The catalytic oxidation of propylene: VI. Mechanistic studies utilizing isotopic tracers

The mechanism of propylene oxidation has been investigated over well-characterized selective oxidation catalysts: Bi2Mo3O12, Bi2MoO6, and Bi3FeMo2O12. Oxygen-18 and deuterated propylene were used as tracers under steady-state reaction conditions over the temperature range 350 to 450 °C. These data indicate that acrolein is formed exclusively via the redox mechanism over the molybdate catalysts and that numerous sublayers of lattice oxygen are involved. Carbon dioxide is formed by the consecutive oxidation of acrolein over Bi2Mo3O12 and Bi2MoO6 and by the consecutive and parallel pathways over Bi3FeMo2O12. The rate-limiting step of acrolein formation is the abstraction of an allylic hydrogen from propylene.