Iron-carbon composite aerogel catalyst for preparing biofuel from syngas and preparation method and application thereof

Abstract

This invention belongs to the field of heterogeneous catalysis and materials synthesis, and discloses an iron-carbon composite aerogel catalyst for the production of biofuel from syngas, its preparation method, and its application. The catalyst uses carbon fiber reinforced carbon aerogel as a framework, on which highly dispersed nano-iron and iron carbide active centers are grown in situ. In preparation, an iron-containing precursor solution formed by iron source, manganese salt, phenolic resin, and hexamethylenetetramine in an organic solvent is mixed with pre-oxidized polyacrylonitrile fibers to form an iron-containing phenolic resin sol. This is followed by a hydrothermal crosslinking reaction to form an iron-containing wet gel. After aging and supercritical CO2 drying, the gel is pyrolyzed in an inert or reducing atmosphere using a one-step temperature-programmed heating process to form the iron-carbon composite aerogel catalyst. This method results in highly dispersed and firmly bonded iron particles, and the catalyst exhibits high activity in Fischer-Tropsch synthesis and high activity against carbon. 10 -C 20 The jet fuel fraction exhibits high selectivity, excellent resistance to sintering, and long-term stability.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalysis and materials synthesis, specifically relating to an iron-carbon composite aerogel catalyst for the production of biofuel from syngas, its preparation method, and its application. Background Technology

[0002] Faced with severe decarbonization pressures on the global aviation industry, sustainable aviation fuel (SAF) is considered crucial for achieving net-zero emissions due to its significant emission reduction potential. Among numerous production technologies, the biomass gasification-Fischer-Tropsch synthesis (FTS) route has become one of the most promising directions for large-scale scalability due to its wide availability of raw materials and excellent product performance. This process first converts biomass into syngas (H2 / CO), and then uses an FTS catalyst to convert it into carbon. 10 -C 20 This mixture, primarily composed of straight-chain hydrocarbons, is an ideal feedstock for producing standard-compliant SAFs through subsequent processes such as hydroisomerization. However, current multi-step processing methods are complex and energy-intensive. Therefore, developing novel FTS catalysts with high selectivity and activity for the direct generation of straight-chain aviation kerosene fractions has become a key breakthrough and urgent need for simplifying processes, reducing costs, and promoting the commercial application of SAFs.

[0003] The performance of a catalyst largely depends on its support. Traditional FTS catalysts (especially iron-based catalysts) often use metal oxides such as Al2O3, SiO2, and TiO2, or activated carbon as supports. However, these supports have inherent limitations in meeting the specific requirements of efficient SAF production: First, most oxide supports have microporous or narrow mesoporous structures, which are not conducive to the rapid diffusion of large molecular hydrocarbon products, easily leading to pore blockage and secondary cracking, reducing liquid fuel yield, and accelerating carbon deposition and deactivation; Second, some supports (such as Al2O3) have acidic sites on their surface, which may trigger undesirable hydrocarbon cracking or isomerization side reactions, interfering with the precise control of the selectivity of the target product; Moreover, during the long-term operation of FTS, the support must withstand reaction heat, phase transformation stress, and possible mechanical wear, and some supports have insufficient strength or the risk of thermal sintering; Finally, excessively strong metal-support interactions may lead to difficulties in the reduction of the active phase, while excessively weak interactions cannot stabilize nanoparticles.

[0004] In recent years, carbon materials have been considered promising supports due to their chemical inertness, tunable surface properties, and good electrical / thermal conductivity. Among them, carbon aerogels stand out as a novel porous carbon material with a three-dimensional continuous network structure, high specific surface area, designable hierarchical pores (micro, meso, and macropores coexisting), and low density. Their unique advantages include: the interconnected open-pore structure greatly optimizes mass transfer efficiency; the hydrophobic surface reduces water poisoning of active sites (FTS is a strong water-electrolytic reaction); the carbon framework itself can act as an electron carrier, modulating the electronic state of active metals; and, most importantly, its structure can be precisely tailored at the molecular level through precursors and synthesis processes. Carbon fiber-reinforced carbon aerogels further enhance these advantages, endowing the support with excellent mechanical toughness, structural integrity, and thermal shock resistance, providing an ideal substrate platform for constructing high-performance, long-life FTS catalysts.

