A photothermal monolithic catalyst, its preparation method and application

Abstract

This invention discloses a photothermal monolithic catalyst, its preparation method, and its application, belonging to the field of rare earth metal catalyst technology. The catalyst uses a three-dimensional network structure of carbon fibers as a carrier, with CeO2 loaded on the surface of the carbon fibers. The CeO2 is formed by in-situ growth of a hierarchical porous Ce-MOF precursor on the carbon fiber surface followed by calcination. This catalyst combines the excellent full-spectrum photothermal conversion performance and three-dimensional network mass transfer advantages of carbon fibers with the abundant pore structure and acid-base active sites of MOF-derived CeO2. Under the synergistic effect of photothermal activity, it can efficiently catalyze the direct reaction of CO2 and methanol to synthesize dimethyl carbonate. The catalyst exhibits high catalytic efficiency, a simple and controllable preparation method, requires no separation or recovery, and demonstrates good stability, maintaining a yield retention rate of over 95% after three cycles. This provides an efficient and feasible technical solution for the large-scale continuous production of CeO2 resources.

Description

Technical Field

[0001] This invention belongs to the field of rare earth metal catalyst technology, and relates to a photothermal monolithic catalyst, particularly to a carbon fiber supported cerium oxide photothermal monolithic catalyst and a carbon fiber supported cerium oxide-metal photothermal monolithic catalyst, as well as their preparation methods and applications. Background Technology

[0002] Since the acceleration of industrialization, carbon dioxide (CO2) emissions have increased significantly. Research on the chemical conversion and utilization of CO2 has made some progress. Among these advancements, the direct reaction of CO2 with methanol to synthesize dimethyl carbonate (DMC) is a promising technology with broad applications. DMC can be used as a reagent in methylation and carbonylation reactions, replacing toxic phosgene and dimethyl sulfate. It can also be used as an electrolyte in lithium-ion batteries and as an intermediate in the synthesis of polycarbonate from oxygenated fuel additives. Compared to traditional DMC synthesis routes (such as the phosgene method, methanol oxidative carbonylation method, and transesterification method), the direct synthesis of DMC from CO2 is a safe, efficient, and sustainable green process, with water as the only byproduct. Therefore, the conversion of CO2 into DMC has both theoretical and practical value.

[0003] However, the direct synthesis of DMC from CO2 and methanol faces a series of technical challenges. First, CO2 molecules are highly stable but chemically inactive, requiring highly efficient catalysts to facilitate their conversion. Second, product selectivity and catalyst stability also limit the industrial application of this reaction. Existing catalysts have low conversion rates and are prone to deactivation at high temperatures. Therefore, developing catalysts with high activity, excellent selectivity, and long-term stability is crucial for the industrialization of this reaction.

[0004] Cerium oxide (CeO2) possesses bifunctional acid-base active sites on its surface, which facilitate the adsorption and activation of methanol and CO2, and exhibits excellent stability. Therefore, CeO2-based catalysts have been extensively studied in the direct synthesis of dimethyl methyl ether (DMC) from CO2. However, this reaction pathway still does not meet the requirements for practical applications, necessitating the development of advanced catalysts and further mechanistic studies. Therefore, the development and construction of novel catalyst systems for the activation of CO2 to DMC is urgently needed. Summary of the Invention

[0005] To address the problems of poor photothermal response, insufficient catalytic activity, and poor stability of catalysts in the CO2-methanol DMC synthesis reaction in existing technologies, as well as the difficulty in separating and recovering traditional powder catalysts and their inability to be applied continuously, this invention provides a photothermal monolithic catalyst, its preparation method, and its application. This catalyst combines the photothermal conversion and mass transfer advantages of the carbon fiber monolithic support with the structural and activity advantages of MOF-derived CeO2, achieving a significant improvement in the photothermal catalytic conversion efficiency of CO2 while meeting the requirements of large-scale continuous production.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a carbon fiber supported cerium oxide photothermal monolithic catalyst: the catalyst uses carbon fiber with a three-dimensional network structure as a carrier, and the surface of the carbon fiber is loaded with CeO2; the CeO2 is formed by growing a multi-level porous Ce-MOF precursor in situ on the surface of the carbon fiber and then calcining it.

