Tungsten-containing metal oxide catalyst as well as preparation method and application thereof

Abstract

The invention relates to a tungsten-containing metal oxide catalyst, which has a chemical formula of C94H160N4O68WO4 and a structural formula shown in the specification. The catalyst synthesized from rare earth tungstate such as La2 (WO4) 3 and Ag2WO4 and beta-CD-TBA can effectively promote the transfer of cyclohexene from an organic phase to a water phase, so that the apparent solubility of cyclohexene in the water phase is effectively improved, the equilibrium mass concentration of cyclohexene in water reaches 5.67 g / L, which is 929 times that in a pure water system, and the yield of cyclohexene is greatly improved. Compared with pure water without the catalyst, the mass transfer rate of the catalyst is improved by about 945 times, and in a system for preparing adipic acid by catalyzing cyclohexene oxidation by taking hydrogen peroxide as an oxidizing agent, the conversion efficiency of cyclohexene and the utilization rate of hydrogen peroxide are effectively improved, so that the yield of adipic acid is improved, and the purity of the prepared adipic acid is effectively improved. In addition, the catalyst has excellent structural stability, and keeps excellent cyclic catalytic stability in cyclic catalytic use.

Description

Technical Field

[0001] This invention relates to the field of metal oxide catalyst technology, specifically to a tungsten-containing metal oxide catalyst, its preparation method, and its application. Background Technology

[0002] Against the backdrop of increasing global awareness of ecological and environmental protection, the green and low-carbon transformation of the chemical industry has become an inevitable trend. Adipic acid, as an important basic organic raw material in the chemical field, can be used to prepare a wide variety of products, including polyurethane foam, nylon 66 (PA66), biodegradable plastic PBAT, plasticizers, high-grade lubricants, food additives, pharmaceutical intermediates, fragrance and flavor control agents, novel monocrystalline materials, plastic foaming agents, coatings, pesticides, adhesives, and dyes. Therefore, the sustainable development of adipic acid production processes is not only related to the structural optimization and green transformation of the chemical industry, but also has a profound impact on the sustainable stability of the global ecological environment.

[0003] Currently, the main industrial production routes for adipic acid include the cyclohexane process and the cyclohexene process. Globally, over 90% of adipic acid production capacity still relies on the traditional cyclohexane oxidation process using benzene as a raw material. In this process, nitric acid with a mass fraction of 50%–60% is typically used as the oxidant. This process not only suffers from severe equipment corrosion and shortened equipment lifespan, but also generates large amounts of nitrogen oxides (NOx) during the reaction. x This has led to severe environmental pollution, making it difficult to meet the current development requirements of green chemical industry and clean production.

[0004] To address the aforementioned issues, researchers have developed a green catalytic oxidation process for the preparation of adipic acid. This process uses hydrogen peroxide as an oxidant to catalytically oxidize cyclohexene in a one-step manner to produce adipic acid. Hydrogen peroxide is a clean oxidant, and its reaction product is water, fundamentally avoiding pollution generated during the oxidation process. For example, Kazuhiko Sato et al. (Science, 1998, 281:1646-1648.) proposed a new green method for synthesizing adipic acid, using 30% hydrogen peroxide to directly oxidize cyclohexene, employing Na2WO4 as a catalyst and a quaternary ammonium salt ([CH3(n-C8H)2)). 17Using [3N]HSO4) as a phase transfer catalyst, without organic solvents, and reacting for 8 hours under multi-stage heating conditions, the final adipic acid yield reached 93%, and the purity of the crystalline product was over 90%. However, this phase transfer catalyst is prone to foaming and severe equipment corrosion during the reaction process, and has high toxicity in the aquatic environment, making it difficult to promote. Patent application document 99121017.4 discloses a clean catalytic oxidation method using peroxytungstate-organic carboxylic acid coordination complex as a catalyst. Although this method does not use organic solvents and toxic phase transfer agents, the organic carboxylic acid ligands are unstable under high-temperature reaction conditions and are prone to sublimation or decomposition, leading to catalyst deactivation and affecting the efficiency of adipic acid preparation. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a tungstate catalyst for the preparation of adipic acid from cyclohexene. This catalyst exhibits excellent catalytic activity and cycling stability, maintaining high catalytic efficiency and selectivity even under prolonged continuous or cyclic operation, demonstrating good regeneration performance and structural stability. These characteristics not only reduce catalyst replacement frequency and operating costs but also further improve the economics and sustainability of the process.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned catalyst.

[0007] A third objective of this invention is to provide applications of the aforementioned catalyst.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] The core of the cyclohexene oxidation method for preparing adipic acid lies in the selective oxidation of cyclohexene, which breaks the double bonds and converts them into carboxyl groups. This method has a simple process. However, in the traditional preparation process, when nitric acid is used as the oxidant, nitric acid, cyclohexene, and catalyst can form a homogeneous system. While using environmentally friendly H2O2 as the catalyst can reduce pollution, H2O2 (aqueous phase) and cyclohexene (oil phase) are immiscible, requiring the addition of a phase transfer catalyst to solve the mass transfer problem.

[0010] A tungsten-containing metal oxide catalyst, characterized in that its chemical formula is C 94 H 160 N4O 68 WO4, the structural formula is .

[0011] Furthermore, the above catalyst is prepared by reacting β-cyclodextrin with toluenesulfonyl chloride (CH3C6H4SO2Cl) to generate mono-6-mono-p-toluenesulfonyl β-cyclodextrin β-CD-OTs, then reacting it with 2-chloroethylamine hydrochloride to generate 2-chloroethylamine β-cyclodextrin CEA-β-CD, and then reacting it with triethylenediamine TED to obtain a white solid β-CD-TBA. The white solid is then reacted with tungstate to obtain the catalyst β-CD-TBAT.

[0012] Furthermore, the β-CD-OTs are prepared by dissolving β-cyclodextrin in an aqueous sodium hydroxide solution to obtain solution 1, dissolving p-toluenesulfonyl chloride (CH3C6H4SO2Cl) in acetonitrile to obtain solution 2, mixing solution 1 and solution 2, and stirring the mixture in an ice-water bath at 0~5℃ for 2~3 hours.

