The influence of the random sequential adsorption of binary mixtures on the kinetics of hydrocarbon hydrogenation reactions

Abstract

The hydrogenation of unsaturated hydrocarbons by transition metal catalysts demonstrates complex kinetic behavior that cannot be represented by mean-field kinetic models. In this paper, a Monte Carlo model of the Horiuti-Polanyi hydrogenation mechanism is introduced and is applied to the hydrogenation of a number of alkenes of varying chain length. We demonstrate that the origin of this anomalous kinetic behavior can be explained by assuming that the adsorption of the hydrocarbon on the catalyst surface approximates a random sequential adsorption (RSA) process. The model is shown to reproduce the kinetic discontinuities observed experimentally for the hydrogenation of ethene and ethyne. Monte Carlo simulations conducted on square lattices for a number of hydrocarbons indicate that the transition between the two kinetic regimes occurs at the point where the hydrocarbon surface coverage exceeds the dimer jamming limit.