Effect of the Coadsorption of CO and O₂ on the Phase Diagram of the Ziff-Gulari-Barshad Model

The effect of the coadsorption of CO and O₂ on the Ziff-Gulari-Barshad surface catalytic reaction system is studied by Monte Carlo simulation. The coadsorption of both species adds an extra reaction step to the classical Ziff-Gulari-Barshad model. It is shown that the second-order phase transition from the reactive state to the O-passivated state in the Ziff-Gulari-Barshad model is eliminated, and the production rate of CO₂ increases linearly along the fraction y_co of CO in gas phase when it is low, in agreement with experimental results. We also find that the increase of the probability of the coadsorption leads to the decrease of the critical value of y_co of the discontinuous phase transition to the CO-passivated state.