Si-b-c-n ceramic microsphere catalyst with high specific surface active iron and its preparation method and application

Abstract

The application belongs to the field of heterogeneous catalysis and material synthesis, and relates to a Si-B-C-N ceramic microsphere catalyst with high specific surface area loaded with active iron and a preparation method and application thereof. The catalyst is prepared by combining the methods of emulsion cross-linking solidification and precursor high-temperature pyrolysis conversion, with polyborosilazane as a precursor, iron acetylacetonate as an iron source, and the addition of cobalt acetylacetonate as a cobalt source and alkylphenol polyoxyethylene ether as an emulsifier. The catalyst has the characteristics of regular microspherical morphology, uniform dispersion of active iron and cobalt species, high specific surface area and excellent catalytic activity, and is suitable for biomass oil hydrogenation, cracking or reforming and other reactions, can significantly improve the yield and quality of biofuel, and has good recycling performance. The application has the advantages of simple process and strong controllability, is suitable for large-scale preparation, and has a wide application prospect in the field of sustainable energy catalysis.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalysis and materials synthesis, and relates to a Si-BCN ceramic microsphere catalyst with high specific surface area supported on active iron, its preparation method and application. This catalyst can be used to produce biofuel from syngas. Background Technology

[0002] Among numerous sustainable aviation fuel (SAF) production technologies, the biomass gasification coupled with Fischer-Tropsch synthesis (FTS) route has attracted considerable attention due to its wide availability of raw materials and good compatibility with existing infrastructure. Its core objective is to efficiently and selectively convert biomass-derived syngas (CO + H2) into C-chain lengths concentrated in C. 10 -C 20 The range of straight-chain alkanes and alkenes is ideal for jet fuel (Jet A / A-1). In this conversion process, the surface properties of the catalyst directly determine the reaction rate, product selectivity, and process economy. High specific surface area is particularly crucial for catalysts used in the FTS process, as it maximizes the exposure of active sites (such as iron carbides), promotes the adsorption and activation of syngas, and provides the necessary surface reaction space and intermediate residence time for the formation of long-chain hydrocarbons, thus directly affecting the yield of jet fuel-range hydrocarbons and the catalyst's production capacity. Therefore, developing catalysts with high specific surface area, excellent stability, and high C2O2 content is essential. 10 -C 20 Developing novel catalysts with high product selectivity is an urgent and significant task for promoting the commercialization of biomass-based FTS processes and meeting the rapidly growing demand for SAF.

[0003] Currently, iron-based catalysts used in FTS processes typically employ impregnation or co-precipitation methods to support the active component on traditional oxide supports such as silica, alumina, and titanium dioxide. While these methods can achieve a relatively high initial specific surface area to some extent, these catalysts face severe challenges under the harsh FTS reaction conditions, and their high specific surface area structure is often difficult to maintain long-term. First, at the reaction temperature, the support surface may undergo sintering or phase transformation, leading to pore structure collapse and a significant decrease in specific surface area. Second, the iron active component is prone to migration, agglomeration, and over-carbonization during the reaction, forming a large inert phase. This not only reduces the number of effective active sites but also clogs the support pores, further exacerbating the loss of specific surface area. In addition, long-chain hydrocarbons generated in the FTS reaction and water produced by side reactions can induce catalyst structural degradation. These factors collectively limit the activity, selectivity, and lifetime of traditional supported catalysts, especially for C640, which requires multi-site synergy and a long surface residence time to generate C640. 10 -C 20The selectivity of long-chain hydrocarbons has encountered bottlenecks. For example, Chinese patent CN121204711A constructs a hollow TiO2 support and loads it with iridium using a template method. While its unique hollow structure is beneficial for mass transfer and utilization of internal surface sites, the limited specific surface area of ​​the TiO2 support itself results in a severe shortage of iron active sites available for long-chain hydrocarbon synthesis, leading to low catalytic efficiency and cost-effectiveness. Chinese patent CN120939932A introduces stable hydroxyl groups onto the TiO2 surface through impregnation and ultraviolet irradiation. These surface hydroxyl groups can efficiently activate oxygen-containing molecules, but the TiO2 support has a low specific surface area, and the hydroxyl groups have limited effect on promoting CO dissociation and chain growth, making it difficult to provide the large number of densely packed specific active sites required for FTS, resulting in low CO conversion and low C conversion. 10 The selectivity is not ideal; Chinese patent CN121314638A utilizes silica sol confinement and programmed carbonization to prepare ultrafine α-MoC. Although it achieves ultra-high dispersion of the active phase and small particle size (~2nm), greatly increasing the number of exposed active sites, MoC's relative CO dissociation ability is weaker than that of iron / cobalt, and its strong oxyphilicity easily leads to excessive hydrogenation of intermediates to generate short-chain hydrocarbons. Therefore, although it has a high specific surface area, its intrinsic reaction pathway is unfavorable for long-chain aviation fuels (C). 10 -C 20 Highly selective synthesis of ).