[0013] Furthermore, the molar ratio of β-cyclodextrin to p-toluenesulfonyl chloride in solutions 1 and 2 is 0.8~1:1, the mass-to-volume ratio of β-cyclodextrin to sodium hydroxide aqueous solution in solution 1 is 20~24g:140~160mL, the sodium hydroxide aqueous solution is obtained by dissolving 4g of sodium hydroxide solid in 150g of deionized water, and the mass-to-volume ratio of toluenesulfonyl chloride to acetonitrile is 4~4.3g:10mL.

[0014] Further, after the reaction is complete, the solution is filtered and the filtrate is collected. After neutralization with hydrochloric acid, it is placed at 4-5℃ for 18-24 hours. The white solid is obtained by filtration and dried. The dried white solid is added to deionized water, boiled, and then filtered immediately. The hot filtrate is collected and placed at 4-5℃ for 18-24 hours. The filter cake is collected by filtration to obtain p-toluenesulfonyl β-cyclodextrin β-CD-OTs.

[0015] Furthermore, the CEA-β-CD is a mixed solution of 2-chloroethylamine hydrochloride and β-CD-OTs dissolved in DMF. The mixed solution is reacted at 80-90℃ for 30-36 hours. After the reaction is completed, ethanol is added to the mixed solution and then filtered to obtain a pale yellow solid. The pale yellow solid is washed three times with ethanol, and the washing product is collected and dried. The dried product is soaked in chloroform for 30-40 minutes, filtered, and washed three times again with ethanol. After drying, 2-chloroethylamine β-cyclodextrin CEA-β-CD is obtained.

[0016] Furthermore, the ratio of 2-chloroethylamine hydrochloride, β-CD-OTs and DMF is 2.2~2.6g: 13~14g: 45~55mL.

[0017] Furthermore, the white solid is obtained by dissolving CEA-β-CD in DMF, then adding triethylenediamine (TED), mixing thoroughly, and reacting at 42-48°C for 4-5 hours.

[0018] Furthermore, the ratio of CEA-β-CD, TED, and DMF is 2.5~3.5: 0.26~0.3g: 18~24mL.

[0019] Furthermore, the reaction of the white solid with tungstate involves adding the white solid and tungstate to deionized water at a molar ratio of 1:1, stirring vigorously at room temperature for 1 hour, filtering the precipitate, evaporating and concentrating the filtrate, and then drying it to obtain the catalyst β-CD-TBAT.

[0020] The tungstate can be Ag2WO4, La2(WO4)3, Ce2(WO4)3, or Pr2(WO4)3, with Ag2WO4 being preferred.

[0021] A method for preparing a tungsten-containing metal oxide catalyst, characterized in that: S1. Prepare p-toluenesulfonyl β-cyclodextrin β-CD-OTs by reacting β-cyclodextrin with p-toluenesulfonyl chloride (CH3C6H4SO2Cl); S2. 2-Chloroethylamine β-cyclodextrin CEA-β-CD was prepared by reacting β-CD-OTs with 2-chloroethylamine hydrochloride. S3. CEA-β-CD is reacted with triethylenediamine (TED) to generate a white solid β-CD-TBA, which is then reacted with silver tungstate (Ag2WO4) to obtain the catalyst β-CD-TBAT.

[0022] Further, in step S1, the reaction involves dissolving β-cyclodextrin in an aqueous sodium hydroxide solution to obtain solution 1, dissolving p-toluenesulfonyl chloride (CH3C6H4SO2Cl) in acetonitrile to obtain solution 2, mixing solution 1 and solution 2, and stirring the mixture in an ice-water bath at 0-5°C for 2-3 hours.

[0023] Furthermore, the molar ratio of β-cyclodextrin to p-toluenesulfonyl chloride in solutions 1 and 2 is 1:1, the mass-to-volume ratio of β-cyclodextrin to sodium hydroxide aqueous solution in solution 1 is 20~24g:140~160mL, the sodium hydroxide aqueous solution is obtained by dissolving 4g of sodium hydroxide solid in 150g of deionized water, and the mass-to-volume ratio of toluenesulfonyl chloride to acetonitrile is 4~4.3g:10mL.

[0024] Further, after the reaction is complete, the solution is filtered and the filtrate is collected. After neutralization with hydrochloric acid, it is placed at 4-5℃ for 18-24 hours. The white solid is obtained by filtration and dried. The dried white solid is added to deionized water, boiled, and then filtered immediately. The hot filtrate is collected and placed at 4-5℃ for 18-24 hours. The filter cake is collected by filtration to obtain p-toluenesulfonyl β-cyclodextrin β-CD-OTs.

[0025] Furthermore, the reaction in step S2 involves dissolving a mixed solution of 2-chloroethylamine hydrochloride and β-CD-OTs in DMF, and then reacting the mixed solution at 80-90°C for 30-36 hours.

[0026] Furthermore, the ratio of 2-chloroethylamine hydrochloride, β-CD-OTs and DMF is 2.2~2.6g: 13~14g: 45~55mL.

[0027] Further, ethanol was added to the mixed solution after the reaction was completed and mixed. Then, the mixture was filtered to obtain a pale yellow solid. The pale yellow solid was washed three times with ethanol, and the washing product was collected and dried. The dried product was soaked in chloroform for 30-40 minutes, filtered, and washed three times with ethanol again. After drying, 2-chloroethylaminoβ-cyclodextrin CEA-β-CD was obtained.

[0028] Furthermore, in step S3, the reaction between CEA-β-CD and triethylenediamine TED involves dissolving CEA-β-CD in DMF, then adding triethylenediamine TED, mixing thoroughly, and reacting at 42-48°C for 4-5 hours.

[0029] Furthermore, the ratio of CEA-β-CD, TED, and DMF is 2.5~3.5: 0.26~0.3g: 18~24mL.

[0030] Furthermore, the reaction with silver tungstate (Ag2WO4) involves adding white solid β-CD-TBA and silver tungstate to deionized water at a molar ratio of 1:1, stirring vigorously at room temperature for 1 hour, filtering the precipitate, evaporating and concentrating the filtrate, and then drying it to obtain the catalyst β-CD-TBAT.

