from synthesis gas, a preparation method and application thereof. The catalyst is prepared by a coaxial electrospinning process, with polyborosilazane as a shell layer, polymethyl methacrylate, polyvinylpyrrolidone and acetylacetone iron as a core layer, and through spinning, solidification, gradient temperature pyrolysis and reduction steps, a hollow ceramic fibrous iron-based catalyst is prepared. The shell layer of the catalyst is converted into a high-strength and high-temperature stable SiBCN ceramic carrier, the core layer is pyrolyzed to form a hollow cavity and in-situ load high-dispersion iron active species, and the catalyst has good mechanical strength, high hydrothermal stability and excellent catalytic activity. The application of the catalyst in a continuous flow fixed bed reactor for preparing biofuel from synthesis gas is suitable for the synthesis of sustainable aviation fuel and other biofuels.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalysis and materials synthesis, specifically relating to a hollow ceramic fibrous iron-based catalyst for the production of biofuel from syngas, its preparation method, and its application. Background Technology

[0002] Biofuels, as an important source of sustainable aviation fuel (SAF) and clean transportation fuel, require efficient and green synthesis technologies that have become an urgent need in the energy and chemical industry. The catalytic conversion of syngas (CO+H2) to produce biofuels (especially CO2-based biofuels) is a key technology. 10 –C 20 High-carbon hydrocarbon (HCH) catalysts represent a promising technological route, with the core being the development of highly efficient catalysts possessing high activity, high selectivity, and high stability. However, traditional supported catalysts generally face problems such as easy sintering of active metals, easy collapse of the support structure, and low mass transfer efficiency under harsh reaction conditions of long-term high temperature, high pressure, and the presence of water vapor. This results in poor catalyst stability, unsatisfactory product selectivity, and short service life, severely restricting their industrial applications. Therefore, how to construct a catalyst system with stable structure, highly dispersed active sites, and excellent mass transfer performance has become a key technological bottleneck that urgently needs to be overcome in this field.

[0003] Currently, research on syngas-to-biofuel conversion largely focuses on Fischer-Tropsch catalysts such as iron-based and cobalt-based catalysts. Iron-based catalysts have attracted much attention due to their low cost and suitable activity in water-gas shift reaction (FTS), and common forms include supported particles and monolithic catalysts. However, existing technologies still have significant limitations. For example, patent CN120515455A uses atomic layer deposition combined with carburizing to construct molybdenum carbide nanoparticles on carbon nanofibers. Although this method is precise and controllable, the carbon support is prone to oxidation, corrosion, and structural collapse in the high-temperature, high-pressure, and water-containing reaction environment, leading to the loss of active sites. Secondly, Chinese patent CN120571620A uses ZIF precursor encapsulation and high-temperature carbonization to derive porous carbon materials with Co-N / P coordination. However, its fine pore structure is prone to collapse or blockage under the harsh hydrothermal conditions of long-term FTS, resulting in the embedding of active sites and hindering reaction mass transfer. While Chinese patent CN120695820A optimized the dispersion of cobalt on oxide supports such as SiO2 through impregnation and vacuum calcination, traditional oxide supports are prone to phase transformation, sintering, or strong interaction with active metals in high-temperature hydrothermal environments, which can also lead to catalyst structural instability and activity decay.

[0004] To address the aforementioned issues, Chinese patent CN106391016A discloses a Fischer-Tropsch synthesis monodisperse iron-based catalyst, employing a CO2-induced microemulsion method to synthesize a Fe@SiO2 core-shell structure. While this achieves uniform dispersion of iron nanoparticles, the spherical particle structure easily causes significant pressure drop in the packed bed, and the SiO2 support may undergo surface hydroxyl condensation under high-temperature hydrothermal conditions, leading to pore collapse. Chinese patent CN111905791A discloses an iron-based catalyst for the preparation of higher alcohols from syngas, using melamine to form g-C3N4 to stabilize the iron nitride active phase. However, this catalyst is in powder form and requires subsequent molding, which may damage the microstructure, and the stability of the carbonitrides during the reaction needs further verification. Chinese patent CN120425370A uses coaxial electrospinning technology to prepare a self-supporting hollow carbon film electrode for water electrolysis to produce hydrogen. However, its carbon support is prone to oxidation and corrosion in the high-temperature aqueous atmosphere of FTS, making it difficult to directly apply to the production of biofuels from syngas.