[0007] To optimize the above technical solution, the specific measures also include: Furthermore, the CeO2 has a rod-shaped structure with a high aspect ratio, abundant porosity and hierarchical pore structure, and an average pore size of 5~9 nm; the carbon fiber is a carbon fiber cloth made of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber or viscose-based carbon fiber, and the diameter of the polyacrylonitrile-based carbon fiber, pitch-based carbon fiber and viscose-based carbon fiber is 1~20 μm; the mass ratio of the carbon fiber to the CeO2 is 0.1~10∶1, preferably 0.5~5∶1.

[0008] Secondly, the present invention also provides a method for preparing the above-mentioned carbon fiber-supported cerium oxide photothermal monolithic catalyst, comprising the following steps: S1: oxidizing the carbon fiber to obtain a carbon fiber support with surface hydroxylation modification; S2: dissolving a polycarboxylic acid in a mixture of water and ethanol to obtain solution A; dissolving a cerium salt and a surfactant in water to obtain solution B; immersing the carbon fiber support obtained in S1 into solution B for ultrasonic dispersion, then slowly adding solution A, adjusting the pH to alkaline, and heating the reaction to obtain a carbon fiber-supported hierarchical porous metal-organic framework material; S3: calcining the carbon fiber-supported hierarchical porous metal-organic framework material obtained in S2 to obtain the carbon fiber-supported cerium oxide photothermal monolithic catalyst.

[0009] Further, the specific method of S1 is as follows: the carbon fiber cloth is ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 20-40 min each, dried at 60-80 ℃, immersed in a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3, oxidized at 60-80 ℃ for 1-3 h, cooled and washed until neutral, and dried at 80-100 ℃ for 6-12 h to obtain a carbon fiber carrier with surface hydroxylation modification.

[0010] Further, in step S2, the polycarboxylic acid is one or more of pyromellitic acid, terephthalic acid, and 1,2,4,5-benzenetetracarboxylic acid; the volume ratio of water to ethanol in the water-ethanol mixture is 1-10:1; the cerium salt is one or more of cerium nitrate hexahydrate, cerium ammonium nitrate, and cerium chloride heptahydrate; the surfactant is one or more of hexadecyltrimethylammonium bromide, polyvinylpyrrolidone, and sodium dodecyl sulfate; the molar ratio of the surfactant to the cerium salt is 0.1-10:1; the molar ratio of the polycarboxylic acid to the cerium salt is 0.5-5; the ultrasonic dispersion time is 30-60 min; the pH adjustment reagent is ammonia or sodium hydroxide solution, adjusting the pH to 9-12; the reaction temperature is 50-80℃, preferably 60-80℃, and the time is 30-120 min.

[0011] Furthermore, in step S3, the calcination is carried out under an inert atmosphere or an air atmosphere, and the calcination temperature is 400~650 ℃, and the time is 2~6 h.

[0012] Thirdly, the present invention also provides a carbon fiber supported cerium oxide-metal monolithic photothermal catalyst: the catalyst is a photothermal monolithic catalyst on which a metal is supported; the metal is one or more of zirconium, lanthanum, praseodymium, neodymium, nickel, copper, bismuth, and titanium.

[0013] Fourthly, the present invention also provides a method for preparing the above-mentioned carbon fiber supported cerium oxide-metal photothermal monolithic catalyst: the above-mentioned carbon fiber supported cerium oxide photothermal monolithic catalyst is immersed in a precursor impregnation solution with a concentration of 0.01~1 mol / L for 0.5~2 h, and then calcined at 400~600 ℃ for 2~4 h to obtain the carbon fiber supported cerium oxide-metal photothermal monolithic catalyst; the precursor impregnation solution is a soluble salt solution of one or more of zirconium, lanthanum, praseodymium, neodymium, nickel, copper, bismuth, and titanium.

