Direct gas-phase epoxidation of propylene over nanostructured molybdenum oxide film catalysts

Mixed molybdenum oxides are widely used catalysts for propylene oxidation to acrolein or acrylic acid or for methanol oxidation in the gas phase. In the present study, however molybdenum oxides exhibited an epoxidation activity in the gas phase. To achieve this activity, the oxidation state, particle sizes and accessibility of molybdenum oxides are needed to be controlled. Such active molybdenum species can be prepared by PVD deposition of molybdenum nanorods and their subsequent oxidation in a controlled atmosphere. Accordingly, monoclinic MoO2 particles with a diameter of < 10 nm can be prepared, which exhibit 42% selectivity to propylene oxide (the byproducts of the oxidation being mainly acrolein and acetone). In comparison, molybdenum-containing catalysts prepared by traditional impregnation methods exhibited practically zero epoxidation activity in gas-phase epoxidation of propylene.

► It is possible to prepare molybdenum nanorods by a PVD technique.
► A mild oxidation of Mo nanorods results in the creation of monoclinic MoO2 nanodomains.
► MoO2 nanodomains exhibit an epoxidation activity in the gas phase.
► Bulky MoO2 or other molybdenum oxides lack this epoxidation activity.