Preparation method and application of a supported cerium-chromium bimetallic catalyst

Abstract

This invention discloses a method for preparing a supported cerium-chromium bimetallic catalyst and its application. First, an appropriate amount of modified alumina nanoparticles are dispersed in water. While stirring thoroughly, a certain amount of cerium and chromium sources are added, and stirring continues. Then, the mixture is heated to a certain temperature to evaporate the water. The resulting solid mixture is transferred to a covered crucible and calcined at a given temperature for a certain time. Finally, the obtained catalyst is ground into powder for later use. Under the action of the supported bimetallic catalyst, cyclohexane and an oxidant are thoroughly mixed in an organic solvent, heated, and reacted to produce cyclohexanone / alcohol. The cyclohexane catalytic oxidation method disclosed in this invention has a simple process, mild reaction conditions, requires no additives, and has low equipment requirements. Furthermore, the disclosed supported catalyst exhibits high catalytic activity, good stability, and no significant decrease in activity after multiple cycles, demonstrating good prospects for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of catalysts and fine chemicals, specifically relating to a method for preparing a supported cerium-chromium bimetallic catalyst and its application in the selective oxidation of cyclohexane to cyclohexanone / alcohol. Background Technology

[0002] In the activation of the CH bond in alkanes, the catalytic oxidation of cyclohexane is an important and widely used fundamental reaction. Its main oxidation products, cyclohexanone and cyclohexanol (collectively referred to as KA oil), are intermediates in the synthesis of important chemical raw materials such as caprolactam and adipic acid, laying a solid foundation for the vigorous development of synthetic fibers such as resins, plastic fibers, and nylon-66. In 2022, the global synthetic fiber market size was approximately US$70 billion, and it is projected to continue growing at a rate of 6.1% until 2025, which also increases the market demand for the raw material KA oil [Journal of Cleaner Production, 2019, 227: 624-633.].

[0003] In industrial production, the selective oxidation of cyclohexane typically uses cobalt salts, boric acid, etc., as catalysts. The oxidation process requires high temperatures (>140℃) and high air / oxygen pressures (0.9–1.0 MPa), and side reactions are prone to occur, reducing the selectivity of KA oil. Furthermore, this process requires large amounts of alkali, which not only increases production costs but also makes the subsequent treatment of alkaline wastewater extremely difficult. Therefore, developing heterogeneous catalysts with high activity and high stability has significant industrial value and application prospects.

[0004] In recent years, researchers have made significant progress in the catalytic oxidation of cyclohexane to KA oil. For example, patent CN201210138434.9 reports a graphitized carbon material-supported Fe / Co / Ni-based catalyst prepared through hydrothermal-high-temperature carbonization-acid leaching steps, achieving a cyclohexane conversion rate of up to 55%, but the overall selectivity for KA oil is only 57%. Patent CN201711267271.3 reports a WO3-supported Ag nanoparticle catalyst that achieves selective oxidation of cyclohexane under photo-thermal coupling conditions, but the cost of the equipment and the use of precious metal catalysts still pose challenges for large-scale industrial applications. Recently, Wang et al. prepared a Cu2O / nanocarbon composite catalyst, achieving a conversion rate of 25.4% and a selectivity of 49.8% with H2O2 as the oxidant; and a conversion rate of 77.1% and a selectivity of 83.9% with tert-butyl hydroperoxide (TBHP) as the oxidant [Applied Surface Science, 2022, 576: 151833.]. Furthermore, thanks to the multi-metal oxide CeMn... 0.25 Co0.75 O x Synergistic effects between different metals, with molecular oxygen as the oxidant, can achieve a cyclohexane conversion of 4.6% and a KA oil selectivity of 93.0% [Chemical Engineering Science, 2023, 277: 118878.].