[0005] In addition, some studies have attempted to encapsulate active components within hollow or porous carbon fibers to improve mass transfer efficiency and optimize product distribution using confinement effects (e.g., Chinese patents CN117779238A and CN112863895A). However, these materials mostly use polyacrylonitrile (PAN) as the carbon source, and the carbon support itself lacks sufficient oxidation resistance and hydrothermal stability. Furthermore, the active components are mostly post-loaded or in-situ grown, making it difficult to achieve a balance between high dispersion of active sites and structural stability.

[0006] Therefore, how to construct a catalyst system that combines excellent mass transfer performance, high dispersion of active centers, and long-term structural stability has become a key technical bottleneck that urgently needs to be solved in this field. Summary of the Invention

[0007] Based on the shortcomings of existing technologies, this invention aims to develop a hollow ceramic fibrous iron-based catalyst for the synthesis of biofuel from syngas, along with its preparation method and application, through innovation in material design and preparation processes. This catalyst uses highly stable SiBCN ceramic as a support framework and combines coaxial electrospinning and programmed heat treatment technologies to achieve in-situ high dispersion loading of iron species while constructing interconnected hollow channels. This simultaneously improves the catalyst's mechanical strength, mass transfer efficiency, and reaction selectivity, further enhancing the catalyst's stability in the FTS biofuel production process while ensuring high activity and selectivity.

[0008] The technical solution of the present invention is as follows: The first aspect of this invention provides a method for preparing a hollow ceramic fibrous iron-based catalyst for the production of biofuel from syngas, comprising the following steps: (1) Preparation of shell spinning solution: Dissolve polyborosilicate (PBSZ) in an organic solvent to obtain solution A; dissolve the spinning aid in an organic solvent to obtain solution B; mix solution A and solution B evenly to obtain shell spinning solution for coaxial electrospinning; (2) Preparation of core spinning solution: Dissolve the pore-forming agent, spinning aid and iron source in an organic solvent and stir evenly to obtain the core spinning solution for coaxial electrospinning; (3) Coaxial electrospinning: The core spinning solution and the shell spinning solution are coaxially electrospinned and collected on a receiving device to obtain iron-containing hollow polymer fiber precursors; (4) Curing and crosslinking: The hollow polymer fiber precursor is subjected to step heating heat treatment in an air atmosphere to evaporate the residual solvent and cure and crosslink it to obtain iron-containing hollow polymer fiber. (5) Pyrolysis and reduction: The iron-containing hollow polymer fibers are pyrolyzed under a flowing inert atmosphere and then reduced under a flowing hydrogen atmosphere to obtain the hollow ceramic fiber iron-based catalyst.

[0009] Preferably, the iron source is iron acetylacetone; the spinning aid includes any one or a combination of two or more of polyvinylpyrrolidone, polyethylene oxide, and cellulose acetate; the organic solvent includes any one or a combination of two or more of tetrahydrofuran, xylene, N,N-dimethylformamide, and isopropanol; and the pore-forming agent is any one or a combination of two or more of polymethyl methacrylate, polystyrene, citric acid, and polyethylene glycol.

[0010] Preferably, the mass ratio of polyborosilazane, organic solvent and spinning aid in step (1) is 5-7:8-10:2.8-4.

[0011] Preferably, the mass ratio of the pore-forming agent, spinning aid, iron source and organic solvent in step (2) is 1-2:2.8-4:1.5-2.5:10-12.

[0012] Preferably, the main process parameters for coaxial electrospinning in step (3) are: voltage of 10-20 kV, drum speed of 180-200 rpm, receiving distance of 10-20 cm, core spinning solution flow rate of 0.4-0.8 mL / h, shell spinning solution flow rate of 1.2-2.4 mL / h, and spinning temperature of 10-40 ℃. Further, the optimal flow rate ratio of the core spinning solution to the shell spinning solution is 1:3.

