Kinetics of Oxidative Dehydrogenation of Propane to Propylene Using Lattice Oxygen of VOX/CaO/γAl2O3 Catalysts

This article presents the kinetics of oxidative dehydrogenation (ODH) of propane to propylene over VOx/ CaO and VOx/CaO-gamma Al2O3 catalysts in the absence of gas phase oxygen. In addition to their catalytic role, the catalysts also serve as the source of lattice oxygen. XRD and temperature -programmed reduction analysis indicate the availability of different types of VOx species on the prepared catalyst surfaces. The presence of CaO influences the formation of VOx species, the reducibility, and the oxygen carrying capacity of the catalysts. All these have a significant influence on propylene selectivity.. The ODH of propane experiments are, conducted in a CREC Riser Simulator under circulating fluidized bed conditions. It is observed than VOx/CaO-gamma Al2O3 displays higher propylene selectivity (94.1%) and lower selectivity of CO2 due to it is moderate active site support interactions. The reaction network and Langmuir Hinshelwood type kinetics model is developed using a wide-ranging set of experiments. The availability of reactive lattice oxygen is expressed by a decay model. Nonlinear regression is employed to estimate activation energies with their respective confidence intervals. The developed model satisfactorily predicted product compositions under various operating conditions. For propylene formation, VOx/CaO-gamma Al2O3 requires lower activation energy (120.3 kJ/mol) than that of VOx/CaO (126.7 kJ/mol). On the contrary, VOx/CaO-gamma Al2O3 needs higher activation energies (55.2 kJ/mol) for undesired CO2 formation as compared to the activation energies for CO2 formation using VOx/CaO catalyst (32.8 kJ/mol). These values are consistent with the product selectivity as observed in the catalyst evaluation experiments.