[0005] On the other hand, compared to TBHP, H2O2 is lower in cost and more environmentally friendly; and compared to oxygen, H2O2 has a stronger oxidizing capacity, especially in liquid-phase reactions, where it can generate a large number of active oxygen species, with water being the only byproduct. Therefore, using hydrogen peroxide as an oxidant to selectively oxidize cyclohexane to KA oil under mild conditions has great application potential. The biggest technical challenge at present is the development of highly active and stable heterogeneous catalysts. Although the aforementioned reported work has made significant progress in the catalytic oxidation of cyclohexane to KA oil, problems such as complex catalyst preparation processes, low catalytic activity, and low selectivity still exist. Therefore, designing and developing novel non-precious metal catalysts to improve the activity of cyclohexane oxidation to KA oil is urgent and has significant economic and social value. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low catalytic activity and low selectivity in the oxidation of cyclohexane to cyclohexanone / alcohol (KA oil) in existing technologies. This invention utilizes a simple method to prepare an alumina-supported bimetallic catalyst and applies it to the selective oxidation of cyclohexane (using hydrogen peroxide as the oxidant and without the introduction of other additives). The catalyst exhibits high selectivity for the target product KA oil, and the entire reaction process is conducted under mild conditions. Furthermore, this catalyst is inexpensive, has a simple preparation process, and good stability, showing promising prospects for industrial application.

[0007] Therefore, this invention provides a method for preparing a supported cerium-chromium bimetallic catalyst. The method includes:

[0008] First, a suitable amount of modified alumina nanoparticles were dispersed in water and stirred thoroughly. Then, a certain amount of cerium and chromium sources were added, and stirring continued for a period of time. Subsequently, the mixture was heated to a certain temperature to evaporate the water. The resulting solid mixture was transferred to a covered crucible and calcined at a given temperature for a certain time. Finally, the obtained catalyst was ground into powder for later use.

[0009] The alumina is commercially available and subsequently modified with organic acids, using one or more of oxalic acid, citric acid, gallic acid, benzenesulfonic acid, glycolic acid, and aminoacetic acid, preferably citric acid; the concentration of the organic acid aqueous solution is 0.01 mol / L. -1 ~0.5 mol / L -1 Further preferably 0.05 mol / L -1.

[0010] The cerium source is one of cerium nitrate, cerium acetate, and cerium acetylacetonate, and the chromium source is one of chromium nitrate, chromium acetate, and chromium acetylacetonate.

[0011] The cerium loading is 1:(5-200), the chromium loading is 1:(5-200), and the loading is based on the mass ratio of the added metal element to the carrier alumina.

[0012] The molar ratio of the bimetallic cerium to chromium is 1:(0.1-5).

[0013] The soaking time is 2h to 10h, more preferably 4h to 8h.

[0014] The temperature at which the water is evaporated is 50℃~100℃, more preferably 80℃;

[0015] The catalyst is calcined at a temperature of 200℃ to 1000℃, preferably 400℃ to 800℃; and the calcination time is 1h to 10h, preferably 2h to 6h.

[0016] Furthermore, another aspect of the present invention provides an application of the catalyst prepared by the above method in fine chemicals, specifically in the selective oxidation of cyclohexane to KA oil, comprising the following:

[0017] The reaction equations for the above reaction process are as follows:

[0018]

[0019] A certain amount of organic solvent was added to a three-necked flask, followed by the raw material cyclohexane, an oxidant, and the supported cerium-chromium bimetallic catalyst prepared by the above method. The mixture was stirred thoroughly and heated to a certain temperature to allow the reaction to proceed. After a period of time, the reaction was completed. Samples were taken for gas chromatography analysis, and quantification was performed using the external standard method.

[0020] Further, the organic solvent is one or more selected from ethanol, acetonitrile, acetic acid, ethyl acetate, chloroform, N,N-dimethylformamide, toluene, p-chlorotoluene, and ethylene glycol. Acetonitrile is preferred.

[0021] Furthermore, the oxidant is preferably hydrogen peroxide (i.e., hydrogen peroxide solution), and the mass fraction is preferably 30%.

[0022] Furthermore, the reaction time is 1h to 10h, preferably 3h to 8h; the reaction temperature is 60℃ to 100℃, preferably 75℃ to 90℃.

[0023] Furthermore, the molar ratio of cyclohexane to hydrogen peroxide is 1:(0.5-10), preferably 1:(1-5).

