Preparation and application of molybdenum-vanadium polyacid-based heterogeneous catalyst

Abstract

This invention relates to the preparation of a molybdenum-vanadium polyacid-based heterogeneous catalyst for the catalytic oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-p-benzoquinone. The purpose of this invention is to solve the problems of difficult recovery of traditional polyacid homogeneous catalysts and poor stability of heterogeneous catalysts. The chemical formula of the molybdenum-vanadium polyacid-based heterogeneous catalyst is Mo. 72 V 30 / CuO x / CoO / NC. The method used: [The text abruptly shifts to a seemingly unrelated topic about Mo, possibly 72 V 30 with CuO x / CoO / NC was dispersed in 30 mL of deionized water and stirred at room temperature for 12 h. The mixture was then transferred to a reaction vessel and maintained at 100 °C for 12 h. After washing and centrifugation, the resulting black powder was the molybdenum-vanadium polyacid-based heterogeneous catalyst Mo. 72 V 30 / CuO x / CoO / NC. This invention provides a polyacid-based heterogeneous catalyst with high catalytic activity and high stability.

Description

Technical Field

[0001] This invention discloses a molybdenum-vanadium polyacid-based heterogeneous catalyst for the catalytic oxidation of 2,3,6-trimethylphenol to synthesize 2,3,5-trimethyl-p-benzoquinone. Background Technology

[0002] Functionalized p-benzoquinones are a class of highly valuable intermediates that play a key role in biopharmaceuticals and fine chemicals. The synthesis of functionalized p-benzoquinones by direct oxidation of alkylphenols is a highly efficient route that maintains the basic framework of the benzene ring and reduces the generation of byproducts. Among them, 2,3,5-trimethyl-p-benzoquinone, a key intermediate of vitamin E, can be directly synthesized by oxidation of 2,3,6-trimethylphenol.

[0003] Polyoxometalates (hereinafter referred to as "polyacids") are inorganic metal-oxygen clusters formed from transition metals. Due to their excellent catalytic oxidation performance, good thermal stability, and chemical stability, they have attracted widespread attention in the field of catalysis. However, the difficulty in recovering homogeneous catalysts hinders their further application. Furthermore, for most polyacid-based heterogeneous catalysts, their catalytic activity is often lower than that of the original polyacid, and the weak binding between the polyacid and the support leads to leaching of the polyacid during the reaction. Therefore, selecting a suitable support material to enhance the binding ability between the two is key to solving these problems.

[0004] Metal-organic frameworks (MOFs) are crystalline porous materials formed by the self-assembly of metal ions / metal clusters and organic ligands through coordination bonds. Their derived carbon materials inherit the high specific surface area of ​​MOFs and also possess the high stability of carbon materials. Furthermore, the metal nodes are transformed in situ into metal / metal oxide nanoparticles, which can be further combined with polyacids. On the one hand, this enhances the structural stability of the catalyst, and on the other hand, it enhances the catalytic activity through a synergistic effect. Therefore, MOFs can serve as an excellent support material. Summary of the Invention

[0005] To overcome the problems of traditional polyacid materials being difficult to recover as homogeneous catalysts and having poor stability and low catalytic efficiency as heterogeneous catalysts, this invention utilizes a hydrothermal method and selects molybdenum-vanadium polyacid (Mo). 72 V 30 and metal-organic framework-derived materials CuO x Using / CoO / NC as a support, a molybdenum-vanadium polyacid-based heterogeneous catalyst was prepared and applied to the catalytic oxidation of 2,3,6-trimethylphenol to synthesize 2,3,5-trimethyl-p-benzoquinone. The catalyst prepared in this invention has high catalytic activity and cycle stability.

[0006] A molybdenum-vanadium polyacid-based heterogeneous catalyst with the chemical formula Mo 72 V 30 / CuO x / CoO / NC, where Mo 72 V 30 The molecular formula is Na₂K₂ 16 (VO)(H2O)5[K 10 ,{(Mo)Mo5O 21 (H2O)3(SO4)} 12 (VO) 30 (H2O) 20 ]·150H2O.

