Benzene hydrogenation over supported and unsupported palladium: II. Reaction model

Abstract

A modified Langmuir-Hinshelwood (L-H) model has been proposed to describe benzene hydrogenation over both unsupported Pd and supported Pd catalysts. A general reaction sequence proposing sequential addition of H atoms to the benzene ring, with no a priori assumption of a rate-determining step, was used because computer analysis allowed the determination of selected rate and adsorption constants. To explain the observed kinetic behavior, it was necessary to include an auxiliary reaction—benzene dehydrogenation to various carbonaceous surface species—which inhibits the principal reaction. This model, which quantitatively includes hydrogen-deficient species that inhibit the hydrogenation reaction, satisfactorily explains all results that were obtained in this study and is also consistent with other reports in the literature related to isotopic exchange and deactivation reactions. To further evaluate this model, the values of the fitted parameters were analyzed with regard to their physical significance, and they were found to be consistent and within theoretical guidelines imposed by L-H kinetics.