A wet oxidation catalyst and a method for its preparation

Abstract

The application discloses a wet oxidation catalyst, which comprises the following raw materials in percentage by weight: 0.1-2% noble metal, 1-10% graphene-based material, and the rest is a carrier, wherein the carrier is modified titanium dioxide, specifically, a rare earth-transition metal-oxygen vacancy-mesoporous three-dimensional gradient titanium dioxide carrier. The application aims at solving the technical problem of poor stability of the catalyst.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and particularly relates to a wet oxidation catalyst and its preparation method. Background Technology

[0002] Pharmaceutical wastewater contains a wide variety of chemical substances with complex compositions. Different processing techniques and reactants can lead to variations in the types and concentrations of these substances. Generally, pharmaceutical wastewater contains high concentrations of ammonia nitrogen, benzene, phenols, and heavy metals, characterized by poor biodegradability, high biotoxicity, and difficulty in degradation. This results in pharmaceutical wastewater posing risks of carcinogenesis, teratogenesis, and mutagenesis. If pharmaceutical wastewater is not treated to meet standards and discharged into the environment, pollutants will accumulate in the soil, water, and atmosphere, causing irreversible harm to human health. Therefore, pharmaceutical companies need to combine multiple water treatment processes to purify their wastewater.

[0003] Catalytic wet air oxidation (CWAO) is a technology that uses air or oxygen as an oxidant and a catalyst to convert large organic molecules in water into CO2, H2O, and small organic acids at temperatures of 125–320 °C and pressures of 0.5–20 MPa. CWAO is characterized by its fast reaction rate, high efficiency, wide application range, and small footprint. It is particularly effective in treating wastewater with high COD concentrations (>20,000 mg L⁻¹), such as pharmaceutical wastewater, as the heat of reaction itself can sustain the reaction, making it highly economical. In the CWAO degradation of medical wastewater, catalyst preparation is the core step. Supported noble metal catalysts exhibit significantly higher catalytic efficiency and longer lifespan, but their widespread use is limited by the high cost of noble metals. To reduce catalyst costs, methods such as reducing the amount of noble metal added or introducing other non-noble metals are commonly used. TiO₂, insoluble in acidic or alkaline solutions, is an excellent catalyst support in CWAO reactions. Therefore, this invention proposes to modify Ru / TiO2 catalysts with heteroatoms, focusing on achieving the catalytic effect of supported noble metal catalysts on high COD medical wastewater.

[0004] Based on the properties of the catalyst, catalytic wet oxidation technology is divided into homogeneous and heterogeneous catalytic wet oxidation. Early research mainly focused on homogeneous catalysts, but this method was gradually phased out because the catalyst dissolving in the waste would cause secondary pollution, requiring subsequent treatment. In recent years, heterogeneous catalysts have become a research hotspot. Heterogeneous catalysts are mainly divided into two categories: noble metals and metal oxides. Among them, metal oxide supported catalysts mostly use rare earth element oxides or their composite oxides as supports, with transition elements such as Cu, Co, Mn, Fe, and Ni supported on these supports. However, the catalysts have poor stability, so it is necessary to improve the existing technology. Summary of the Invention

[0005] This invention provides a wet oxidation catalyst and its preparation method to solve the technical problem of poor stability of existing catalysts.

[0006] In view of this, the present invention provides a wet oxidation catalyst comprising the following raw materials by weight percentage: 0.1-2% noble metals, 1-10% graphene-based materials, and the remainder being a support, wherein the support is modified titanium dioxide, specifically a rare earth-transition metal-oxygen vacancy-mesoporous three-dimensional gradient titanium dioxide support.

[0007] Optionally, the modified titanium dioxide is prepared by the following method:

[0008] A1: Disperse anatase titanium dioxide in dilute nitric acid, mix thoroughly, vacuum filter, wash, and dry to obtain the acid-etched matrix;

[0009] A2: Dissolve rare earth salts and transition metal salts in water to obtain a doping solution; place the acid-etched matrix into the doping solution, mix evenly, place in an oil bath to form a sol, adjust the pH value, continue stirring, let stand and age, vacuum filter, wash, dry, and obtain an intermediate.

[0010] A3: Spread the intermediate on an alumina ceramic boat, place it in a constant temperature zone, first pass argon gas to remove oxygen, then switch to a CO / Ar mixed gas, heat and hold, heat again and hold, start natural cooling, turn off CO, and keep the remaining argon gas at room temperature, take it out, grind, and sieve to obtain modified titanium dioxide.