[0007] The preparation of a molybdenum-vanadium polyacid-based heterogeneous catalyst includes the following steps:

[0008] (1) Mo 72 V 30 Synthesis:

[0009] First, 2.6 g of NaVO3 was added to 55 mL of water at 60℃ and stirred for 15 min until completely dissolved, yielding solution A. Separately, 6 g of Na2MoO4·2H2O was dissolved in 75 mL of water and stirred for 15 min, yielding solution B. After solution A cooled to room temperature, solution B was added, and stirring continued for 15 min. Then, 0.9 g of N2H4·H2SO4 was added, and the solution gradually turned dark purple. Stirring continued at room temperature for 3 h. Next, 20 mL of KCl aqueous solution containing 3 g of KCl was added, and after stirring for 5 min, the solution was transferred to a 250 mL Erlenmeyer flask. The flask was left open in the air for 4 days, during which dark purple crystals precipitated from the solution. After filtration, the crystals were collected, washed several times with ethanol, and dried at room temperature for 24 h to obtain purplish-black crystals, which were Mo. 72 V 30 .

[0010] (2) CuO x Synthesis of / CoO / NC: First, 1.5 g of 1,3,5-pyromellitic acid was dissolved in 45 mL of a mixed solvent of ethanol and N,N-dimethylformamide (volume ratio 1:1), labeled as solution A; separately, 3.1 g of Cu(NO3)2·3H2O was dissolved in 22.5 mL of water, labeled as solution B. Both solutions were stirred separately at room temperature for 10 min to ensure complete dissolution. Then, solution B was added to solution A and stirring was continued for 30 min. The mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and maintained at 110 °C for 10 h. The resulting blue microcrystals were centrifuged, washed with ethanol, and dried under vacuum at 60 °C for 12 h to obtain HKUST-1.

[0011] The synthesized HKUST-1 (50 mg) was ultrasonically dispersed in 50 mL of methanol and stirred for 30 min to obtain a homogeneous suspension, labeled as solution A. 8 mmol of 2-methylimidazole was dissolved in 50 mL of methanol and stirred for 30 min, labeled as solution B. 2 mmol of Co(NO3)2·6H2O was added to solution A and stirred vigorously for 30 min to form solution C. Solution B was poured into solution C and stirred vigorously for 4 h. The resulting solid was collected by centrifugation, washed three times with methanol, and dried under vacuum at 60 °C for 12 h to obtain a purple powder, which was HKUST-1@ZIF-67.

[0012] The synthesized HKUST-1@ZIF-67 was uniformly spread in a ceramic boat and pyrolyzed in a tube furnace under a continuous argon flow. The heating rate was 5 °C / min. -1 Under these conditions, the temperature is raised to 450℃ and held for 2 hours. After the temperature is cooled down to room temperature, the resulting powder is CuO. x / CoO / NC.

[0013] (3) Mo 72 V 30 / CuO x Synthesis of / CoO / NC: First, 30 mg of CuO... x / CoO / NC and 400 mg of Mo 72 V 30 Add to 30 mL of deionized water and stir at room temperature for 12 h. Then transfer to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and maintain at 100 °C for 12 h. After cooling to room temperature, wash three times with ethanol and then dry in a vacuum oven at 60 °C for 12 h. The resulting powder is Mo. 72 V 30 / CuO x / CoO / NC.

[0014] A molybdenum-vanadium polyacid-based heterogeneous catalyst is mainly used in the catalytic oxidation of 2,3,6-trimethylphenol to synthesize 2,3,5-trimethyl-p-benzoquinone.

[0015] The application method described above is as follows: Analysis was performed using a Thermo Fisher U3000 high-performance liquid chromatograph, and the conversion rate of the reaction substrate and the yield of the product were calculated using the external standard method. Prepare 0.1-1.0 mg / mL solutions respectively. -1Standard solutions of 2,3,6-trimethylphenol and 2,3,5-trimethyl-p-benzoquinone were analyzed, and their corresponding peak areas were determined by high-performance liquid chromatography (HPLC). A standard curve was plotted by linearly fitting the peak areas against the concentrations. The catalytic oxidation reaction was carried out in a three-necked flask equipped with a reflux condenser. First, the substrate and catalyst were added to a 10 mL three-necked flask, followed by the addition of 1 mL of acetonitrile and stirring to ensure complete dissolution of the substrate. When the temperature reached the predetermined level, 30% H₂O₂ was added. At regular intervals, 0.1 mL samples were taken, diluted, and the conversion rates of 2,3,6-trimethylphenol and the yield of 2,3,5-trimethyl-p-benzoquinone were calculated based on the standard curve.

