Lotus-shaped ceramic fiber iron-ruthenium-based catalyst for synthesizing biofuel and preparation method and application thereof

Abstract

This invention belongs to the field of heterogeneous catalysis and materials synthesis, and discloses a lotus-root-shaped ceramic fiber iron-ruthenium-based catalyst for the synthesis of biofuels, its preparation method, and its application. The catalyst is prepared using a coaxial electrospinning process, with polysilazane, an iron source, and a spinning aid as the shell spinning solution, and a mixture containing polysilazane, an iron source, a ruthenium source, a pore-forming agent, and a spinning aid as the core spinning solution, thus obtaining a lotus-root-shaped iron-ruthenium-containing ceramic fiber precursor. This precursor is then subjected to stepwise temperature curing, inert atmosphere pyrolysis, and hydrogen reduction to form the lotus-root-shaped ceramic fiber iron-ruthenium-based catalyst. This catalyst exhibits excellent mechanical strength, high hydrothermal stability, and good reaction mass transfer performance, making it suitable for the production of biofuels from syngas in a fixed-bed reactor.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalysis and materials synthesis, specifically relating to a lotus root-shaped ceramic fiber iron-ruthenium-based catalyst for the synthesis of biofuels, its preparation method, and its application. Background Technology

[0002] Fischer-Tropsch synthesis (FTS) is an important pathway for the catalytic conversion of syngas (CO + H2) into liquid hydrocarbon fuels. Its products are mainly straight-chain alkanes and olefins, and it is a key production technology for biofuels, especially sustainable aviation fuel (SAF). The production of biofuels from syngas obtained through biomass gasification or water electrolysis coupled with CO2 hydrogenation via FTS has become a research hotspot in the field of green energy. Among the FTS products, C... 10 -C 20 Medium- and long-chain hydrocarbons are ideal precursors for the preparation of SAF (Salicylic Acid Fuel). Currently, industrially, crude FTS products are mainly modified through subsequent hydroisomerization and selective cracking processes to improve their low-temperature fluidity and combustion performance, meeting the stringent standards for aviation fuel. However, traditional iron-based or cobalt-based FTS catalysts often face problems during the reaction process, such as easy sintering of active components, severe carbon deposition, poor hydrothermal stability, and a wide product distribution, leading to... 10 -C 20 The limited range selectivity and short catalyst lifetime restrict its application efficiency in high space velocity and high conversion continuous flow reaction systems.

[0003] In FTS catalyst systems, the support not only disperses and stabilizes the active components but also directly affects reaction mass transfer, heat conduction, and resistance to carbon deposition. Currently used catalyst supports (such as porous oxides like γ-Al₂O₃, SiO₂, and TiO₂), while possessing certain specific surface area and mechanical strength, are prone to phase transitions, sintering, or structural collapse in the high-temperature, high-pressure, and high-vapor-pressure FTS reaction environment, leading to the aggregation and deactivation of active sites. Furthermore, the interaction between these supports and the active metal is weak, making it difficult to achieve high dispersion and stable anchoring of metal particles. Additionally, carbon deposition easily occurs on the support surface during syngas conversion, clogging pores and reducing mass transfer efficiency.