[0011] Furthermore, the modified titanium dioxide is prepared using the following method:

[0012] A1: Disperse anatase titanium dioxide in 8% dilute nitric acid, mix evenly, vacuum filter, wash with water 3-5 times, and dry to obtain the acid-etched matrix;

[0013] A2: Dissolve rare earth salts and transition metal salts in water to obtain a doping solution; place the acid-etched matrix into the doping solution, mix evenly, and perform an oil bath at 50-70℃ to form a sol. Adjust the pH value to 8-9 with ammonia water, continue stirring for 1-2 hours, let stand and age for 10-18 hours, vacuum filter, wash with water until no white precipitate is detected by silver nitrate test, and dry at 80-120℃ for 8-12 hours to obtain an intermediate.

[0014] A3: Spread the intermediate on an alumina ceramic boat with a thickness of <1cm, place it in the constant temperature zone of a tube furnace, first purge oxygen with argon gas at a flow rate of 200ml / min for 20-40min, then switch to an 8% CO / Ar mixed gas at a flow rate of 200ml / min, heat to 300-400℃ and hold for 0.5-1.5h, then heat again to 400-600℃ and hold for 1-3h, then allow it to cool naturally to below 50℃, turn off the CO, and keep it at room temperature with the remaining argon gas, remove it, grind it, and pass it through a 200-mesh sieve to obtain modified titanium dioxide;

[0015] In step A2, the amount of water added per 1g of rare earth salt and transition metal salt is 200-400mL.

[0016] Optionally, the molar ratio of rare earth elements to transition metal elements in the doping solution of step A2 is (2-3):1.

[0017] Optionally, in step A2, the total molar amount of metal elements in the dopant solution to the molar ratio of the acid-etched substrate is 1:(25-35).

[0018] Optionally, the rare earth salt is one or more of cerium nitrate and lanthanum nitrate; the transition metal salt is one or more of cobalt nitrate and nickel nitrate.

[0019] Optionally, the precious metal is one or more of Ru, Pd, Pt, Ir and Rh.

[0020] Optionally, the graphene-based material is one or more of the following: virgin graphene, graphene oxide, reduced graphene oxide, functionalized graphene, and graphene composite materials.

[0021] Optionally, the graphene-based material is pretreated with a polyelectrolyte solution before use.

[0022] Optionally, the specific steps for pretreating the graphene-based material are as follows:

[0023] B1: Add polydiallyldimethylammonium chloride to water and mix well to obtain mixture a;

[0024] Graphene is placed in water and mixed evenly to obtain mixture b;

[0025] B2: Add mixture b to mixture a and stir to form a gel, thus obtaining a composite system;

[0026] B3: Add a reducing agent to the composite system, heat to increase the temperature, stir to react, centrifuge, wash the solid, freeze dry, and obtain the pretreated graphene-based material.

[0027] Furthermore, the specific steps for pretreating the graphene-based material are as follows:

[0028] B1: Add polydiallyldimethylammonium chloride to water and mix well to obtain mixture a;

[0029] Graphene is placed in water and mixed evenly to obtain mixture b;

[0030] B2: Add mixture b to mixture a and stir for 1-3 hours to form a gel, thus obtaining a composite system;

[0031] B3: Add a reducing agent to the composite system, heat to 60-100℃, stir for 3-5 hours, centrifuge, wash the solid with water until neutral, freeze dry at -50-(-30)℃ for 15-25 hours to obtain the pretreated graphene-based material;

[0032] In step B1, the amount of water added per 1g of polydiallyldimethylammonium chloride is 400-600mL, and the amount of water added per 1g of graphene is 200-400mL. In step B3, the amount of reducing agent added per 1g of polydiallyldimethylammonium chloride is 40-60mL, and the reducing agent is hydrazine hydrate with a concentration of 80%.

[0033] A method for preparing a wet oxidation catalyst includes the following steps:

[0034] S1: Dissolve the precious metal precursor salt in water and mix evenly to obtain the impregnation solution;

[0035] S2: The carrier is immersed in the impregnation solution, then removed, dried, and calcined to obtain the precursor;

[0036] S3: Place the graphene-based material in water, add the precursor, mix evenly, centrifuge, and then dry and calcine the solid to obtain a wet oxidation catalyst.

