Hysteresis phenomena in CO catalytic oxidation system in the presence of inhomogeneities of the catalyst surface.

Abstract

The hysteresis phenomena in the CO catalytic oxidation system are studied by Monte Carlo simulation in the presence of the inhomogeneities of the catalyst surface. We show that the O-passivated state is destroyed due to the inhomogeneities of the surface, in contrast to the classical Ziff-Gulari-Barshad model. The defects on the surface have a significant effect on the hysteresis transition points. Most importantly, the supercritical nucleation and growth of the O adatom island during the transition from a low reactivity to a high reactivity states are closely related to the inhomogeneities of the catalyst surface. It is shown that the width of the hysteresis loop shrinks as the scan rate beta(CO) of y(CO) (the fraction of CO in gas phase) decreases, but there exists a finite width of the hysteresis loop even if beta(CO) becomes infinitely small. On the other hand, the width of the hysteresis loop decreases with decreasing the diffusion rate, and even the hysteresis loop may disappear for a slow diffusion. These simulation results are in good consistency with the previous relevant experimental results.