[0004] To address these issues, research typically proceeds in two directions. One approach involves modifying carbon materials, introducing nitrogen species, or doping with other metal elements. For example, Chinese patent CN121042103A, based on a MOF-derived carbon-embedded iron catalyst, exhibits excellent CO yield and mass transfer performance in reverse water-gas shift (RWGS) due to its abundant mesoporous structure and high iron loading, providing high-quality syngas precursors for FTS reactions. However, its lack of promoter regulation and high-temperature pyrolysis preparation may limit its selective control over long-chain hydrocarbon products in the complex FTS reaction. Chinese patent CN121155619A employs a biochar-supported Fe-Mn-Ce ternary system. The support possesses a high specific surface area and well-developed mesoporous structure, and the intermetallic synergistic effect is expected to optimize electronic structure and mass transfer efficiency, potentially enhancing chain growth activity in FTS. However, this catalyst was originally designed for oxidation reactions; if directly used in the reducing atmosphere of FTS, its surface state and metal ratio need to be reconstructed and adjusted. Chinese patent CN121338834A constructs an iron single-atom catalyst through axial halogen coordination, achieving extremely high metal dispersion and electronic structure regulation, with outstanding intrinsic activity. Furthermore, the carbon nanotube support is beneficial for reaction mass transfer, and it has the potential to achieve efficient conversion in FTS. However, its halogen coordination may be unstable in the high-temperature, hydrogen-rich FTS environment, and the synthesis process is complex, posing challenges to large-scale preparation and long-term stability.

[0005] Another approach involves combining catalysts with structured supports, utilizing the regularized pores and confinement effects provided by the support to stabilize active components and optimize mass transfer. Electrospinning technology, due to its advantages such as the ability to prepare continuous nanofibers, simple operation, and tunable structure, shows great promise in the field of structured catalyst supports. Existing technologies have reported various methods for preparing fiber catalyst supports using electrospinning. For example, Chinese patent CN104496469A discloses a method for preparing dense micro / nano ceramic fibers using coaxial electrospinning. Through the design of a shell polymer and a core ceramic precursor, dense ceramic fibers are obtained after sintering. However, its structure is solid and dense, lacking a porous structure conducive to mass transfer. Chinese patent CN105256406A further employs coaxial electrospinning technology, using paraffin wax, silicone oil, etc., as core sacrificial materials to prepare hollow SiOC ceramic fibers. However, the resulting fibers have a single hollow cavity structure with a smooth internal surface, making it difficult to effectively anchor active metal particles. Chinese patent CN112176457A prepared porous SiZrNOC fibers by adding polystyrene pore-forming agent to the spinning solution, achieving a combination of porous structure and fiber flexibility. However, its pore distribution is random and lacks regularity of directional connectivity, and it does not involve in-situ loading of active metals.

[0006] In summary, although existing technologies have achieved the porous, hollow, or flexible transformation of ceramic fibers, the following technical bottlenecks still exist: (1) It is difficult to construct directional, interconnected, and orderly porous channels inside the fibers to achieve efficient mass and heat transfer; (2) The active metal components are mostly loaded using the post-impregnation method, which limits the dispersion and weakens the binding force with the carrier, making them prone to migration and aggregation during the reaction; (3) The carrier materials are mostly oxides or carbon materials, and their stability needs to be improved under the high temperature and high water vapor partial pressure environment of the FTS reaction; (4) It is difficult to achieve the integrated construction of carrier molding, pore construction, and active site loading, resulting in complex processes and poor repeatability.

[0007] Therefore, there is an urgent need to develop a novel structured catalyst that is simple to process, has a controllable structure, and possesses high activity, high selectivity, and excellent stability to meet the industrial application requirements of syngas to biofuel (especially SAF fraction). Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, this invention provides a lotus root-like ceramic fiber iron-ruthenium-based catalyst for the synthesis of biofuels, its preparation method, and its application. Using coaxial electrospinning technology, polysilazane is used as the ceramic precursor, and iron and ruthenium sources are used as active component precursors. By precisely controlling the spinning formulation, curing procedure, pyrolysis process, and reduction conditions, a SiCN ceramic fiber-supported iron-ruthenium-based catalyst with a lotus root-like interconnected porous structure is constructed in one step.

