MONTE-CARLO SIMULATION OF A SURFACE-REACTION MODEL WITH LOCAL INTERACTION

Influence of the interaction between nearest-neighbor adatoms in a reaction of catalyzed oxidation of carbon monoxide has been studied by Monte Carlo simulation. The transition probabilities are chosen in the Arrhenius form, and the activation energy is divided into two additive terms, corresponding to the action of the substrate and to the interaction between nearest adatoms, respectively. When the interaction makes desorption easier or hinders adsorption the behavior is similar: Three steady state regimes or phases were observed; in the first phase, the surface is poisoned by oxygen; in the second phase there is a reactive steady state in which carbon dioxide is continuously produced, and in the third phase, the surface is poisoned by carbon monoxide. The transition from the O-poisoned phase to the reactive phase is continuous, or second order, and the transition from the reaction to the CO-poisoned phase is first order. The same occurs when the interaction is not considered. The interaction makes the second zone wider, where carbon dioxide is being produced. When the interaction makes easier adsorption or hinders desorption only two phases are observed: In the first phase the surface is poisoned by oxygen and in the second phase it is poisoned by carbon monoxide and the transition from one to another is first order.