[0016] Compared with the prior art, the present invention has the following characteristics:

[0017] This invention utilizes a hydrothermal synthesis method to synthesize molybdenum-vanadium polyacid (Mo). 72 V 30 and metal-organic framework derived materials CuO x A heterogeneous catalyst with high stability was successfully prepared using / CoO / NC. x The robust bonding of / CoO / NC solves the problems of difficult recovery of homogeneous polyacid catalysts and weak bonding ability of heterogeneous polyacid catalysts, thus enhancing the catalytic cycle stability. The generation of peroxypolyacid species during the reaction is the main reason for the high catalytic activity. CuO, as a strong Lewis acid, can accept the lone pair electrons of phenolic hydroxyl groups, initiating electron transfer from the substrate to the metal, thereby weakening the OH bond and promoting the formation of reaction intermediates. CoO, on the other hand, efficiently activates hydrogen peroxide through a "Fenton-like reaction," continuously generating oxygen-containing free radicals. x The "activation-oxidation" tandem reaction mechanism driven by CoO further enhances its catalytic activity. In the catalytic oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-p-benzoquinone, a conversion rate of 99.4% and a yield of 96.3% were achieved within 2 minutes, and its catalytic activity was significantly higher than that of pure polyacids and supports. Attached Figure Description

[0018] Figure 1 The infrared spectrum of a molybdenum-vanadium polyacid-based heterogeneous catalyst prepared in Example 1 of this invention is shown below.

[0019] Figure 2 The X-ray powder diffraction pattern of a molybdenum-vanadium polyacid-based heterogeneous catalyst prepared in Example 1 of this invention is shown below.

[0020] Figure 3 The X-ray photoelectron spectrum of a molybdenum-vanadium polyacid-based heterogeneous catalyst prepared in Example 1 of this invention is shown below.

[0021] Figure 4These are scanning electron microscope (SEM) images of a molybdenum-vanadium polyacid-based heterogeneous catalyst prepared in Example 1 of this invention at different stages of its preparation.

[0022] Figure 5 The N2 adsorption-desorption isotherm and pore size distribution diagram of the molybdenum-vanadium polyacid-based heterogeneous catalyst prepared in Example 1 of this invention are shown.

[0023] Figure 6 This is a comparison diagram of the catalytic activity of a molybdenum-vanadium polyacid-based heterogeneous catalyst prepared in Example 1 of this invention.

[0024] Figure 7 The graph shows the catalytic activity data of a molybdenum-vanadium polyacid-based heterogeneous catalyst prepared in Example 1 of this invention after 5 cycles.

[0025] Figure 8 The infrared and X-ray powder diffraction spectra of the molybdenum-vanadium polyacid-based heterogeneous catalyst prepared in Example 1 of this invention before and after reaction are shown.

[0026] Figure 9 This is a flowchart illustrating the preparation process of a molybdenum-vanadium polyacid-based heterogeneous catalyst as described in Example 1 of the present invention. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0028] Example 1: Preparation and application of a molybdenum-vanadium polyacid-based heterogeneous catalyst, comprising the following preparation steps:

[0029] (1) Mo 72 V 30 Synthesis:

[0030] First, 2.6 g of NaVO3 was added to 55 mL of water at 60℃ and stirred for 15 min until completely dissolved, yielding solution A. Separately, 6 g of Na2MoO4·2H2O was dissolved in 75 mL of water and stirred for 15 min, yielding solution B. After solution A cooled to room temperature, solution B was added, and stirring continued for 15 min. Then, 0.9 g of N2H4·H2SO4 was added, and the solution gradually turned dark purple. Stirring continued at room temperature for 3 h. Next, 20 mL of KCl aqueous solution containing 3 g of KCl was added, and after stirring for 5 min, the solution was transferred to a 250 mL Erlenmeyer flask. The flask was left open in the air for 4 days, during which dark purple crystals precipitated from the solution. After filtration, the crystals were collected, washed several times with ethanol, and dried at room temperature for 24 h to obtain purplish-black crystals, which were Mo. 72 V 30 .

