Epoxidation of propylene over gold catalysts supported on non-porous silica

Abstract

Non-porous silica was used as a carrier of Au/Ti-SiO 2 catalysts for the direct vapor-phase epoxidation of propylene in the copresence of H 2 and O 2, because the smooth surfaces were expected to facilitate the desorption of propylene oxide (PO). Their catalytic performances were inferior to those of Au/TS-1 and Au/Ti-MCM catalysts, however, an interesting feature was that propylene epoxidation over Au/Ti-SiO 2 appreciably depended on calcination temperature of the Ti-SiO 2 support. Higher calcination temperature benefits PO production at reaction temperatures above 100°C. IR and HRTEM analyses showed that the interaction between titanium oxides and silica was intensified to form more isolated TiO 4 units with tetrahedral coordination on the surfaces of Ti-SiO 2 supports with an increase in heat treatment temperature. These isolated TiO 4 sites incorporated in silica surface layers are assumed to be an important structural factor for the selective deposition of Au particles and the selective PO formation.