[0013] Preferably, the specific procedure for the stepped heating heat treatment in step (4) is as follows: heat to 100-120 ℃ at a heating rate of 5-10 ℃ / min, and keep at this temperature for 3-5 h, during which the pore-forming agent is kept stable; then heat to 200-250 ℃ at a heating rate of 2-5 ℃ / min, and heat treat at this temperature for 3-6 h to ensure that the organic solvent is completely evaporated.

[0014] Preferably, the pyrolysis in step (5) is as follows: under the protection of a flowing inert atmosphere, the temperature is increased from room temperature to 400-450 ℃ at a heating rate of 5-10 ℃ / min, and held at this temperature for 1-3 h. During this process, the pore-forming agent undergoes thermal decomposition and forms hollow pores. Then, the temperature is increased to 700-1200 ℃ at a heating rate of 1-3 ℃ / min, and held at this temperature for 3-6 h. Then, the temperature is reduced at 600-700 ℃ for 3-6 h in a hydrogen atmosphere. The gas hourly space velocity of both the inert atmosphere and the hydrogen is 600-1800 h⁻¹. –1 .

[0015] A second aspect of the present invention provides a hollow ceramic fibrous iron-based catalyst, which is prepared using the above-described preparation method.

[0016] The third aspect of the present invention provides the application of the above-mentioned hollow ceramic fibrous iron-based catalyst in the synthesis gas to biofuel reaction.

[0017] Preferably, the specific steps of the application are as follows: The catalyst is loaded into the catalyst bed of a continuous flow high-pressure fixed-bed reactor, and preheating layers are placed above and below the catalyst bed. The reactor is then activated at 400-550 °C for at least 1 h under a flowing hydrogen atmosphere. Subsequently, the catalyst bed is cooled to a reaction temperature of 250-350 °C, the hydrogen supply is shut off, and syngas is introduced with a gas hourly space velocity (GHSV) of 1200-12000 h⁻¹. –1 The pressure is 2.0-4.0 MPa.

[0018] The advantages and beneficial effects of this invention are: 1. Integrated and precise structural design: Using coaxial electrospinning technology, polymer fiber precursors with well-defined hollow structures are prepared. Subsequent heat treatment simultaneously achieves carrier molding, hollow structure construction, and highly dispersed loading of active sites, realizing the integrated and precise construction of the catalyst's macroscopic structure and microscopic active centers. The process is simple and has good repeatability.

[0019] 2. Excellent performance and high stability of the support material: Polyborosilazane (PBSZ) is selected as the precursor of the shell ceramic. The B and N elements in the SiBCN support have a unique chemical anchoring effect and a suitable metal-support interaction with the iron active species. The interaction is neither too strong nor too weak. Its pyrolysis product, SiBCN ceramic, has excellent high-temperature hydrothermal stability, oxidation resistance and mechanical strength. It can effectively resist carbon deposition and structural collapse during the reaction process, and significantly improve the long-term stability of the catalyst in harsh reactions such as syngas to biofuel production.

[0020] 3. Optimized Iron Source Selection and Ratio for Better Active Site Formation: Using iron acetylacetone as the iron source offers advantages such as good solubility in solvents and thermal decomposition behavior that matches the polymer. This facilitates the stable formation of hollow structures during pyrolysis and the in-situ generation of highly dispersed iron-based active species, enhancing catalytic activity. Compared to traditional iron salts such as ferric nitrate and ferric chloride, iron acetylacetone avoids the damage to the fiber structure caused by violent decomposition and gas release during pyrolysis. This ensures that iron species are in-situ and uniformly loaded within the ceramic support while the pore-forming agent decomposes to form a hollow structure. SEM characterization shows that the iron nanoparticles are highly dispersed on the inner wall of the hollow fibers, with no obvious agglomeration, providing abundant active sites for the catalytic reaction.

