Oxidative dehydrogenation of propane over VMgO: kinetic investigation by nonlinear regression analysis

Abstract

The reaction kinetics of the oxidative dehydrogenation of propane over VMgO was investigated by nonlinear regression techniques. Data were collected by performing a factorial design of experiments about a set of standard reaction conditions. In the power law models examined, the reaction rates had a higher dependence on the hydrocarbon gas phase partial pressures than on that of oxygen, suggesting the catalyst was more nearly fully oxidized or saturated with surface oxygen. Gas phase reactions were considered not to occur to any significant extent. By examination of various mechanistic models, we propose a general model based on the following observations. Propane was found to react with surface oxygen species to form adsorbed propene that can subsequently desorb to the gas phase. Adsorbed propene can be further oxidized to carbon oxides. The oxygen surface concentration could not be described as being in equilibrium with the gas phase, models in which oxygen reacted, to reoxidize the catalyst fit the data better. It was further found that the selectivity of the catalyst may be affected by previous conditions to which the catalyst was exposed. Exposing the catalyst initially to oxidizing conditions may reduce its selectivity for propene.