Carbon fiber-based monolithic catalyst for photo-thermal synthesis of dimethyl carbonate from carbon dioxide and methanol and preparation method thereof

Abstract

The application discloses a carbon fiber-based monolithic catalyst for photo-thermal synthesis of dimethyl carbonate from carbon dioxide and methanol and a preparation method thereof. The monolithic catalyst comprises a carbon fiber monolithic carrier and an active component loaded on the surface of the carbon fiber monolithic carrier. The carbon fiber monolithic carrier is a self-supporting three-dimensional network structure carbon fiber material, and the active component is one or more metal oxides in Ce, Zr, Ti, La, Pr, Nd, Bi and W corresponding oxides, and is uniformly loaded on the surface of the carbon fiber monolithic carrier to form an active layer. Compared with the existing powder catalyst, the catalyst has the advantages of stable monolithic structure, easy separation and recovery, convenient fixed packing, suitability for continuous reaction and the like, and has photo-thermal response capability and catalytic activity, and has a good application prospect in the photo-thermal catalytic synthesis of dimethyl carbonate from carbon dioxide and methanol.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a carbon fiber-based monolithic catalyst for the photothermal synthesis of dimethyl carbonate from carbon dioxide and methanol, and its preparation method. Background Technology

[0002] Among numerous CO2 conversion technologies, catalytic conversion has attracted widespread attention due to its high efficiency and controllability. However, traditional thermocatalytic processes typically require high temperature and pressure conditions, resulting in high energy consumption and demanding equipment requirements. While photocatalysis can utilize solar energy to drive reactions at ambient temperature and pressure, it generally suffers from problems such as rapid recombination of photogenerated carriers, low utilization of the solar spectrum, and insufficient exposure of catalyst active sites, leading to limited conversion efficiency. Carbon fiber materials, due to their excellent conductivity, high specific surface area, good chemical stability, weavability, and high mechanical strength, have become highly promising carrier materials in the field of catalysis. Patent CN 201811564670.0 discloses a method for catalytically growing carbon nanotubes on the surface of carbon fiber fabric, which reduces the growth temperature and improves the mechanical properties of the composite material by using a bimetallic catalyst. CN 202411836979.6 discloses a photothermal-electrothermal fabric that achieves synergistic photothermal and electrothermal applications in seawater desalination by constructing a TiO2 insulating layer and a polypyrrole photothermal layer, demonstrating the application potential of carbon fiber in photothermal conversion. CN 201710008525.3 discloses a nickel-based catalyst supported on a carbon fiber and metal oxide composite support for the reforming of methane into syngas. This technology utilizes carbon fiber to improve the support performance. CN 202311017283.6 designs a Pt-loaded Y-doped TiO2 nanoarray carbon fiber cloth for the thermo-photocatalytic synergistic degradation of formaldehyde.

[0003] While existing technologies have demonstrated the use of carbon fibers as catalyst supports or photothermal materials, and research on catalysts for CO2 conversion exists, the following problems and shortcomings remain: Most CO2 conversion catalysts are in powder form, leading to difficulties in separation and recovery, easy agglomeration and deactivation, and large bed pressure drops in practical applications, making it difficult to meet the requirements of continuous and large-scale operations. Existing photocatalysts have low utilization rates of the full spectrum of solar energy, especially the near-infrared light, which accounts for approximately 50% of solar energy, limiting their energy conversion efficiency. Pure thermocatalysis processes are energy-intensive, while pure photocatalysis often suffers from insufficient reaction driving force and limited efficiency. Research on monolithic photothermal catalysts that can synergistically utilize light and heat energy to drive CO2 conversion under mild conditions is still insufficient. The comprehensive advantages of carbon fibers as monolithic catalyst supports have not been fully utilized in the field of CO2 conversion. Their inherent conductivity promotes charge transfer, their three-dimensional network structure facilitates reactant mass transfer and multiple scattering absorption of light, and their good mechanical properties allow for processing into various reactor configurations. Summary of the Invention

[0004] Technical Objective: To address the shortcomings of existing technologies, this invention discloses a carbon fiber-based monolithic catalyst for the photothermal synthesis of dimethyl carbonate from carbon dioxide and methanol, and its preparation method. This addresses the following problems with existing catalysts for the synthesis of dimethyl carbonate from carbon dioxide and methanol: difficulty in separating and recovering powdered catalysts, easy agglomeration and deactivation, and unfavorable for continuous reactions; insufficient synergistic utilization of light and heat energy in conventional catalytic systems, resulting in low photothermal conversion efficiency; and difficulty in simultaneously achieving dispersion of active sites and structural stability, thus affecting reaction activity, selectivity, and lifespan.