[0031] (2) CuO xSynthesis of / CoO / NC: First, 1.5 g of 1,3,5-pyromellitic acid was dissolved in 45 mL of a mixed solvent of ethanol and N,N-dimethylformamide (volume ratio 1:1), labeled as solution A; separately, 3.1 g of Cu(NO3)2·3H2O was dissolved in 22.5 mL of water, labeled as solution B. Both solutions were stirred separately at room temperature for 10 min to ensure complete dissolution. Then, solution B was added to solution A and stirring was continued for 30 min. The mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and maintained at 110 °C for 10 h. The resulting blue microcrystals were centrifuged, washed with ethanol, and dried under vacuum at 60 °C for 12 h to obtain HKUST-1.

[0032] The synthesized HKUST-1 (50 mg) was ultrasonically dispersed in 50 mL of methanol and stirred for 30 min to obtain a homogeneous suspension, labeled as solution A. 8 mmol of 2-methylimidazole was dissolved in 50 mL of methanol and stirred for 30 min, labeled as solution B. 2 mmol of Co(NO3)2·6H2O was added to solution A and stirred vigorously for 30 min to form solution C. Solution B was poured into solution C and stirred vigorously for 4 h. The resulting solid was collected by centrifugation, washed three times with methanol, and dried under vacuum at 60 °C for 12 h to obtain a purple powder, which was HKUST-1@ZIF-67.

[0033] The synthesized HKUST-1@ZIF-67 was uniformly spread in a ceramic boat and pyrolyzed in a tube furnace under a continuous argon flow. The heating rate was 5 °C / min. -1 Under these conditions, the temperature is raised to 450℃ and held for 2 hours. After the temperature is cooled down to room temperature, the resulting powder is CuO. x / CoO / NC.

[0034] (3) Mo 72 V 30 / CuO x Synthesis of / CoO / NC: First, 30 mg of CuO... x / CoO / NC and 400 mg of Mo 72 V 30 Add to 30 mL of deionized water and stir at room temperature for 12 h. Then transfer to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and maintain at 100 °C for 12 h. After cooling to room temperature, wash three times with ethanol and then dry in a vacuum oven at 60 °C for 12 h. The resulting powder is Mo. 72 V 30 / CuO x / CoO / NC.

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0036] Figure 1 The image shows the infrared spectrum of a molybdenum-vanadium polyacid-based heterogeneous catalyst. CuO x / CoO / NC at 607 cm -1 The peak at this location corresponds to the characteristic peak of ν(Cu / Co-O). For Mo... 72 V 30 Located at 965 cm -1 796 cm -1 and 580 cm -1 The characteristic peaks at these locations can be attributed to ν(Mo=O) / ν(V=O), ν(Mo-OV), and ν(Mo-O-Mo), respectively. For the catalyst Mo... 72 V 30 / CuO x / CoO / NC, Mo can still be clearly observed 72 V 30 The characteristic peaks indicate that Mo 72 V 30 It has been successfully loaded onto the carrier, and its structure was not damaged during the loading process. Furthermore, it was observed that the structure belongs to Mo... 72 V 30 The characteristic peaks of Mo showed varying degrees of redshift, which may be due to the synthesis process. 72 V 30 Structure and CuO x The result of / CoO / NC interaction, while the mixed catalyst Mo obtained through physical mixing 72 V 30 +CuO x This phenomenon was not observed in / CoO / NC, further demonstrating that hydrothermal conditions promoted the interaction between the two and enhanced the structural stability of the catalyst.

[0037] Figure 2 The image shows the X-ray powder diffraction pattern of a molybdenum-vanadium polyacid-based heterogeneous catalyst. 72 V 30 / CuO x The spectrum of / CoO / NC clearly shows that it belongs to CuO. x / CoO / NC and Mo 72 V 30 The characteristic diffraction peaks indicate that Mo 72 V 30 It has been successfully loaded into the carrier, and its crystal structure remains intact after loading.