[0024] Furthermore, the mass ratio of cyclohexane to catalyst is 1:(0.01-0.2), preferably 1:(0.03-0.1).

[0025] Through the above technical solution, this invention provides a novel non-precious metal catalyst and catalytic reaction process for the selective oxidation of cyclohexane to KA oil. Compared with existing technologies, the method provided by this invention not only improves the conversion rate of the feedstock cyclohexane and the selectivity of the target product KA oil, but also utilizes a catalyst that is low in cost, stable, and recyclable. Furthermore, the method provided by this invention does not require expensive equipment, has low production costs, and requires no other additives, thus possessing promising prospects for industrial application. Detailed Implementation

[0026] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following detailed embodiments were commercially available. Unless otherwise specified, room temperature is expressed as 25°C.

[0027] It is worth noting that the content of substances before and after the reaction was obtained by gas chromatography analysis.

[0028] The chromatographic analysis conditions were as follows: FuLi chromatograph (FuLi9790Ⅱ), capillary column (PB-50, 30m × 0.32mm × 0.33μm), flame ionization detector (FID); injection port temperature 250℃, detector temperature 250℃, column temperature increased from 50℃ to 250℃ (10℃ min). -1 Incubate for 2 minutes. The cyclohexane conversion and cyclohexanone / cyclohexanol selectivity are calculated using the following formulas:

[0029]

[0030]

[0031]

[0032] KA oil selectivity (%) = cyclohexanol selectivity (%) + cyclohexanone selectivity (%)

[0033] Specific embodiments and comparative examples of the present invention are as follows:

[0034] Example 1

[0035] Add 1g of Al2O3 powder to 0.5mol / L -1The sample was thoroughly impregnated in a citric acid solution for 3 hours, then filtered and dried to obtain solid C1. C1 was dispersed in 10 mL of deionized water, followed by the addition of 0.714 mmol cerium acetate and 1.923 mmol chromium acetate. The mixture was stirred thoroughly and impregnated for 5 hours. Subsequently, the water was evaporated at 80 °C to obtain solid C2. Solid C2 was transferred to a crucible and placed in a muffle furnace, calcined at 600 °C for 4 hours, then annealed. After cooling to room temperature, the solid was ground to obtain the target catalyst C3.

[0036] The target catalyst C3 obtained in the above examples was applied to the selective oxidation of cyclohexane. 5 mL of acetonitrile was added as a solvent to a three-necked flask, followed by the sequential addition of 10 mmol of cyclohexane, 20 mmol of 30 wt% H₂O₂, and 50 mg of catalyst C3. The reaction was carried out at 60 °C for 5 h. After the reaction was complete, a sample was taken and dried over anhydrous sodium sulfate, followed by gas chromatography analysis and quantification using the external standard method. The cyclohexane conversion rate after 5 hours was 45.6%, and the selectivity for KA oil was 98.5%.

[0037] Furthermore, the catalyst was separated by simple centrifugation, and the recovered catalyst was thoroughly washed successively with ethanol and water, then dried for later use. Under the same reaction conditions as described above, it was used in the catalytic oxidation of cyclohexane to KA oil, and this cycle was repeated. In the fifth reaction, the recovered catalyst achieved a cyclohexane conversion of 44.2% and a KA oil selectivity of 98.0% in the catalytic oxidation of cyclohexane to KA oil.

[0038] Example 2

[0039] Add 1g of Al2O3 powder to 0.5mol / L -1 The sample was thoroughly impregnated in a citric acid solution for 3 hours, then filtered and dried to obtain solid C1. C1 was dispersed in 10 mL of deionized water, followed by the addition of 1.071 mmol cerium acetate and 1.923 mmol chromium acetate. The mixture was stirred thoroughly and impregnated for 5 hours. Subsequently, the water was evaporated at 80 °C to obtain solid C2. Solid C2 was transferred to a crucible and placed in a muffle furnace, calcined at 600 °C for 4 hours, then annealed. After cooling to room temperature, the solid was ground to obtain the target catalyst C3.

