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

This article presents the kinetics of oxidative dehydrogenation (ODH) of propane to propylene over VO_x/CaO and VO_x/CaO-γAl₂O₃ 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 VO_x species on the prepared catalyst surfaces. The presence of CaO influences the formation of VO_x 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 that VO_x/CaO-γAl₂O₃ 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, VO_x/CaO-γAl₂O₃ requires lower activation energy (120.3 kJ/mol) than that of VO_x/CaO (126.7 kJ/mol). On the contrary, VO_x/CaO-γAl₂O₃ needs higher activation energies (55.2 kJ/mol) for undesired CO₂ formation as compared to the activation energies for CO₂ formation using VO_x/CaO catalyst (32.8 kJ/mol). These values are consistent with the product selectivity as observed in the catalyst evaluation experiments. (Chemical Equation Presented).