Kinetic model for heterogeneous catalysis: Cluster and percolation properties

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Abstract
A lattice model for heterogeneous catalysis on a flat metal surface (i.e., oxidation of carbon monoxide on platinum) has been investigated in mean field approximation and by Monte Carlo simulations. The cluster structure has been determined as a function of a single parameter YCO, directly related to the partial pressure of the carbon monoxide. At low YCO the surface is covered by a percolating oxygen cluster with small dispersed CO islands. As YCO is increased, the oxygen ceases to percolate. In parallel the CO clusters resp. the clusters of unoccupied sites increase in size and percolate just about when the system gets poisoned by the CO. The structure of the large clusters of all three types can be modeled by correlated percolation. The slowing down of the kinetics near the poisoning transition has been investigated and is shown to be related to the diffusion of clusters of unoccupied sites.