[0031] Most specifically, a method for preparing a tungsten-containing metal oxide catalyst is characterized by comprising the following steps: S1. Synthesis of p-toluenesulfonyl β-cyclodextrins (β-CD-OTs) S101. Dissolve β-cyclodextrin in an aqueous sodium hydroxide solution to obtain solution 1, and dissolve p-toluenesulfonyl chloride (CH3C6H4SO2Cl) in acetonitrile to obtain solution 2. Mix solution 1 and solution 2 and stir the mixture in an ice-water bath at 0-5°C for 2-3 hours. The molar ratio of β-cyclodextrin to p-toluenesulfonyl chloride in solution 1 and solution 2 is 0.8-1:1. The mass-volume ratio of β-cyclodextrin to aqueous sodium hydroxide solution in solution 1 is 20-24 g: 140-160 mL. The aqueous sodium hydroxide solution is obtained by dissolving 4 g of solid sodium hydroxide in 150 g of deionized water. The mass-volume ratio of toluenesulfonyl chloride to acetonitrile is 4-4.3 g: 10 mL. S102. After the reaction of S101 is completed, filter the solution and collect the filtrate. Add hydrochloric acid to neutralize it, place it at 4~5℃ for 18~24h, filter to obtain a white solid, and dry it. S103. Add the dried white solid to deionized water, boil it, and then filter it immediately. Collect the hot filtrate and place it at 4~5℃ for 18~24h. Filter the filter cake to obtain p-toluenesulfonyl β-cyclodextrin β-CD-OTs. S2. Synthesis of 2-chloroethylaminoβ-cyclodextrin (CEA-β-CD) S201. A mixed solution of 2-chloroethylamine hydrochloride and β-CD-OTs dissolved in DMF is placed in a mixture and reacted at 80-90°C for 30-36 hours. The ratio of the amounts of 2-chloroethylamine hydrochloride, β-CD-OTs and DMF is 2.2-2.6 g: 13-14 g: 45-55 mL. S202. Add ethanol to the mixed solution and mix, then filter to obtain a pale yellow solid. Wash the pale yellow solid with ethanol three times, collect the washing product and dry it. Soak the dried product in chloroform for 30-40 minutes, filter it and wash it with ethanol three times again. After drying, 2-chloroethylaminoβ-cyclodextrin CEA-β-CD is obtained. S3. Synthesis catalyst S301. Dissolve CEA-β-CD in DMF, then add triethylenediamine (TED), mix well, and react at 42-48℃ for 4-5 hours. The ratio of CEA-β-CD, TED, and DMF is 2.5-3.5: 0.26-0.3g: 18-24mL. S302. The solution after the reaction in S301 is filtered and the filter cake is collected to obtain a white solid β-CD-TBA. β-CD-TBA is washed three times with anhydrous ethanol and dried at 40~50℃. The dried β-CD-TBA and silver tungstate Ag2WO4 are added to deionized water at a molar ratio of 1:1. After stirring vigorously at room temperature for 1 hour, the precipitate is filtered. The filtrate is evaporated, concentrated and dried to obtain the catalyst β-CD-TBAT.

[0032] The application of the above catalyst in the preparation of adipic acid by oxidizing cyclohexene.

[0033] The present invention has the following technical effects: The tungsten-containing metal oxide catalyst synthesized in this invention can effectively promote the transfer of cyclohexene from the organic phase to the aqueous phase, thereby effectively improving the apparent solubility of cyclohexene in the aqueous phase. The equilibrium mass concentration of cyclohexene in water reaches 5.67 g / L, which is 929 times that in the pure water system. Its mass transfer rate is about 945 times higher than that in pure water without a catalyst. In the system of catalyzing the oxidation of cyclohexene to prepare adipic acid using hydrogen peroxide as an oxidant, it effectively improves the conversion efficiency of cyclohexene and the utilization rate of hydrogen peroxide, thereby increasing the yield of adipic acid and effectively improving the purity of the prepared adipic acid.

[0034] Furthermore, this catalyst exhibits excellent structural stability and maintains excellent cyclic catalytic stability during cyclic catalytic use. Attached Figure Description

[0035] Figure 1 Synthesis route of the catalyst in this invention.

[0036] Figure 2 : FT-IR spectra of β-CD-OTs in this invention.

[0037] Figure 3 : FT-IR spectrum of CEA-β-CD in this invention.

[0038] Figure 4 : FTIR spectra of β-CD-TBA and β-CD-TBAT prepared in this invention.

[0039] Figure 5 : 1H NMR spectra of β-CD-TBA and β-CD-TBAT prepared in this invention.

[0040] Figure 6 Scanning electron microscope (SEM) image of the catalyst prepared in this invention.

[0041] Figure 7 : The effect of the catalyst of this invention on the solubility of cyclohexene is shown in the graph.

[0042] Figure 8 The effect of different catalyst addition amounts on catalytic oxidation reactions.

[0043] Figure 9 The effect of different catalytic reaction times on catalytic oxidation reactions.

[0044] Figure 10 : A physical image of adipic acid prepared from cyclohexene using the catalyst of this invention.

[0045] Figure 11 XRD pattern of adipic acid prepared by the catalyst of this invention.

[0046] Figure 12 FTIR spectrum of adipic acid prepared by the catalyst of this invention.

[0047] Figure 13 The conductivity of the catalyst solution of the present invention under different catalytic cycles is shown below.

[0048] Figure 14 The yield of adipic acid prepared by the catalyst after different catalytic cycles varies.

[0049] Figure 15 FT-IR spectra of the catalyst before and after recycling.

[0050] Figure 16 The effect of the catalyst on the catalytic oxidation reaction in Example 1 and Comparative Example 1.

[0051] Figure 17 The effect of catalysts on catalytic oxidation reactions in Example 1 and Comparative Examples 2 and 3. Detailed Implementation