[0005] To further enhance the mechanical strength of carbon aerogels, researchers have attempted to introduce reinforcements. For example, Chinese patents CN118954482A and CN120309376A disclose methods for preparing fiber-reinforced phenolic-based carbon aerogel composites, using pre-oxidized polyacrylonitrile (PAN) fibers as reinforcements and utilizing the synergistic shrinkage effect during carbonization to prevent cracking of the composite material. However, these patents only focus on the mechanical and thermal properties of the material, without addressing the introduction of any catalytically active components or exploring the potential advantages of this structure in catalytic reactions.

[0006] In the research of iron-based FTS catalysts, researchers have developed various confinement strategies to improve the dispersion and stability of the active component. For example, Chinese patent CN104368344A confines the cobalt active component within the pores of a mesoporous carbon support; Chinese patent CN111821976A fills iron-based nanoparticles into the cavities of carbon-based nanocages, utilizing the three-dimensional confinement effect of the cavities to suppress particle sintering. However, the above studies all adopt the traditional approach of first preparing the support and then loading the active component. For aerogel supports with complex three-dimensional network structures, the precursor solution of the active component is difficult to penetrate uniformly into the depths of the network, resulting in metal particles being mainly loaded on the surface of the support. This limits the dispersion and makes the catalyst prone to migration, aggregation, and loss during high-temperature reactions, making it difficult to guarantee the long-term stability of the catalyst.

[0007] In recent years, single-atom catalysts have become a research hotspot in pursuit of higher atom utilization and unique catalytic performance. For example, Chinese patent CN114824329A loaded iron ions onto phenolic resin spheres via electrostatic adsorption and then carbonized them to obtain an iron single-atom catalyst; Chinese patent CN115395026A constructed an N-doped carbon aerogel supported on Fe single atoms through directional freeze-drying combined with a metal-organic coordination strategy. These studies have demonstrated the feasibility of introducing metal species in situ during the formation of carbon materials. However, the application areas of the above studies are mainly in electrocatalysis (such as oxygen reduction reaction), and their core focus is on the construction and identification of single-atom sites. For thermocatalytic systems involving fiber reinforcement, hierarchical channel construction, and multi-metal synergy (such as Fischer-Tropsch synthesis), how to achieve the integrated synergistic integration of macroscopic structure construction (fiber reinforcement), mesoscopic channel regulation (aerogel network), and microscopic active site anchoring (in situ introduction of iron / manganese) in the same process remains a gap that has not yet been revealed by existing technologies.

[0008] In summary, developing an FTS catalyst that simultaneously achieves macroscopic mechanical strength, mesoscopic mass transfer efficiency, and microscopic active site stability, while also enabling precise control of product selectivity, remains a pressing technical challenge in this field. In particular, the simultaneous, in-situ, and uniform introduction and anchoring of catalytic active centers during the construction of fiber-reinforced carbon aerogels to achieve integrated structure-function synthesis, and the elucidation of the deep synergistic mechanisms among these elements, are crucial for advancing the efficient and targeted synthesis of SAFs. Summary of the Invention

[0009] To address the following technical shortcomings of existing Fischer-Tropsch synthesis catalysts in the preparation of sustainable aviation fuel (SAF): 1. The active component (iron) is prone to migration, agglomeration, and sintering under high-temperature reaction conditions, leading to rapid catalyst deactivation; 2. Traditional carriers (oxides, activated carbon) have simple pore structures and low mass transfer efficiency, which is not conducive to long-chain hydrocarbons (C6N2, C4N2, C4N2, C4N2). 10 -C 20 The generation and diffusion of ); 3. Existing research on fiber-reinforced carbon aerogels only focuses on their mechanical properties as structural / thermal insulation materials, without addressing the introduction of catalytically active components, and even less revealing the interaction mechanism between reinforcing fibers and active metals; 4. Traditional processes that first prepare the support and then load the active component are difficult to achieve highly uniform dispersion of metals within complex three-dimensional networks, resulting in low utilization of active sites and poor stability. 5. The synergistic mechanism of manganese auxiliaries in the unique fiber reinforcement-in-situ confinement system is poorly understood, making it impossible to precisely control the product's selectivity towards C. 10 -C 20 Aviation kerosene fraction enrichment.

[0010] This invention provides an iron-carbon composite aerogel catalyst for the production of biofuel from syngas, its preparation method and application, by using carbon fiber reinforced carbon aerogel as a framework, on which highly dispersed nano-iron and iron carbide active centers are grown in situ.