[0014] Fifthly, the present invention also provides the application of the above-mentioned photothermal monolithic catalyst in the photothermal conversion of carbon dioxide: for the photothermal catalytic reaction of direct synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0015] Furthermore, the photothermal catalytic reaction for the direct synthesis of dimethyl carbonate from carbon dioxide and methanol uses simulated sunlight or focused sunlight as the light source and is carried out continuously in a batch reactor or a fixed-bed reactor; the solid-liquid ratio of the photothermal monolithic catalyst to methanol is 0.01~0.1 g:1 mL, the initial carbon dioxide pressure is 0.1~3 MPa, the reaction temperature is 80~180 ℃, and the reaction time is 0.5~24 h; the residence time in the fixed-bed reactor is 1~30 min.

[0016] The beneficial effects of this invention are as follows: I. This invention combines the full-spectrum photothermal conversion capability of the carbon fiber monolithic carrier with the catalytic activity of MOF-derived CeO2 to construct a highly efficient photothermal synergistic catalytic system. Carbon fiber can efficiently absorb solar energy and convert it into heat energy, synergistically interacting with the photocatalytic process of the active sites. This allows CO2 to be efficiently activated with relatively low external heat input, significantly improving solar energy utilization efficiency and reducing process energy consumption. It exhibits a wide photothermal response range and excellent catalytic performance.

[0017] Second, the modified carbon fiber surface is rich in hydroxyl groups, which is conducive to the in-situ growth and uniform loading of Ce-MOF precursor, effectively inhibits CeO2 particle agglomeration, and improves the exposure of active sites; its three-dimensional network structure greatly promotes the mass transfer and diffusion of reactants / products, and its excellent conductivity accelerates charge transfer, inhibits photogenerated carrier recombination, and further improves catalytic efficiency.

[0018] Third, the catalyst has a self-supporting three-dimensional integral structure, which eliminates the need for separation and recovery, solving the recovery problem of traditional powder catalysts, simplifying the operation process and reducing catalyst loss and operating costs. It can be directly adapted to batch or fixed-bed reactors, providing a convenient foundation for large-scale continuous production. The preparation method is simple and controllable, with moderate cost, and is easy to scale up, providing a new technical path for the resource utilization of CO2. Attached Figure Description

[0019] Figure 1 These are SEM images of the photothermal monolithic catalyst. In the figure, A is the SEM image of CeO2-1 / CF prepared in Example 1, and B is the SEM image of CeO2-LaPr / CF prepared in Example 5. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments.

[0021] Example 1 This embodiment provides a carbon fiber-supported cerium oxide monolithic photothermal catalyst for carbon dioxide photothermal conversion, and the preparation method includes the following steps: S1: Take 2.0 g of carbon fiber cloth and ultrasonically clean it for 30 min each in acetone, anhydrous ethanol, and deionized water, and then dry it at 80℃. Then immerse it in a 1:3 mixture of concentrated nitric acid and concentrated sulfuric acid in 50 mL and treat it in a water bath at 70℃ for 1 h. After removal, wash it with deionized water until neutral and dry it at 100℃ for 6 h to obtain a carbon fiber carrier with hydroxylated surface.

[0022] S2: Dissolve 0.84 g of trimesic acid (BTC) in a mixed solvent of 10 mL deionized water and 10 mL ethanol, stirring to obtain solution A. Separately, dissolve 0.87 g of cerium nitrate hexahydrate and 0.036 g of hexadecyltrimethylammonium bromide in 90 mL of deionized water, stirring to obtain solution B. Immerse the carbon fiber support obtained in S1 in solution B and ultrasonically disperse for 30 min. Under magnetic stirring, slowly add solution A to solution B containing the carbon fiber support, and adjust the pH to 10 with ammonia. React at 60 ℃ for 30 min. After the reaction is complete, remove the product, wash it three times alternately with deionized water and ethanol, and dry it at 70 ℃ for 24 h to obtain a carbon fiber-supported hierarchical porous metal-organic framework material.

