Pattern formation in heterogeneous catalytic reactions with promoters and poisons

Using one of the simplest models of heterogeneous catalytic reactions occurring on a single-crystal surface and including promoters or poisons, we have performed generic Monte Carlo simulations of the growth of islands composed of reactants and promoters or poisons in the case when the lateral interaction between these species is attractive. The results obtained indicate that in reaction with promoters the islands are traveling and their growth is eventually terminated. These two features are rationalized taking into account that the reaction primarily occurs inside islands and under chemically reactive conditions the balance of adsorbate diffusion there and outside islands can hardly be maintained if the islands are frozen or grow asymptotically. In reaction with poison, in contrast, the model predicts asymptotic power-law island-size growth, because in this case the situation inside islands is kinetically stable and accordingly the conditions in the overlayer are close to those occurring during the Ostwald ripening. The growth exponent obtained for this regime, x approximately or equal to 0.25, is however somewhat smaller than that expected for the Ostwald ripening.