A Tunnel Model for Activated Hydrogen Dissociation on Metal Surfaces

Abstract

Activated dissociative adsorption of a hydrogen molecule on metal surfaces is studied in the framework of the precursor mediated dissociation (PMD) mechanism according to which the dissociation proceeds through a molecular-adsorbed state (precursor) which then dissociates to H atoms. The PMD activation energies and rate constants are calculated by considering quantum transitions from various vibration levels of initial state into a continuous manifold of energies of the final dissociated state. The geometric parameters required are taken from the literature for a nickel surface while on other metals the same geometry is assumed to hold but the energies differ. This approach is applied to gain an insight into specific details of the reaction mechanism. The Bronsted–Evans–Polanyi relationship coefficients are obtained and used for prediction of the catalytic reactivity of a wide range of (111) metals and alloys. Hydrogen kinetic isotope effect (KIE) of the reaction on the palladium surface and its temperatu...