Bi-Si mesoporous zeolites(II) Reaction mechanism and optimisation of reaction conditions in styrene oxidation
Bi-Si mesoporous molecular zeolites(Bi-Si) was synthesized by the hydrothermal method with ethyl silicate (TEOS)as silica source, Bi(NO_3)_3·5H_2O as Bi source, and cetyltrimethylammonium bromide(CTAB)as template. Bi-Si catalyst had high ordering structures and high reaction activity in oxidation of styrene with hydrogen peroxide to benzaldehyde. The effects of solvents, reaction time, reaction temperature, oxidant concentration and Bi-Si concentration on the oxidation of styrene to benzaldehyde were studied systematically. It was found that in the following reaction conditions: catalyst 0.075 g, styrene 1.5 ml, methanol 25 ml,H_2O_2(30%) 4.5 ml, T =80 ℃, t =2 h,the conversion of styrene was 43.1%, the selectivity to benzaldehyde was 73.5%,the yield of benzaldehyde reached 31.7%.The possible reaction mechanism could be that one styrene molecule reacted with two H_2O_2 molecules on two joined catalytically active sites.