[0011] The technical solution of this invention is: The first aspect of this invention provides a method for preparing an iron-carbon composite aerogel catalyst for the production of biofuel from syngas, comprising the following steps: (1) Preparation of precursor solution: Dissolve phenolic resin, hexamethylenetetramine, manganese salt and iron source together in an organic solvent, stir thoroughly, and prepare a uniform iron-containing precursor solution; (2) Dispersing reinforcing fibers: An appropriate amount of pre-oxidized polyacrylonitrile fibers are ultrasonically emulsified and dispersed, added to the iron-containing precursor solution, and stirred evenly to form an iron-containing phenolic resin mixed sol. (3) Gelification and cross-linking: The iron-containing phenolic resin mixture is subjected to a hydrothermal cross-linking reaction to obtain an iron-containing wet gel; (4) Aging: The iron-containing wet gel was placed in anhydrous ethanol for aging to strengthen its three-dimensional network framework and obtain aged iron-containing wet gel. (5) Supercritical drying: The aged iron-containing wet gel was subjected to supercritical CO2 drying to obtain iron-containing carbon fiber reinforced phenolic resin composite aerogel. (6) Pyrolysis carbonization and activation: The composite aerogel is pyrolyzed and carbonized under a flowing inert atmosphere, and then activated under a flowing hydrogen atmosphere to obtain the iron-carbon composite aerogel catalyst.

[0012] Preferably, the mass ratio of the pre-oxidized polyacrylonitrile fiber to phenolic resin, hexamethylenetetramine, manganese salt, iron source and organic solvent is 0.1-0.6:0.8-1.6:0.1-0.6:0.01-0.2:1-2:10-12.

[0013] Preferably, the organic solvent comprises any one or a combination of two or more of tetrahydrofuran, xylene, N,N-dimethylformamide, and anhydrous ethanol, and the iron source is iron acetylacetonate. The manganese salt is manganese acetylacetonate.

[0014] Preferably, the pre-oxidation temperature of the pre-oxidized polyacrylonitrile fiber in step (2) is 195-255 °C.

[0015] Preferably, the ultrasonic emulsification time in step (2) is 20-30 min.

[0016] Preferably, the temperature of the hydrothermal crosslinking reaction in step (3) is 100-120 °C and the time is 3-5 h.

[0017] Preferably, the aging time in step (4) is 3-5 days.

[0018] Preferably, the conditions for supercritical CO2 drying in step (5) are: temperature 45-60 ℃ and pressure 8.3-9 MPa.

[0019] Preferably, the pyrolysis carbonization process in step (6) is as follows: the iron-containing carbon fiber reinforced phenolic resin composite aerogel is placed in a high-temperature box-type atmosphere sintering furnace and pyrolyzed in an inert atmosphere. The temperature is increased to 800-1400 ℃ at a heating rate of 3-6 ℃ / min for 1-3 h, followed by slow cooling to room temperature to obtain iron-containing carbon fiber reinforced carbon aerogel. The activation process is as follows: the iron-containing carbon fiber reinforced carbon aerogel is reduced in a hydrogen atmosphere at a reduction temperature of 600-700 ℃ and held at this temperature for at least 3 h, then cooled to room temperature to obtain an iron-carbon composite aerogel catalyst. The gas hourly space velocity (VHSV) of both the inert atmosphere and hydrogen is 600-1800 h⁻¹. –1 .

[0020] The second aspect of the present invention provides an iron-carbon composite aerogel catalyst, which is prepared by the above method, using carbon fiber reinforced carbon aerogel as a framework, on which highly dispersed nano-iron and iron carbide active centers are grown in situ.

[0021] A third aspect of the present invention provides the application of the above-mentioned iron-carbon composite aerogel catalyst in the preparation of sustainable aviation fuel or biofuel.

[0022] Preferably, the specific steps of the application are as follows: The iron-carbon composite aerogel 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 catalyst was then heated to 400-550 °C for reduction and activation in a flowing hydrogen atmosphere for 1-5 h. 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.