[0009] The technical solution of the present invention is as follows: The first aspect of this invention provides a method for preparing a lotus root-shaped ceramic fiber iron-ruthenium-based catalyst for synthesizing biofuels, comprising the following steps: (1) Preparation of shell spinning solution: Dissolve polysilazane, iron source and spinning aid in organic solvent to obtain shell spinning solution for coaxial electrospinning; (2) Preparation of core spinning solution: Dissolve polysilazane, iron source, ruthenium source, pore-forming agent and spinning aid in an organic solvent and stir evenly to obtain core spinning solution for coaxial electrospinning; the pore-forming agent is any one or a combination of two or more of polystyrene, polymethyl methacrylate, citric acid and polyethylene glycol. (3) Coaxial electrospinning: The core spinning solution and the shell spinning solution are coaxially electrospinned, and the iron-ruthenium ceramic fiber precursor is collected on the receiving device; (4) Curing, pyrolysis, and reduction: The iron-ruthenium-containing ceramic fiber precursor is dried and cured in an oven to obtain a cured fiber felt, which is then pyrolyzed under an inert atmosphere and then reduced under a flowing hydrogen atmosphere to obtain the lotus root-shaped ceramic fiber iron-ruthenium-based catalyst.

[0010] Preferably, the organic solvents in steps (1) and (2) each include any one or a combination of two or more of tetrahydrofuran, xylene, N,N-dimethylformamide and isopropanol, and the spinning aids in steps (1) and (2) each include any one or a combination of two or more of polyvinylpyrrolidone, polyethylene oxide and cellulose acetate.

[0011] Preferably, the iron source in steps (1) and (2) is iron acetylacetone, and the ruthenium source in step (2) is ruthenium acetylacetone.

[0012] Preferably, in step (1), the mass ratio of the polysilazane, iron source, organic solvent, and spinning aid is 4.5-5:0.5-1:8-12:1-2.

[0013] Preferably, in step (2), the mass ratio of the polysilazane, pore-forming agent, spinning aid, iron source, ruthenium source, and organic solvent is 0.5-1:1-2:0.5-2:1.5-2.5:0.02-0.04:10-12.

[0014] Preferably, in step (3), the process parameters for coaxial electrospinning are: receiving distance of 15-25 cm, spinning voltage of 15-22 kV, core spinning solution flow rate of 0.8-1 mL / h, and shell spinning solution flow rate of 1-1.5 mL / h.

[0015] Preferably, in step (4), the specific curing procedure is as follows: heating to 100-120 ℃ at a heating rate of 5-10 ℃ / min and holding at this temperature for 3-5 h, during which the pore-forming agent is kept stable; then heating to 200-250 ℃ at a heating rate of 2-5 ℃ / min and heat-treating at this temperature for at least 3 h to ensure that the organic solvent is completely evaporated.

[0016] Preferably, in step (4), the pyrolysis specifically involves: heating from room temperature to 200-350 ℃ at a heating rate of 5-10 ℃ / min under an inert atmosphere, and holding at this temperature for 1-2 h. During this process, the pore-forming agent undergoes thermal decomposition and forms uniform and interconnected pores. Then, the temperature is increased to 700-1200 ℃ at a heating rate of 1-3 ℃ / min, and held at this temperature for at least 3 h to obtain iron-ruthenium-containing rhomboid ceramic fibers with a dense and uniform surface and interconnected core layers. Finally, the rhomboid ceramic fiber iron-ruthenium-based catalyst is reduced at 600-700 ℃ for 3-5 h under a hydrogen atmosphere. The gas hourly space velocity (VHSV) of both the inert atmosphere and hydrogen is 600-1800 h⁻¹. –1 .

[0017] A second aspect of the present invention provides an iron-ruthenium-based catalyst with lotus root-like ceramic fibers, which is prepared by the method described above.

[0018] The third aspect of this invention provides the application of the aforementioned lotus root-shaped ceramic fiber iron-ruthenium-based catalyst in the preparation of biofuel.

[0019] Preferably, the application involves synthesizing biofuel from syngas in a continuous flow high-pressure fixed-bed reactor, and the specific steps are as follows: The catalyst is loaded into the catalyst bed of a continuous flow high-pressure fixed-bed reactor, with preheating layers 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 250-350 °C, the hydrogen supply is shut off, and syngas is introduced to adjust the pressure to 2.0-4.0 MPa to initiate the reaction. The syngas volume hourly space velocity (GHSV) is 1200-12000 h⁻¹. –1 .

