EXTENDED MEAN FIELD APPROACH TO ANALYZING PATTERN FORMATION IN SURFACE CHEMICAL REACTIONS

EE MOLA, DA KING, IM IRURZUN, M RAFTI, JL VICENTE

SURFACE REVIEW AND LETTERS

World Scientific

Lugar: Singapur; Año: 2004 vol. 11 p. 57 - 70

0218-625X

In this paper we apply a model of surface chemical reactions to describe pattern formation in the CO oxidation on Pt(100). The model is an extended mean field approximation (EMFA), where two coupling processes are included: gas global coupling (to take into account the mass chemical reaction balance) and CO diffusion. The surface is divided into M×M cells; inside each of them the mean field approximation (MFA) is fulfilled. Anisotropic diffusion between nearest neighbor cells and gas coupling among all cells are also allowed. The EMFA goes beyond the traditional reaction–diffusion approaches with Fickian terms, in favor of a more general mass balance equation that consistently incorporates the coupling between CO diffusion and the nonlinear phase transition of the substrate. In this paper we study three different cases: (a) homogeneous coverage oscillations — when CO and O2 partial pressures are kept constant and the whole set of M×M cells have the same value of partial coverages and phase fractions; in this case the system exhibits self-oscillations, such as those experimentally observed; (b) inhomogeneous coverage oscillations — when CO and O2 partial pressures are kept constant and inhomogeneities of coverage are present; the system evolves by CO diffusion between nearest neighbor cells; (c) gas global coupling — when gas global coupling is allowed and inhomogeneities of coverage are present, there are oscillations in the gas phase that follow the surface evolution.