Phase transitions in the Ziff-Gulari-Barshad model operating on periodic conditions.

We investigated the dynamical behavior of the Ziff, Gulari, and Barshad model considering the adsorption rates of the carbon monoxide and oxygen molecules on a catalytic surface as a periodic function of time. For a two-dimensional square lattice and using the Monte Carlo simulation method, we found the stationary states of the model for various values of the amplitude and period of oscillation, taking into account different periodic expressions for the adsorption rates. Depending on the values of the parameters of the model, as well as of the form of the periodic adsorption rates, the stationary states can be active or inactive. For each periodic adsorption rate used in this work we determined a phase diagram in the plane amplitude versus period of oscillation. These phase diagrams can exhibit continuous and/or discontinuous lines separating the active phase from the inactive ones, and a nonexpected new discontinuous transition line separating the two absorbing states. Moreover, we also observed that the area of the active phase shows a strong dependence on the way how the periodic adsorption rates are applied on the system, and in specific situations the phase poisoned by oxygen atoms can even disappear.