[0023] S3: The carbon fiber-supported hierarchical porous metal-organic framework material obtained in S2 was placed in a muffle furnace and heated to 400 °C at 5 °C / min under air atmosphere. It was then calcined at a constant temperature for 6 h and naturally cooled to obtain the carbon fiber-supported cerium oxide photothermal monolithic catalyst, denoted as CeO2-1 / CF.

[0024] According to the weighing calculation, the mass ratio of carbon fiber to CeO2 is approximately 10:1.

[0025] SEM images of CeO2-1 / CF are shown below. Figure 1 As shown in the figure, cerium oxide is uniformly dispersed and anchored on the surface of carbon fibers, forming an integral structure based on carbon fibers.

[0026] Example 2 This embodiment provides a carbon fiber-supported cerium oxide monolithic photothermal catalyst for carbon dioxide photothermal conversion, and the preparation method includes the following steps: S1: Take 2.0 g of carbon fiber cloth and ultrasonically clean it for 30 min each in acetone, anhydrous ethanol, and deionized water, and then dry it at 80℃. Then immerse it in a 1:3 mixture of concentrated nitric acid and concentrated sulfuric acid in 50 mL and treat it in a water bath at 70℃ for 1 h. After removal, wash it with deionized water until neutral and dry it at 100℃ for 6 h to obtain a carbon fiber carrier with hydroxylated surface.

[0027] S2: 4.2 g BTC and 3.1 g 1,2,4,5-benzenetetracarboxylic acid were dissolved in a mixed solvent of 20 mL deionized water and 20 mL ethanol, and stirred to obtain solution A. Separately, 8.68 g cerium ammonium nitrate and 1.45 g sodium dodecyl sulfate were dissolved in 90 mL deionized water, and stirred to obtain solution B. The carbon fiber support obtained in S1 was immersed in solution B and ultrasonically dispersed for 30 min. Under magnetic stirring, solution A was slowly added dropwise to solution B containing the carbon fiber support, and the pH was adjusted to 10 with ammonia. The reaction was carried out at 80 ℃ for 120 min. After the reaction was completed, the product was removed, washed three times alternately with deionized water and ethanol, and dried at 70 ℃ for 24 h to obtain a carbon fiber-supported hierarchical porous metal-organic framework material.

[0028] S3: The carbon fiber-supported hierarchical porous metal-organic framework material obtained in S2 was placed in a muffle furnace and heated to 600 °C at 5 °C / min under air atmosphere. It was then calcined at a constant temperature for 2 h and naturally cooled to obtain the carbon fiber-supported cerium oxide photothermal monolithic catalyst, denoted as CeO2-2 / CF.

[0029] According to the weighing calculation, the mass ratio of carbon fiber to CeO2 is approximately 1:1.

[0030] Example 3 This embodiment provides a carbon fiber-supported cerium oxide monolithic photothermal catalyst for carbon dioxide photothermal conversion, and the preparation method includes the following steps: S1: Take 2.0 g of carbon fiber cloth and ultrasonically clean it for 30 min each in acetone, anhydrous ethanol, and deionized water, and then dry it at 80℃. Then immerse it in a 1:3 mixture of concentrated nitric acid and concentrated sulfuric acid in 50 mL and treat it in a water bath at 70℃ for 1 h. After removal, wash it with deionized water until neutral and dry it at 100℃ for 6 h to obtain a carbon fiber carrier with hydroxylated surface.

[0031] S2: 6.4 g of terephthalic acid (BDC), 2.1 g of BTC, and 1.0 g of 1,2,4,5-benzenetetracarboxylic acid were dissolved in a mixed solvent of 30 mL of deionized water and 30 mL of ethanol, and stirred to obtain solution A. Separately, 17.36 g of cerium chloride hexahydrate and 29.0 g of polyvinylpyrrolidone (PVP) were dissolved in 90 mL of deionized water, and stirred to obtain solution B. The carbon fiber support obtained in S1 was immersed in solution B and ultrasonically dispersed for 30 min. Under magnetic stirring, solution A was slowly added dropwise to solution B containing the carbon fiber support, and the pH was adjusted to 10 with ammonia. The reaction was carried out at 50 ℃ for 120 min. After the reaction was completed, the product was taken out, washed three times alternately with deionized water and ethanol, and dried at 70 ℃ for 24 h to obtain a carbon fiber-supported hierarchical porous metal-organic framework material.