[0038] Figure 3The image shows the X-ray photoelectron spectrum of a molybdenum-vanadium polyacid-based heterogeneous catalyst. The fine spectra at Mo 3d and V 2p are shown for Mo. 72 V 30 The binding energy can be attributed to Mo at 235.8 eV and 232.6 eV. 6+ 3D 3 / 2 and 3D 5 / 2 At 223.8 eV and 216.5 eV, it belongs to V. 4+ 2p 1 / 2 and 2p 3 / 2 Prove that in Mo 72 V 30 In this context, Mo and V exhibit valences of +6 and +4, respectively. For Mo... 72 V 30 / CuO x / CoO / NC, it can be clearly observed that it belongs to Mo 6+ The binding energy shifts towards lower energies, which may be due to electrons moving from CuO. x / CoO / NC has been transferred to Mo 72 V 30 This is due to the fact that, for V 2p, the peaks at 223.4 eV and 215.9 eV, where the binding energy is located, are attributed to V 2p, respectively. 1 / 2 With V 2p 3 / 2 Prove V 5+ The existence of V indicates that during the recombination process, 4+ Oxidized to V 5+ In the XPS spectrum of Cu 2p, for CuO x / CoO / NC, at binding energies of 954.9 and 934.6 eV, are attributed to Cu. 2+ 2p 1 / 2 and 2p 3 / 2 The values ​​at 952.8 eV and 932.4 eV belong to Cu. + / 0 2p 1 / 2 and 2p 3 / 2 And for Mo 72 V 30 / CuO x / CoO / NC, belonging to Cu 2+ The proportion compared to CuO x The increase in / CoO / NC is attributed to Cu. + / 0 The proportion of CuO decreases. In the XPS spectrum of Co 2p, CuO x / CoO / NC exhibits two characteristic peaks at 796.2 eV and 780.5 eV, which are attributed to Co, respectively. 2+ 2p 1 / 2 and 2p 3 / 2Additionally, the peaks at 803.1 eV and 786.3 eV belong to Co satellites. For Mo... 72 V 30 / CuO x / CoO / NC, it can be clearly observed that it belongs to Co 2+ The binding energy shifts towards lower energies. Through the above analysis, the binding energies of Mo, V, Cu, and Co all changed, proving that in Mo… 72 V 30 with CuO x Significant electron transfer occurred between / CoO / NC, and their strong interaction significantly enhanced the stability of the catalyst.

[0039] Figure 4 The image shows scanning electron microscope (SEM) images of a molybdenum-vanadium polyacid-based heterogeneous catalyst at different preparation stages. The evolution from HKUST-1 to Mo was investigated using SEM. 72 V 30 / CuO x Morphological and structural changes at different stages of the / CoO / NC process. SEM images of HKUST-1 show a smooth octahedral structure with an average particle size of approximately 18 µm. When ZIF-67 was grown on the HKUST-1 surface via in-situ growth, HKUST-1@ZIF-67 retained the octahedral structure, but the surface became rough, indicating successful growth of ZIF-67 on the HKUST-1 surface. After high-temperature carbonization, the ligands in the precursor (1,3,5-pyromellitic acid and 2-methylimidazole) were transformed into N-doped amorphous carbon materials, intercalated with CuO. x And CoO species. Carbide materials still retain their octahedral morphology, even when combined with Mo. 72 V 30 No significant structural changes were observed after the composite was formed, demonstrating that the derived carbon material possesses excellent structural stability.

[0040] Figure 5 This image shows the N2 adsorption-desorption isotherm and pore size distribution of a molybdenum-vanadium polyacid-based heterogeneous catalyst. (From CuO) x / CoO / NC and Mo 72 V 30 / CuO x In the nitrogen adsorption-desorption isotherms and pore size distributions of / CoO / NC, both exhibit typical Type IV curve characteristics with a significant hysteresis loop, indicating the presence of a mesoporous structure. Calculations based on BET theory show that CuO... x The specific surface area of ​​ / CoO / NC is 81.37 m². 2 g -1 The average pore size is 14.95 nm. Mo 72V 30 / CuO x The specific surface area of ​​ / CoO / NC is 43.13 m². 2 g -1 The average pore size is 5.83 nm, similar to CuO. x Compared to / CoO / NC, both the specific surface area and average pore size decreased, which proves that Mo 72 V 30 Successfully loaded onto CuO x The catalyst's high specific surface area and unique porous structure not only facilitate the attachment of active sites but also provide sufficient space for the adsorption and reaction of the substrate.