[0052] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0053] The synthetic route for preparing the target catalyst in this invention is as follows: Figure 1 As shown, the specific operation steps are as follows: Example 1 A method for preparing a catalyst for adipic acid includes the following steps: S1. Synthesis of p-mono-6-p-toluenesulfonyl β-cyclodextrins (β-CD-OTs) S101. β-Cyclodextrin is dissolved in an aqueous sodium hydroxide solution to obtain solution 1, and p-toluenesulfonyl chloride (CH3C6H4SO2Cl) is dissolved in acetonitrile to obtain solution 2. Solutions 1 and 2 are mixed and reacted at 300 rpm for 3 hours under an ice-water bath at 2°C. The molar ratio of β-cyclodextrin to p-toluenesulfonyl chloride in solutions 1 and 2 is 1:1. The mass-to-volume ratio of β-cyclodextrin to aqueous sodium hydroxide solution in solution 1 is 22.4 g: 150 mL. The aqueous sodium hydroxide solution is obtained by dissolving 4 g of solid sodium hydroxide in 150 g of deionized water. The mass-to-volume ratio of toluenesulfonyl chloride to acetonitrile is 4.2 g: 10 mL. S102. After the reaction of S101 is completed, filter the solution and collect the filtrate. Add hydrochloric acid to neutralize it, place it at 5℃ for 22h, filter it to obtain a white solid, and then dry it. S103. Add the dried white solid to deionized water, boil it, and then filter it immediately. Collect the hot filtrate and place it at 5°C for 20 hours. Filter the filter cake to obtain p-toluenesulfonyl β-cyclodextrin β-CD-OTs. S2. Synthesis of 2-chloroethylaminoβ-cyclodextrin (CEA-β-CD) S201. A mixed solution of 2-chloroethylamine hydrochloride and β-CD-OTs dissolved in DMF is placed in an environment of 85°C and reacted for 32 hours. The ratio of the amounts of 2-chloroethylamine hydrochloride, β-CD-OTs and DMF is 2.4 g: 13.5 g: 50 mL. S202. Add ethanol to the mixed solution and mix, then filter to obtain a pale yellow solid. Wash the pale yellow solid with ethanol three times, collect the washing product and dry it. Soak the dried product in chloroform for 35 minutes, filter it and wash it with ethanol three times again. After drying, 2-chloroethylaminoβ-cyclodextrin CEA-β-CD is obtained. S3. Synthesis catalyst β-CD-TBAT S301. Dissolve CEA-β-CD in DMF, then add triethylenediamine (TED), mix well, and react at 42~48℃ for 4~5h. The ratio of CEA-β-CD, TED, and DMF is 3g: 0.28g: 20mL. S302. The solution after the reaction in S301 is filtered, and the filter cake is collected to obtain a white solid β-CD-TBA. β-CD-TBA is washed three times with anhydrous ethanol and dried at 45°C. The dried β-CD-TBA and silver tungstate Ag2WO4 are added to deionized water at a molar ratio of 1:1 (the total mass ratio of β-CD-TBA and Ag2WO4 to deionized water is 1:30). The mixture is stirred vigorously at 750 rpm for 1 h at room temperature. The precipitate is then filtered, and the filtrate is evaporated, concentrated, and dried to obtain the catalyst β-CD-TBAT.

[0054] The β-CD-OTs synthesized in step S1 are as follows Figure 2 As shown, at 1370~1350 cm - ¹ and 1180~1160 cm - ¹Attributable to the S=O stretching vibration (sulfonyl group), indicating successful synthesis of β-CD-OTs in this example. The FT-IR spectrum of the synthesized β-CD-OTs from step S2 is shown below. Figure 3 As shown, at 3300 cm -1 Vibrations of the primary amino group belonging to 2-chloroethylamine, 1650 cm -1 It belongs to the in-plane bending vibration of NH, 750~700 cm. -¹Belonging to C-Cl indicates that CEA-β-CD was successfully synthesized in this example.

[0055] The infrared spectra of β-CD-TBA and β-CD-TBAT prepared in step S3 are as follows: Figure 4 As shown, the characteristic peaks of β-CD-TBA appear at 3380 cm⁻¹, 1080 cm⁻¹, 1028 cm⁻¹, and 780 cm⁻¹, respectively. These characteristic peaks are attributed to the stretching vibrations of the -OH groups, -CO- bonds, and 1,4-glycosidic bonds in the chemical structures of β-cyclodextrin and triethylenediamine (TEDA) in β-CD-TBA, as well as the stretching vibrations of the octahedral cyclic -CC-backbone. We observed that the above infrared characteristic peaks for β-CD-TBA also exist in the infrared spectrum for β-CD-TBAT, and two new peaks appear at 856 and 758 cm⁻¹ in the infrared spectrum of β-CD-TBAT. These peaks are attributed to the stretching vibrations of -WO.

[0056] Figure 5 The images show the 1H NMR spectra of β-CD-TBA and β-CD-TBAT. In the 1H NMR spectra, the chemical shifts of β-CD-TBA appear at 4.97 ppm (H1), 3.49 ppm (H2), 3.79 ppm (H3), 3.45 ppm (H4), 3.68-3.70 ppm (H5 and H6), and 2.75 ppm (H7). These chemical shifts originate from β-CD and TEDA, respectively. Our observations also revealed that the NMR spectra of the β-CD-TBAT sample were similar to those of the β-CD-TBA sample, with no significant shifts observed in H1 and H3. However, in the corresponding β-CD-TBAT spectrum, the peak positions of H2 (Δδ=0.02 ppm), H4 (Δδ=0.01 ppm), H5 and H6 (Δδ=0.05 ppm), and H7 (Δδ=0.25 ppm) showed a clear high-field shift.

[0057] Combined infrared spectroscopy and 1H NMR spectroscopy analysis show that we have successfully synthesized the target catalyst β-CD-TBAT.

[0058] The scanning electron microscope (SEM) image of the final target catalyst synthesized by the above method is shown below. Figure 6 As shown.

[0059] Test on the effect of catalyst on cyclohexene solubility: The solubility changes of cyclohexene in different systems, with and without a catalyst (β-CD-TBAT as the catalyst), were tested, and the results are as follows: Figure 7As shown, under the same reaction time conditions, the equilibrium mass concentration of cyclohexene in the aqueous solution containing the phase transfer catalyst prepared in this embodiment of the invention (cyclohexene: 5 mL; H2O: 22.97 mL; β-CD-TBAT: 1.02 g) was 5.67 g / L, significantly higher than the equilibrium mass concentration of 0.0061 g / L in the pure water system without the phase transfer catalyst. The mass transfer rate in the catalyst system was 141.8 mg / L·min, while the mass transfer rate in the pure water system was 0.15 mg / L·min, approximately 945 times that of the pure water system. These test results indicate that the phase transfer catalyst prepared in this invention can significantly promote the transfer of cyclohexene from the organic phase to the aqueous phase, thereby effectively improving the apparent solubility of cyclohexene in the aqueous phase. By adding the phase transfer catalyst, the mass transfer resistance of cyclohexene in the aqueous phase is significantly reduced, allowing more cyclohexene molecules to disperse into the aqueous system. Therefore, the phase transfer catalyst prepared in this invention has excellent phase transfer function, which can significantly improve the interphase mass transfer conditions of the reaction system, and is beneficial to the further oxidation reaction of cyclohexene in the aqueous phase, thereby improving the formation efficiency of the target product. Furthermore, the solubility of cyclohexene in water was tested when the catalyst was replaced with β-CD-CEA and Ag2WO4, respectively. In the system with Ag2WO4 added, the maximum solubility of cyclohexene was 0.0062 g / L, which was not much different from that in pure water, indicating that the presence of tungstate has almost no effect on the solubility of cyclohexene. In the system with CEA-β-CD added, the maximum solubility of cyclohexene was only 1.564 g / L, far less than the 5.67 g / L of the β-CD-TBAT system.

