Atomistic and multiscale modeling of CO-oxidation on Pd(1Â 0Â 0) and Rh(1Â 0Â 0): From nanoscale fluctuations to mesoscale reaction fronts

We describe recent developments in realistic multisite lattice-gas modeling of CO-oxidation on the unreconstructed (1 0 0) surfaces of Pd and Rh. Such models must incorporate the following features: multiple adsorption sites for CO; numerous short-ranged repulsive adspecies interactions; very high CO mobility and significant O mobility on the surface; and the appropriate Langmuir-Hinshelwood adsorption-desorption and reaction dynamics and energetics. The preferred binding site for CO depends on the substrate: bridge sites for Pd(1 0 0), and on-top sites for Rh(1 0 0). These models can address fundamental aspects of behavior for extended single-crystal surfaces: ordering and temperature-programmed-desorption for single-adspecies systems; mixed adlayer ordering and reactive steady-states as well as temperature-programmed-reaction for the two-adspecies reaction system. Such modeling is also effective in analyzing fluctuation effects for CO-oxidation in nanoscale systems, e.g., Field-Emitter-Tips or supported nanoclusters. A separate challenge is to incorporate this type of realistic atomistic-level description into a multiscale treatment of mesoscale spatial pattern formation and reaction front propagation where characteristic lengths are on the order of microns. This can be achieved within a heterogeneous coupled lattice-gas (HCLG) simulation approach which also requires as input a precise treatment of chemical diffusion in the mixed interacting adlayer.