[0005] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution.

[0006] A carbon fiber-based monolithic catalyst includes a carbon fiber monolithic support and an active component loaded on the surface of the carbon fiber monolithic support; the carbon fiber monolithic support is a self-supporting three-dimensional network structure carbon fiber material, and the active component is a combination of one or more metal oxides selected from the oxides of Ce, Zr, Ti, La, Pr, Nd, Bi, and W, and the active component is uniformly loaded on the surface of the carbon fiber monolithic support to form an active layer.

[0007] Furthermore, the carbon fiber integral carrier is one or more combinations of carbon fiber cloth, carbon fiber felt, and carbon fiber paper.

[0008] Furthermore, the carbon fiber carrier undergoes an oxidation pretreatment, and its surface contains one or more oxygen-containing functional groups, including hydroxyl, carboxyl, and carbonyl groups.

[0009] Furthermore, the mass ratio of the carbon fiber carrier to the active component ranges from 0.1:1 to 10:1.

[0010] The preparation method of a carbon fiber-based monolithic catalyst according to any of the above-described methods includes the following steps: Step 1: Pre-treat the carbon fiber carrier to remove surface impurities and perform oxidative modification; Step 2: Dissolve one or more metal sources in a solvent to obtain a precursor solution of the active component; Step 3: Immerse the pretreated carbon fiber monolithic carrier in the precursor solution, and through deposition, impregnation, hydrothermal treatment, self-assembly or a combination thereof, so that the active component precursor is attached to the surface of the carbon fiber monolithic carrier to obtain a sample. Step 4: Wash, dry and calcine the sample obtained in Step 3 to obtain the carbon fiber-based monolithic catalyst.

[0011] Furthermore, the oxidation modification in step one is performed using a mixed acid treatment of nitric acid and sulfuric acid. At this time, step three involves immersing the pretreated carbon fiber carrier in the precursor solution, and also includes adding an alkaline regulator to adjust the pH of the precursor solution to 8-11.

[0012] Furthermore, when hydrothermal treatment is used in step three, the hydrothermal treatment temperature range is 120–180℃, and the time range is 6–24 hours.

[0013] Furthermore, in step four, the calcination temperature ranges from 400 to 600°C, and the calcination time ranges from 2 to 6 hours.

[0014] The application of a carbon fiber-based monolithic catalyst in the photothermal synthesis of dimethyl carbonate from carbon dioxide and methanol according to any of the claims is described above. The carbon fiber-based monolithic catalyst is applied to the reaction process of photothermal synthesis of dimethyl carbonate from carbon dioxide and methanol, and the reaction is carried out under the synergistic conditions of light and heat.

[0015] Furthermore, during the heating process, the reaction temperature ranges from 60 to 180°C, and the carbon dioxide pressure ranges from 0.1 to 3.0 MPa.

[0016] Beneficial effects: 1. The catalyst of this invention integrates the full-spectrum photothermal conversion capability of a carbon fiber substrate with a supported highly efficient catalytic active center. Carbon fibers can efficiently absorb the solar spectrum and convert it into heat energy. Synergistically with the photocatalytic process of the active site, CO2 can be efficiently activated and converted with relatively low external heat input, significantly improving solar energy utilization efficiency and reducing process energy consumption.

[0017] 2. The three-dimensional interconnected carbon fiber network creates an ideal microenvironment for the catalytic reaction. The porous structure greatly promotes the mass transfer and diffusion of reactants / products, and the excellent conductivity accelerates charge transfer and inhibits recombination. The active components are firmly and stably dispersed in this structure, enabling the catalyst to simultaneously possess high activity, high selectivity, and excellent long-term operational durability.

[0018] 3. The invented catalyst has a self-supporting three-dimensional integral structure, which solves the problem of recycling traditional powder catalysts, simplifies the operation process, and reduces catalyst loss and operating costs, providing a convenient foundation for large-scale continuous production. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0020] The present invention discloses a carbon fiber-based monolithic catalyst comprising a carbon fiber monolithic support and an active component loaded on the surface of the carbon fiber monolithic support; the carbon fiber monolithic support is a self-supporting three-dimensional network structure carbon fiber material, and the active component is a combination of one or more metal oxides selected from the oxides of Ce, Zr, Ti, La, Pr, Nd, Bi, and W, wherein the active component is uniformly loaded on the surface of the carbon fiber monolithic support to form an active layer.