[0004] In recent years, polymer-derived ceramics (PDCs) have been widely used in ceramic fibers, ceramic coatings, and ceramic matrix composites due to their advantages such as high molecular structure designability, uniform composition, and excellent high-temperature stability. Among them, Si-BCN ceramics derived from the pyrolysis conversion of polyborosilazane precursors exhibit an amorphous structure, excellent oxidation resistance, and high-temperature stability (maintaining stability above 1400 °C), demonstrating potential as a novel catalyst support. However, there are currently no reports on the use of Si-BCN ceramics as a catalyst support for free radical scintillation (FTS). Existing patents involving polyborosilazane or SiBCN ceramics, such as Chinese patent CN102108125A (carbon-free polyborosilazane), Chinese patent CN108821778A (high-temperature microwave absorbing material), Chinese patent CN105694048A (high-temperature resistant binder), and Chinese patent CN115959911A (microwave absorbing ceramic), all focus on structural ceramics, microwave absorbing materials, binders, and other fields. Their technical solutions and the technical problems they solve are completely different from the catalytic applications involved in this invention.

[0005] Furthermore, regarding the preparation of iron-containing ceramic microspheres, existing patents, such as Chinese patent CN104692804A, disclose a method for preparing porous Fe-Si-C ceramic microspheres, which obtains Fe-containing microspheres through emulsion and pyrolysis of polyferrocene-based silanes; and Chinese patent CN109847749A discloses a Si-C-Fe hybrid microsphere catalyst for the reduction of nitroaromatics at room temperature. However, the microsphere supports prepared by these patents are Fe-Si-C or Si-C systems, lacking boron, and applied to different catalytic reactions (nitroaromatic reduction), their catalytic performance in the FTS to SAF reaction has not been reported. Compared with iron, metals such as cobalt and ruthenium are also commonly used active components in FTS, but they are expensive and their synergistic effects with different supports vary, making it difficult to directly replace iron-based catalysts to meet the technical requirements of low cost and high selectivity.

[0006] In summary, there is an urgent need in the existing technology for a method that can maintain structural integrity, high specific surface area, and highly dispersed active sites under FTS reaction conditions for a long period of time, and for C 10 -C 20 Novel iron-based catalysts with high selectivity for long-chain hydrocarbons. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, this invention provides a Si-BCN ceramic microsphere catalyst with high specific surface area loaded with active iron, its preparation method and application. By utilizing the synergistic effect of emulsion template confined crosslinking and precursor programmed pyrolysis, a Si-BCN ceramic microsphere catalyst with high specific surface area loaded with active iron is prepared, further improving the specific surface area of ​​the catalyst while ensuring high activity and selectivity.

[0008] The technical solution of this invention is: The first aspect of this invention provides a method for preparing a Si-BCN ceramic microsphere catalyst with high specific surface area supported on active iron, comprising the following steps: (1) Preparation of precursor emulsion: Dissolve the emulsifier in an organic solvent, then add polyborosilicate, cobalt salt and iron acetylacetone, and emulsify and ultrasonically disperse to form a uniform precursor emulsion; the emulsifier includes any one or a combination of two or more of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, polyoxyethylene dehydrated sorbitan fatty acid ester, and alkyl polyglycoside; (2) Crosslinking and curing molding: The precursor emulsion is placed in a reaction vessel and crosslinking and curing reaction is carried out to obtain iron-loaded precursor polymer microspheres; (3) Pyrolysis conversion: The precursor polymer microspheres loaded with iron are subjected to programmed temperature pyrolysis in an inert atmosphere or a vacuum atmosphere, and after cooling, Si-BCN ceramic microspheres loaded with active iron are obtained. (4) Reduction: The Si-BCN ceramic microspheres loaded with active iron are reduced under a flowing hydrogen atmosphere to obtain the Si-BCN ceramic microsphere catalyst with high specific surface area loaded with active iron.