[0037] Furthermore, a method for preparing a wet oxidation catalyst includes the following steps:

[0038] S1: Dissolve the precious metal precursor salt in water and mix thoroughly to obtain an impregnation solution with a concentration of 0.01-0.05 mol / L;

[0039] S2: Immerse the carrier in the impregnation solution for 4-12 hours, then remove it and dry it at 80-120℃ for 2-4 hours, and then calcine it at 300-800℃ for 1-4 hours to obtain the precursor.

[0040] S3: Graphene-based material is placed in water to prepare a solution of 0.5-1.5 g / L. The precursor is added, mixed evenly, centrifuged, and the solid is dried at 80-120℃ for 2-4 h and calcined at 300-800℃ for 1-2 h to obtain a wet oxidation catalyst.

[0041] Among them, the precursor salt is nitrate, hydrochloride, carboxylate, organic acid salt, etc., and the mass ratio of graphene-based material to precursor in step S3 is (1-10):100.

[0042] As can be seen from the above technical solutions, the embodiments of the present invention have the following advantages:

[0043] 1. This invention uses graphene-based materials to coat the catalyst, which improves the stability of the catalyst and provides a dispersion substrate for the catalyst particles with the unique structure of the coating material, preventing agglomeration. At the same time, the abundant functional groups on its surface enhance the adsorption of organic matter.

[0044] 2. This invention uses a modified titanium dioxide support. After acid etching with dilute nitric acid, the density of hydroxyl groups (-OH) on the surface of the anatase titanium dioxide increases significantly. At the same time, the pore structure (pore size, specific surface area) inside the support is regulated. Acid etching produces a more uniform mesoporous structure, reducing structural stress caused by "dead pores" or agglomeration. The abundant -OH groups on the surface can serve as "anchoring points" for subsequent rare earth / transition metal ions, enhancing the binding force between metal ions and the support through coordination, and preventing the active metal components from being washed away by solvents or dissolved at high temperatures during the reaction. Afterward, an argon atmosphere is used to remove oxygen first to prevent oxidation of intermediates. Subsequent CO reduction can reduce some high-valence transition metal ions to low-valence states without destroying the anatase structure of titanium dioxide.

[0045] Furthermore, titanium dioxide is prone to "crystal transformation" or "grain growth" in the high-temperature, highly oxidizing environment of wet oxidation, leading to a sharp decrease in specific surface area. Rare earth elements can be doped into the titanium dioxide lattice, occupying lattice vacancies or interstitial sites, inhibiting lattice migration, thereby preventing crystal transformation and grain aggregation, maintaining the porous structure and high specific surface area of ​​the support, facilitating improved wastewater treatment efficiency, and enhancing stability. Transition metals are the core active centers in wet oxidation, catalyzing the generation of strong oxidizing free radicals such as •OH from O2 or H2O2, rapidly degrading organic pollutants, preventing pollutants from adsorbing and accumulating on the catalyst surface to form "stubborn carbon deposits," and indirectly improving the long-term stability of the catalyst.

[0046] Therefore, through the synergistic effect of rare earth elements and transition metal elements, the lattice stability, active component anchoring, oxygen storage and release effects of rare earth elements, and the efficient oxidation catalysis effect of transition metals, the synergistic optimization of "stability-activity" is achieved: it not only solves the pain point of poor stability of traditional catalysts, but also significantly improves the COD removal rate.

[0047] 3. This invention pre-treats the graphene-based material before use, utilizing the electrostatic interaction between the graphene sheets and polydiallyldimethylammonium chloride to arrange the graphene sheets in an orderly manner, supporting the graphene sheets, preventing agglomeration, and forming a porous structure. This is beneficial to improving the stability of the catalyst and also to improving the catalyst's treatment effect on wastewater. Detailed Implementation

[0048] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in the present invention can be purchased on the market or prepared by existing methods.

[0049] Rare earth salts are selected from cerium nitrate, transition metal salts are selected from cobalt nitrate, precious metals are selected from ruthenium, and metal salts are nitrates.

[0050] Preparation Example 1

[0051] A carrier, namely modified titanium dioxide, is prepared by the following method:

[0052] A1: Disperse anatase titanium dioxide in 8% dilute nitric acid, mix thoroughly, vacuum filter, wash with water 5 times, and dry to obtain the acid-etched matrix.

