Supported Tungsten-gallium Polyoxometalate Catalyst

Epoxides are a kind of fine chemical raw materials and pharmaceutical intermediates with wide applications. The most important way to form epoxides is the epoxidation of olefins. Epoxidation plays an important role in both organic synthesis and chemical industry. Therefore, the study of olefin epoxidation has always been a hot spot in chemical industry.

A supported tungsten-gallium polyoxometalate catalyst has been proposed, which can be used for epoxidation of cyclolefins. The preparation steps include:

1)36.3g Na₂WO_4·2H₂O was dissolved in 60 mL deionized water to form a solution with a concentration of 1.8mol/L. Then 6G acetic acid with a concentration of 0.1mol/L was added and heated to boiling.

2)Ga(NO₃)₃ solution of 1 mol/L was prepared.

3)Under the condition of electromagnetic stirring, the Ga(NO₃)₃ solution obtained in step 2 of 10mL was dripped into step 1, stirred for 30 minutes, and the solution pH was adjusted to 8.5 at the same time.

4)The solid sodium acetate of 20g was gradually added to the solution obtained in step 3 in batches and cooled to room temperature to obtain GaW 11 mixture.

5)Filtration step 4) GaW 11 mixture is washed with methanol and dried several times.

6)Take step 5) and add 0.054 mmol solid and 0.064 mmol aminopropyl triethoxysilane into 10 ml deionized water, stirring continuously for 2 hours at room temperature.

7)Then 8.75 ml absolute ethanol, 1.2 mmol tetrabutyl silicate and 1.5 ml 30% ammonia water were dripped into step 6. Under room temperature, electromagnetic stirring was carried out for 24 hours to complete the one-step formation of silicon dioxide and the loading of POMs on silicon oxide. The pore size of the carrier is 10-20 nm.

8)The mixture obtained in step 7 was centrifuged at a centrifugal speed of 2000 rpm. The lower sediment was washed several times with ethanol solution with a volume ratio of 1:1. Finally, it was dried in a drying dish to obtain a supported tungsten-gallium polyoxometalate catalyst.

Supported tungsten-gallium polyoxometalate catalyst was applied to the epoxidation of cyclolefins under mild catalytic conditions, no solvent was needed in the catalytic process, the oxidant was green and pollution-free molecular oxygen, and the epoxidation of cyclohexene had higher conversion and selectivity.

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