[0040] The target catalyst C3 obtained in the above examples was applied to the selective oxidation of cyclohexane. 5 mL of acetonitrile was added as a solvent to a three-necked flask, followed by the sequential addition of 10 mmol of cyclohexane, 20 mmol of 30 wt% H₂O₂, and 50 mg of catalyst C3. The reaction was carried out at 60 °C for 5 h. After the reaction was complete, a sample was taken and dried over anhydrous sodium sulfate, followed by gas chromatography analysis and quantification using the external standard method. The cyclohexane conversion rate after 5 hours was 35.6%, and the selectivity for KA oil was 96.5%.

[0041] Furthermore, the catalyst was separated by simple centrifugation, and the recovered catalyst was thoroughly washed successively with ethanol and water, then dried for later use. Under the same reaction conditions as described above, the catalyst was used in the catalytic oxidation of cyclohexane to KA oil, and this cycle was repeated. In the fifth reaction, the recovered catalyst achieved a cyclohexane conversion of 35.0% and a KA oil selectivity of 97.5% in the catalytic oxidation of cyclohexane to KA oil.

[0042] Example 3

[0043] Add 1g of Al2O3 powder to 0.5mol / L -1 The sample was thoroughly impregnated in a citric acid solution for 3 hours, then filtered and dried to obtain solid C1. C1 was dispersed in 10 mL of deionized water, followed by the addition of 0.714 mmol cerium acetate and 3.077 mmol chromium acetate. The mixture was stirred thoroughly and impregnated for 5 hours. Subsequently, the water was evaporated at 80 °C to obtain solid C2. Solid C2 was transferred to a crucible and placed in a muffle furnace, calcined at 600 °C for 4 hours, then annealed. After cooling to room temperature, the solid was ground to obtain the target catalyst C3.

[0044] The target catalyst C3 obtained in the above examples was applied to the selective oxidation of cyclohexane. 5 mL of acetonitrile was added as a solvent to a three-necked flask, followed by the sequential addition of 10 mmol of cyclohexane, 20 mmol of 30 wt% H₂O₂, and 50 mg of catalyst C3. The reaction was carried out at 60 °C for 5 h. After the reaction was complete, a sample was taken and dried over anhydrous sodium sulfate, followed by gas chromatography analysis and quantification using the external standard method. The cyclohexane conversion rate after 5 hours was 55.2%, and the selectivity for KA oil was 96.8%.

[0045] Furthermore, the catalyst was separated by simple centrifugation, and the recovered catalyst was thoroughly washed successively with ethanol and water, then dried for later use. Under the same reaction conditions as described above, the catalyst was used in the catalytic oxidation of cyclohexane to KA oil, and this cycle was repeated. In the fifth reaction, the recovered catalyst achieved a cyclohexane conversion of 54.0% and a KA oil selectivity of 96.5% in the catalytic oxidation of cyclohexane to KA oil.

[0046] Example 4

[0047] Add 1g of Al2O3 powder to 0.5mol / L -1 The sample was thoroughly impregnated in a citric acid solution for 3 hours, then filtered and dried to obtain solid C1. C1 was dispersed in 10 mL of deionized water, followed by the addition of 0.714 mmol cerium acetate and 3.077 mmol chromium acetate. The mixture was stirred thoroughly and impregnated for 5 hours. Subsequently, the water was evaporated at 80 °C to obtain solid C2. Solid C2 was transferred to a crucible and placed in a muffle furnace, calcined at 600 °C for 4 hours, then annealed. After cooling to room temperature, the solid was ground to obtain the target catalyst C3.

[0048] The target catalyst C3 obtained in the above examples was applied to the selective oxidation of cyclohexane. 5 mL of acetonitrile was added as a solvent to a three-necked flask, followed by the sequential addition of 10 mmol of cyclohexane, 30 mmol of 30 wt% H₂O₂, and 50 mg of catalyst C3. The reaction was carried out at 60 °C for 5 h. After the reaction was complete, a sample was taken and dried over anhydrous sodium sulfate, followed by gas chromatography analysis and quantification using the external standard method. The cyclohexane conversion rate after 5 hours was 62.2%, and the selectivity for KA oil was 95.8%.