[0053] A2: Cerium nitrate and cobalt nitrate were dissolved in water to obtain a doping solution; the acid-etched matrix was placed in the doping solution and mixed evenly. The mixture was then subjected to an oil bath at 60°C to form a sol. The pH was adjusted to 8.5 with ammonia water, and stirring was continued for 1.5 hours. The mixture was allowed to stand for 14 hours, then vacuum filtered. The mixture was washed with water until no white precipitate was detected by silver nitrate testing. The mixture was then dried at 100°C for 10 hours to obtain an intermediate.

[0054] A3: Spread the intermediate on an alumina ceramic boat with a thickness of <1cm, place it in the constant temperature zone of a tube furnace, first purge oxygen with argon gas at a flow rate of 200ml / min for 30min, then switch to an 8% CO / Ar mixed gas at a flow rate of 200ml / min, heat to 350℃ and hold for 1h, then heat again to 500℃ and hold for 2h, then allow it to cool naturally to below 50℃, turn off CO, and keep the remaining argon gas at room temperature, remove, grind, and pass through a 200-mesh sieve to obtain modified titanium dioxide;

[0055] In step A2, the amount of water added per 1g of rare earth salt and transition metal salt is 300mL. The molar ratio of cerium in cerium nitrate to cobalt in cobalt nitrate in the doping solution of step A2 is 2:1. The molar ratio of the total molar amount of metal elements in the doping solution of step A2 to the molar amount of the acid-etched substrate is 1:25.

[0056] Preparation Example 2

[0057] One carrier, namely modified titanium dioxide, differs from preparation example 1 in that the amount of cerium nitrate added is different. In preparation example 2, step A2, the molar ratio of cerium in cerium nitrate to cobalt in cobalt nitrate is 2.5:1.

[0058] Preparation Example 3

[0059] One carrier, namely modified titanium dioxide, differs from that in Preparation Example 1 in that the amount of cerium nitrate added is different. In Preparation Example 3, step A2, the molar ratio of cerium in cerium nitrate to cobalt in cobalt nitrate is 3:1.

[0060] Preparation Example 4

[0061] One type of carrier, namely modified titanium dioxide, differs from preparation example 2 in that the amount of acid-etched matrix added is different. In preparation example 4, step A2, the total molar amount of metal elements in the doping solution is 1:30 to the molar ratio of the acid-etched matrix.

[0062] Preparation Example 5

[0063] One type of carrier, namely modified titanium dioxide, differs from preparation example 2 in that the amount of acid-etched matrix added is different. In preparation example 5, step A2, the total molar amount of metal elements in the doping solution and the molar ratio of the acid-etched matrix are 1:35. Example Example

[0064] A wet oxidation catalyst, the raw material ratio of which is shown in Table 1.

[0065] A method for preparing a wet oxidation catalyst includes the following steps:

[0066] S1: Dissolve ruthenium nitrate in water and mix well to obtain an impregnation solution with a concentration of 0.03 mol / L;

[0067] S2: The carrier prepared using Preparation Example 1 was immersed in the impregnation solution for 8 hours, then removed and dried at 100°C for 3 hours, and then calcined at 500°C for 2 hours to obtain the precursor.

[0068] S3: Graphene-based material is placed in water to prepare a 1 g / L solution. The precursor is added, mixed evenly, centrifuged, and the solid is dried at 100°C for 3 h and calcined at 500°C for 1.5 h to obtain a wet oxidation catalyst.

[0069] In step S3, the mass ratio of graphene-based material to precursor is 5:100.

[0070] Examples 2-5

[0071] A wet oxidation catalyst differs from Example 1 in that the raw material ratio is different, as shown in Table 1.

[0072] Table 1. Weight percentage of each raw material (%)

[0073] raw material Example 1 Example 2 Example 3 Example 4 Example 5 precious metals 0.1 1 2 1 1 Graphene-based materials 1 1 1 5 10 carrier margin margin margin margin margin

[0074] Examples 6-9

[0075] A wet oxidation catalyst, which differs from Example 4 in that the source of the support is different. The supports in Examples 6-9 were prepared using Preparation Examples 2-5, respectively. Example

[0076] A wet oxidation catalyst, which differs from Example 8 in that the graphene-based material undergoes the following pretreatment before use:

[0077] B1: Add polydiallyldimethylammonium chloride to water and mix well to obtain mixture a;