[0023] The advantages and beneficial effects of this invention are: 1. This invention abandons the traditional approach of "preparing the carrier first, then loading the active component," and pioneers a one-step synthesis method that directly introduces an active iron source (such as iron acetylacetone) into the phenolic resin / fiber precursor. The iron source is uniformly "woven" into the organic polymer framework at the molecular level from the initial formation of the aerogel three-dimensional network. During the subsequent programmed pyrolysis process, polymer carbonization (forming a conductive carbon network and a robust carbon fiber reinforcement) and in-situ reduction, confinement, and carbonization of the iron precursor (the iron precursor is in-situ reduced and confined within the growing carbon matrix) are simultaneously achieved. This process spontaneously forms highly dispersed, size-controllable nano-iron / iron carbide active centers that strongly interact with the carbon carrier. This unique process of "simultaneous completion of carrier growth and active site anchoring" essentially constructs a "nanoreactor" type composite structure: the continuous network and hierarchical pores of the carbon aerogel provide unobstructed mass transfer channels from the macroscopic to the nanoscale, while the nano-iron / iron carbide active centers confined at the carbon framework nodes achieve extremely high thermodynamic stability.

[0024] 2. Multiple mechanisms synergistically enhance catalytic performance Excellent thermal stability and long lifespan: The three-dimensional network of carbon aerogel provides rigid confinement to the nano-iron particles, effectively inhibiting surface migration, sintering, and agglomeration of active components at high reaction temperatures. First, the conductive carbon skeleton promotes rapid electron transfer during the reaction, potentially optimizing the kinetics of CO dissociation and chain initiation. Simultaneously, the interconnected open-pore hierarchical structure ensures efficient transport of syngas reactants to active sites and facilitates the rapid detachment of generated liquid hydrocarbon products (especially long-chain products) from active sites into the fluid phase, significantly suppressing carbon deposition side reactions caused by excessive polymerization. This results in excellent long-term operational stability of the catalyst. The physical confinement effect and strong interfacial bonding of the nanoparticles enable the catalyst to exhibit superior anti-sintering and anti-carbon deposition capabilities under high-temperature Fischer-Tropsch synthesis conditions, significantly extending catalyst lifespan.

[0025] High activity and high selectivity: Highly dispersed and electronically optimized nano-active sites endow the catalyst with excellent initial activity. The in-situ confined nano-iron / iron carbide active centers, firmly anchored by the carbon network, exhibit strong iron-carbon interfacial interactions, which can regulate the electron cloud density of the active metal, thereby affecting its chain growth probability for products with different carbon numbers. The addition of manganese promoters forms a synergistic effect with iron. By precisely controlling the precursor composition and pyrolysis conditions, this interfacial state can be "tailored," guiding the reaction pathway towards the formation of C. 10 -C 20 The directional tilting of the aviation kerosene fraction allows for precise enhancement of selectivity for target products, potentially overcoming the limitations of traditional SAF product distribution. The unique synergistic effect of staged pores and interface effects significantly improves its selectivity for sustainable aviation fuel target fractions (C). 10 -C 20The selectivity of ).

[0026] The introduction of carbon fiber enhances the toughness and structural integrity of the entire aerogel framework, enabling the catalyst to have good wear resistance and crush resistance in industrial reactors such as slurry beds or fixed beds, thus ensuring the process stability of long-term operation.

[0027] The process is simple and highly controllable: the one-step synthesis method simplifies the traditional multi-step process into a continuous and integrated process, reduces production links, improves efficiency, and the designability of the precursor solution makes it easier to precisely control the composition and structure of the catalyst.

[0028] 3. This invention discovers a critical window (195-255℃) for the pre-oxidation degree of pre-oxidized polyacrylonitrile fibers. Within this window, the fiber can achieve perfect synergistic shrinkage with the phenolic resin matrix (avoiding cracking) and provide an appropriate amount of surface oxygen-containing functional groups for anchoring iron ions, thereby achieving precise control over the dispersion of iron species. Below this window, shrinkage is mismatched and anchoring points are insufficient; above this window, the fiber becomes over-carbonized and brittle, losing its chemical bonding ability. Attached Figure Description

[0029] Figure 1 Transmission electron microscopy image of the iron-carbon composite aerogel catalyst prepared in Example 1; Figure 2 Transmission electron microscopy image of the iron-carbon composite aerogel catalyst prepared in Example 2; Figure 3 Transmission electron microscopy (TEM) image of the iron-carbon composite aerogel catalyst prepared in Example 3.