[0049] Furthermore, the catalyst was separated by simple centrifugation, and the recovered catalyst was thoroughly washed successively with ethanol and water, then dried for later use. Under the same reaction conditions as described above, the catalyst was used in the catalytic oxidation of cyclohexane to KA oil, and this cycle was repeated. In the fifth reaction, the recovered catalyst achieved a cyclohexane conversion of 61.0% and a KA oil selectivity of 95.5% in the catalytic oxidation of cyclohexane to KA oil.

[0050] Example 5

[0051] Add 1g of Al2O3 powder to 0.5mol / L -1 The sample was thoroughly impregnated in a citric acid solution for 3 hours, then filtered and dried to obtain solid C1. C1 was dispersed in 10 mL of deionized water, followed by the addition of 0.714 mmol cerium acetate and 3.077 mmol chromium acetate. The mixture was stirred thoroughly and impregnated for 5 hours. Subsequently, the water was evaporated at 80 °C to obtain solid C2. Solid C2 was transferred to a crucible and placed in a muffle furnace, calcined at 600 °C for 4 hours, then annealed. After cooling to room temperature, the solid was ground to obtain the target catalyst C3.

[0052] The target catalyst C3 obtained in the above examples was applied to the selective oxidation of cyclohexane. 5 mL of acetonitrile was added as a solvent to a three-necked flask, followed by the sequential addition of 10 mmol of cyclohexane, 30 mmol of 30 wt% H₂O₂, and 80 mg of catalyst C3. The reaction was carried out at 60 °C for 5 h. After the reaction was complete, a sample was taken and dried over anhydrous sodium sulfate, followed by gas chromatography analysis and quantification using the external standard method. The cyclohexane conversion rate after 5 hours was 65.2%, and the selectivity for KA oil was 96.6%.

[0053] Furthermore, the catalyst was separated by simple centrifugation, and the recovered catalyst was thoroughly washed successively with ethanol and water, then dried for later use. Under the same reaction conditions as described above, it was used in the catalytic oxidation of cyclohexane to KA oil, and this cycle was repeated. In the fifth reaction, the recovered catalyst achieved a cyclohexane conversion of 64.8% and a KA oil selectivity of 95.5% in the catalytic oxidation of cyclohexane to KA oil.

[0054] Comparative Example 1

[0055] Add 1g of Al2O3 powder to 0.5mol / L -1 The sample was thoroughly impregnated in a citric acid solution for 3 hours, then filtered and dried to obtain solid C1. C1 was dispersed in 10 mL of deionized water, followed by the addition of 0.714 mmol cerium acetate and 0.325 mmol chromium acetate. The mixture was stirred thoroughly and impregnated for 5 hours. Subsequently, the water was evaporated at 80 °C to obtain solid C2. Solid C2 was transferred to a crucible and placed in a muffle furnace, calcined at 600 °C for 4 hours, then annealed. After cooling to room temperature, the solid was ground to obtain the target catalyst C3.

[0056] The target catalyst C3 obtained in the above examples was applied to the selective oxidation of cyclohexane. 5 mL of acetonitrile was added as a solvent to a three-necked flask, followed by the sequential addition of 10 mmol of cyclohexane, 30 mmol of 30 wt% H₂O₂, and 50 mg of catalyst C3. The reaction was carried out at 60 °C for 5 h. After the reaction was complete, a sample was taken and dried over anhydrous sodium sulfate, followed by gas chromatography analysis and quantification using the external standard method. The cyclohexane conversion rate after 5 hours was 12.2%, and the selectivity for KA oil was 68.8%.

[0057] Furthermore, the catalyst was separated by simple centrifugation, and the recovered catalyst was thoroughly washed successively with ethanol and water, then dried for later use. Under the same reaction conditions as described above, the catalyst was used in the catalytic oxidation of cyclohexane to KA oil, and this cycle was repeated. In the fifth reaction, the recovered catalyst achieved a cyclohexane conversion of 11.0% and a KA oil selectivity of 67.5% in the catalytic oxidation of cyclohexane to KA oil.