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. The catalyst structure can be pre-designed. A composite fiber precursor with a well-defined lotus-root structure is obtained using coaxial electrospinning technology. The shell layer uses polysilazane (PSZ) as the high-temperature resistant, high-strength ceramic support for the catalyst, while the core layer (containing iron acetylacetonate, a pore-forming agent, and a spinning aid) is pre-designed as a "sacrificial template" and an active metal precursor. Through subsequent heat treatment, the organic matter in the core layer decomposes and escapes, forming continuous and interconnected lotus-root-shaped channels. Simultaneously, the iron and ruthenium sources, within the confined space formed by the pyrolysis of the core layer, undergo pyrolysis and reduction treatment, transforming into highly dispersed iron-ruthenium-based active species, which are then in-situ anchored in the SiCN ceramic matrix. This process simultaneously completes the support formation, lotus-root-shaped structure construction, and in-situ, highly dispersed loading of active sites, achieving the integrated and precise construction of the catalyst's "macrostructure" and "microscopic active center."

[0021] 2. The selection of catalyst shell material was ingenious. The choice of polysilazane (PSZ) as the ceramic precursor was a key creative innovation. Its pyrolysis product, SiCN ceramic, possesses excellent high-temperature hydrothermal stability, oxidation resistance, and mechanical properties, making it an ideal alternative to traditional oxide supports under harsh reaction conditions. This significantly improves the catalyst's activity and stability in highly exothermic and carbon-depositing reactions such as syngas-to-biofuel production. The specific mass ratio of the substances in the shell spinning solution ensured that the precursor solution possessed suitable electrospinning rheological and electrical properties, crucial for the successful spinning of continuous, uniform, lotus-root-shaped ceramic fibers.

[0022] 3. Using acetylacetone iron as the iron source is advantageous because the iron source has good solubility in organic solvents, enabling it to form a homogeneous and stable spinning solution with pore-forming agents and spinning aids. Its thermal decomposition behavior matches that of the pore-forming agents and spinning aids, facilitating the stable formation of a lotus-root-like structure and the in-situ generation of active iron species during pyrolysis. The specific mass ratio of each substance in the core layer spinning solution is the core parameter for achieving a balance between the spinnability of the core layer solution, ensuring iron content, and forming an ideal lotus-root-like structure. Adding a small amount of ruthenium acetylacetone forms Fe-Ru bimetallic nanoalloy particles with iron during pyrolysis. Through electronic synergistic effects, the electron density of iron is modulated, precisely controlling the generation ratio of iron carbide (Fe3C / Fe5C2), thereby optimizing the chain growth probability and significantly improving C... 10 -C 20 Hydrocarbon selectivity; at the same time, the introduction of trace amounts of ruthenium can inhibit carbon deposition and extend catalyst life, achieving a synergistic effect of exchanging extremely low amounts of precious metals for a significant leap in catalytic performance.

[0023] 4. Programmed Pyrolysis and Reduction in Different Atmospheres. Following pyrolysis in an inert atmosphere, the introduction of flowing hydrogen for reduction is a crucial step. This selectively reduces iron oxides or iron species interacting with the support that may form during pyrolysis to highly catalytically active metallic iron or iron carbide phases. Controlling the gas space velocity ensures mass transfer and reduction efficiency. Separating pyrolysis (inert gas) and reduction (hydrogen) at different temperatures represents a significant optimization over traditional one-step reduction or direct pyrolysis in hydrogen, allowing for more precise control over the composition and dispersion of the final active phase. Attached Figure Description