[0021] 4. A rational heat treatment process ensures intact morphology: A stepped heating heat treatment process is employed, first thoroughly removing residual solvent at 100-120 °C, then curing and crosslinking in air at 200-250 °C, significantly improving the thermal stability of the precursor fibers. This segmented treatment ensures that during subsequent gradient heating pyrolysis, the polymethyl methacrylate pore-forming agent decomposes in an orderly manner to form a regular hollow structure, while the iron source is uniformly diffused and distributed within the ceramic matrix. Compared to direct rapid heating, the heat treatment process of this invention maintains the integrity of the fiber morphology, avoids structural defects, and provides a process guarantee for the controllable preparation of hollow structures.

[0022] 5. Programmed Atmosphere Control and Precise Active Phase Regulation: A step-by-step treatment method of "inert atmosphere pyrolysis + hydrogen atmosphere reduction" is employed. First, PBSZ is fully ceramized in an inert atmosphere to form a stable SiBCN support framework. Then, hydrogen reduction converts the iron species into the active iron phase. Compared to the traditional one-step hydrogen pyrolysis, this step-by-step method avoids interference between support ceramization and active phase reduction, achieving precise control over the chemical state and dispersion of the active iron species. Comparative verification shows that the catalyst obtained through this step-by-step treatment exhibits superior active phase dispersion and catalytic selectivity.

[0023] 6. Optimized spinning process parameters for reproducible structure fabrication: Through systematic optimization of key parameters in coaxial electrospinning (receiving distance, voltage, and core / shell flow rate ratio), stable coaxial co-spinning of the core spinning solution (containing iron source and pore-forming agent) and the shell spinning solution (containing PBSZ) was achieved. In particular, a 1:3 core / shell flow rate ratio ensured the reproducible fabrication of fiber precursors with clear, continuous, and uniform core-shell structures, providing process assurance for the controllable construction of hollow structures and the consistency of catalyst performance. Comparative verification showed that deviations from this flow rate ratio resulted in structural defects such as incomplete core-shell structures and uneven fiber diameters.

[0024] 7. Hollow Structure Enhances Mass Transfer and Product Selectivity: The hollow fiber structure of the catalyst provides efficient mass transfer channels for reactants and products. Simultaneously, its internal cavities have a spatial confinement effect on reaction intermediates, inhibiting premature desorption of low-carbon hydrocarbons and promoting carbon chain growth, thereby increasing C0.05. 10 -C 20 Selectivity for higher carbon hydrocarbons. Attached Figure Description

[0025] Figure 1 This is a process flow diagram for preparing hollow ceramic fibrous iron-based catalysts according to the present invention; Figure 2 SEM image of the hollow ceramic fibrous iron-based catalyst prepared in Example 1; Figure 3 SEM image of the hollow ceramic fibrous iron-based catalyst prepared in Comparative Example 5; Figure 4 SEM image of the hollow ceramic fibrous iron-based catalyst prepared in Comparative Example 8. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific implementation examples. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0027] Example 1 A method for preparing a hollow ceramic fibrous iron-based catalyst includes the following steps: (1) Preparation of shell spinning solution: 5 g of polyborosilazane was dissolved in 8 g of tetrahydrofuran and stirred thoroughly until homogeneous to prepare solution A. Next, 3 g of isopropanol and 1.5 g of N,N-dimethylformamide were mixed and stirred thoroughly. Then, 2.8 g of polyvinylpyrrolidone was added to this mixed solvent and stirred thoroughly to obtain solution B. Solution A and solution B were mixed and stirred for 2 h to obtain shell spinning solution.

[0028] (2) Preparation of core spinning solution: Add 1 g of polymethyl methacrylate and 1.5 g of iron acetylacetonate to 10 g of N,N-dimethylformamide and stir thoroughly. Then add 3.2 g of polyvinylpyrrolidone and stir for 2 h to obtain the core spinning solution.

[0029] (3) Perform coaxial electrospinning. Place the shell spinning solution and the core spinning solution on the electrospinning machine, adjust the electrospinning process parameters, connect the high voltage power supply, start the electrospinning process, and receive the iron-containing hollow polymer fiber precursor through the receiving device. The process parameters of coaxial electrospinning are: voltage of 18 kV, drum speed of 180 rpm, material collection distance of 20 cm, core spinning solution flow rate of 0.8 mL / h, and shell spinning solution flow rate of 2.4 mL / h.

