The Ag-MoO₃/ZrO₂ catalyst for the direct gas phase epoxidation of propylene was prepared. The in situ FT-IR technology was employed to study the adsorption and reaction behavior of propylene, propylene oxide (PO) and the mixture gas of propylene and oxygen on the surface of ZrO₂ support and Ag-MoO₃/ZrO₂ catalyst. The studies show that propylene adsorbed on ZrO₂ support or 20%Ag-4%MoO₃/ZrO₂ catalyst is stable. When the reaction temperature is more than 400 ℃, the ring-opening reaction of propylene oxide adsorbed on ZrO₂ support happens; over the 20%Ag-4%MoO₃/ZrO₂ catalyst, the ring-opening reaction of adsorbed propylene oxide occurs at 300 ℃. As the reaction temperature rises to 400 ℃, propylene adsorbed reacts with oxygen adsorbed on ZrO₂ support to form water and CO₂; over the 20%Ag-4%MoO₃/ZrO₂ catalyst, this surface reaction just takes place at 350 ℃. Comparing with the unsupported Ag-MoO₃ catalyst, the presence of ZrO₂ support can increase the selectivity of PO and while decrease the conversion of propylene.

Key words: propylene, gas phase epoxidation, propylene oxide, Ag-MoO₃/ZrO₂ catalyst, in situ FT-IR