[0021] The carbon fiber carrier is selected from one or more combinations of carbon fiber cloth, carbon fiber felt, and carbon fiber paper. The carbon fiber carrier undergoes oxidation pretreatment, and its surface contains one or more oxygen-containing functional groups selected from hydroxyl, carboxyl, and carbonyl groups.

[0022] The mass ratio of the carbon fiber carrier to the active component ranges from 0.1:1 to 10:1.

[0023] In some embodiments of the present invention, the active component comprises a composite metal oxide formed by two or more corresponding metal oxides. The carbon fiber carrier is pre-oxidized to introduce oxygen-containing functional groups on its surface, thereby enhancing the loading stability and dispersion uniformity of the active component on the carbon fiber surface.

[0024] The catalyst of this invention has the advantages of stable overall structure, easy separation and recovery, convenient immobilization and filling, and suitability for continuous reaction. It also has photothermal response capability and catalytic activity, and has good application prospects in the photothermal catalytic synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0025] Unless otherwise stated, the pretreatment method of the carbon fiber monolithic carrier in the following embodiments is as follows: the carbon fiber cloth is ultrasonically cleaned in acetone, ethanol and deionized water for 30 minutes each, and dried at 80°C; then it is immersed in a mixed acid with a volume ratio of concentrated nitric acid and concentrated sulfuric acid of 1:3 and treated in a water bath at 70°C for 2 hours; after being taken out, it is washed with deionized water until neutral and dried at 80°C for later use.

[0026] This invention also discloses a method for preparing a carbon fiber-based monolithic catalyst, comprising the following steps: Step 1: Pre-treat the carbon fiber carrier to remove surface impurities and perform oxidative modification; The monolithic carbon fiber carrier is a self-supporting three-dimensional mesh structure carbon fiber material, preferably one or a combination of carbon fiber cloth, carbon fiber felt, and carbon fiber paper. The monolithic carbon fiber carrier serves both as a loading skeleton for the active components and as the structural basis for filling and fixing the monolithic reactor. The monolithic carbon fiber carrier undergoes an oxidation pretreatment to remove surface impurities and introduce oxygen-containing functional groups onto its surface. These oxygen-containing functional groups include one or more of hydroxyl, carboxyl, and carbonyl groups, thereby improving the anchoring ability and dispersion uniformity of the active components on the surface of the monolithic carbon fiber carrier.

[0027] Step 2: Dissolve one or more metal sources in a solvent to obtain an active component precursor solution; wherein the metal source is Ce, Zr, Ti, La, Pr, Nd, Bi, or W. In the active component precursor solution, the active component is one or more metal oxides selected from the corresponding oxides of Ce, Zr, Ti, La, Pr, Nd, Bi, and W. A conventional solvent is used in this step, ensuring sufficient dispersion / dissolution of the metal source; ethanol, deionized water, etc., can be used.

[0028] Step 3: Immerse the pretreated carbon fiber monolithic carrier in the precursor solution, and through deposition, impregnation, hydrothermal treatment, self-assembly or a combination thereof, so that the active component precursor is attached to the surface of the carbon fiber monolithic carrier to obtain a sample. In this invention, by controlling the type, composition and distribution of active components on the surface of the carbon fiber carrier, the surface active site characteristics, interface state and photothermal response performance of the catalyst can be improved, thereby enhancing its adaptability to the photothermal catalytic synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0029] Step 4: Wash, dry and calcine the sample obtained in Step 3 to obtain the carbon fiber-based monolithic catalyst.

[0030] In this invention, the oxidation modification in step one is performed using a mixed acid treatment of nitric acid and sulfuric acid. At this time, step three involves immersing the pretreated carbon fiber carrier in the precursor solution and also includes adding an alkaline regulator to adjust the pH of the precursor solution to 8-11. When hydrothermal treatment is used in step three, the hydrothermal treatment temperature range is 120–180℃, and the time range is 6–24 hours.

[0031] In step four, the calcination temperature ranges from 400 to 600°C, and the calcination time ranges from 2 to 6 hours.