[0024] Figure 1 The process flow diagram for preparing the lotus root-shaped ceramic fiber iron-ruthenium-based catalyst of this invention is shown below; Figure 2 Scanning electron microscope image of the lotus root-like ceramic fiber iron-ruthenium-based catalyst prepared in Example 1; Figure 3 The image shows a scanning electron microscope (SEM) image of the lotus root-shaped ceramic fiber iron-ruthenium-based catalyst prepared in Comparative Example 2. Figure 4 The image shows a scanning electron microscope (SEM) image of the lotus root-shaped ceramic fiber iron-ruthenium-based catalyst prepared in Comparative Example 3. Figure 5 The image shows a scanning electron microscope (SEM) image of the lotus root-like ceramic fiber iron-ruthenium-based catalyst prepared in Comparative Example 7. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0026] Example 1 A method for preparing a lotus root-shaped ceramic fiber iron-ruthenium-based catalyst for the synthesis of biofuels, comprising the following steps: (1) Prepare shell spinning solution by dissolving 4.5 g polysilazane, 0.5 g iron acetylacetone and 1 g polyvinylpyrrolidone in 8 g tetrahydrofuran solution and stirring at room temperature for 2 h until the solution is clear and transparent to obtain shell spinning solution. (2) Prepare the core spinning solution by dissolving 0.5 g polysilazane, 1 g polystyrene, 1.2 g polyvinylpyrrolidone, 0.02 g ruthenium acetylacetonate and 1.5 g iron acetylacetonate in 10 g N,N-dimethylformamide and stirring until homogeneous to obtain the core spinning solution. (3) Perform coaxial electrospinning. Place the core spinning solution and the shell spinning solution on the electrospinning machine, adjust the electrospinning process parameters, connect the high voltage power supply, start the coaxial electrospinning process, and receive the iron-ruthenium ceramic fiber precursor obtained through the receiving device. The process parameters of coaxial electrospinning are: voltage of 16 kV, drum speed of 180 rpm, material collection distance of 20 cm, core spinning solution flow rate of 1 mL / h, and shell spinning solution flow rate of 1.5 mL / h.

[0027] (4) Place the iron-ruthenium ceramic fiber precursor in an oven, heat it to 100 ℃ at 5 ℃ / min and keep it at that temperature for 3 h in an air atmosphere, then heat it to 250 ℃ at 2 ℃ / min and heat it for 3 h to ensure that the organic solvent is completely evaporated to obtain the cured fiber felt. (5) The cured fiber felt was heated from room temperature to 300 ℃ in a nitrogen atmosphere at a rate of 5 ℃ / min and held for 1 h to ensure that the polystyrene pore-forming agent underwent thermal decomposition and formed pores. Then, the temperature was increased to 700 ℃ at a rate of 1 ℃ / min and held for 3 h for pyrolysis to form iron-ruthenium-containing lotus root-like ceramic fibers with a dense and uniform surface and interconnected core layers. Subsequently, it was reduced at 700 ℃ in a hydrogen atmosphere for 3 h, wherein the volume hourly space velocity of nitrogen and hydrogen was 600 h⁻¹. -1 Ultimately, a lotus root-like ceramic fiber iron-ruthenium-based catalyst was obtained.

[0028] The scanning electron microscope image of the lotus root-like ceramic fiber iron-ruthenium-based catalyst prepared in Example 1 is shown below. Figure 2 As shown, from Figure 2 It can be seen that the prepared lotus root-like ceramic fiber iron-ruthenium-based catalyst has a clear lotus root-like structure, with a dense and smooth fiber surface and continuous and interconnected longitudinal cavities inside, which confirms that the pre-designed porous channels were successfully constructed by coaxial electrospinning combined with heat treatment.

[0029] Example 2 The preparation steps of Example 2 are the same as those of Example 1, except that the amount of polysilazane added in step (1) is 5g.

[0030] Example 3 The preparation steps of Example 3 are the same as those of Example 1, except that the amount of pore-forming agent polystyrene added in step (2) is 2 g.

