(651a) Oxidative Dehydrogenation of Propane Using CO2 over Molybdenum Oxycarbidic Catalysts

Transition metal carbides have been shown to catalyze oxidative dehydrogenation of alkanes using CO₂ as a soft oxidant. In this work, we investigate reactive pathways of propane and CO₂ including oxidative dehydrogenation to form propylene, reforming to form CO, and hydrogenolysis to form C₂ and C₁ hydrocarbons over molybdenum oxycarbidic formulations at ambient pressure and 803 – 843 K. Co-feeds of CO₂ and H₂ can result in an order of magnitude change in steady-state propane dehydrogenation rates at constant propane pressure, and these rate changes are reversible. Product carbon selectivities vary between >95% dehydrogenation, >80% reforming, or >95% hydrogenolysis depending upon reaction conditions and the introduction of co-feeds. CO₂ co-feed can produce alkane-derived CO via a reforming pathway, and excess H₂ can result in methane produced via propane hydrogenolysis. Product selectivities and rates can be rationalized and quantitatively fit using a proposed kinetic model predicated upon surface site interconversion between oxidized or reduced active sites as functions of H₂/CO₂ co-feed partial pressures.