[0058] Comparative Example 2

[0059] Add 1g of Al2O3 powder to 0.5mol / L -1 The sample was thoroughly impregnated in a citric acid solution for 3 hours, then filtered and dried to obtain solid C1. C1 was dispersed in 10 mL of deionized water, followed by the addition of 0.714 mmol cerium acetate and 0.325 mmol chromium acetate. The mixture was stirred thoroughly and impregnated for 5 hours. Subsequently, the water was evaporated at 80 °C to obtain solid C2. Solid C2 was transferred to a crucible and placed in a muffle furnace, calcined at 800 °C for 4 hours, then annealed. After cooling to room temperature, the solid was ground to obtain the target catalyst C3.

[0060] The target catalyst C3 obtained in the above examples was applied to the selective oxidation of cyclohexane. 5 mL of acetonitrile was added as a solvent to a three-necked flask, followed by the sequential addition of 10 mmol of cyclohexane, 30 mmol of 30 wt% H₂O₂, and 50 mg of catalyst C3. The reaction was carried out at 60 °C for 5 h. After the reaction was complete, a sample was taken and dried over anhydrous sodium sulfate, followed by gas chromatography analysis and quantification using the external standard method. The cyclohexane conversion rate after 5 hours was 23.2%, and the selectivity for KA oil was 75.5%.

[0061] Furthermore, the catalyst was separated by simple centrifugation, and the recovered catalyst was thoroughly washed successively with ethanol and water, then dried for later use. Under the same reaction conditions as described above, the catalyst was used in the catalytic oxidation of cyclohexane to KA oil, and this cycle was repeated. In the fifth reaction, the recovered catalyst achieved a cyclohexane conversion of 22.0% and a KA oil selectivity of 74.0% in the catalytic oxidation of cyclohexane to KA oil.

[0062] Comparative Example 3

[0063] Add 1g of Al2O3 powder to 0.5mol / L -1 The sample was thoroughly impregnated in a citric acid solution for 3 hours, then filtered and dried to obtain solid C1. C1 was dispersed in 10 mL of deionized water, followed by the addition of 0.714 mmol cerium acetate and 0.325 mmol chromium acetate. The mixture was stirred thoroughly and impregnated for 5 hours. Subsequently, the water was evaporated at 80 °C to obtain solid C2. Solid C2 was transferred to a crucible and placed in a muffle furnace, calcined at 600 °C for 4 hours, then annealed. After cooling to room temperature, the solid was ground to obtain the target catalyst C3.

[0064] The target catalyst C3 obtained in the above examples was applied to the selective oxidation of cyclohexane. 5 mL of acetonitrile was added as a solvent to a three-necked flask, followed by the sequential addition of 10 mmol of cyclohexane, 30 mmol of 30 wt% H₂O₂, and 50 mg of catalyst C3. The reaction was carried out at 40 °C for 5 h. After the reaction was complete, a sample was taken and dried over anhydrous sodium sulfate, followed by gas chromatography analysis and quantification using the external standard method. The cyclohexane conversion rate after 5 hours was 17.2%, and the selectivity for KA oil was 58.2%.

[0065] Furthermore, the catalyst was separated by simple centrifugation, and the recovered catalyst was thoroughly washed successively with ethanol and water, then dried for later use. Under the same reaction conditions as described above, the catalyst was used in the catalytic oxidation of cyclohexane to KA oil, and this cycle was repeated. In the fifth reaction, the recovered catalyst achieved a cyclohexane conversion of 16.0% and a KA oil selectivity of 57.8% in the catalytic oxidation of cyclohexane to KA oil.

[0066] Comparative Example 4

[0067] Add 1g of Al2O3 powder to 0.5mol / L -1 The sample was thoroughly impregnated in a citric acid solution for 3 hours, then filtered and dried to obtain solid C1. C1 was dispersed in 10 mL of deionized water, followed by the addition of 0.714 mmol cerium acetate and 0.325 mmol chromium acetate. The mixture was stirred thoroughly and impregnated for 5 hours. Subsequently, the water was evaporated at 80 °C to obtain solid C2. Solid C2 was transferred to a crucible and placed in a muffle furnace, calcined at 600 °C for 4 hours, then annealed. After cooling to room temperature, the solid was ground to obtain the target catalyst C3.