[0030] Figure 4 The image shows a scanning electron microscope (SEM) image of the iron-carbon composite aerogel catalyst prepared in Example 1. Detailed Implementation

[0031] 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.

[0032] Example 1 A method for preparing an iron-carbon composite aerogel catalyst includes the following steps: (1) Weigh 1 g of phenolic resin, 0.4 g of hexamethylenetetramine, 0.01 g of manganese acetylacetone and 1 g of iron acetylacetone, dissolve them together in 10 g of anhydrous ethanol, stir thoroughly, and prepare a uniform iron-containing precursor solution. (2) Place 0.4 g of polyacrylonitrile fiber in an oven and pre-oxidize it at 235 °C. Disperse the pre-oxidized polyacrylonitrile fiber with an ultrasonic emulsifier for 20 min and break it up. Add it to the above iron-containing precursor solution and stir evenly to form an iron-containing phenolic resin mixed sol. (3) The iron-containing phenolic resin mixture was placed in a high-pressure hydrothermal reactor and subjected to a hydrothermal crosslinking reaction in a 100 ℃ oven for 5 h to obtain an iron-containing wet gel. (4) The iron-containing wet gel was placed in anhydrous ethanol for 3 days to strengthen its three-dimensional network skeleton and obtain aged iron-containing wet gel.

[0033] (5) The solvent anhydrous ethanol in the aged iron-containing wet gel was replaced by a CO2 supercritical drying device. The CO2 supercritical drying was carried out at a temperature of 45 ℃ and 8.3 MPa to obtain iron-containing carbon fiber reinforced phenolic resin composite aerogel. (6) The iron-containing carbon fiber reinforced phenolic resin composite aerogel was placed in a high-temperature box-type atmosphere sintering furnace and pyrolyzed and carbonized in a flowing nitrogen atmosphere. The temperature was increased to 1000 °C at a heating rate of 5 °C / min for 3 h, followed by slow cooling to room temperature to obtain iron-containing carbon fiber reinforced carbon aerogel (C / C). The activation process was as follows: the iron-containing carbon fiber reinforced carbon aerogel was reduced in a flowing hydrogen atmosphere, held at 600 °C for 3 h, and cooled to room temperature to obtain the iron-carbon composite aerogel catalyst. The gas hourly space velocity (VHSV) of both the inert atmosphere and hydrogen was 600 h⁻¹. -1 The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of the iron-carbon composite aerogel catalyst prepared in Example 1 are shown below. Figure 1 , Figure 4 As shown, the active iron and iron carbide particles are highly dispersed and uniformly confined within the carbon aerogel framework.

[0034] Example 2 The difference from Example 1 is that the amount of phenolic resin added in step (1) is 1.6 g.

[0035] Transmission electron microscopy (TEM) image of the iron-carbon composite aerogel catalyst prepared in Example 2 is shown below. Figure 2 As shown, after increasing the amount of phenolic resin, the active iron and iron carbide particles still remain uniformly dispersed, but the density of the carbon aerogel skeleton is increased.

[0036] Example 3 The difference from Example 1 is that the amount of iron acetylacetone added in step (1) is 2 g.

[0037] Transmission electron microscopy (TEM) image of the iron-carbon composite aerogel catalyst prepared in Example 3 is shown below. Figure 3As shown, it can be seen that after increasing the amount of iron source, the density of confined iron and iron carbide active particles in the carbon aerogel skeleton increases significantly, but the particles still maintain a relatively uniform dispersion state.

[0038] Example 4 The difference from Example 1 is that the aging time in step (4) is 4 days.

[0039] Example 5 The difference from Example 1 is that the pyrolysis carbonization temperature in step (6) is 1400 °C.

[0040] Example 6 The difference from Example 1 is that the hydrogen atmosphere reduction temperature in step (6) is 700 °C.

[0041] Comparative Example 1 The only difference from Example 1 is that in step (1), the phenolic resin is replaced with epoxy resin.

[0042] Comparative Example 2 The only difference from Example 1 is that the pyrolysis carbonization temperature in step (6) is 500 °C.

[0043] Comparative Example 3 The only difference from Example 1 is that the hydrogen atmosphere reduction is missing in step (6).

[0044] Comparative Example 4 The only difference from Example 1 is that the pre-oxidation temperature in step (2) is 180 °C.

[0045] Comparative Example 5 The only difference from Example 1 is that the pre-oxidation temperature in step (2) is 260 °C.

