Gas phase hydrogenation of o- and p-xylene on NiAl2O3 — Kinetic modelling Original Research Article

A mechanistic rate model was developed to describe the gas phase hydrogenation kinetics of o-xylene and p-xylene on a NiAl2O3 catalyst at temperatures between 403 and 493 K. The mechanistic scheme comprises consecutive and pairwise hydrogen addition steps to the aromatic molecules adsorbed on the catalyst surface. Competitive as well as non-competitive quasi-equilibrated adsorption of the reactants were accounted for. An experimentally observed cyclic olefin is assumed to be the key intermediate, determining the stereoselectivity of the main products (cis- and trans-dimethylcyclohexanes) by its adsorption properties. All the main features of the observed reaction kinetics, including a rate maximum in the overall rate as a function of temperature as well as the production rates of the main products and the intermediate cyclic olefin, were satisfactorily predicted by the rate model. The calculated model parameters were consistent with thermodynamics and previously reported parameters for elementary steps.