Propene Total Oxidation over Morphologically Diverse Co3O4: A Systematic Characterization and Kinetic Study

Volatile organic compounds (VOCs) have adverse effects on both humans and the environment. Catalytic abatement of VOC emissions is regarded as an efficient solution, and transition metal oxides, like Co3O4, are promising catalysts due to their high activity, abundance and low cost. Previous studies have correlated catalytic activity with the Co3+/Co2+ ratio, absorbed oxygen species and specific exposed facets. However, the reaction mechanism and the active oxygen species remain unclear. This work focuses on propene oxidation over Co3O4 catalysts that were synthesized by four different methods, leading to significant morphological differences. Despite variability in specific surface area, particle size/geometry and population of oxygen species, catalytic experiments showed similar specific rates but different apparent activation energies (Eapp). Propene-TPD/TPSR experiments confirmed the participation of lattice oxygen and indicated that chemisorbed oxygen is used at low reaction temperatures, while lattice oxygen is activated at higher temperatures. Detailed kinetic experiments revealed complex kinetic behavior that can be explained by the simultaneous operation of two pathways: a competitive Langmuir–Hinshelwood (LH) mechanism and a redox, Mars–van Krevelen (MvK) mechanism. Catalytic and kinetic data suggest that any structural differences observed in the prepared catalysts did not affect the intrinsic activity nor the mechanism of propene oxidation.