[0046] Comparative Example 6 The difference from Example 1 is that manganese acetylacetone is not used in step (1). Step (1) is as follows: Weigh 1 g of phenolic resin, 0.4 g of hexamethylenetetramine and 1 g of iron acetylacetone and dissolve them together in 10 g of anhydrous ethanol. Stir thoroughly to prepare a uniform iron-containing precursor solution.

[0047] Comparative Example 7 The only difference from Example 1 is that manganese acetylacetonate is replaced with nickel acetylacetonate in step 1.

[0048] Comparative Example 8 A method for preparing iron-carbon composite aerogel catalyst by post-impregnation includes the following steps: (1) Weigh 1 g of phenolic resin, 0.4 g of hexamethylenetetramine and 0.01 g of manganese acetylacetone, dissolve them in 10 g of anhydrous ethanol, stir thoroughly, and prepare an iron-free precursor solution; (2) Place 0.4 g of polyacrylonitrile fiber in an oven and pre-oxidize it at 235 °C. Disperse the pre-oxidized polyacrylonitrile fiber with an ultrasonic emulsifier for 20 min and break it up. Add it to the above precursor solution and stir evenly to form a phenolic resin mixed sol. (3) The phenolic resin mixture was placed in a high-pressure hydrothermal reactor and subjected to a hydrothermal crosslinking reaction in a 100 ℃ oven for 5 h to obtain an iron-free wet gel. (4) The iron-free wet gel was placed in anhydrous ethanol for 3 days to age, and the aged iron-free wet gel was obtained. (5) The solvent anhydrous ethanol in the aged iron-free wet gel was replaced by a CO2 supercritical drying device. The CO2 supercritical drying was carried out at a temperature of 45 ℃ and 8.3 MPa to obtain carbon fiber reinforced phenolic resin composite aerogel. (6) The carbon fiber reinforced phenolic resin composite aerogel was placed in a high-temperature box-type atmosphere sintering furnace and pyrolyzed in a flowing nitrogen atmosphere. The temperature was increased to 1000 ℃ at a heating rate of 5 ℃ / min and pyrolyzed for 3 h. Then it was slowly cooled to room temperature to obtain an iron-free carbon fiber reinforced carbon aerogel (C / C) carrier. (7) Weigh 1 g of iron acetylacetone and dissolve it in 10 g of anhydrous ethanol to prepare a post-impregnation solution. Immerse the iron-free carbon fiber reinforced carbon aerogel carrier obtained in step (6) into the above post-impregnation solution, stir and impregnate at room temperature for 12 h, and then dry in an oven at 60 ℃ for 12 h to obtain a composite material loaded with iron precursor. (8) The composite material obtained in step (7) is reduced in a flowing hydrogen atmosphere by heating to 600 ℃ at a rate of 5 ℃ / min and holding for 3 h at a gas hourly space velocity of 600 h⁻¹. -1 After cooling to room temperature, an iron-carbon composite aerogel catalyst was obtained.

[0049] Performance testing and analysis The iron-carbon composite aerogel catalysts prepared in Examples 1-6 and Comparative Examples 1-8 were respectively loaded into the catalyst bed of a continuous fixed-bed hydrogenation reactor. The catalyst loading amount was 1.0 g, and inert quartz sand was filled above and below the catalyst bed. After loading, in-situ reduction pretreatment was first performed at atmospheric pressure and a gas space velocity of 600 h⁻¹. –1The catalyst bed was activated by reduction at 500 °C for 3 h under a hydrogen atmosphere with a heating rate of 5 °C / min. After reduction, the catalyst bed was cooled to 280 °C, the hydrogen supply was shut off, and syngas was introduced. The reaction was carried out at a temperature of 280 °C, a pressure of 4.0 MPa, and a gas space velocity of 3000 h⁻¹. –1 Under these conditions, syngas (H2:CO volume ratio of 2.0) was introduced into the reactor and operated continuously for 50 h. Catalyst performance was evaluated by CO conversion, target product selectivity, and the rate of decrease in conversion per h.

[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 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: 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.