[0009] Preferably, in step (1), the organic solvent includes any one or a combination of two or more of acetonitrile, tetrahydrofuran, xylene, N,N-dimethylformamide, and anhydrous ethanol; the cobalt salt is cobalt acetylacetonate; and the emulsification and ultrasonic dispersion time is 20-30 min.

[0010] Preferably, the mass ratio of the emulsifier, organic solvent, cobalt salt, polyborosilicate, and iron acetylacetone is 0.7-1:20-25:0.01-0.1:2-4:0.2-0.5.

[0011] Preferably, the temperature of the crosslinking curing reaction in step (2) is 200-260 °C and the reaction time is 4-12 h.

[0012] Preferably, the inert atmosphere in step (3) is an argon atmosphere; the programmed heating rate is 2-10 ℃ / min; the final temperature of the pyrolysis is 800-1400 ℃, and the holding time is 0.5-3 h.

[0013] Preferably, in step (4), the reduction temperature is 600-700 °C and the temperature is maintained for 3-6 h; the gas hourly space velocity of hydrogen is 600-1800 h⁻¹. -1 .

[0014] A second aspect of the present invention provides a Si-BCN ceramic microsphere catalyst with high specific surface area loaded with active iron prepared by the above preparation method.

[0015] The third aspect of this invention provides the application of the above-mentioned high specific surface area Si-BCN ceramic microsphere catalyst loaded with active iron in the preparation of sustainable aviation fuel.

[0016] 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.

[0017] The advantages and beneficial effects of this invention are: 1. This invention utilizes an integrated process of "emulsion template confinement - precursor simultaneous pyrolysis," achieving both support formation and active site loading in a single process. This process in-situ constructs a Si-BCN ceramic microsphere support with abundant mesopores, resulting in a catalyst with an ultra-high specific surface area. It also atomically disperses and chemically anchors the nano-iron active phase within a rigid ceramic network, fundamentally solving the core problems of easy specific surface area loss and active site agglomeration / sintering in traditional catalysts. Iron atoms are captured by the in-situ generated Si-BCN ceramic framework, achieving atomically dispersed and chemically anchored nano-iron active phase. The introduction of boron not only improves the thermal stability of the ceramic support but also forms a unique electronic synergistic effect with the iron active centers. Although cobalt and ruthenium are also common active metals in Fischer-Tropsch synthesis, iron exhibits the best performance in the SiBCN support system. Cobalt-based catalysts show superior performance in C... 10 -C 20 The selectivity of the ruthenium-based catalyst is significantly low, with products leaning towards short-chain hydrocarbons; while the methane selectivity of the ruthenium-based catalyst is too high. This further demonstrates that the inventiveness of this invention lies not only in the selection of the SiBCN support, nor solely in the selection of iron, but also in the unique synergistic effect produced by the specific combination of Fe and SiBCN, which cannot be replaced by other metals or supports.

[0018] 2. The catalyst of this invention exhibits high intrinsic activity and high C content in the Fischer-Tropsch synthesis (FTS) reaction for the production of sustainable aviation fuel (SAF). 10 -C 20 Selectivity and exceptional stability for long-chain hydrocarbons. The high specific surface area and interconnected pores greatly promote mass transfer and chain growth; the inertness and anchoring effect of the ceramic framework ensure that the catalyst maintains stable activity and selectivity under harsh reaction conditions of high temperature, high pressure and water-containing gas, and its lifetime is significantly extended.

[0019] 3. The preparation process of this invention is simple, controllable, and easy to scale up, avoiding complex multi-step loading processes. The catalyst's excellent durability means longer single-cycle operation time and less frequent replacement, thereby significantly reducing catalyst consumption and operating costs per unit of fuel production. Attached Figure Description

[0020] Figure 1 SEM image of the Si-BCN ceramic microsphere catalyst with high specific surface area loaded with active iron prepared in Example 1; Figure 2 SEM image of the Si-BCN ceramic microsphere catalyst with high specific surface area loaded with active iron prepared for Comparative Example 1; Figure 3 SEM image of the Si-BCN ceramic microsphere catalyst with high specific surface area loaded with active iron prepared in Comparative Example 3; Figure 4SEM image of the Si-BCN ceramic microsphere catalyst with high specific surface area loaded with active iron prepared for Comparative Example 4. Detailed Implementation

[0021] 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.

