Core–Shell–Shell Microsphere Catalysts Containing Au Nanoparticles for Styrene Epoxidation

Abstract

An efficient heterogeneous nanocatalyst consisting of silica microsphere core decorated with Au nanoparticles shell encapsulated with a porous silica shell was successfully synthesized. The resulting core–shell–shell nanocatalyst catalyzed styrene epoxidation in toluene in the presence of a radical initiator and an oxidant tert-butyl hydroperoxide (TBHP) under inert atmosphere, giving ~100 % reactant conversion and 61 % selectivity towards the corresponding epoxide product at 80 °C. The maximum turnover frequency (TOF) of the catalyst was found to be 10400 h−1 at 80 °C under nitrogen atmosphere. The material also catalyzed trans-stilbene under similar condition, affording 52 % reactant conversion and 55 % selectivity towards trans-stilbene oxide product in 6 h. The catalyst was shown to be recycled and reused multiple times without losing its catalytic activity. Moreover, the Au nanoparticles in the catalyst did not undergo any significant leaching during the catalytic reactions. Porous SiO2–AuNPs–SiO2 core–shell–shell microsphere catalyst for epoxidation reaction was successfully synthesized. The catalyst was synthesized by anchoring Au nanoparticles (AuNPs) on the surface of silica microspheres, then encapsulating the AuNPs with silica shells and finally etching the outer silica shells into nanoporous silica shells. The catalyst exhibited heterogeneous catalytic activity for epoxidation of styrene and trans-stilbene and was proven to be easily recyclable and reusable in multiple cycles without significant loss of catalytic activity.