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During CO-oxidation on Pt(100), CO diffuses in a ‘‘disordered environment’’ produced by a complex pattern of reconstructed and unreconstructed regions of the substrate. Macroscopic diffusion of CO is effectively only possible on percolating 1×1-regions of the substrate. We treat the spatio-temporal behavior observed in this reaction system accounting in the simple way for the percolative nature of CO-diffusion. This is done via incorporation into the reaction-diffusion equations of a suitable chemical diffusion coefficient, exploiting ideas from the theory of transport in disordered media. We use these equations to analyze the propagation of reactive, O-rich pulses into a CO-covered 1×1-background. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

For surface reactions on single-crystal substrates which involve highly mobile adspecies, there is a vast separation in natural time and length scales. Adspecies hop rates can be many orders of magnitude larger than rates for other processes. Strong spatial correlations or ordering can exist on the atomic scale, while spatial pattern formation occurs on a macroscopic scale due to high diffusivity. An efficient analysis of such systems is provided by a ‘‘hybrid treatment’’ which we apply here to the monomer–dimer surface reaction model in the case of coexisting immobile dimer adspecies and highly mobile monomer adspecies. Specifically, we combine a mean-field treatment of the ‘‘randomized’’ mobile adspecies, and a lattice-gas description of the immobile adspecies. Monte Carlo simulations then reveal bistability and ‘‘critical’’ bifurcation phenomena, while precisely accounting for the influence of correlations in the immobile adspecies distribution. A corresponding analysis of the evolution of macroscopic spatial inhomogeneities is achieved through parallel simulation of the distributed macroscopic points with distinct correlated states and adspecies coverages. These simulations are appropriately coupled to describe diffusive mass transport of the mobile adspecies. In this way, we examine for this model the propagation and structure of chemical waves, corresponding to interface between bistable reactive states, and thereby determine the relative stability of these states. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a developed lattice-gas model to describe reactive removal of a preadsorbed, mixed nitrogen oxide + carbon monoxide adlayer covering a platinum(100) surface. Analysis of lattice-gas model behavior; Removal of the adlayer; Provision of rate equation formulation for the initial disperse stage; Development of chemical diffusion treatment.

Analyzes chemical wave propagation in a lattice-gas model for carbon monoxide-oxidation with varying degrees of carbon monoxide-mobility. Role of hydrodynamic reaction-diffusion equation in the carbon monoxide-mobility propagation; Effect of oxygen coverage on the chemical diffusivity of carbon monoxide; Details on the hybrid approach.