[0031] Example 4 The preparation steps of Example 4 are the same as those of Example 1, except that the amount of iron acetylacetone added in step (2) is 2.5 g.

[0032] Example 5 The preparation steps of Example 5 are the same as those of Example 1, except that the pyrolysis temperature in step (5) is 1200℃.

[0033] Example 6 The preparation steps of Example 6 are the same as those of Example 1, except that the hydrogen reduction temperature in step (5) is 600°C.

[0034] Comparative Example 1 The only difference from Example 1 is that in step (1), polysilazane is replaced with polycarbosilane.

[0035] Comparative Example 2 The only difference from Example 1 is that the pyrolysis temperature in step (5) is increased to 1500 °C.

[0036] Scanning electron microscope image of the lotus root-like ceramic fiber iron-ruthenium-based catalyst prepared in Comparative Example 2 is shown below. Figure 3 As shown, from Figure 3 It can be seen that when the pyrolysis temperature rises to 1500 ℃, the fiber shrinks severely, and the original continuous lotus root-like cavities inside almost completely collapse. This indicates that the excessively high pyrolysis temperature destroys the preset lotus root-like structure, thereby affecting the catalytic effect of the catalyst.

[0037] Comparative Example 3 The only difference from Example 1 is that the hydrogen reduction temperature in step (5) is raised to 800 °C.

[0038] Scanning electron microscope image of the lotus root-like ceramic fiber iron-ruthenium-based catalyst prepared in Comparative Example 3 is shown below. Figure 4 As shown, from Figure 4 It can be seen that when the reduction temperature is raised to 800 ℃, although the overall lotus root structure of the fiber is preserved to some extent, some cavities are blocked, indicating that excessively high reduction temperature will cause the iron-ruthenium active species to migrate and grow, which is not conducive to the high dispersion state of the active components.

[0039] Comparative Example 4 The only difference from Example 1 is that step (5) was not reduced in a hydrogen atmosphere.

[0040] Comparative Example 5 The only difference from Example 1 is that ruthenium acetylacetone is not added in step (2).

[0041] Comparative Example 6 The only difference from Example 1 is that in step (2), ruthenium acetylacetone is replaced with platinum acetylacetone.

[0042] Comparative Example 7 The only difference from Example 1 is that the amount of polystyrene added in step (2) is 0.1 g.

[0043] Scanning electron microscope image of the lotus root-like ceramic fiber iron-ruthenium-based catalyst prepared in Comparative Example 7 is shown below. Figure 5 As shown, from Figure 5 It can be seen that when the amount of polystyrene pore-forming agent added in the core spinning solution is reduced from 1 g to 0.1 g, the resulting fiber fails to form a continuous, interconnected lotus root-like cavity, and only a small number of isolated, fine, irregular pores appear. The fiber density increases significantly, indicating that insufficient pore-forming agent cannot effectively construct the pre-set interconnected porous structure.

[0044] Comparative Example 8 The difference from Example 1 lies in the method of introducing the active metal component, the specific steps of which are as follows: (1) Pre-preparation of carrier: Following the method of steps (1) to (4) in Example 1, prepare the shell spinning solution (polysilazane, polyvinylpyrrolidone dissolved in tetrahydrofuran) and the core spinning solution (polysilazane, polystyrene, polyvinylpyrrolidone dissolved in N,N-dimethylformamide, without adding any metal precursors), and prepare a metal-free lotus root-like SiCN ceramic fiber carrier by coaxial electrospinning, curing crosslinking and inert atmosphere pyrolysis (400 ℃ for 1 h, 700 ℃ for 3 h).

[0045] (2) Equal volume impregnation loading: The above-mentioned carrier is placed in a vacuum impregnation device. According to the total metal content of iron and ruthenium in Example 1, an ethanol solution (metal precursor solution) containing iron acetylacetone and ruthenium acetylacetone is prepared. The metal precursor solution is uniformly loaded onto the surface and pores of the carrier by the equal volume impregnation method. After standing at room temperature for 12 h, it is vacuum dried at 80 ℃ for 12 h.