[0032] In this invention, a carbon fiber-based monolithic catalyst is applied to the photothermal synthesis of dimethyl carbonate from carbon dioxide and methanol. During this reaction, the reaction is carried out under synergistic conditions of light and heat. During heating, the reaction temperature ranges from 60 to 180°C, and the carbon dioxide pressure ranges from 0.1 to 3.0 MPa. The monolithic catalyst can be fixed integrally within the reactor for use, facilitating post-reaction separation and recovery, and enabling continuous operation.

[0033] The present invention will be further described below with reference to the embodiments.

[0034] Example 1: Preparation of Ce-Zr oxide / carbon fiber based monolithic catalyst; Take 2 g (3 cm × 5 cm) of pretreated carbon fiber cloth for later use. Weigh 2.17 g of Ce(NO3)3·6H2O and 1.61 g of ZrOCl2·8H2O, dissolve them in a mixed solvent of 40 mL ethanol and 20 mL deionized water, and stir magnetically for 30 minutes to obtain a clear precursor solution. Immerse the pretreated carbon fiber cloth in the precursor solution, adjust the pH of the system to about 10 with ammonia, and then transfer it to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and react at 160 °C for 12 hours. After the reaction is completed, allow it to cool naturally, remove the carbon fiber cloth, wash it three times alternately with deionized water and ethanol, and dry it overnight at 80 °C. Place the dried sample in a tube furnace, heat it to 550 °C at 2 °C / min under a nitrogen atmosphere, hold it at that temperature for 4 hours, and after natural cooling, obtain the Ce-Zr oxide / carbon fiber based monolithic catalyst, denoted as CZ / CF. The mass of the loaded active component is approximately 1.2 times the mass of the overall carbon fiber carrier.

[0035] Example 2: Preparation of BiWO / carbon fiber photothermal monolithic catalyst; Take 2 g of pretreated carbon fiber cloth for later use. Weigh 0.97 g of Bi(NO3)3·5H2O and dissolve it in 20 mL of 0.4 mol / L dilute nitric acid to obtain solution A. Weigh 0.165 g of Na2WO4·2H2O and dissolve it in 20 mL of deionized water to obtain solution B. Under stirring, slowly add solution B dropwise to solution A to obtain a precursor solution. Adjust the pH of the system to approximately 7 with ammonia. Immerse the pretreated carbon fiber cloth in this suspension and transfer it to a high-pressure reactor. React at 180℃ for 8 hours. After the reaction is complete, allow it to cool naturally, remove the carbon fiber cloth, wash and dry it sequentially, and calcine it at 500℃ for 3 hours in air to obtain the Bi-W oxide / carbon fiber-based monolithic catalyst, denoted as BW / CF.

[0036] Example 3: Preparation of Ti oxide / carbon fiber based monolithic catalyst; Take 2 g of pretreated carbon fiber cloth for later use. Measure 10 mL of tetrabutyl titanate and slowly add it dropwise to 40 mL of anhydrous ethanol, stirring continuously to form solution A. Mix 5 mL of deionized water, 10 mL of anhydrous ethanol, and 2 mL of concentrated hydrochloric acid to form solution B. Under vigorous stirring, slowly add solution B dropwise to solution A, and continue stirring for 2 hours to obtain a transparent sol, which is the precursor solution. Immerse the pretreated carbon fiber cloth in the sol and coat it using an dip-coating method. After drying at room temperature, repeat the coating twice. Subsequently, dry at 80℃ for 12 hours and calcine at 450℃ for 3 hours in air atmosphere to obtain a Ti oxide / carbon fiber-based monolithic catalyst, denoted as T / CF.

[0037] Example 4: Preparation of Ce-Zr-Ti oxide / carbon fiber based monolithic catalyst; Take 2 g of pretreated carbon fiber cloth for later use. Weigh 1.95 g of Ce(NO3)3·6H2O, 1.45 g of ZrOCl2·8H2O, and 0.34 g of TiCl4, and dissolve them together in a mixed solvent of 40 mL ethanol and 20 mL deionized water. Stir magnetically until clear to obtain a solution, which is used as the pre-driving solution. Immerse the pretreated carbon fiber cloth in this solution, adjust the pH of the system to 9 with ammonia, and then transfer it to a high-pressure reactor for treatment at 150 °C for 10 hours. After the reaction is completed, allow it to cool naturally, remove the sample, wash and dry it, and then calcine it at 500 °C for 4 hours under a nitrogen atmosphere to obtain the Ce-Zr-Ti oxide / carbon fiber based monolithic catalyst, denoted as CZT / CF.

