A new irreversible Monte Carlo simulation model, based upon the reaction of carbon monoxide and oxygen on.a catalytic surface, is presented. Active sites and inactive sites are introduced on a two- dimensional square lattice. Active sites of a certain concentration are distributed randomly over inactive sites, forming the model of two- dimensional lattice of active sites distribution. Diffusion, especially directional diffusion, of the adsorbed particles is taken into account on the basis of ZGB model. Active sites and their nearest-neighbor (nn) sites are assumed as reaction center and the role of inactive sites is to convey substances by diffusion for the reaction. The model reverts to the ZGB model, which includes surface diffusion when the concentration of active sites c_a = 1. In the case that c_a = 1 and only O-diffusion is taken into account (when the probability of O- diffusion reaches 0.3), the simulation results show that the second- order phase transition disappears completely. The formation rate of each site of CO_2 increases continuously with the decreasing of the concentration of active sites (c_a), which shows that the efficiency of the active sites increased.

Key words: DIFFUSION, OXYGEN, CARBON MONOXIDE, CATALYTIC REACTION, MONTECARLO SIMULATIONS, CATALYTIC ACTIVITY