COMPETITION EFFECTS IN SURFACE-DIFFUSION CONTROLLED REACTIONS - THEORY AND BROWNIAN DYNAMICS SIMULATIONS

Abstract

Surface diffusion controlled reactions on a heterogeneous catalyst surface comprising randomly placed circular reactive sites are considered. The diffusing species adsorbs onto the surface following Langmuir-Hinshelwood kinetics and reacts instantaneously on contact with a reactive site. Approximate theories are formulated to describe the process for high concentrations of the reactive sites, when competition between the sites is significant, following three different approaches: (i) modification of the single sink theory; (ii) using a cell model; and (iii) using an effective medium theory. The predictions of the theories are compared with the results of multiparticle Brownian dynamics simulations for the overall reaction rate, the bulk concentration of the reactive species, and the ensemble averaged concentration profile around a reactive site. The effective medium theory is found to give the best results among the theories considered, and the predictions are in good agreement with the computational results.