Dual-component gas pretreatment for Au/TS-1: Enhanced propylene epoxidation with oxygen and hydrogen

Abstract

Direct epoxidation of propylene (C3H6) with oxygen (O2) and hydrogen (H2) over gold catalysts is an efficient and environmentally benign process to produce propylene oxide (PO). Herein, Au/TS-1 was used to catalyze propylene epoxidation, and its pretreatment effect under different gas atmospheres was carefully investigated. The results showed that Au/TS-1 pretreated with H2-C3H6 exhibited much better catalytic performance than that pretreated with single-component gas of H2, O2 and C3H6, dual-component gas of H2-O2 and O2-C3H6, and feed gas of H2+O2+C3H6. UV/vis/NIR spectra, O2-TPO-MS and 29Si NMR indicated that the pretreatment of Au/TS-1 using H2-C3H6 led to hydrophobic catalyst surfaces functionalized by hydrocarbon species, consequently facilitating the C3H6 adsorption and PO desorption. HAADF-STEM showed that H2-C3H6 pretreatment caused the formation of small Au nanoparticles (NPs) with an average size of ˜2.1 nm. The common effect of small Au NPs and hydrophobic surface was speculated to be responsible for the excellent catalytic performance of Au/TS-1 pretreated with H2-C3H6.