Gas phase propylene epoxidation over Au supported on titanosilicates with different Ti chemical environments

Abstract

Three Ti-containing porous materials − a mesoporous Ti-MCM-41 with distorted tetrahedral framework Ti sites (denoted as Ti-MCM-41-C), a microporous titanium silicate (TS-1) with tetrahedral framework Ti sites and a hybrid Ti-MCM-41 containing TS-1 microstructure (denoted as Ti-MCM-41-H) were used to prepare supported Au catalysts for gas phase propylene epoxidation in the presence of H2 and O2. Both catalyst structures and catalytic reaction kinetics were investigated in detail. The kinetic results show that the apparent activation energies for both PO and CO2 formation follow the order of Au/Ti-MCM-41-C<Au/Ti-MCM-41-H<Au/TS-1. Besides, the adsorption behaviors of propylene on the catalysts were strongly affected by the chemical environment of the framework Ti sites and pore structure in the supports. The adsorption capacity follows the order of Au/Ti-MCM-41-H>Au/TS–1>Au/Ti-MCM-41-C, in consistence with the order of propylene conversion rate, and the adsorption stability follows the order of Au/TS–1>Au/Ti-MCM-41-H>Au/Ti-MCM-41-C, in consistence with the order of apparent activation energy. These results demonstrated that the adsorption strength of propylene on the titanosilicates supports strongly affected the catalytic behavior, and implied that the support with balanced defective Ti sites and mesoporous/microporous structure may be a promising approach in the preparation of high-performance supported Au catalysts.