[0060] Catalytic performance test: Under normal pressure, 1.02 g of the catalyst prepared in Example 1 was fully dissolved in 22.97 mL of a 30% hydrogen peroxide solution and stirred for 5 min. After the catalyst was completely dissolved, the temperature was raised to 75 °C and maintained for 30 min. Simultaneously, cyclohexene was slowly added to the reaction system at a molar ratio of cyclohexene to hydrogen peroxide of 1:4.5. After 30 min, the temperature was raised to 80 °C and maintained for another 30 min. Then, the temperature was raised to 85 °C and maintained until the reaction was complete. Samples were taken directly at intervals and titrated with 0.1 mol / L sodium hydroxide solution to directly and quantitatively determine the adipic acid product. Details are as follows: The reaction solution at a certain moment was placed in a 5°C refrigerator to cool and crystallize (the reaction will stop when the temperature decreases). The precipitated solid was filtered, washed with ice water, dried, and weighed to obtain the mass m of adipic acid, and the volume V3 of the filtrate was measured. A volume V1 of the filtrate was transferred to an Erlenmeyer flask, and 1-2 drops of phenolphthalein reagent were added to the Erlenmeyer flask. The solution was then titrated with sodium hydroxide standard solution to the endpoint, and the volume V2 of sodium hydroxide standard solution consumed in the titration was read. The yield of adipic acid was calculated using formula (1).

[0061] In the formula, m(g) — mass of crystalline adipic acid; M — molar mass of adipic acid; C s —Concentration of sodium hydroxide standard solution, C s = 0.1000mol / L; V1 (mL) — Sampling volume; V2 (mL) — Volume of sodium hydroxide standard solution consumed in the titration; V3 (mL) — Volume of the reaction solution; X—Adipic acid yield; n-cyclohexene dosage; The concentration of adipic acid is calculated using formula (2):

[0062] In the formula, C t —The concentration of adipic acid at time t; V t —Sampling volume at time t.

[0063] The overall yield of adipic acid was 87.648%, which is considered a relatively high yield.

[0064] Quantitative determination of cyclohexene in reaction solution using chemical titration: To accurately determine the conversion rate of cyclohexene in the reaction system, iodometric titration was used for indirect quantitative analysis of the cyclohexene content in the system before and after the reaction. The detection method includes the following steps: (1) Sampling: Before the start of the cyclohexene oxidation reaction and after the reaction, take an appropriate amount of reaction solution sample (1–2 mL), cool it to room temperature immediately, seal and store it for later use to prevent further reaction or volatilization of cyclohexene; (2) Sample pretreatment: Place the obtained reaction solution sample in an iodine flask and dilute with an appropriate amount of deionized water; (3) Reaction treatment: Under light-protected conditions, add excess standard bromine solution (or bromine water) to the sample solution to allow bromine to undergo an addition reaction with cyclohexene (C6H2O). 10 +Br2→C6H 10 After the reaction (Br2), the remaining unreacted bromine in the system is an indirect indicator of the amount of cyclohexene not consumed. (4) Iodine release: Add excess potassium iodide (KI) solution to the above reaction mixture. The remaining bromine reacts with iodide ions to generate iodine (Br2 + 2I). →2Br (+I2), the generated iodine is brown in solution.

[0065] (5) Titration determination: The generated iodine was titrated with standard sodium thiosulfate solution (Na2S2O3). The concentration of the sodium thiosulfate solution was c(Na2S2O3) = 0.01 mol / L, and it was standardized by the potassium dichromate-iodine method. During the titration, the iodine was gradually reduced to iodide ions, and the solution color gradually lightened from brown. When the solution turned light yellow, 2–3 drops of starch indicator were added, and the titration continued until the blue color disappeared, which was the endpoint. The volume of sodium thiosulfate consumed, V (mL), was recorded.

[0066] (6) Blank correction: Using pure solvent without cyclohexene as a control, follow the same steps and record the blank volume V0.

[0067] (7) Calculation: Based on the stoichiometric relationship of the reaction, the volume of sodium thiosulfate determined by iodometric titration is directly proportional to the amount of remaining bromine. Therefore, the amount of cyclohexene in the sample can be deduced. (Amount of remaining bromine) The calculation formula is:

[0068] In the formula, —The amount of bromine remaining; V (mL) — Volume of sodium thiosulfate consumed; V0 (mL) — Blank titration volume —Standard sodium thiosulfate solution concentration.

[0069] The amount of cyclohexene can be calculated based on a 1:1 reaction ratio of bromine to cyclohexene:

[0070] From this, we can obtain n0 before the reaction and n after the reaction. t The amount of cyclohexene.

[0071] The conversion rate of cyclohexene is calculated using the following formula:

[0072] By calculating the cyclohexene conversion rate and combining it with the adipic acid yield measurement results, the selectivity of the reaction was further calculated, providing a basis for evaluating the catalyst activity.

[0073] The effects of different catalyst addition amounts on cyclohexene conversion, adipic acid yield, and hydrogen peroxide utilization were tested using the above method, thereby systematically evaluating the catalytic performance of the catalyst. Cyclohexene: 5 mL (0.049 mol), 30% H₂O₂: 22.97 mL (0.22 mol), catalyst dosage: 0.3-1.5 g; reaction temperature: 85℃, reaction time: 2 h. The effect of catalyst addition amount on catalytic efficiency was studied, and the results are as follows: Figure 8 As shown, when the catalyst loading increased from 0.3 g to 0.9 g, the conversion rate of cyclohexene increased sharply from 75.1% to 96.1%, while the yield of adipic acid gradually increased from 1.3% to 3.8%, and the utilization rate of hydrogen peroxide also improved from 94.5% to 97.4%. When the catalyst loading was greater than 0.9 g, the improvement in catalytic efficiency was very limited. Therefore, we determined the optimal catalyst loading to be 0.9 g.

