1. Gas-Phase Epoxidation of Propylene over Gold Catalysts
W. Nicholas Delgass, Department of Chemical Engineering, Purdue University, IN
The catalytic single-step, direct vapor phase propylene oxide (PO) reaction using a mixture of propylene, oxygen, and hydrogen under ambient pressure was improved by introducing titanium silicate (TS-1) as the support. Hydrogen is postulated to form HOOH, acting as the electrophyllic oxidant for the epoxidation. However, the current best PO conversion (~8%) and selectivity (~80%) are still short of the goal of
PO conversion ~ 10% and PO selectivity ~90%.
Two different approaches are proposed to improve the catalytic performance. The first approach is to introduce a novel mesoporous titanium silicate support (MTS-9) in which the pore size is around 8 nm while the walls inside the material have the TS-1 crystal structure. MTS-9 is therefore expected to alleviate possible mass transfer issue caused by TS-1 without loosing the intrinsic catalytic activity.
We are also exploring the possibility of enhancing activity by alloying Au with other metals over TS-1. An Au-Pd catalyst recently has been shown to possess superior activity in liquid phase H2O2 synthesis. Therefore, an Au-Pd/TS-1 catalyst is expected to increase the PO conversion by providing either higher in-situ H2O2 production rate or a synergistic effect on the epoxidation reaction by further lowering of its activation energy.
We have right now successfully synthesized TS-1 and rebuild our PO reaction system. Our next goal will be to prepare MTS-9 material as well as Au-Pd/TS-1 catalysts and investigate the their effects on the PO catalytic performance.