[0038] Example 5: Preparation of Ce-Zr-La oxide / carbon fiber based monolithic catalyst; Take 2 g of pretreated carbon fiber cloth for later use. Weigh 2.17 g of Ce(NO3)3·6H2O, 1.29 g of ZrOCl2·8H2O, and 0.43 g of La(NO3)3·6H2O, and dissolve them together in a mixed solvent of 40 mL ethanol and 20 mL deionized water. Stir magnetically until clear to obtain a solution, which is used as the pre-driving solution. Immerse the pretreated carbon fiber cloth in the solution, adjust the pH of the system to 10 with ammonia, and then transfer it to a high-pressure reactor and treat it at 140 °C for 14 hours. After the reaction is completed, allow it to cool naturally, remove the sample, wash and dry it, and then calcine it at 520 °C for 3.5 hours under a nitrogen atmosphere to obtain the Ce-Zr-La oxide / carbon fiber based monolithic catalyst, denoted as CZL / CF.

[0039] Example 6: Preparation of Ce-Zr-Pr-Nd oxide / carbon fiber based monolithic catalyst; Referring to the method in Example 5, La(NO3)3·6H2O was replaced in equal molar amounts with a mixture of Pr(NO3)3·6H2O and Nd(NO3)3·6H2O, wherein the molar ratio of Pr to Nd was 1:1, and the other conditions remained unchanged, to obtain a Ce-Zr-Pr-Nd oxide / carbon fiber based monolithic catalyst, denoted as CZPN / CF.

[0040] Comparative Example 1: Preparation of Powdered Ce-Zr Oxide Catalyst Without adding a carbon fiber carrier, the Ce and Zr precursor solutions prepared in Example 1 were subjected to hydrothermal treatment under the same conditions (160°C, 12 hours). The resulting precipitate was filtered, washed, dried, and calcined at 550°C for 4 hours before being ground into powder to obtain a powdered Ce-Zr oxide catalyst, which served as a comparative catalyst.

[0041] Example 7: Performance evaluation of carbon fiber-based monolithic catalyst in the photothermal synthesis of dimethyl carbonate from carbon dioxide and methanol; The catalysts were evaluated in a 100 mL high-pressure photothermal reactor with a quartz window. Carbon fiber-based monolithic catalysts prepared in Examples 1 to 6 and the powdered catalyst of Comparative Example 1 were taken, with the total mass of the active component in each catalyst controlled to be 0.1 g, and 20 mL of anhydrous methanol was added. After purging with gas, CO2 was introduced to an initial pressure of 1.0 MPa. The reactor was placed in a heating mantle, and the catalyst surface was vertically irradiated through the quartz window using a 300 W xenon lamp. Stirring was started and the rotation speed was controlled at 500 rpm. The temperature was raised to 130 °C and maintained for 3 hours. After the reaction was completed, the reactor was allowed to cool naturally to room temperature, and the liquid product was analyzed by gas chromatography. The results are shown in Table 1.

[0042] The reaction results are shown in Table 1.

[0043] Table 1 Comparison of reaction performance of different catalysts , Table 1 shows that the carbon fiber-based monolithic catalyst prepared in this invention exhibits good catalytic activity and cycling stability in the photothermal synthesis of dimethyl carbonate from carbon dioxide and methanol. Compared with powdered catalysts, the monolithic catalyst can be directly removed from the reaction system after use, which is simple to operate, easy to separate and recover, and shows a higher yield retention capacity.

[0044] Example 8: Effect of different reaction conditions on the reaction performance of CZ / CF catalyst; Using the CZ / CF catalyst prepared in Example 1, with the active component in the catalyst fixed at 0.1 g, methanol at 20 mL, and reaction time at 6 hours, and with xenon lamp irradiation conditions kept constant, the effects of different temperatures and initial carbon dioxide pressure on the reaction results were investigated. The results are shown in Table 2.

[0045] Table 2. Reaction results of CZ / CF catalyst under different reaction conditions ,

[0046] Table 2 shows that the CZ / CF catalyst can effectively catalyze the synthesis of dimethyl carbonate from CO2 and methanol within the reaction temperature and CO2 pressure range defined in the claims. Even under mild boundary conditions of 80°C and 0.1 MPa, DMC formation can still be detected, demonstrating the applicability of the catalyst under a wide range of conditions. The preferred reaction conditions are 130–180°C and 1.0–3.0 MPa.