[0074] Since the reaction time is 2 hours, cyclohexene will rapidly participate in the reaction within these two hours. However, because the oxidation of cyclohexene to adipic acid is a multi-step reaction, the intermediate product cannot be converted to adipic acid in time. Therefore, in the early stage of the reaction, the conversion rate of cyclohexene will be much greater than the yield of adipic acid. Therefore, under the optimal catalyst addition, the yield of adipic acid was further observed by extending the reaction time. The results are as follows. Figure 9 As shown, the yield of adipic acid was significantly lower when the reaction time was short, indicating that the intermediate product did not have time to react in large quantities. With increasing time, the yield of adipic acid increased from 15.5% to 87.6% within 5-20 hours. At 20 hours, the yield of adipic acid was 0.876%, the utilization rate of hydrogen peroxide was 0.844%, and the conversion rate of cyclohexene was 0.997%, indicating that cyclohexene was almost completely converted. In the later stages of the reaction, since the hydrolysis of the intermediate product does not require the consumption of hydrogen peroxide, the ineffective decomposition of hydrogen peroxide predominated, and the utilization rate of hydrogen peroxide decreased accordingly.

[0075] Adipic acid products obtained by catalytic reaction, such as Figure 10 As shown, the obtained product was purified by crystallization and then characterized for phase and functional groups. Its XRD pattern is shown in the figure. Figure 11 As shown in the XRD pattern, the product exhibits typical adipic acid crystal form characteristic peaks; the FT-IR pattern is shown in the figure. Figure 12 As shown, it also exhibits an absorption peak of carboxyl stretching vibration consistent with that of standard adipic acid. These results demonstrate that the catalyst described in this invention possesses excellent catalytic activity and selectivity, and can efficiently catalyze the oxidation of cyclohexene to high-purity adipic acid.

[0076] The conductivity of a catalyst reflects the ion concentration, migration ability, and stability in the catalytic system. By recovering the catalyst and recycling it to catalyze the preparation of adipic acid from cyclohexene, the conductivity of the catalyst solution at different cycle numbers is shown below. Figure 13 As shown, the conductivity of the catalyst solution remained stable without significant fluctuations during multiple cycles, indicating that the active centers of the catalyst were not lost, resulting in high catalytic cycle efficiency and excellent reaction selectivity.

[0077] The yield of adipic acid in the catalytic preparation of cyclohexene at different cycle numbers is as follows: Figure 14 As shown, the yield of adipic acid to cyclohexene remains stable and does not decrease during repeated catalytic cycles, maintaining a high level, indicating that the catalyst has excellent catalytic stability.

[0078] The FT-IR spectra of the catalysts after 0 catalytic cycles and 5 catalytic cycles are shown below. Figure 15 As shown, the functional groups of the catalyst did not differ significantly after five catalytic cycles, further demonstrating the catalyst's excellent structural stability and recyclability. In the route using cyclohexene hydroxide peroxide, compared to traditional catalytic systems, the phase transfer catalyst prepared in this invention maintains excellent catalytic performance while not producing harmful gases such as nitrogen oxides during the reaction, exhibiting environmental friendliness and belonging to the category of green and efficient catalysts.

[0079] Existing technologies utilize Ag₂WO₄ as a catalyst, but this requires an acidic ionic liquid (1,2-dimethyl-3-dodecylimidazolium hydrogen sulfate), which has certain adverse environmental impacts, as both a reaction medium and a co-catalyst. We attempted to use Ag₂WO₄ alone as a catalyst to catalyze the oxidation of cyclohexene to adipic acid in an aqueous system. However, due to phase separation, insufficient acidity, and other factors, the cyclohexene conversion rate and H₂O₂ utilization were low, and the selectivity for adipic acid was extremely low, resulting in the failure to successfully produce high-purity adipic acid. Furthermore, Ag₂WO₄ alone essentially lost its catalytic activity after one cycle.

[0080] Example 2 A method for preparing a catalyst for adipic acid includes the following steps: S1. Synthesis of p-mono-6-mono-p-toluenesulfonyl β-cyclodextrins (β-CD-OTs) S101. Dissolve β-cyclodextrin in an aqueous sodium hydroxide solution to obtain solution 1, and dissolve p-toluenesulfonyl chloride (CH3C6H4SO2Cl) in acetonitrile to obtain solution 2. Mix solution 1 and solution 2 and stir at 300 rpm for 2 h in an ice-water bath at 0°C. The molar ratio of β-cyclodextrin to p-toluenesulfonyl chloride in solution 1 and solution 2 is 0.8:1. The mass-volume ratio of β-cyclodextrin to aqueous sodium hydroxide solution in solution 1 is 20 g: 140 mL. The aqueous sodium hydroxide solution is obtained by dissolving 4 g of solid sodium hydroxide in 150 g of deionized water. The mass-volume ratio of toluenesulfonyl chloride to acetonitrile is 4 g: 10 mL. S102. After the reaction of S101 is completed, filter the solution and collect the filtrate. Add hydrochloric acid to neutralize it, place it at 4℃ for 24 hours, filter it to obtain a white solid, and then dry it. S103. Add the dried white solid to deionized water, boil it, and then filter it immediately. Collect the hot filtrate and place it at 4°C for 18 hours. Filter the filter cake to obtain p-toluenesulfonyl β-cyclodextrin β-CD-OTs. S2. Synthesis of 2-chloroethylaminoβ-cyclodextrin (CEA-β-CD) S201. A mixed solution of 2-chloroethylamine hydrochloride and β-CD-OTs dissolved in DMF is placed in a solution and reacted at 80°C for 36 h. The ratio of the amounts of 2-chloroethylamine hydrochloride, β-CD-OTs and DMF is 2.2 g: 13 g: 45 mL. S202. Add ethanol to the mixed solution and mix, then filter to obtain a pale yellow solid. Wash the pale yellow solid with ethanol three times, collect the washing product and dry it. Soak the dried product in chloroform for 30 minutes, filter it and wash it with ethanol three times again. After drying, 2-chloroethylaminoβ-cyclodextrin CEA-β-CD is obtained. S3. Synthesis catalyst S301. Dissolve CEA-β-CD in DMF, then add triethylenediamine (TED), mix well, and react at 42°C for 5 hours. The ratio of CEA-β-CD, TED, and DMF is 2.5:0.26 g:18 mL. S302. The solution after the reaction in S301 is filtered, and the filter cake is collected to obtain a white solid. The white solid is washed three times with anhydrous ethanol and dried at 40°C. The dried β-CD-TBA and silver tungstate Ag2WO4 are added to deionized water at a molar ratio of 1:1 (the total mass ratio of β-CD-TBA and Ag2WO4 to deionized water is 1:30). The mixture is stirred vigorously at 750 rpm for 1.2 h at room temperature. The precipitate is then filtered, and the filtrate is evaporated, concentrated, and dried to obtain the catalyst β-CD-TBAT.