[0032] S3: The carbon fiber-supported hierarchical porous metal-organic framework material obtained in S2 was placed in a muffle furnace and heated to 650 °C at 5 °C / min under air atmosphere. It was then calcined at a constant temperature for 2 h and naturally cooled to obtain the carbon fiber-supported cerium oxide photothermal monolithic catalyst, denoted as CeO2-3 / CF.

[0033] According to the weighing calculation, the mass ratio of carbon fiber to CeO2 is approximately 0.1:1.

[0034] Example 4 This embodiment provides a carbon fiber-supported cerium oxide-metal photothermal monolithic catalyst for carbon dioxide photothermal conversion. The preparation method is as follows: The CeO₂⁻ / CF catalyst prepared in Example 2 is used as a substrate for secondary loading. A 0.1 mol / L zirconium oxynitrate aqueous solution is prepared as the impregnation solution. The CeO₂⁻ / CF catalyst is immersed in this solution for 2 h, then removed and dried at 100 °C, followed by calcination at 500 °C for 3 h in air to obtain the carbon fiber-supported cerium oxide-metal photothermal monolithic catalyst, denoted as CeO₂-Zr / CF.

[0035] Example 5 This embodiment provides a carbon fiber-supported cerium oxide-metal photothermal monolithic catalyst for carbon dioxide photothermal conversion. The preparation method is as follows: The CeO₂⁻³ / CF catalyst prepared in Example 3 is used as a substrate for secondary loading. A mixed impregnation solution containing lanthanum nitrate and praseodymium nitrate is prepared, with a total metal ion concentration of 0.5 mol / L and a La to Pr molar ratio of 1:1. The CeO₂⁻³ / CF catalyst is immersed in this solution for 0.5 h, then dried at 100 °C, and subsequently calcined at 550 °C for 2.5 h in air to obtain the carbon fiber-supported cerium oxide-metal photothermal monolithic catalyst, denoted as CeO₂-LaPr / CF.

[0036] SEM images of CeO2-LaPr / CF are shown below. Figure 1 As shown in the figure, cerium oxide-metal is uniformly dispersed and anchored on the carbon fiber surface, forming an integral structure based on carbon fiber.

[0037] Example 6 This embodiment provides a carbon fiber-supported cerium oxide-metal photothermal monolithic catalyst for carbon dioxide photothermal conversion. The preparation method is as follows: The CeO₂⁻¹ / CF catalyst prepared in Example 1 is used as a substrate for secondary loading. A mixed impregnation solution containing zirconium nitrate, lanthanum nitrate, nickel nitrate, and copper nitrate is prepared, with a total metal ion concentration of 1.0 mol / L and a molar ratio of 1:1:1:1 for the four metal ions. The CeO₂⁻¹ / CF catalyst is immersed in this solution for 0.5 h, then dried at 100 °C, and subsequently calcined at 600 °C for 2 h in air to obtain the carbon fiber-supported cerium oxide-metal photothermal monolithic catalyst, denoted as CeO₂-ZrLaNiCu / CF.

[0038] Example 7 This embodiment provides a carbon fiber-supported cerium oxide-metal photothermal monolithic catalyst for carbon dioxide photothermal conversion. The preparation method is as follows: The CeO₂⁻ / CF catalyst prepared in Example 2 is used as a substrate for secondary loading. A mixed impregnation solution containing tetrabutyl titanate (dissolved in a small amount of ethanol), bismuth nitrate, and neodymium nitrate is prepared, with a total metal ion concentration of 0.01 mol / L and a molar ratio of titanium, bismuth, and neodymium of 1:2:1. The CeO₂⁻ / CF catalyst is immersed in this solution for 2 h, then dried at 120 °C, and subsequently calcined at 400 °C for 4 h in air to obtain the carbon fiber-supported cerium oxide-metal photothermal monolithic catalyst, denoted as CeO₂-TiBiNd / CF.