[0046] (3) Subsequent processing: The loaded fibers were subjected to hydrogen reduction according to step (5) of Example 1 (700 °C, 3 h, volume hourly space velocity 600 h⁻¹). -1 Finally, a supported lotus root-shaped ceramic fiber iron-ruthenium-based catalyst was obtained.

[0047] Performance Testing and Analysis The lotus root-shaped ceramic fiber iron-ruthenium-based catalysts prepared in Examples 1-6 and Comparative Examples 1-8 were loaded into the catalyst bed of a continuous flow high-pressure fixed-bed hydrogenation reactor. The catalyst loading amount was 1.0 g. The catalyst 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, the hydrogen supply was turned off, and syngas was switched on. 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 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.

[0048] 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.

[0049] 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 Selective ( 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.

[0050] 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.

[0051] Table 1. Test results of the catalyst in the preparation of SAF.

[0052] As shown in Table 1, Example 1 exhibits the best performance, C 10 –C 20 The hydrocarbon selectivity reached 69.80%, the CO conversion rate was 70.03%, and the decrease rate was only 0.011%. Although the performance of Examples 2-6 fluctuated slightly after adjusting various parameters and reduction temperature, it still maintained a high level, which verified the rationality of the process window of the present invention.

[0053] Comparative Example 1 replaces polysilazane with polycarbosilane, C 10 -C 20 The hydrocarbon selectivity and CO conversion rate decreased to 58.39% and 50.05%, respectively, and the rate of decrease in conversion rate per hour increased to 0.12%, proving that the chemical composition and electronic properties of the SiCN support are irreplaceable.

[0054] Comparative Examples 2 and 3 respectively increased the pyrolysis temperature to 1500 °C and the reduction temperature to 800 °C. 10 -C 20 Hydrocarbon selectivity decreased to 49.63% and 44.21%, with conversion rates decreasing by as much as 0.14% and 0.19% per hour, respectively. Figure 3 and Figure 4 As shown, excessively high temperatures lead to carrier densification and interfacial structure damage; Comparative Example 4, lacking hydrogen reduction, exhibited a selectivity decrease to 41.87% and a conversion rate decrease of 0.21% per h, demonstrating the crucial role of the reduction step in active phase formation; Comparative Example 5 did not add ruthenium acetylacetone, and Comparative Example 6 replaced ruthenium acetylacetone with platinum acetylacetone, C 10 -C 20 Hydrocarbon selectivity decreased to 46.88% and 39.57%, respectively, with conversion rates decreasing by as much as 0.24% and 0.34% per hour, strongly demonstrating the specific synergistic effect between iron and ruthenium, and that ruthenium acetylacetone cannot be replaced.

[0055] Comparative Example 7 reduced the amount of pore-forming agent to 0.1 g, C10 -C 20 Hydrocarbon selectivity decreased to 38.65%, and the conversion rate decreased at a rate of 0.37% per hour. Figure 5 As shown, an appropriate amount of pore-forming agent is key to constructing the lotus root-like hollow structure and providing a confinement effect; Comparative Example 8, which uses a method of preparing the support first and then impregnating and loading, exhibits the worst performance (C). 10 -C 20 The hydrocarbon selectivity was 36.54% and the conversion rate decreased by 0.57% per hour, demonstrating that the integrated preparation method of introducing metals in situ has significant advantages in terms of dispersibility and metal-support interaction.

[0056] In summary, this invention achieves the integrated preparation method of C by optimizing the SiCN ceramic support composition, precisely controlling the pyrolysis and reduction temperatures, constructing an iron-ruthenium bimetallic synergistic system, optimizing the amount of pore-forming agent, and employing an in-situ metal introduction method. 10 –C 20 The invention achieves a synergistic improvement in hydrocarbon selectivity, conversion rate, and stability. Comparative examples, considering factors such as carrier composition, process parameters, metal types, structural design, and introduction methods, fully demonstrate the synergy and irreplaceability of the technical solution, yielding unexpected technical results.

