M. Tammaro et Jw. Evans, CHEMICAL DIFFUSIVITY AND WAVE-PROPAGATION IN SURFACE-REACTIONS - LATTICE-GAS MODEL MIMICKING COOXIDATION WITH HIGH CO-MOBILITY, The Journal of chemical physics, 108(2), 1998, pp. 762-773
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.