Kinetics of coadsorption of dioxygen and ammonia at a Zn(0001) surface: a theoretical model

Abstract

The experimentally observed kinetics of the coadsorption of dioxygen and ammonia at a Zn(0001) surface have been modelled theoretically. The rate-limiting step involves a precursor dioxygen—ammonia surface complex, formed via ammonia and dioxygen surface diffusion. The system of differential equations describing the model provides a solution that is in good agreement with the experimental results when account is taken of the dependence of the enthalpy of ammonia adsorption on the coverage of chemisorbed oxygen O^2–(a). Thermodynamic arguments are shown to account for the observed large increase (ca. 10³) in the probability of dioxygen dissociation during coadsorption, compared with that observed with dioxygen alone. Electrostatic interactions within the precursor {NH₃–O^–₂} zinc complex are suggested to provide a low-energy pathway to the observed chemisorbed products.