[0022] Example 1 A method for preparing a Si-BCN ceramic microsphere catalyst with high specific surface area supported on active iron includes the following steps: (1) Preparation of precursor emulsion: Dissolve 0.7 g of alkylphenol polyoxyethylene ether in 20 g of acetonitrile, then gradually add 2 g of polyborosilicate, 0.2 g of iron acetylacetone and 0.01 g of cobalt acetylacetone to the solution for emulsification, and ultrasonically disperse for 20 min to obtain a uniform precursor emulsion.

[0023] (2) Crosslinking and curing molding: The precursor emulsion is placed in a reaction vessel and crosslinking and curing reaction is carried out to obtain iron-loaded precursor polymer microspheres. The temperature of the crosslinking and curing reaction is 200 °C and the reaction time is 6 h. (3) Pyrolysis conversion: The precursor polymer microspheres loaded with iron were subjected to programmed temperature pyrolysis in a vacuum atmosphere; the programmed temperature rise rate was 2 ℃ / min, the final pyrolysis temperature was 800 ℃, the holding time was 0.5 h, and after cooling, Si-BCN ceramic microspheres loaded with active iron were obtained. (4) Reduction: The Si-BCN ceramic microspheres loaded with active iron were reduced in a flowing hydrogen atmosphere at a reduction temperature of 600 °C and held at this temperature for 3 h; the gas hourly space velocity of hydrogen was 600 h⁻¹. -1 Ultimately, a Si-BCN ceramic microsphere catalyst with high specific surface area loaded with active iron was obtained.

[0024] Example 2 The only difference from Example 1 is that the amount of alkylphenol polyoxyethylene ether added in step (1) is 1 g.

[0025] Example 3 The only difference from Example 1 is that the amount of polyborosilazane added in step (1) is 4 g.

[0026] Example 4 The only difference from Example 1 is that the amount of iron acetylacetone added in step (1) is 0.5 g.

[0027] Example 5 The only difference from Example 1 is that the final pyrolysis temperature in step (3) is 1400 °C.

[0028] Example 6 The only difference from Example 1 is that the hydrogen reduction temperature in step (4) is 700 °C.

[0029] Comparative Example 1 The only difference from Example 1 is that in step (1), polyborosilazane is replaced with polycarbosilane.

[0030] Comparative Example 2 The only difference from Example 1 is that the pyrolysis temperature in step (3) is increased to 500 °C.

[0031] Comparative Example 3 The only difference from Example 1 is that the hydrogen reduction temperature in step (4) is raised to 1000 °C.

[0032] Comparative Example 4 The only difference from Example 1 is that the polyborosilazane in step (1) is replaced with polysilazane.

[0033] Comparative Example 5 The only difference from Example 1 is that the alkylphenol polyoxyethylene ether in step (1) is replaced with polyoxyethylene octylphenol ether.

[0034] Comparative Example 6 The purpose is to compare with Example 1. The specific steps are as follows: The difference between Comparative Example 6 and Example 1 lies in the different methods of introducing the iron source. The specific steps are as follows: (1) Preparation of pure Si-BCN ceramic microsphere carrier: Following the steps (1) to (3) of Example 1, an emulsifier solution and a polyborosilicate solution were prepared without adding acetylacetone iron. The mixture underwent emulsification, cross-linking and curing reaction (200 °C, 6 h) and programmed temperature pyrolysis (heating to 800 °C at 2 °C / min, holding for 0.5 h, vacuum degree ≤ 6.7 × 10⁻⁶). -2 (MPa), to prepare iron-free pure Si-BCN ceramic microsphere carriers.

[0035] (2) Equal volume impregnation loading: According to the total iron content in Example 1 (the mass of iron corresponding to 0.2 g of acetylacetone iron), prepare an ethanol solution of acetylacetone iron, and uniformly load the metal precursor solution into the above pure Si-BCN ceramic microsphere carrier by equal volume impregnation method. After standing at room temperature for 12 h, it is vacuum dried at 80 ℃ for 12 h.