[0052] Table 1 Catalyst Test Results

[0053] The results are shown in Table 1. As can be seen from Examples 1-6, the obtained iron-carbon composite aerogel catalysts all exhibited excellent catalytic performance within the preparation parameter range described in this application. Among them, Example 1 showed the best performance at C... 10 -C 20 The hydrocarbon selectivity reached 75.63%, the CO conversion rate was 74.80%, and the conversion rate decreased at a rate of only 0.030% per hour. In Examples 2-6, the amount of phenolic resin, iron content, aging time, pyrolysis carbonization temperature, and reduction temperature were adjusted respectively. Although the performance fluctuated slightly, it still maintained high selectivity and stability, verifying the rationality of the process window of this application.

[0054] Comparative Example 1 replaced phenolic resin with epoxy resin, C 10 -C 20 Hydrocarbon selectivity decreased to 52.34%, CO conversion rate decreased to 61.13%, and the rate of decrease in conversion rate per hour surged to 0.136%. This indicates that phenolic resin is irreplaceable as a carbon precursor. After pyrolysis, it forms a carbon skeleton with suitable pore structure and mechanical strength, achieving good interfacial matching with pre-oxidized fibers. In contrast, after pyrolysis, epoxy resin has a dense carbon structure and shrinkage mismatch, leading to easy aggregation of active components.

[0055] Comparative Example 2 had a pyrolysis carbonization temperature of only 500 ℃, C 10 -C 20 The hydrocarbon selectivity was 50.67%, the CO conversion rate was 57.78%, and the conversion rate decreased at a rate as high as 0.154% per hour. Insufficient pyrolysis temperature resulted in poor electrical conductivity and insufficient mechanical strength of the carbon skeleton, making it difficult for iron species to be converted into the active iron carbide phase (Fe3C / Fe5C2), which has few active sites and an unstable structure.

[0056] Comparative Example 3 lacks the hydrogen reduction step, C 10 -C 20 Hydrocarbon selectivity decreased to 49.65%, CO conversion was 56.38%, and the conversion rate decreased by 0.198% per hour. This demonstrates that hydrogen reduction is key to the formation of the active iron carbide phase. Unreduced iron mainly exists in the oxidized state and cannot efficiently catalyze chain growth reactions.

[0057] In Comparative Example 4, the pre-oxidation temperature was adjusted to 180 ℃, and in Comparative Example 5, the pre-oxidation temperature was 260 ℃. The fiber shrinkage rate did not match the matrix, resulting in microcracks; insufficient oxygen-containing functional groups on the surface led to increased iron particle size and poor dispersion. The C content of Comparative Example 4... 10 -C 20 The hydrocarbon selectivity, CO conversion rate, and rate of decrease in conversion rate per hour were 47.58%, 55.64%, and 0.221%, respectively. (Comparative Example 5) 10 -C 20The hydrocarbon selectivity, CO conversion rate, and the rate of decrease in conversion rate per hour were 45.90%, 54.72%, and 0.253%, respectively, proving that there is a "golden window" for the degree of pre-oxidation. Too low or too high a degree of pre-oxidation cannot achieve synergistic contraction and efficient anchoring.

[0058] Comparative Example 6 did not add manganese additive, while Comparative Example 7 replaced manganese with a nickel additive with similar properties. The performance of both was significantly degraded: Comparative Example 6 showed a decrease in C... 10 -C 20 Hydrocarbon selectivity 44.35%, CO conversion rate 52.84%, conversion rate decrease rate per h 0.264%; Comparative Example 7 C 10 -C 20 The hydrocarbon selectivity was 42.70%, the CO conversion rate was 50.91%, and the rate of decrease in conversion rate per hour was 0.287%. This indicates that manganese is not a simple additive, but rather acts as a structural and electronic additive in synergy with iron to precisely regulate the valence state distribution, dispersion state, and iron carbide formation ratio of iron. This allows for precise control over the chain growth probability and the selectivity of jet fuel fractions. The introduction of manganese is irreplaceable.

[0059] The catalyst prepared by the post-impregnation method in Comparative Example 8 has a C 10 -C 20 The hydrocarbon selectivity of 41.10% and the CO conversion rate of 49.20% were significantly lower than those of all other examples, and the conversion rate decreased by as much as 0.334% per hour, indicating that the iron species were unevenly distributed and had a weak interaction with the carbon support, resulting in catalytic activity and stability that were significantly lower than those of the one-step preparation sample of this invention.

