Dynamics of front propagation in the catalytic CO oxidation on Pt(100)

The dynamics of CO and O chemical fronts propagating through a Pt(100) substrate are simulated using cellular automaton techniques. The cellular automaton accounts for the adsorption of both molecular species CO and O-2 on a platinum substrate, as well as the reaction kinetics between these species and the diffusion of CO on the substrate. The influence of inert sites (defects) is also considered. The chemical front is generated in two different situations: In the first one, the sample is initially covered by CO and the front is generated by depositing a layer of O atoms. The system is then subject to more O-2 molecules which can adsorb and react with the other CO molecules and the interface moves as the reaction proceeds. It is found that the fluctuation of the interface in a clean sample follows the Kardar-Parisi-Zhang equation and, in this case, a microscopic description in terms of a stochastic process is also proposed. In a second situation, the adsorption and diffusion of CO are allowed in addition to the previous reaction mechanisms. In this case, it is found that the growth obeys the scaling relation, w(L, t) similar to L(alpha)f (t/L-z), and our numerical results tend to indicate a continuous dependence of the exponents beta and alpha on the diffusion of CO. The reflecting and diffracting properties of the waves moving in the media with different composition (one part clean and the other containing inert sites) are also investigated herein. The results agree well with the experimental work of Asakura et al. [Surf. Sci. 374, 125 (1997)] and in particular it is found that the chemical concentration waves during heterogeneously catalyzed reactions obey Snell's law. (C) 1999 American Institute of Physics. [S0021-9606(99)70316-8].