[0030] (4) Curing and crosslinking: The iron-containing hollow polymer fiber precursor is heated to 120 °C at a heating rate of 10 °C / min and kept at this temperature for 5 h. During this stage, the polymethyl methacrylate pore-forming agent is kept stable. Then, it is heated to 250 °C at a heating rate of 5 °C / min and heat-treated at this temperature for 3 h to ensure that the organic solvent is completely evaporated, thus obtaining the iron-containing hollow polymer fiber.

[0031] (5) High-temperature pyrolysis and reduction: Under the protection of a flowing inert atmosphere, the iron-containing hollow polymer fibers were heated from room temperature to 450 ℃ at a heating rate of 10 ℃ / min and held at this temperature for 1 h. During this process, the polymethyl methacrylate pore-forming agent underwent thermal decomposition and formed hollow pores. Then, the temperature was increased to 700 ℃ at a heating rate of 3 ℃ / min and held at this temperature for 3 h. The reduction temperature under a hydrogen atmosphere was 600 ℃ and held at this temperature for 3 h. The gas hourly space velocity of both the inert atmosphere and hydrogen was 600 h⁻¹. –1 Hollow ceramic fibrous iron-based catalyst was obtained.

[0032] SEM image of the hollow ceramic fibrous iron-based catalyst prepared in Example 1 is shown below. Figure 2 As shown, from Figure 2 The hollow structure of the fiber can be clearly observed, and the iron nanoparticles are uniformly dispersed on the inner wall surface of the fiber without obvious agglomeration, providing abundant active centers for catalytic reactions.

[0033] Example 2 The difference from Example 1 is that the amount of polyborosilazane added in step (1) is 6 g.

[0034] Example 3 The difference from Example 1 is that the amount of pore-forming agent polymethyl methacrylate added in step (2) is 2 g.

[0035] Example 4 The difference from Example 1 is that the amount of iron acetylacetone added in step (2) is 2.5 g.

[0036] Example 5 The difference from Example 1 is that the pyrolysis temperature in step (5) is 1200 °C.

[0037] Example 6 The difference from Example 1 is that the hydrogen reduction temperature in step (5) is 700 °C.

[0038] Comparative Example 1 The only difference from Example 1 is that in step (1), polyborosilicate is replaced with polycarbosilane.

[0039] Comparative Example 2 The only difference from Example 1 is that the pyrolysis temperature in step (5) is increased to 1600 °C.

[0040] Comparative Example 3 The only difference from Example 1 is that the hydrogen reduction temperature in step (5) is increased to 1000 °C.

[0041] Comparative Example 4 The only difference from Example 1 is that iron acetylacetone in step (2) is replaced with iron oxalate.

[0042] Comparative Example 5 The only difference from Example 1 is that the stepped heating in step (5) is replaced with a single heating. Specifically, under the protection of a flowing inert atmosphere, the cured iron-containing hollow polymer fibers are heated from room temperature to 700 ℃ at a heating rate of 10 ℃ / min and held at this temperature for 3 h; the reduction temperature under a hydrogen atmosphere is 600 ℃ and held at this temperature for 3 h; the gas hourly space velocity of both the inert atmosphere and hydrogen is 600 h⁻¹. –1 Hollow ceramic fibrous iron-based catalyst was obtained.

[0043] SEM image of the hollow ceramic fibrous iron-based catalyst prepared in Comparative Example 5 is shown below. Figure 3 As shown. From Figure 3 It can be seen that direct pyrolysis by heating in one step leads to obvious defects in the fiber structure, with some areas of the hollow structure collapsing or deforming. This indicates that stepped heating is crucial for maintaining the integrity of the hollow structure and the uniform dispersion of the active components.

[0044] Comparative Example 6 The only difference from Example 1 is that iron acetylacetonate in step 2 is replaced with cobalt acetylacetonate.

[0045] Comparative Example 7 The only difference from Example 1 is that iron acetylacetone in step 2 is replaced with ruthenium acetylacetone.

[0046] Comparative Example 8 The only difference from Example 1 is that polymethyl methacrylate is not added in step 2.

