Performance, Reaction Pathway, and Pretreatment of Au Catalyst Precursor in H₂/O₂ Atmosphere for the Epoxidation of Propylene

Gas-phase epoxidation of propylene in the copresence of H2 and O2 was performed over the catalyst of Au on as-synthesized TS-1 that contained a small amount of anatase TiO2. The catalytic performance was studied by washing or nonwashing the catalyst precursor to modulate the content of purity (K, Cl) and then calcining the samples in O2 or H2 prior to reaction. The results show that the catalytic performance of Au/TS-1 can be improved without washing (more K+ and Au maintained) and O2 pretreatment. It was found that the calcination in O2 was able to maintain more metallic Au and form more surface-active oxygen species and thus providing a better yield of propylene oxide with the assistance of potassium. Interestingly, more acrolein can be produced over the catalysts with respect to the in situ calcination in O2 than that in H2 when the feed only contained 10% O2 and 10% propylene in argon, while there was no formation of propylene oxide. On the other hand, the catalyst precursor calcined in H2 prefers the formation of successive oxygenates of PO.