[0068] The target catalyst C3 obtained in the above examples was applied to the selective oxidation of cyclohexane. 5 mL of acetonitrile was added as a solvent to a three-necked flask, followed by the sequential addition of 10 mmol of cyclohexane, 30 mmol of 30 wt% H₂O₂, and 50 mg of catalyst C3. The reaction was carried out at 60 °C for 2 h. After the reaction was complete, a sample was taken and dried over anhydrous sodium sulfate, followed by gas chromatography analysis and quantification using the external standard method. The cyclohexane conversion rate after 5 hours was 9.2%, and the selectivity for KA oil was 77.2%.

[0069] Furthermore, the catalyst was separated by simple centrifugation, and the recovered catalyst was thoroughly washed successively with ethanol and water, then dried for later use. Under the same reaction conditions as described above, the catalyst was used in the catalytic oxidation of cyclohexane to KA oil, and this cycle was repeated. In the fifth reaction, the recovered catalyst achieved a cyclohexane conversion of 9.0% and a KA oil selectivity of 76.3% in the catalytic oxidation of cyclohexane to KA oil.

[0070] Comparative Example 5

[0071] Add 1g of Al2O3 powder to 0.5mol / L -1 The sample was thoroughly impregnated in a citric acid solution for 3 hours, then filtered and dried to obtain solid C1. C1 was dispersed in 10 mL of deionized water, followed by the addition of 0.714 mmol cerium acetate and 0.325 mmol chromium acetate. The mixture was stirred thoroughly and impregnated for 5 hours. Subsequently, the water was evaporated at 80 °C to obtain solid C2. Solid C2 was transferred to a crucible and placed in a muffle furnace, calcined at 600 °C for 4 hours, then annealed. After cooling to room temperature, the solid was ground to obtain the target catalyst C3.

[0072] The target catalyst C3 obtained in the above examples was applied to the selective oxidation of cyclohexane. 5 mL of acetonitrile was added as a solvent to a three-necked flask, followed by the sequential addition of 10 mmol of cyclohexane, 30 mmol of 30 wt% H₂O₂, and 30 mg of catalyst C3. The reaction was carried out at 45 °C for 2 h. After the reaction was complete, a sample was taken and dried over anhydrous sodium sulfate, followed by gas chromatography analysis and quantification using the external standard method. The cyclohexane conversion rate after 5 hours was 5.2%, and the selectivity for KA oil was 55.6%.

[0073] Furthermore, the catalyst was separated by simple centrifugation, and the recovered catalyst was thoroughly washed successively with ethanol and water, then dried for later use. Under the same reaction conditions as described above, the catalyst was used in the catalytic oxidation of cyclohexane to KA oil, and this cycle was repeated. In the fifth reaction, the recovered catalyst achieved a cyclohexane conversion of 4.8% and a KA oil selectivity of 56.3% in the catalytic oxidation of cyclohexane to KA oil.

[0074] As can be seen from the above examples and comparative examples, the catalyst prepared by the present invention has a very different effect on the subsequent preparation of KA oil depending on the preparation conditions and amounts. This can be clearly seen from the obtained cyclohexane conversion rate and the percentage of KA oil selectivity.