[0047] SEM image of the hollow ceramic fibrous iron-based catalyst prepared in Comparative Example 8 is shown below. Figure 4 As shown. From Figure 4 It can be observed that, due to the absence of polymethyl methacrylate pore-forming agent, a regular hollow structure could not be formed inside the fiber, and the whole structure was solid or dense. This indicates that the pore-forming agent is a key factor in the construction of the hollow structure.

[0048] Comparative Example 9 The only difference from Example 1 is that the flow rates of the core spinning solution and the shell spinning solution in step 3 are changed, specifically: the flow rate of the core spinning solution is 1 mL / h and the flow rate of the shell spinning solution is 3 mL / h.

[0049] Performance Testing and Analysis The hollow ceramic fibrous iron-based catalysts prepared in Examples 1-6 and Comparative Examples 1-9 were loaded into a continuous flow fixed-bed hydrogenation reactor at a catalyst loading rate of 1.0 g. The bed was filled with inert quartz sand on both the top and bottom. After loading, in-situ reduction pretreatment was first performed at atmospheric pressure and a gas hourly space velocity of 600 h⁻¹. –1 The temperature was increased to 500 °C at a rate of 5 °C / min and held for 3 h under a hydrogen atmosphere. After reduction, the temperature was lowered to 280 °C, then the hydrogen supply was shut off and the feedstock for hydrogenation was switched. The reaction was carried out at a temperature of 280 °C, a pressure of 4.0 MPa, and a gas hourly space velocity of 3000 h⁻¹. –1 Under the specified conditions, syngas (H2:CO volume ratio of 2.0:1) was introduced into the reactor and operated continuously for 50 h. Catalyst performance was evaluated by CO conversion, target product selectivity, and catalyst stability.

[0050] Stability was characterized by continuous operation for 50 hours. This 50-hour reaction time was chosen because preliminary experiments showed that catalyst deactivation mainly occurred within the first 50 hours. This time window effectively reflects the initial deactivation trend and carbon deposition behavior of the catalyst, while also considering efficiency evaluation, making it suitable for catalyst screening and comparison. Samples were taken every hour for analysis, and the rate of conversion decrease over time was calculated. All tests were performed in at least two parallel experiments, and the results were the arithmetic mean.

[0051] CO conversion rate ( X CO ） According to the raw gas ( F CO,in ) and CO concentration in exhaust gas (F CO,out The concentration difference is calculated using the following formula: C 10 -C 20 Selectivity ( S C10-C20 ) is defined as the total number of carbon moles (n) of hydrocarbons with 10-20 carbon atoms in the product. C10-C20 ) as a percentage of the total carbon moles of all hydrocarbons (n 总烃） The percentage is calculated using the following formula: Conversion rate decline rate ( R deact The absolute value of the slope of the linear fit of CO conversion rate with time within the reaction interval of 38-50 h is taken, and the formula is: Where h represents hours, This represents the CO conversion rate at a reaction time of x hours within a reaction range of 38–50 h. This represents the CO conversion rate within a reaction range of 38–50 h, at a reaction time of x+12 hours.

[0052] During the continuous reaction period of 38–50 h for each catalyst group, C 10 -C 20 The results of hydrocarbon selectivity, CO conversion, and the rate of decrease in catalyst conversion per hour are shown in Table 1.

[0053] Table 1. Data on the role of catalysts in the preparation of SAF.

[0054] As shown in Table 1, examples 1-6 demonstrate that, within the preparation parameter range described in this invention, the obtained hollow ceramic fibrous iron-based catalysts all exhibit excellent catalytic performance. Example 1 showed the best performance, with C... 10 –C 20 The hydrocarbon selectivity reached 61.20%, the CO conversion rate was 71.05%, and the conversion rate decreased at a rate of only 0.015%, demonstrating high selectivity, high activity, and excellent stability. Examples 2-6 adjusted the dosage of polyborosilazane, the amount of pore-forming agent, the iron content, the pyrolysis temperature, and the reduction temperature, respectively. Although the performance fluctuated slightly, it remained at a high level, verifying the rationality of the process window of this invention.

