Epoxidation of styrene by anhydrous t-butyl hydroperoxide over Au/TiO₂ catalysts

Abstract

Nanosize gold deposited on TiO₂, by homogeneous deposition-precipitation (HDP) using urea as the precipitation agent is an active/selective and reusable catalyst for the epoxidation of styrene (at 82°C) by anhydrous t-butyl hydroperoxide (TBHP). The activity and epoxide selectivity of the Au/TiO₂ catalyst in the epoxidation is increased with increasing the Au loading on the TiO₂ support. The Au/TiO₂ catalyst prepared by the deposition precipitation using sodium hydroxide as the precipitation agent (DP method) has much lower gold loading and also lower Au dispersion and consequently possesses lower epoxidation activity as compared to that prepared by the HDP method. The styrene oxide selectivity is not influenced very significantly by the catalyst preparation method or by the Au loading (except at the very low Au loading). In the Au/TiO₂ catalysts prepared by both the methods, Au is found to exist in both the metallic (Au°) and cationic (Au³⁺) forms.