[0078] Graphene is placed in water and mixed evenly to obtain mixture b;

[0079] B2: Add mixture b to mixture a and stir for 2 hours to form a gel, thus obtaining a composite system;

[0080] B3: Add a reducing agent to the composite system, heat to 80℃, stir for 4 hours, centrifuge, wash the solid with water until neutral, freeze dry at -40℃ for 20 hours to obtain the pretreated graphene-based material;

[0081] In step B1, the amount of water added per 1g of polydiallyldimethylammonium chloride is 500mL, and the amount of water added per 1g of graphene is 300mL. In step B3, the amount of reducing agent added per 1g of polydiallyldimethylammonium chloride is 50mL, and the reducing agent is hydrazine hydrate with a concentration of 80%.

[0082] Comparative Example

[0083] Comparative Example 1

[0084] A wet oxidation catalyst, which differs from Example 1 in that the support is titanium dioxide.

[0085] Comparative Example 2

[0086] A wet oxidation catalyst, which differs from Example 1 in that cerium nitrate in step A2 of the support preparation process is replaced by cobalt nitrate in equal amounts.

[0087] Comparative Example 3

[0088] A wet oxidation catalyst, which differs from Example 1 in that cobalt nitrate in step A2 of the support preparation process is replaced with an equal amount of cerium nitrate.

[0089] Performance testing

[0090] The wet oxidation catalysts in Examples 1-10 and Comparative Examples 1-3 were subjected to the following performance tests:

[0091] Catalyst evaluation: The catalysts from Examples 1-10 and Comparative Examples 1-3 were loaded into a wet oxidation reactor. Wastewater and oxygen were mixed and then subjected to catalytic wet oxidation reaction. The residence time of wastewater in the effective section of the reactor was 30 min, the reaction temperature was 300℃, the reaction pressure was 10 MPa, and the volume ratio of oxygen to wastewater was 300.

[0092] The wastewater was acrylonitrile refining wastewater with a COD value of 30,000 mg / L. The reactor was a fixed-bed reactor with an inner diameter of 14 mm and a length of 600 mm. The catalyst was evaluated by measuring the initial COD removal rate after 24 hours of continuous operation, and the final COD removal rate was measured after 300 hours of continuous operation. The activity reduction rate was calculated based on the change in activity before and after the evaluation, using the following formula:

[0093] Activity reduction rate (%) = [(initial activity - final activity) / initial activity] × 100%

[0094] The activity reduction rate was used as an evaluation index for catalyst stability. The lower the value, the more stable the catalyst performance, and vice versa. The test results are shown in Table 2. The activity reduction rate is retained to two decimal places.

[0095] Table 2 Test Results

[0096] project Initial activity (%) Final activity (%) Activity reduction rate (%) Example 1 95.6 93.5 2.20 Example 2 96.3 94.9 1.45 Example 3 96.1 94.5 1.66 Example 4 97.2 96.2 1.03 Example 5 97.1 95.9 1.24 Example 6 97.9 97.2 0.72 Example 7 97.6 96.8 0.82 Example 8 98.5 98.1 0.41 Example 9 98.3 97.8 0.51 Example 10 99.5 99.3 0.20 Comparative Example 1 85.2 75.4 11.50 Comparative Example 2 90.3 84.6 6.31 Comparative Example 3 90.1 84.3 6.43

[0097] The wet oxidation catalyst of the present invention, through the synergistic effect between the raw materials, not only enables the catalyst to have a better treatment effect on wastewater, but also improves the stability of the catalyst, wherein the activity reduction rate is 0.20-2.20%.

[0098] Combining Example 1 and Comparative Examples 1-3, it can be seen that the activity reduction rate of Example 1 is 2.20%, which is significantly lower than that of Comparative Examples 1-3. This indicates that modified titanium dioxide is more suitable as a support. Through the lattice stabilization of rare earth elements, the anchoring of active components, the oxygen storage and release effects, and the efficient oxidation catalytic effect of transition metals, the synergistic optimization of "stability-activity" is achieved, which not only significantly improves the COD removal rate but also enhances the stability of the catalyst.

[0099] As can be seen from Examples 1-5, the activity reduction rate of Example 4 was 1.03%, indicating that the amount of each raw material added in Example 4 was more appropriate.

