18O tracer studies of catalytic oxidations of olefin over transition metal or metal oxide catalysts : I. Oxidation of propylene over SnO 2MoO 3 catalyst

Abstract

The route of oxygen incorporation into oxidized products has been studied in the heterogeneous oxidation of propylene by molecular oxygen over stannic oxide combined with molybdenum trioxide in the presence of [ 18O]H 2O tracer. 18O tracer is incorporated into the acetone produced but is not incorporated into the acrolein produced simultaneously with acetone. Incorporation of 18O tracer into the acetone does not depend on the exchange reaction between molecular oxygen and water or the exchange reaction between acetone and water. These results lead to the conclusion that there are two different active species of oxygen on the catalyst surface, one of which is derived from water and the other from molecular oxygen. Oxidation to acetone depends on the interaction with an active species derived from a water molecule, while oxidation to acrolein depends on a species derived from molecular oxygen. The mechanism of acetone formation seems to involve the surface reaction between a carbonium ion and the active species of water to form an alcoholic intermediate.