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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.