[0039] Example 8 The photothermal catalytic reaction for the direct synthesis of dimethyl carbonate from carbon dioxide and methanol was carried out in a high-pressure photothermal reactor with a quartz window and a fixed-bed reactor. Accurately weighed amounts of the catalysts and CeO2 powder prepared in Examples 1, 2, 3, 4, 5, 6, and 7 were used, employing a specific catalyst / methanol solid-liquid ratio (g:mL).

[0040] An appropriate volume of anhydrous methanol was added to the reactor, and the air inside the reactor was replaced five times with CO2 gas. Then, CO2 was introduced to the specified initial pressure (MPa), the temperature was raised to the reaction temperature (°C), and the reaction was carried out for a certain time (h); or a woven catalyst was packed in a fixed bed, and methanol and CO2 were preheated and mixed before being introduced into the catalyst bed at a specific temperature (°C) for a fixed residence time (min). At the same time, a 300W xenon lamp was used to simulate sunlight being vertically irradiated through a quartz window.

[0041] After the reaction was complete, the liquid product was collected and subjected to qualitative and quantitative analysis by gas chromatography to calculate the yield (m mmol) of dimethyl carbonate (DMC). DMC / g 催化剂 The results are shown in Table 1.

[0042] Table 1. DMC synthesis performance of catalysts in Examples 1-7

[0043] As can be seen from Table 1, the monolithic catalysts prepared by this invention all exhibit superior catalytic activity and stability compared to traditional powder catalysts. The monolithic catalyst has a lifespan of up to 200 h and can be adapted to both batch reactors and fixed-bed reactors, providing convenience for large-scale continuous production.

[0044] Specifically, the monolithic catalyst of this invention uses a three-dimensional network carbon fiber cloth as a carrier. After being modified by mixed acid oxidation, MOF-derived rod-shaped CeO2 active components are loaded through an in-situ growth-calcination process to form a self-supporting monolithic structure. The catalyst combines the excellent full-spectrum photothermal conversion performance and three-dimensional network mass transfer advantages of carbon fiber with the rich pore structure and acid-base active sites of MOF-derived CeO2. Under the synergistic effect of photothermal activity, it can efficiently catalyze the direct reaction of CO2 and methanol to synthesize dimethyl carbonate. The catalyst of this invention has high catalytic efficiency, a simple and controllable preparation method, requires no separation or recovery, exhibits good stability, and maintains a yield retention rate of over 95% after three cycles. This provides an efficient and feasible technical solution for the large-scale continuous production of CeO2 resources.

[0045] In this invention, unless otherwise stated, scientific and technical terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, the reagents, materials, and procedures used herein are all widely used in the relevant fields.

[0046] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A carbon fiber-supported cerium oxide photothermal monolithic catalyst, characterized in that: The catalyst uses carbon fibers with a three-dimensional network structure as a carrier, and CeO2 is loaded on the surface of the carbon fibers; the CeO2 is formed by growing a hierarchical porous Ce-MOF precursor in situ on the surface of the carbon fibers and then calcining it.

2. The carbon fiber supported cerium oxide photothermal monolithic catalyst according to claim 1, characterized in that: The CeO2 has a rod-like structure with a hierarchical porous structure and an average pore size of 5~9 nm. The carbon fiber is a carbon fiber cloth made of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber or viscose-based carbon fiber, wherein the diameter of the polyacrylonitrile-based carbon fiber, pitch-based carbon fiber and viscose-based carbon fiber is 1~20 μm. The mass ratio of the carbon fiber to the CeO2 is 0.1 to 10:

1.

3. The method for preparing the carbon fiber-supported cerium oxide photothermal monolithic catalyst as described in claim 1 or 2, characterized in that: Includes the following steps: S1: The carbon fiber is oxidized to obtain a carbon fiber carrier with surface hydroxylation modification; S2: Dissolve polycarboxylic acid in a mixture of water and ethanol to obtain solution A; dissolve cerium salt and surfactant in water to obtain solution B; immerse the carbon fiber support obtained in S1 in solution B and disperse it ultrasonically, then slowly add solution A dropwise, adjust the pH to alkaline, heat the reaction, and obtain a multi-level porous metal-organic framework material supported on carbon fiber. S3: The carbon fiber-supported hierarchical porous metal-organic framework material obtained in S2 is calcined to obtain the carbon fiber-supported cerium oxide photothermal monolithic catalyst.