[0081] Example 3 A method for preparing a catalyst for adipic acid includes the following steps: S1. Synthesis of p-mono-6-mono-p-toluenesulfonyl β-cyclodextrins (β-CD-OTs) S101. Dissolve β-cyclodextrin in an aqueous sodium hydroxide solution to obtain solution 1, and dissolve p-toluenesulfonyl chloride (CH3C6H4SO2Cl) in acetonitrile to obtain solution 2. Mix solution 1 and solution 2 and react with stirring at 300 rpm for 2.5 h at 5 °C in an ice-water bath. The molar ratio of β-cyclodextrin to p-toluenesulfonyl chloride in solution 1 and solution 2 is 0.9:1. The mass-volume ratio of β-cyclodextrin to aqueous sodium hydroxide solution in solution 1 is 24 g: 160 mL. The aqueous sodium hydroxide solution is obtained by dissolving 4 g of solid sodium hydroxide in 150 g of deionized water. The mass-volume ratio of toluenesulfonyl chloride to acetonitrile is 4.3 g: 10 mL. S102. After the reaction of S101 is completed, filter the solution and collect the filtrate. Add hydrochloric acid to neutralize it, place it at 5°C for 24 hours, filter it to obtain a white solid, and then dry it. S103. Add the dried white solid to deionized water, boil it, and then filter it immediately. Collect the hot filtrate and place it at 5°C for 24 hours. Filter the filter cake to obtain p-toluenesulfonyl β-cyclodextrin β-CD-OTs. S2. Synthesis of 2-chloroethylaminoβ-cyclodextrin (CEA-β-CD) S201. A mixed solution of 2-chloroethylamine hydrochloride and β-CD-OTs dissolved in DMF is placed in a solution and reacted at 90°C for 30 h. The ratio of the amounts of 2-chloroethylamine hydrochloride, β-CD-OTs and DMF is 2.6 g: 14 g: 55 mL. S202. Add ethanol to the mixed solution and mix, then filter to obtain a pale yellow solid. Wash the pale yellow solid with ethanol three times, collect the washing product and dry it. Soak the dried product in chloroform for 40 min, filter it and wash it with ethanol three times again. After drying, 2-chloroethylaminoβ-cyclodextrin CEA-β-CD is obtained. S3. Synthesis catalyst S301. Dissolve CEA-β-CD in DMF, then add triethylenediamine (TED), mix well, and react at 48°C for 4 hours. The ratio of CEA-β-CD, TED, and DMF is 3.5: 0.3g: 24mL. S302. The solution after the reaction in S301 is filtered, and the filter cake is collected to obtain a white solid. The white solid is washed three times with anhydrous ethanol and dried at 50°C. The dried β-CD-TBA and silver tungstate Ag2WO4 are added to deionized water at a molar ratio of 1:1 (the total mass ratio of β-CD-TBA and Ag2WO4 to deionized water is 1:30). The mixture is stirred vigorously at 750 rpm for 1.5 h at room temperature. The precipitate is then filtered, and the filtrate is evaporated, concentrated, and dried to obtain the catalyst β-CD-TBAT.

[0082] Comparative Example 1: Following the process of Example 1, β-CD was replaced with α-CD and γ-CD respectively to prepare α-CD-TBAT and γ-CD-TBAT.

[0083] The catalytic performance of the catalysts in Example 1 and Comparative Example 1 was compared under the following experimental conditions: Experimental conditions: 5 mL cyclohexene, 22.97 mL 30% H₂O₂, 0.36 mmol / L catalyst, reaction temperature 85℃, reaction time 20 h. The performance of each catalyst is as follows: Figure 16 As shown, the catalytic efficiency in Example 1 was the highest, with an adipic acid yield of 87.6%, while the catalytic efficiency of α-CD-TBAT in Comparative Example 1 was the lowest, with an adipic acid yield of 66.9%.

[0084] Comparative Example 2: The synthesis of β-cyclodextrin-pyridine quaternary ammonium tungstate (β-CD-PQAT) was carried out as follows: S1. Same as in Example 1, β-CD-OTs were prepared; S2. CEA-β-CD was prepared in the same manner as in Example 1; S3. Preparation of β-cyclodextrin-pyridine quaternary ammonium tungstate (β-CD-PQAT) S301. Dissolve 3.59 g of 2-chloroethylamino β-cyclodextrin (CEA-β-CD) in 20 mL of N,N-dimethylformamide (DMF). After complete dissolution, add 0.24 mL of pyridine (the molar ratio of pyridine to CEA-β-CD is 1:1), mix well, and react at 45 °C for 5 h. S302. Specifically referring to step S302 of Example 1, β-CD-PQAT is obtained.

[0085] Comparative Example 3: Synthesis of β-Cyclodextrin Polyethylene Polyamine Quaternary Ammonium Tungstate (β-CD-PPQAT) S1. Same as in Example 1, β-CD-OTs were prepared; S2. CEA-β-CD was prepared in the same manner as in Example 1; S3. Preparation of β-cyclodextrin-polyethylene-polyamine quaternary ammonium tungstate (β-CD-PPQAT) S301. Dissolve 3.59 g of 2-chloroethylamino β-cyclodextrin (CEA-β-CD) in 10 mL of N,N-dimethylformamide (DMF). After complete dissolution, add 10 mL of N,N-dimethylformamide (DMF) solution containing 0.41 g of polyethylenepolyamine (average molecular weight = 275) (molar ratio of polyethylenepolyamine to CEA-β-CD is 1.5:1). Stir at room temperature for 1 hour, filter to collect the precipitate, and wash three times with anhydrous ethanol to obtain β-cyclodextrin-based polyethylenepolyamine quaternary ammonium salt (β-CD-PPQA). S302. Same as step S302 in Example 1, β-CD-PPQAT is prepared.

[0086] The catalysts prepared in Example 1, Comparative Examples 2 and 3 were tested and compared under the same catalytic conditions described above. The results are as follows: Figure 17 As shown, Example 1 exhibited the highest catalytic efficiency, with an adipic acid yield of 87.6%, while Comparative Example 2 showed the lowest catalytic efficiency, with an adipic acid yield of only 44.5%. In summary, compared to Comparative Examples 1-3, the catalyst prepared in this invention demonstrates superior catalytic performance.

