Kinetic Model of the Dehydrogenation of Methylcyclohexane over Monometallic and Bimetallic Pt Catalysts

Various kinetic models were developed for methylcyclohexane (MCH) dehydrogenation over supported Pt catalysts. The best fitting mechanistic model is of the non-Langmuirian/noncompetitive Horiuti-Polanyi type. In this model, the Horiuti-Polanyi aromatic hydrogenation mechanism, which assumes an atomic hydrogen addition to aromatics on the catalyst surface, is applied in reverse to MCH dehydrogenation. The model also assumes that hydrogen and MCH molecules adsorb noncompetitively On two different types of sites to accommodate the observed near zero-order dependence of reaction rate on MCH and the negative order dependence upon hydrogen. To account for the increase in the hydrogen inhibition effect with pressure, a non-Langmuirian adsorption isotherm is adopted, which assumes a nonlinear dependency between the adsorption equilibrium constant for hydrogen and the system pressure. The reversible and irreversible deactivation kinetics are satisfactorily included in the kinetic model.