[0041] Figure 6 This is a comparison of the catalytic activities of a molybdenum-vanadium polyacid-based heterogeneous catalyst. The graph shows that for Mo… 72 V 30 A 91.1% conversion rate of 2,3,6-trimethylphenol and an 83.5% yield of 2,3,5-trimethyl-p-benzoquinone were achieved, with CuO as the base material. x / CoO / NC catalyst can achieve a 40.1% conversion of 2,3,6-trimethylphenol and a 19.8% yield of 2,3,5-trimethyl-p-benzoquinone. Mo is then stirred... 72 V 30 with CuO x A mixture of CoO and NC catalysts can achieve an 82.8% conversion of 2,3,6-trimethylphenol and a 70.8% yield of 2,3,5-trimethyl-p-benzoquinone. Mo... 72 V 30 / CuO x / CoO / NC achieved a 99.4% conversion rate of 2,3,6-trimethylphenol and a 96.3% yield of 2,3,5-trimethyl-p-benzoquinone, significantly higher than Mo. 72 V 30 CuO x The comparison of the catalytic activities of the above different catalysts, including CoO / NC and physically mixed catalysts, further demonstrates that the synergistic effect between polyacids and supports is the main reason for the high activity of the catalysts.

[0042] Figure 7 This is a graph showing the catalytic activity data of a molybdenum-vanadium polyacid-based heterogeneous catalyst after 5 cycles. After multiple catalytic oxidation experiments, Mo... 72 V 30 / CuO xThe catalytic activity of / CoO / NC did not show a significant decrease. After the fifth experiment, the conversion rates of 2,3,6-trimethylphenol and 2,3,5-trimethyl-p-benzoquinone remained at 96.5% and 91.5%, respectively, demonstrating that Mo 72 V 30 / CuO x / C exhibits excellent cycling stability.

[0043] Figure 8 This is a comparison of infrared spectra and X-ray powder diffraction patterns before and after the reaction of a molybdenum-vanadium polyacid-based heterogeneous catalyst. 72 V 30 / CuO x The infrared spectrum of / CoO / NC clearly shows that its characteristic peaks did not change significantly before and after the reaction, indicating that the catalyst structure remained unchanged. Further XRD analysis of the catalyst Mo before and after the reaction... 72 V 30 / CuO x The / CoO / NC catalyst was tested, and the characteristic peaks after the reaction showed no significant change compared with those before the reaction, further demonstrating the structural stability of the catalyst.

[0044] Figure 9 This is a flowchart illustrating the preparation process of a molybdenum-vanadium polyacid-based heterogeneous catalyst.

[0045] In summary, this embodiment utilizes a hydrothermal synthesis method and selects molybdenum-vanadium polyacid (Mo). 72 V 30 and metal-organic framework derived materials CuO x / CoO / NC successfully prepared a highly stable heterogeneous catalyst, which exhibited excellent catalytic activity in the catalytic oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-p-benzoquinone.

Claims

1. Preparation and application of a molybdenum-vanadium polyacid-based heterogeneous catalyst, characterized in that... A molybdenum-vanadium polyacid-based heterogeneous catalyst with the chemical formula Mo 72 V 30 / CuO x / CoO / NC, where Mo 72 V 30 The molecular formula is Na₂K₂ 16 (VO)(H2O)5[K 10 ,{(Mo)Mo5O 21 (H2O)3(SO4)} 12 (VO) 30 (H2O) 20 ]·150H2O, used in the catalytic oxidation of 2,3,6-trimethylphenol to synthesize 2,3,5-trimethyl-p-benzoquinone.

