CHEMICAL DIFFUSION IN MIXED ADLAYERS AND WAVE-PROPAGATION IN SURFACE-REACTIONS

Spatial pattern formation and wave propagation in surface reactions ar e often controlled by the chemical diffusion of adsorbed reactant spec ies in mixed adlayers. We characterize the intrinsically coverage-depe ndent and tensorial nature of such diffusion, emphasizing that these f eatures result from the influence of site-blocking by coadsorbed speci es, even in the absence of other interactions. The coverage dependence is shown to depend on the relative hop rates of the various reactants . These features are also shown to significantly influence the spatiot emporal behavior in simple, atomistic lattice-gas models of surface re actions. This is illustrated with two examples: trigger wave propagati on in a bistable system characteristic of CO oxidation, and the remova l of unstable NO+CO adlayers, controlled by dissociation-mediated NO r eduction. (C) 1998 Elsevier Science B.V.