[0055] The analysis of the results of Comparative Examples 1-8 above shows that catalyst performance is affected by multiple factors synergistically, mainly including: support composition, pyrolysis and reduction temperatures, metal type, iron source selection, stepped heating process, and hollow structure design. This invention achieves C through precise matching and synergistic optimization of these factors. 10 –C 20 Hydrocarbons exhibit high selectivity and high stability.

[0056] Comparative Example 1 replaced polyborosilazane with polycarbosilane, its C 10 –C 20 The hydrocarbon selectivity decreased to 45.30%, the CO conversion rate decreased to 55.20%, and the rate of decrease in conversion rate per hour increased to 0.12%, indicating that element B is not inert. It changes the acidity and basicity and electronic properties of the support surface in synergy with element N, thereby achieving chemical anchoring and electronic modulation of iron species, thus significantly improving catalytic performance.

[0057] Comparative Examples 2 and 3 showed significant performance degradation when the pyrolysis temperature was increased to 1600 °C and the reduction temperature to 1000 °C, respectively. 10 –C 20 Hydrocarbon selectivity decreased to 44.10% and 42.90%, respectively, and the conversion rate decreased by 0.17% and 0.21% per h, respectively. This indicates that excessively high pyrolysis temperature leads to densification of the SiBCN support structure, a decrease in specific surface area, and excessive sintering of iron species. Excessively high reduction temperature destroys the iron-support interface structure, which is not conducive to the stable existence of the active iron carbide phase. In Comparative Example 4, when the iron source was replaced with other iron sources, the selectivity and conversion rate also decreased significantly. This indicates that there are multiple synergistic effects between the SiBCN support and specific iron sources. Using other iron sources may cause defects in fiber morphology, obvious agglomeration of iron particles, and a significant decrease in activity.

[0058] Combining Table 1 and Figure 3 Analysis shows that Comparative Example 5 indicates that replacing the stepped heating process with a single heating process causes defects and structural collapse on the fiber surface, leading to a deterioration in catalyst performance. Comparative Examples 6 and 7, which replaced the iron source with a cobalt source and a ruthenium source respectively, showed performance significantly lower than in Example 1. 10 –C 20 Hydrocarbon selectivity was 39.30% and 38.10%, respectively, and the conversion rate decreased by as much as 0.34% and 0.39% per hour, respectively, strongly demonstrating a specific synergistic effect between the SiBCN support and iron. This synergy cannot be reproduced by other metals such as cobalt and ruthenium, reflecting the uniqueness and inventiveness of the metal-support combination of this invention; Figure 4 As shown, in Comparative Example 8, the core layer without the addition of the pore-forming agent polymethyl methacrylate forms a solid structure, resulting in a conversion rate of 42.60% and C. 10 –C 20The hydrocarbon selectivity decreased to 36.90%, indicating that the confinement effect provided by the hollow structure plays a crucial role in regulating product distribution and suppressing the formation of low-carbon hydrocarbons. In Comparative Example 9, increasing the flow rates of the core spinning solution and the shell spinning solution altered the fiber wall thickness, resulted in uneven iron distribution, and exhibited the worst performance, demonstrating that a reasonable flow rate ratio is critical for forming a uniform hollow structure.

[0059] Therefore, this invention achieves C by selecting SiBCN ceramic precursor, constructing hollow fiber structure, optimizing pyrolysis and reduction processes, and utilizing the multiple synergistic effects between iron and SiBCN support. 10 –C 20 The invention exhibits superior performance with a hydrocarbon selectivity greater than 60% and a conversion rate greater than 70%. Comparative examples, considering factors such as carrier composition, metal type, process parameters, and structural design, fully demonstrate the synergy and irreplaceability of the technical solution, achieving unexpected technical results.