[0036] (3) Subsequent reduction treatment: The loaded microspheres were subjected to hydrogen reduction according to step (4) of Example 1 (reduction temperature 600 ℃, heat preservation for 3 h, hydrogen gas volume hourly space velocity 600 h⁻¹). -1 Finally, a supported Si-BCN ceramic microsphere catalyst was obtained.

[0037] Comparative Example 7 The only difference from Example 1 is that iron acetylacetone in step (1) is replaced with manganese acetylacetone.

[0038] Performance Testing and Analysis The high specific surface area Si-BCN ceramic microsphere catalysts with active iron supported on them, prepared in Examples 1-6 and Comparative Examples 1-7, were loaded into the catalyst bed of a continuous flow fixed-bed hydrogenation reactor. The catalyst loading amount was 1.0 g, and 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 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 gas was turned 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 the reactor was run continuously for 50 h. The performance of the prepared Si-BCN ceramic microsphere catalyst with high specific surface area supported on active iron was evaluated by CO conversion, target product selectivity, catalyst stability, and specific surface area.

[0039] 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. The specific surface area of ​​the catalyst was determined using the BET method based on adsorption isotherms.

[0040] 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.

[0041] 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.

[0042] Table 1. Specific surface area and catalytic results of the catalysts prepared in Examples 1-6 and Comparative Examples 1-7.

[0043] As can be seen from the data in Table 1, the specific surface area of ​​the Si-BCN ceramic microsphere catalyst prepared in Example 1 is 648 m². 2 / g、C 10 –C 20 The invention achieved optimal results in four key indicators: hydrocarbon selectivity (64.87%), CO conversion rate (64.52%), and conversion rate decrease rate (0.12% per hour). This demonstrates that the invention successfully constructed a microsphere structure with high specific surface area and highly exposed active sites through an integrated emulsification-crosslinking-pyrolysis process. In Examples 2-6, although the performance indicators fluctuated slightly with adjustments to parameters such as emulsifier dosage, ceramic precursor dosage, iron content, pyrolysis final temperature, and reduction temperature, they all remained at a high level, indicating that the preparation method described in this invention has good process adaptability and parameter tolerance. Figure 1 This is a SEM image of the high specific surface area Si-BCN ceramic microsphere catalyst with supported active iron prepared in Example 1. Figure 1 It can be seen that the catalyst has a regular spherical morphology, the surface is rich in mesoporous structure, and no obvious iron particle agglomeration was observed, indicating that the iron active phase is highly dispersed.

[0044] Regarding the chemical composition of the carrier, in Comparative Example 1, after replacing polyborosilazane with polycarbosilane, the specific surface area decreased to 392 m². 2 / g, C 10 –C 20The hydrocarbon selectivity and CO conversion rate decreased to 48.36% and 49.27%, respectively, demonstrating that element B plays a crucial role in anchoring and dispersing iron species by regulating the surface chemical environment and electronic properties of the support. Figure 2 SEM images of the high specific surface area Si-BCN ceramic microsphere catalyst with active iron prepared in Comparative Example 1 show obvious iron nanoparticle aggregation on the surface of the ceramic microspheres, and the mesoporous structure becomes loose and inhomogeneous. This further indicates that without boron, the active iron phase is difficult to be effectively anchored and dispersed. Comparative Example 4 further replaced the polyborosilicate with a boron-free polysilazane, and the performance also deteriorated significantly, again confirming the indispensability of boron in constructing high specific surface area and active centers. The SEM images of the high specific surface area Si-BCN ceramic microsphere catalyst with active iron prepared in Comparative Example 4 are shown below. Figure 4 As shown, in the absence of boron, severe aggregation of iron nanoparticles occurs on the surface of the ceramic microspheres, resulting in irregular microsphere morphology and even localized rupture, with the mesoporous structure almost disappearing. This further confirms the indispensability of boron in stabilizing the ceramic framework and dispersing the iron-active phase.

[0045] Regarding the pyrolysis and reduction processes, in Comparative Example 2, the pyrolysis temperature was reduced to 500 °C, resulting in insufficient ceramization. In Comparative Example 3, the reduction temperature was increased to 1000 °C, which damaged the metal-support interface. Both processes showed significant performance degradation, indicating that the pyrolysis and reduction temperature window selected in this invention is crucial for balancing support structural stability and active phase formation. The SEM image of the high specific surface area Si-BCN ceramic microsphere catalyst with active iron supported in Comparative Example 3 is shown below. Figure 3 As shown, due to the excessively high reduction temperature, the iron-active phase underwent severe agglomeration, and sintering adhesion occurred on the surface of the ceramic microspheres. This indicates that the excessively high reduction temperature disrupted the stability of the metal-support interface.