[0075] For example, Example 1 and Comparative Example 1 are basically similar in terms of composition and conditions. The difference lies in that in Example 1, "C1 was dispersed in 10 mL of deionized water, followed by the addition of 0.714 mmol of cerium acetate and 1.923 mmol of chromium acetate," while in Comparative Example 1, "C1 was dispersed in 10 mL of deionized water, followed by the addition of 0.714 mmol of cerium acetate and 0.325 mmol of chromium acetate, stirred thoroughly, and soaked for 5 hours." Due to the difference in the molar ratio of cerium and chromium, it can be seen that in Example 1, "20 mmol of 30 wt% H2O2 and 50 mg of catalyst C3 were reacted at 60°C." The reaction was carried out for 5 hours. After the reaction was complete, samples were taken and dried with anhydrous sodium sulfate, followed by gas chromatography analysis and quantification using the external standard method. The cyclohexane conversion rate after 5 hours was 45.6%, and the selectivity of KA oil was 98.5%. However, in Comparative Example 1, "30 mmol of 30 wt% H2O2 and 50 mg of catalyst C3 were reacted at 60 °C for 5 hours. After the reaction was complete, samples were taken and dried with anhydrous sodium sulfate, followed by gas chromatography analysis and quantification using the external standard method. The cyclohexane conversion rate after 5 hours was 12.2%, and the selectivity of KA oil was 68.8%." The difference in cyclohexane conversion rate and KA oil selectivity between the two is significant. While the amount of H2O2 also differs, the main difference lies in the molar ratio of cerium to chromium.

[0076] Similarly, as can be seen from Examples 1 and 2, the difference between the two is also the molar ratio of cerium to chromium; all other components and conditions are the same. In Example 1, "0.714 mmol of cerium acetate and 1.923 mmol of chromium acetate were added," while in Example 2, "1.071 mmol of cerium acetate and 1.923 mmol of chromium acetate were added." The catalysts prepared in both examples, used under the same conditions, yielded the following products: In Example 1, "the cyclohexane conversion rate after 5 hours was 45.6%, and the selectivity for KA oil was 98.5%." In Example 2, "the cyclohexane conversion rate after 5 hours was 35.6%, and the selectivity for KA oil was 96.5%." It can be seen that the different molar ratios of cerium and chromium affect the cyclohexane conversion rate and the selectivity for KA oil.

[0077] Furthermore, a more detailed comparison can be made from the specific components of Examples 3, 4, 5 and the comparative examples.

[0078] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These modifications should also be considered as part of the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a supported cerium-chromium bimetallic catalyst, characterized in that, The method comprises the following steps: First, disperse a proper amount of modified alumina nanoparticles in water, and then add a certain amount of cerium source and chromium source under stirring, and continue to stir; then heat the mixture to a certain temperature, and evaporate water; transfer the obtained solid mixture to a covered crucible, and calcine at a given temperature for a certain time; finally, grind the obtained catalyst into powder for standby; The modified alumina nanoparticles are obtained by modifying alumina with an organic acid, and the organic acid used is one or more of oxalic acid, citric acid, gallic acid, benzene sulfonic acid, hydroxyacetic acid and aminoacetic acid; the concentration of the organic acid aqueous solution is 0.01 mol / L -1 ~ 0.5 mol / L -1 ; The cerium source is one of cerium nitrate, cerium acetate and cerium acetylacetone; the chromium source is one of chromium nitrate, chromium acetate and chromium acetylacetone; The cerium loading is 1:(5-200), and the chromium loading is 1:(5-200), wherein the loading is the mass ratio of the added metal element to the carrier alumina; the molar ratio of cerium to chromium is 1:(0.1-5), and the impregnation time is 2-10 hours; The calcination temperature is 200-1000℃, and the calcination time is 1-10 hours; The prepared supported cerium-chromium bimetallic catalyst is applied to the catalyst for the oxidation of cyclohexane to prepare KA oil, and when applied, a certain amount of organic solvent is added into a three-necked flask, and then cyclohexane, hydrogen peroxide and the prepared supported cerium-chromium bimetallic catalyst are added in sequence; after stirring, heat to a certain temperature to react, and the reaction is completed after a period of time; take samples for gas chromatography analysis, and quantitatively analyze by external standard method; the organic solvent is one or more of ethanol, acetonitrile, acetic acid, ethyl acetate, chloroform, N,N-dimethylformamide, toluene, p-chlorotoluene and ethylene glycol; the reaction time is 3-8 hours, and the reaction temperature is 60-100℃; the molar ratio of cyclohexane to hydrogen peroxide is 1:(0.5-10); and the mass ratio of cyclohexane to catalyst is 1:(0.01-0.2).

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