CHEMICAL DIFFUSIVITY AND WAVE-PROPAGATION IN SURFACE-REACTIONS - LATTICE-GAS MODEL MIMICKING COOXIDATION WITH HIGH CO-MOBILITY

We analyze the spatiotemporal behavior in a lattice-gas model for the monomor-dimer reaction on surfaces. This model. which mimics catalytic CO-oxidation, includes a mobile monomer adspecies (representing CO), an immobile dissociatively adsorbed dimer species (representing O), an d a finite reaction rate (for CO2 production). We characterize in deta il the propagation of the chemical wave or reaction front produced whe n the stable reactive steady-state of the model displaces the metastab le. CO-poisoned state, In the regime of high CO-mobility, such propaga tion can be described directly within a ''hydrodynamic'' reaction-diff usion equation formalism. However, we show that the chemical diffusivi ty of CO is dependent on the O coverage, reflecting the percolative na ture of CO-transport through a background of immobile O. We also empha size that gradients in the coverage of immobile O induce a diffusive f lux in the highly mobile CO. These features significantly influence wa ve propagation and reaction front structure. In addition, our analysis accounts for the feature that in this hydrodynamic regime, correlatio ns persist in the distribution of adsorbed immobile O, and that these influence the reaction kinetics, the steady states, and the percolatio n and diffusion properties. To this end, we utilize a ''hybrid'' appro ach which incorporates a mean-field reaction-diffusion treatment of ad sorbed CO, coupled with a lattice-gas treatment of adsorbed O [Tammaro et al., J. Chem. Phys. 103, 10277 (1995)]. (C) 1998 American Institut e of Physics.