[0057] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for preparing an iron-ruthenium-based catalyst with lotus root-like ceramic fibers, characterized in that, The steps are as follows: (1) Preparation of shell spinning solution: dissolve polysilazane, iron source and spinning aid in organic solvent to obtain shell spinning solution for coaxial electrospinning; the mass ratio of polysilazane, iron source, organic solvent and spinning aid is 4.5-5:0.5-1:8-12:1-2; (2) Preparation of core spinning solution: Dissolve polysilazane, iron source, ruthenium source, pore-forming agent and spinning aid in an organic solvent and stir evenly to obtain a core spinning solution for coaxial electrospinning; the pore-forming agent is any one or a combination of two or more of polystyrene, polymethyl methacrylate, citric acid and polyethylene glycol; the mass ratio of polysilazane, pore-forming agent, spinning aid, iron source, ruthenium source and organic solvent is 0.5-1:1-2:0.5-2:1.5-2.5:0.02-0.04:10-12; the ruthenium source is ruthenium acetylacetone; (3) Coaxial electrospinning: The core spinning solution and the shell spinning solution are coaxially electrospinned, and the iron-ruthenium ceramic fiber precursor is collected on the receiving device; (4) Curing, pyrolysis, and reduction: The iron-ruthenium-containing ceramic fiber precursor is dried and cured in an oven to obtain a cured fiber felt, which is then pyrolyzed under an inert atmosphere and reduced under a flowing hydrogen atmosphere to obtain the lotus root-shaped ceramic fiber iron-ruthenium-based catalyst. The specific curing procedure is as follows: heating to 100-120 ℃ at a heating rate of 5-10 ℃ / min and holding at this temperature for 3-5 h, then heating to 200-250 ℃ at a heating rate of 2-5 ℃ / min and heat-treated at this temperature for at least 3 h; the pyrolysis procedure is as follows: heating from room temperature to 200-350 ℃ at a heating rate of 5-10 ℃ / min and holding at this temperature for 1-2 h; then heating to 700-1200 ℃ at a heating rate of 1-3 ℃ / min and holding at this temperature for at least 3 h, and finally reducing at 600-700 ℃ for 3-5 h under a hydrogen atmosphere. h; the gas hourly space velocity (VHSV) of both inert atmosphere and hydrogen is 600-1800 h. –1 ; The iron source mentioned in steps (1) and (2) is iron acetylacetone.

2. The preparation method according to claim 1, characterized in that, The organic solvents mentioned in steps (1) and (2) include any one or a combination of two or more of tetrahydrofuran, xylene, N,N-dimethylformamide and isopropanol; the spinning aids mentioned in steps (1) and (2) include any one or a combination of two or more of polyvinylpyrrolidone, polyethylene oxide and cellulose acetate.

3. The preparation method according to claim 1, characterized in that, In step (3), the process parameters for coaxial electrospinning are: receiving distance of 15-25 cm, spinning voltage of 15-22 kV, core spinning solution flow rate of 0.8-1 mL / h, and shell spinning solution flow rate of 1-1.5 mL / h.

4. A lotus root-like ceramic fiber iron-ruthenium-based catalyst, characterized in that, It is prepared using the method described in any one of claims 1-3.

5. The application of the lotus root-shaped ceramic fiber iron-ruthenium-based catalyst as described in claim 4 in the preparation of biofuel, characterized in that, The catalyst was loaded into the catalyst bed of a continuous flow high-pressure fixed-bed reactor, and preheating layers were placed above and below the catalyst bed. The reactor was then activated at 400-550 °C for at least 1 h under a flowing hydrogen atmosphere. Subsequently, the catalyst bed was cooled to a reaction temperature of 250-350 °C, the hydrogen supply was shut off, and syngas was 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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