4. The method for preparing the carbon fiber-supported cerium oxide photothermal monolithic catalyst according to claim 3, characterized in that: The specific method of S1 is as follows: the carbon fiber cloth is ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 20-40 min each, dried at 60-80 ℃, immersed in a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3, oxidized at 60-80 ℃ for 1-3 h, cooled and washed until neutral, and dried at 80-100 ℃ for 6-12 h to obtain a carbon fiber carrier with surface hydroxylation modification.

5. The method for preparing the carbon fiber-supported cerium oxide photothermal monolithic catalyst according to claim 3, characterized in that: In S2, the polycarboxylic acid is one or more of pyromellitic acid, terephthalic acid, and 1,2,4,5-benzenetetracarboxylic acid; in the mixture of water and ethanol, the volume ratio of water to ethanol is 1~10:

1. The cerium salt is one or more of cerium nitrate hexahydrate, cerium ammonium nitrate, and cerium chloride heptahydrate; the surfactant is one or more of hexadecyltrimethylammonium bromide, polyvinylpyrrolidone, and sodium dodecyl sulfate; the molar ratio of the surfactant to the cerium salt is 0.1 to 10:

1. The molar ratio of the polycarboxylic acid to the cerium salt is 0.5 to 5; The ultrasonic dispersion time is 30-60 min; The pH-adjusting reagent is ammonia or sodium hydroxide solution, used to adjust the pH to 9-12; The reaction is carried out at a temperature of 50-80 °C for a time of 30-120 min.

6. The method for preparing the carbon fiber-supported cerium oxide photothermal monolithic catalyst according to claim 3, characterized in that: In step S3, the calcination is carried out under an inert atmosphere or an air atmosphere, at a temperature of 400~650 ℃, for a time of 2~6 h.

7. A carbon fiber-supported cerium oxide-metal photothermal monolithic catalyst, characterized in that: The catalyst is a photothermal monolithic catalyst with metal loaded on the carbon fiber-supported cerium oxide photothermal monolithic catalyst as described in claim 1. The metal is one or more of zirconium, lanthanum, praseodymium, neodymium, nickel, copper, bismuth, and titanium.

8. The method for preparing the carbon fiber supported cerium oxide-metal photothermal monolithic catalyst as described in claim 7, characterized in that: The carbon fiber supported cerium oxide photothermal monolithic catalyst of claim 1 is immersed in a precursor impregnation solution with a concentration of 0.01~1 mol / L for 0.5~2 h, and then calcined at 400~600 ℃ for 2~4 h to obtain the carbon fiber supported cerium oxide-metal photothermal monolithic catalyst. The precursor impregnation solution is a soluble salt solution of one or more of zirconium, lanthanum, praseodymium, neodymium, nickel, copper, bismuth, and titanium.

9. The application of the monolithic photothermal catalyst as described in claim 1 or 7 in the photothermal conversion of carbon dioxide, characterized in that: It is used for the photothermal catalytic reaction of direct synthesis of dimethyl carbonate from carbon dioxide and methanol.

10. The application of the photothermal monolithic catalyst according to claim 9 in the photothermal conversion of carbon dioxide, characterized in that: The photothermal catalytic reaction for the direct synthesis of dimethyl carbonate from carbon dioxide and methanol uses simulated sunlight or focused sunlight as the light source and is carried out continuously in a batch reactor or a fixed-bed reactor. The solid-liquid ratio of the photothermal monolithic catalyst to methanol is 0.01~0.1 g:1 mL, the initial carbon dioxide pressure is 0.1~3 MPa, the reaction temperature is 80~180 ℃, and the reaction time is 0.5~24 h; The residence time in a fixed-bed reactor is 1 to 30 minutes.

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