[0060] In summary, this application achieves a high degree of catalyst structural matching and precise control of catalytic performance by optimizing the carbon precursor, precisely controlling the pre-oxidation temperature, pyrolysis carbonization temperature, and reduction activation steps, and introducing the synergistic effect of manganese and iron. The comparative examples, from different perspectives, verify the necessity and synergy of the key process parameters and component selection, collectively constituting the completeness of the technical solution of this application.

[0061] 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 within 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-carbon composite aerogel catalyst for the production of biofuel from syngas, characterized in that, Includes the following steps: (1) Preparation of precursor solution: Dissolve phenolic resin, hexamethylenetetramine, manganese salt and iron source together in an organic solvent, stir thoroughly, and prepare a uniform iron-containing precursor solution; (2) Dispersing reinforcing fibers: An appropriate amount of pre-oxidized polyacrylonitrile fibers are ultrasonically emulsified and dispersed, added to the iron-containing precursor solution, and stirred evenly to form an iron-containing phenolic resin mixed sol; the pre-oxidation temperature of the pre-oxidized polyacrylonitrile fibers is 195-255 ℃. (3) Gelification and cross-linking: The iron-containing phenolic resin mixture is subjected to a hydrothermal cross-linking reaction to obtain an iron-containing wet gel; (4) Aging: The iron-containing wet gel was placed in anhydrous ethanol for aging to obtain aged iron-containing wet gel; (5) Supercritical drying: The aged iron-containing wet gel was subjected to supercritical CO2 drying to obtain iron-containing carbon fiber reinforced phenolic resin composite aerogel. (6) Pyrolysis carbonization and activation: The composite aerogel is pyrolyzed and carbonized under a flowing inert atmosphere, and then activated under a flowing hydrogen atmosphere to obtain the iron-carbon composite aerogel catalyst. The pyrolysis carbonization conditions are: pyrolysis at a heating rate of 3-6 °C / min to 800-1400 °C for 1-3 h.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the pre-oxidized polyacrylonitrile fiber, phenolic resin, hexamethylenetetramine, manganese salt, iron source and organic solvent is 0.1-0.6: 0.8-1.6: 0.1-0.6: 0.01-0.2: 1-2: 10-12.

3. The preparation method according to claim 1, characterized in that, The organic solvent in step (1) includes any one or a combination of two or more of tetrahydrofuran, xylene, N,N-dimethylformamide and anhydrous ethanol, the iron source is iron acetylacetone, and the manganese salt is manganese acetylacetone.

4. The preparation method according to claim 1, characterized in that, The ultrasonic emulsification time in step (2) is 20-30 min.

5. The preparation method according to claim 1, characterized in that, The temperature of the hydrothermal crosslinking reaction in step (3) is 100-120 ℃ and the crosslinking time is 3-5 h; the aging time in step (4) is 3-5 days.

6. The preparation method according to claim 1, characterized in that, The conditions for supercritical CO2 drying in step (5) are: temperature 45-60 ℃ and pressure 8.3-9 MPa.

7. The preparation method according to claim 1, characterized in that, The pyrolysis and carbonization process in step (6) is as follows: the iron-containing carbon fiber reinforced phenolic resin composite aerogel is placed in a high-temperature box-type atmosphere sintering furnace and pyrolyzed in an inert atmosphere. The temperature is increased to 800-1400 ℃ at a heating rate of 3-6 ℃ / min for 1-3 h, and then slowly cooled to room temperature to obtain iron-containing carbon fiber reinforced carbon aerogel. The activation process is as follows: the iron-containing carbon fiber reinforced carbon aerogel is reduced in a hydrogen atmosphere at a reduction temperature of 600-700 ℃ and held at this temperature for at least 3 h. After cooling to room temperature, the iron-carbon composite aerogel catalyst is obtained. The gas hourly space velocity of both the inert atmosphere and hydrogen is 600-1800 h⁻¹. –1 .

8. An iron-carbon composite aerogel catalyst, characterized in that, The method described in any one of claims 1-7 is used to prepare a carbon fiber reinforced carbon aerogel as a framework on which highly dispersed nano-iron and iron carbide active centers are grown in situ.

9. The application of the iron-carbon composite aerogel catalyst as described in claim 8 in the preparation of sustainable aviation fuel or biofuel.

10. The application according to claim 9, characterized in that, The iron-carbon composite aerogel 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 catalyst was then heated to 400-550 °C for reduction and activation in a flowing hydrogen atmosphere for 1-5 h. 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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