[0060] The embodiments of the present invention have been described in detail above, but the above description is only a preferred embodiment of the present invention and should not be construed as limiting the scope of protection of the present invention. Any equivalent modifications or improvements made based on the substantial content of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a hollow ceramic fibrous iron-based catalyst for the production of biofuel from syngas, characterized in that, Includes the following steps: (1) Preparation of shell spinning solution: Dissolve polyborosilicate in an organic solvent to obtain solution A; dissolve the spinning aid in an organic solvent to obtain solution B; mix solution A and solution B evenly to obtain shell spinning solution for coaxial electrospinning; (2) Preparation of core spinning solution: Dissolve the pore-forming agent, spinning aid and iron source in an organic solvent and stir evenly to obtain the core spinning solution for coaxial electrospinning; (3) Coaxial electrospinning: The core spinning solution and the shell spinning solution are coaxially electrospinned and collected on a receiving device to obtain iron-containing hollow polymer fiber precursors; (4) Curing and crosslinking: The hollow polymer fiber precursor is subjected to step heating heat treatment in an air atmosphere to obtain iron-containing hollow polymer fibers; (5) Pyrolysis and reduction: The iron-containing hollow polymer fibers are pyrolyzed under a flowing inert atmosphere and then reduced under a flowing hydrogen atmosphere to obtain the hollow ceramic fiber iron-based catalyst.

2. The preparation method according to claim 1, characterized in that, The iron source is iron acetylacetone; the spinning aid includes any one or a combination of two or more of polyvinylpyrrolidone, polyethylene oxide, and cellulose acetate; the organic solvent includes any one or a combination of two or more of tetrahydrofuran, xylene, N,N-dimethylformamide, and isopropanol; and the pore-forming agent is any one or a combination of two or more of polymethyl methacrylate, polystyrene, citric acid, and polyethylene glycol.

3. The preparation method according to claim 1, characterized in that, The mass ratio of polyborosilazane, organic solvent and spinning aid mentioned in step (1) is 5-7:8-10:2.8-4.

4. The preparation method according to claim 1, characterized in that, The mass ratio of the pore-forming agent, spinning aid, iron source and organic solvent mentioned in step (2) is 1-2:2.8-4:1.5-2.5:10-12.

5. The preparation method according to claim 1, characterized in that, The process parameters for coaxial electrospinning in step (3) are as follows: voltage 10-20 kV, drum speed 180-200 rpm, receiving distance 10-20 cm, core spinning solution flow rate 0.4-0.8 mL / h, shell spinning solution flow rate 1.2-2.4 mL / h, and spinning temperature 10-40 ℃.

6. The preparation method according to claim 1, characterized in that, The specific procedure for the stepped heating heat treatment in step (4) is as follows: heat to 100-120 ℃ at a heating rate of 5-10 ℃ / min and hold at this temperature for 3-5 h; then heat to 200-250 ℃ at a heating rate of 2-5 ℃ / min and heat treat at this temperature for 3-6 h.

7. The preparation method according to claim 1, characterized in that, The pyrolysis described in step (5) is as follows: under the protection of a flowing inert atmosphere, the temperature is increased from room temperature to 400-450 ℃ at a heating rate of 5-10 ℃ / min, and held at this temperature for 1-3 h. Then, the temperature is increased to 700-1200 ℃ at a heating rate of 1-3 ℃ / min, and held at this temperature for 3-6 h. Then, the temperature is reduced at 600-700 ℃ for 3-6 h under a hydrogen atmosphere. The gas hourly space velocity of both the inert atmosphere and the hydrogen is 600-1800 h⁻¹. –1 .

8. A hollow ceramic fibrous iron-based catalyst, characterized in that, It is prepared according to the preparation method according to any one of claims 1-7.

9. The application of the hollow ceramic fibrous iron-based catalyst as described in claim 8 in the synthesis of biofuel from syngas.

10. The application according to claim 9, characterized in that, The catalyst is loaded into the catalyst bed of a continuous flow high-pressure fixed-bed reactor, and preheating layers are placed above and below the catalyst bed. The reactor is then activated at 400-550 °C for at least 1 h under a flowing hydrogen atmosphere. Subsequently, the catalyst bed is cooled to a reaction temperature of 250-350 °C, the hydrogen supply is shut off, and syngas is introduced with a gas hourly space velocity (GHSV) of 1200-12000 h⁻¹. –1 The pressure is 2.0-4.0 MPa.

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