Kinetic insights into reaction pathways of acrolein formation in propylene epoxidation by H2 and O2 over Au/TS-1 catalyst

Abstract

Propylene epoxidation by H2 and O2 to propylene oxide (HOPO), as a novel method for PO production, has attracted widespread attention due to its economic and environmental advantages. Acrolein is a notable byproduct arising in HOPO reaction over Au/TS-1 catalyst, and is traditionally thought to be exclusively formed on Au site through propylene oxidation. However, on the intraporous and external surface Au sites of Au-Ti catalysts, the HOPO reaction have been shown to proceed by different mechanisms, yet the effect of active sites distribution on acrolein formation is far from being understood. Herein, we found that the reaction orders in acrolein formation on Au/TS-1 catalyst (H2, 0.19; O2, 0.44; C3H6, 0.44) relative to Au/TS-1 with blocked pores (Au/TS-1-B) catalyst (H2, −0.36; O2, 0.61; C3H6, 0.52) were quite different, suggesting a variation in the reaction pathway on the catalysts with different Au locations. Moreover, it is found that PO can be converted to acrolein by O2 on TS-1 zeolite, which is absent on TS-1-B zeolite without micropores. Consequently, acrolein formation on Au/TS-1 catalyst can proceed through two parallel pathways: propylene hydro-oxidation on Au site, and PO conversion by O2 inside micropores. Furthermore, by designing and preparing the Au/TS-1 catalysts with different structures, the Au locations are closely related to acrolein formation mechanism and kinetic behaviors. This work provides kinetic insights into the acrolein formation pathways in the HOPO reaction on Au/TS-1 catalyst, and is helpful to the rational design and preparation of efficient catalysts with high selectivity.