2. The preparation and application of the molybdenum-vanadium polyacid-based heterogeneous catalyst according to claim 1 are carried out according to the following steps: (1) Mo 72 V 30 Synthesis: First, add 2.6 g of NaVO3 to 55 mL of water at 60℃ and stir for 15 min until completely dissolved to obtain solution A. Separately, dissolve 6 g of Na2MoO4·2H2O in 75 mL of water and stir for 15 min to obtain solution B. After solution A has cooled to room temperature, add solution B to it. Continue stirring for 15 min. Then add 0.9 g N2H4·H2SO4, and the solution gradually turns blackish-purple. Continue stirring at room temperature for 3 h. Next, add 20 mL of KCl aqueous solution containing 3 g KCl, stir for 5 min, and then transfer to a 250 mL Erlenmeyer flask. Leave the Erlenmeyer flask open in the air for 4 days, and dark purple crystals precipitate from the solution. After filtration, collect the crystals, wash several times with ethanol, and dry at room temperature for 24 h to obtain purplish-black crystals, which is Mo. 72 V 30 . (2) CuO x Synthesis of / CoO / NC: First, 1.5 g of 1,3,5-pyromellitic acid was dissolved in a mixed solvent of 45 mL ethanol and N,N-dimethylformamide (volume ratio 1:1), labeled as solution A; separately, 3.1 g of Cu(NO3)2·3H2O was dissolved in 22.5 mL of water, labeled as solution B. Both solutions were stirred separately at room temperature for 10 min to ensure complete dissolution. Then, solution B was added to solution A and stirring was continued for 30 min. The mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and maintained at 110 °C for 10 h. The resulting blue microcrystals were centrifuged, washed with ethanol, and dried under vacuum at 60 °C for 12 h to obtain HKUST-1. The synthesized HKUST-1 (50 mg) was ultrasonically dispersed in 50 mL of methanol and stirred for 30 min to obtain a homogeneous suspension, labeled as solution A. 8 mmol of 2-methylimidazole was dissolved in 50 mL of methanol and stirred for 30 min, labeled as solution B. 2 mmol of Co(NO3)2·6H2O was added to solution A and stirred vigorously for 30 min to form solution C. Solution B was poured into solution C and stirred vigorously for 4 h. The resulting solid was collected by centrifugation, washed three times with methanol, and dried under vacuum at 60 °C for 12 h to obtain a purple powder, which was HKUST-1@ZIF-67. The synthesized HKUST-1@ZIF-67 was uniformly spread in a ceramic boat and pyrolyzed in a tube furnace under a continuous argon flow. The heating rate was 5 °C / min. -1 Under these conditions, the temperature is raised to 450℃ and held for 2 hours. After the temperature is cooled down to room temperature, the resulting powder is CuO. x / CoO / NC. (3) Mo 72 V 30 / CuO x Synthesis of / CoO / NC: First, 30 mg of CuO... x / CoO / NC and 400 mg of Mo 72 V 30 Add to 30 mL of deionized water and stir at room temperature for 12 h. Then transfer to a 50 mL polytetrafluoroethylene-lined high-pressure reactor and maintain at 100 °C for 12 h. After cooling to room temperature, wash three times with ethanol and then dry in a vacuum oven at 60 °C for 12 h. The resulting powder is Mo. 72 V 30 / CuO x / CoO / NC.

3. The preparation and application of the molybdenum-vanadium polyacid-based heterogeneous catalyst according to claim 2, characterized in that... The molybdenum-vanadium polyacid mentioned in step three is Mo 72 V 30 .

4. The preparation and application of the molybdenum-vanadium polyacid-based heterogeneous catalyst according to claim 2, characterized in that... The carrier precursor mentioned in step two is HKUST-1@ZIF-67.

5. The preparation and application of the molybdenum-vanadium polyacid-based heterogeneous catalyst according to claim 2, characterized in that... The reaction temperature and time described in step three are 100℃ and 12 h, respectively.

6. The preparation and application of the molybdenum-vanadium polyacid-based heterogeneous catalyst according to claim 1, characterized in that... The molybdenum-vanadium polyacid-based heterogeneous catalyst was applied to the catalytic oxidation of 2,3,6-trimethylphenol to synthesize 2,3,5-trimethyl-p-benzoquinone. Within a 2-minute reaction time, the conversion rate of 2,3,6-trimethylphenol was 99.4%, and the yield of 2,3,5-trimethyl-p-benzoquinone was 96.3%.

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