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

Abstract

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 CC and CO 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.