A kinetic model for propylene oxidation on a mixed metal oxide catalyst

We report a kinetic model that describes in quantitative detail the formation and consumption rates of all C₁–C₆ byproducts in propylene oxidation to acrolein at 623 K on a mixed metal oxide catalyst. The kinetic model highlights the existence of two key surface intermediates, a propylene-derived allyl species and an acrolein-derived ethenyl species, as precursors to all heavy C₄–C₆ products via additive reactions with C[dbnd]C and C[dbnd]O bonds of propylene and oxygen-containing compounds. The model reproduces experimental molar amounts of 19 C₁–C₆ products as well as of propylene, oxygen, and water reactants as a function of propylene conversion assessed in 30 independent experiments. The model is further validated by comparing the model output to the measured isotopic distributions of C₅ products during isotopic tracer experiments with acrylic acid-¹³C₃ as a probe molecule. The surface coverages of relevant species are assessed as a function of propylene conversion to infer the involvement of lattice oxygen, surface hydroxyl, and lattice oxygen vacancies as well as the major and minor pathways for the formation and consumption of the allyl and ethenyl surface species.