[0100] As can be seen from Examples 4 and 6-9, the activity reduction rate of Example 8 was 0.41%, indicating that the support prepared by Example 4 was more suitable. Furthermore, the amount of cerium nitrate and cobalt nitrate added in Example 4 was also more appropriate. Too little addition would affect the wastewater treatment efficiency; while too much cerium nitrate would lead to excessive lattice defects in the support, forming complex centers and reducing catalytic activity. Too much cobalt nitrate would lead to severe lattice distortion, damaging the purity of titanium dioxide and also reducing activity, thus affecting the stability of the catalyst. Therefore, only when the amount of cerium nitrate and cobalt nitrate added is within a certain range can the catalyst have better stability.

[0101] Combining Examples 8 and 10, it can be seen that the activity reduction rate of Example 10 is 0.20%, indicating that pretreatment of graphene-based materials before use is more appropriate. By utilizing the electrostatic interaction between graphene sheets and polydiallyldimethylammonium chloride, the graphene sheets are arranged in an orderly manner, preventing agglomeration and forming a porous structure, which is beneficial to improving the stability of the catalyst and also to improving the catalyst's treatment effect on wastewater.

[0102] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wet oxidation catalyst, characterized in that: The raw materials include the following weight percentages: 0.1-2% precious metals, 1-10% graphene-based materials, and the remainder as a carrier. The carrier is modified titanium dioxide, specifically a rare earth-transition metal-oxygen vacancy-mesoporous three-dimensional gradient titanium dioxide carrier. The modified titanium dioxide is prepared by the following method: A1: Disperse anatase titanium dioxide in dilute nitric acid, mix evenly, vacuum filter, wash, and dry to obtain an acid-etched matrix; A2: Dissolve rare earth salts and transition metal salts in water to obtain a doping solution; place the acid-etched matrix into the doping solution, mix evenly, place in an oil bath to form a sol, adjust the pH value, continue stirring, allow to stand for aging, vacuum filter, wash, and dry to obtain an intermediate. A3: Spread the intermediate on an alumina ceramic boat, place it in a constant temperature zone, first pass argon gas to remove oxygen, then switch to a CO / Ar mixed gas, heat and hold, heat again and hold, start natural cooling, turn off CO, and keep the remaining argon gas at room temperature, take it out, grind, and sieve to obtain modified titanium dioxide.

2. The wet oxidation catalyst according to claim 1, characterized in that: The molar ratio of rare earth elements to transition metal elements in the doping solution of step A2 is (2-3):

1.

3. The wet oxidation catalyst according to claim 1, characterized in that: In step A2, the total molar amount of metal elements in the doping solution to the molar ratio of the acid-etched substrate is 1:(25-35).

4. The wet oxidation catalyst according to claim 1, characterized in that: The rare earth salt is one or more of cerium nitrate and lanthanum nitrate; the transition metal salt is one or more of cobalt nitrate and nickel nitrate.

5. The wet oxidation catalyst according to claim 1, characterized in that: The precious metal is one or more of Ru, Pd, Pt, Ir and Rh.

6. The wet oxidation catalyst according to claim 1, characterized in that: The graphene-based material is one or more of the following: original graphene, graphene oxide, reduced graphene oxide, functionalized graphene, and graphene composite materials.

7. The wet oxidation catalyst according to claim 6, characterized in that: The graphene-based material is pretreated with a polyelectrolyte solution before use.

8. The wet oxidation catalyst according to claim 6, characterized in that: The specific steps for pretreating the graphene-based material are as follows: B1: Add polydiallyldimethylammonium chloride to water and mix evenly to obtain mixture a; Add graphene to water and mix evenly to obtain mixture b; B2: Add mixture b to mixture a and stir to form a gel, thus obtaining a composite system; B3: Add a reducing agent to the composite system, heat to increase the temperature, stir to react, centrifuge, wash the solid, freeze dry, and obtain the pretreated graphene-based material.

9. A method for preparing a wet oxidation catalyst as described in any one of claims 1-8, characterized in that, The process includes the following steps: S1: Dissolve the precious metal precursor salt in water, mix thoroughly to obtain an impregnation solution; S2: Immerse the carrier in the impregnation solution, then remove it, dry it, and calcine it to obtain the precursor; S3: Place the graphene-based material in water, add the precursor, mix evenly, centrifuge, and then dry and calcine the solid to obtain a wet oxidation catalyst.