Monte Carlo simulation of hysteresis behaviour of CO oxidation on surfaces

The Monte Carlo method is applied to analyse the hysteresis behaviour of CO oxidation within an idealized model, taking into account adsorption. desorption, reaction and CO diffusion processes. Two cases are considered corresponding to different hierarchies of the process rates: (i) a CO diffusion rate much higher than the reaction rate. which in turn is much higher than adsorption or desorption rates; (ii) a CO diffusion rate comparable with adsorption or desorption rates and much lower than the reaction rate. A hybrid model is used to simulate the fast diffusion case, retaining the stochastic character of all processes on the surface. The standard detailed diffusion idea is incorporated in the low diffusion model. changing the procedure of picking up diffusion candidates. The surface evolution is followed continuously when increasing or decreasing stepwise the CO impingement rate, starting at values outside the reactive region. The influences of the CO desorption and diffusion on the hysteresis characteristics as well as the time sensitivity of the transition point, are discussed. (C) 1997 Elsevier Science B.V.