[0047] Example 9: Effects of different energy input methods on the reaction performance of CZL / CF catalyst; Using the CZL / CF catalyst prepared in Example 5, the effects of different energy input methods on the reaction results were investigated under the conditions of a fixed active component mass of 0.1 g, methanol dosage of 20 mL, initial CO2 pressure of 2.0 MPa, and reaction time of 4 hours. Wherein: Condition A: Combined light and heat treatment, heating to 130°C and irradiating with xenon lamp; Condition B: Heating only, 130℃, no light exposure; Condition C: Illumination only, 25°C, xenon lamp illumination.

[0048] Table 3. Reaction results under different energy input methods , The results show that, under the same temperature conditions, the introduction of light significantly increases the yield of dimethyl carbonate, indicating a synergistic effect between light and heating. The reaction activity is low under light alone, suggesting that heat plays a crucial role in driving the synthesis of dimethyl carbonate from carbon dioxide and methanol. The carbon fiber-based monolithic catalyst described in this invention achieves good catalytic performance under synergistic light and heating conditions.

[0049] Those skilled in the art will understand that the above-described embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of this application. Any person skilled in the art can make their own modifications and alterations without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A carbon fiber-based monolithic catalyst, characterized in that: It includes a carbon fiber carrier and an active component loaded on the surface of the carbon fiber carrier; the carbon fiber carrier is a self-supporting three-dimensional mesh structure carbon fiber material, and the active component is a combination of one or more metal oxides selected from the oxides of Ce, Zr, Ti, La, Pr, Nd, Bi, and W, and the active component is uniformly loaded on the surface of the carbon fiber carrier to form an active layer.

2. The carbon fiber-based monolithic catalyst according to claim 1, characterized in that: The carbon fiber monolithic carrier is one or more of the following: carbon fiber cloth, carbon fiber felt, and carbon fiber paper.

3. The carbon fiber-based monolithic catalyst according to claim 1, characterized in that: The carbon fiber carrier undergoes oxidation pretreatment, and its surface contains one or more oxygen-containing functional groups, including hydroxyl, carboxyl, and carbonyl groups.

4. The carbon fiber-based monolithic catalyst according to claim 1, characterized in that: The mass ratio of the carbon fiber carrier to the active component ranges from 0.1:1 to 10:

1.

5. A method for preparing a carbon fiber-based monolithic catalyst according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Pre-treat the carbon fiber carrier to remove surface impurities and perform oxidative modification; Step 2: Dissolve one or more metal sources in a solvent to obtain a precursor solution of the active component; Step 3: Immerse the pretreated carbon fiber monolithic carrier in the precursor solution, and through deposition, impregnation, hydrothermal treatment, self-assembly or a combination thereof, so that the active component precursor is attached to the surface of the carbon fiber monolithic carrier to obtain a sample. Step 4: Wash, dry and calcine the sample obtained in Step 3 to obtain the carbon fiber-based monolithic catalyst.

6. The method for preparing a carbon fiber-based monolithic catalyst according to claim 5, characterized in that: The oxidation modification in step one is performed using a mixed acid treatment of nitric acid and sulfuric acid. At this time, step three involves immersing the pretreated carbon fiber carrier in the precursor solution, and also includes adding an alkaline regulator to adjust the pH of the precursor solution to 8-11.

7. The method for preparing a carbon fiber-based monolithic catalyst according to claim 5, characterized in that: When hydrothermal treatment is used in step three, the hydrothermal treatment temperature range is 120–180℃, and the time range is 6–24 hours.

8. The method for preparing a carbon fiber-based monolithic catalyst according to claim 5, characterized in that: In step four, the calcination temperature ranges from 400 to 600°C, and the calcination time ranges from 2 to 6 hours.

9. The application of a carbon fiber-based monolithic catalyst according to any one of claims 1-4 in the photothermal synthesis of dimethyl carbonate from carbon dioxide and methanol, characterized in that: A carbon fiber-based monolithic catalyst is used in the photothermal synthesis of dimethyl carbonate from carbon dioxide and methanol, with the reaction proceeding under synergistic conditions of light and heat.

10. The application of the carbon fiber-based monolithic catalyst according to claim 9 in the photothermal synthesis of dimethyl carbonate from carbon dioxide and methanol, characterized in that: During the heating process, the reaction temperature ranges from 60 to 180°C, and the carbon dioxide pressure ranges from 0.1 to 3.0 MPa.