Claims

1. A tungsten-containing metal oxide catalyst characterized by: Chemical formula C 94 H 160 N4O 68 WO4, having the structural formula 。 2. A method of producing a tungsten-containing metal oxide catalyst as claimed in claim 1, characterized by, comprising the following steps: S1. reacting β-cyclodextrin and p-toluenesulfonyl chloride (CH3C6H4SO2Cl) to prepare mono 6-mono-p-toluenesulfonyl β-cyclodextrin β-CD-OTs; S2. reacting β-CD-OTs and 2-chloroethylamine hydrochloride to prepare 2-chloroethylamine β-cyclodextrin (CEA-β-CD); S3. reacting CEA-β-CD with triethylenediamine TED to generate white solid β-CD-TBA, and then reacting β-CD-TBA with silver tungstate Ag2WO4 to obtain catalyst β-CD-TBAT.

3. The method for preparing a tungsten-containing metal oxide catalyst as described in claim 2, characterized in that: The reaction in step S1 is to dissolve β-cyclodextrin in sodium hydroxide aqueous solution to obtain solution 1, dissolve p-toluenesulfonyl chloride CH3C6H4SO2Cl in acetonitrile to obtain solution 2, mix solution 1 and solution 2, and stir under the condition of ice water bath at 0-5℃ for 2-3h.

4. A process for the preparation of a tungsten-containing metal oxide catalyst as claimed in claim 2 or 3, characterized in that: The molar ratio of β-cyclodextrin and p-toluenesulfonyl chloride in the solution 1 and solution 2 is 0.8-1:1, the mass-volume ratio of β-cyclodextrin and sodium hydroxide aqueous solution in the solution 1 is 20-24g:140-160mL, the sodium hydroxide aqueous solution is a sodium hydroxide solution obtained by dissolving 4g of sodium hydroxide solid in 150g of deionized water, and the mass-volume ratio of toluenesulfonyl chloride and acetonitrile is 4-4.3g:10mL.

5. A method of preparing a tungsten-containing metal oxide catalyst according to any one of claims 2 to 4, characterized in that: The reaction in step S2 is to dissolve 2-chloroethylamine hydrochloride and β-CD-OTs in DMF to obtain a mixed solution, and then heat the mixed solution to 80-90℃ and react for 30-36h.

6. The method for preparing a tungsten-containing metal oxide catalyst as described in claim 5, characterized in that: The amount ratio of 2-chloroethylamine hydrochloride, β-CD-OTs and DMF is 2.2-2.6g:13-14g:45-55mL.

7. The method for preparing a tungsten-containing metal oxide catalyst as described in claim 6, characterized in that: The reaction of CEA-β-CD and triethylenediamine TED in step S3 is to dissolve CEA-β-CD in DMF, then add triethylenediamine TED, mix uniformly, and then react at 42-48℃ for 4-5h.

8. The method for preparing a tungsten-containing metal oxide catalyst as described in claim 7, characterized in that: The amount ratio of CEA-β-CD, TED and DMF is 2.5-3.5:0.26-0.3g:18-24mL.

9. A method for producing a tungsten-containing metal oxide catalyst, characterized by, comprising the following steps: S1. Synthesis of mono 6-mono-p-toluenesulfonyl β-cyclodextrin (β-CD-OTs) S101, dissolve β-cyclodextrin in sodium hydroxide aqueous solution to obtain solution 1, dissolve p-toluenesulfonyl chloride (CH3C6H4SO2Cl) in acetonitrile to obtain solution 2, mix solution 1 and solution 2, and stir under the condition of ice water bath at 0-5℃ for 2-3h, the molar ratio of β-cyclodextrin and p-toluenesulfonyl chloride in the solution 1 and solution 2 is 0.8-1:1, the mass-volume ratio of β-cyclodextrin and sodium hydroxide aqueous solution in the solution 1 is 20-24g:140-160mL, the sodium hydroxide aqueous solution is a sodium hydroxide solution obtained by dissolving 4g of sodium hydroxide solid in 150g of deionized water, and the mass-volume ratio of toluenesulfonyl chloride and acetonitrile is 4-4.3g:10mL; S102, the solution after the reaction in S101 is filtered to collect the filtrate, which is neutralized with hydrochloric acid and then placed in 4-5℃ for 18-24h, and the white solid is obtained by filtration and dried; S103, the white solid after drying is added to deionized water and boiled immediately, and the hot filtrate is collected and placed in 4-5℃ for 18-24h, and the filter cake is collected by filtration to obtain p-toluenesulfonyl β-cyclodextrin β-CD-OTs; S2. Synthesis of 2-chloroethylamine β-cyclodextrin (CEA-β-CD) S201. A mixed solution of 2-chloroethylamine hydrochloride and β-CD-OTs in DMF is prepared, and the mixed solution is placed in 80-90℃ for 30-36h, and the amount of 2-chloroethylamine hydrochloride, β-CD-OTs and DMF is 2.2-2.6g: 13-14g: 45-55mL; S202. Ethanol is added to the mixed solution, and then the light yellow solid is obtained by filtration, which is washed with ethanol for 3 times, and the washed product is collected and dried, and the dried product is soaked in chloroform for 30-40min, then filtered and washed with ethanol for 3 times, and dried to obtain 2-chloroethylamine β-cyclodextrin CEA-β-CD; S3. Synthesis of catalyst S301. CEA-β-CD is dissolved in DMF, then triethylene diamine TED is added, and the mixture is uniformly mixed and reacted at 42-48℃ for 4-5h, and the amount of CEA-β-CD, TED and DMF is 2.5-3.5: 0.26-0.3g: 18-24mL; S302. The solution after reaction in S301 is filtered to collect the filter cake to obtain white solid β-CD-TBA, which is washed with anhydrous ethanol for 3 times and dried at 40-50℃, and the dried β-CD-TBA and silver tungstate Ag2WO4 are added to deionized water in a molar ratio of 1:1, and the precipitate is filtered after stirring at room temperature for 1h, and the filtrate is evaporated and dried to obtain the catalyst β-CD-TBAT.

10. The use of the catalyst prepared by the method of claim 9 in the oxidation of cyclohexene to prepare adipic acid.

Images