[0046] The type of emulsifier has a decisive influence on microsphere molding. In Comparative Example 5, the performance decreased significantly after the emulsifier was replaced with polyoxyethylene octylphenol ether, indicating that the alkylphenol polyoxyethylene ether selected in this invention has unique advantages in terms of emulsion stability, microsphere particle size uniformity, and subsequent pyrolysis structure retention.

[0047] Regarding the method of metal introduction, Comparative Example 6 adopted the method of first preparing a pure carrier and then impregnating and loading it. Its performance was significantly lower than that of Example 1, which proves that the integrated strategy of in-situ emulsification to introduce metals described in this invention can achieve uniform distribution and strong interfacial bonding of metal species inside the microspheres, which is unmatched by the traditional post-impregnation method.

[0048] Comparative Example 7 showed a significant decrease in performance after the iron source was replaced with manganese acetylacetone, indicating that there is a specific matching relationship between the Si-BCN support and iron, and that other transition metals such as manganese cannot replicate the catalytic performance of iron in this system.

[0049] In summary, this invention achieves a balance of high specific surface area, high activity, high selectivity, and high stability through a multi-synergistic strategy of "B-doped support chemical anchoring - emulsifier optimization and morphology control - in-situ introduction to strengthen the interface - precise matching of pyrolysis and reduction". The comparative examples systematically verify the completeness and inventiveness of the technical solution of this invention from the perspectives of support composition, process window, emulsifier type, metal introduction method, and metal type. The catalytic performance improvement achieved far exceeds conventional expectations in the field.

[0050] 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 Si-BCN ceramic microsphere catalyst with high specific surface area supported on active iron, characterized in that, The steps are as follows: (1) Preparation of precursor emulsion: The emulsifier is dissolved in an organic solvent, and then polyborosilazane, cobalt salt and iron acetylacetone are added. After emulsification and ultrasonic dispersion, a uniform precursor emulsion is formed; the emulsifier is alkylphenol polyoxyethylene ether; the cobalt salt is cobalt acetylacetone; the mass ratio of the emulsifier, organic solvent, cobalt salt, polyborosilazane and iron acetylacetone is 0.7-1:20-25:0.01-0.1:2-4:0.2-0.5; (2) Crosslinking and curing molding: The precursor emulsion is placed in a reaction vessel and crosslinking and curing reaction is carried out to obtain iron-loaded precursor polymer microspheres; the temperature of the crosslinking and curing reaction is 200-260 ℃ and the reaction time is 4-12 h; (3) Pyrolysis conversion: The precursor polymer microspheres loaded with iron are subjected to programmed temperature pyrolysis in an inert or vacuum atmosphere, and Si-BCN ceramic microspheres loaded with active iron are obtained after cooling; the programmed temperature rise rate is 2-10 ℃ / min; the final temperature of the pyrolysis is 800-1400 ℃, and the holding time is 0.5-3 h; (4) Reduction: The Si-BCN ceramic microspheres loaded with active iron are reduced in a flowing hydrogen atmosphere to obtain the Si-BCN ceramic microsphere catalyst with high specific surface area loaded with active iron. The reduction temperature is 600-700 °C and the temperature is maintained for 3-6 h.

2. The preparation method according to claim 1, characterized in that, In step (1), the organic solvent includes any one or a combination of two or more of acetonitrile, tetrahydrofuran, xylene, N,N-dimethylformamide, and anhydrous ethanol.

3. The preparation method according to claim 1, characterized in that, The inert atmosphere mentioned in step (3) is an argon atmosphere.

4. The preparation method according to claim 1, characterized in that, In step (4), the gas hourly space velocity of hydrogen is 600-1800 h⁻¹. –1 .

5. A Si-BCN ceramic microsphere catalyst with high specific surface area loaded with active iron, prepared by the preparation method according to any one of claims 1-4.

6. The application of a Si-BCN ceramic microsphere catalyst with high specific surface area supported on active iron as described in claim 5 in the preparation of sustainable aviation fuel.

7. The application according to claim 6, 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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