  We studied in this work a modified version of the Ziff, Gulari and Barshad
(ZGB) model in which the adsorption probabilities of CO and O2 are site
dependent. We employed Monte Carlo simulations to determine the phase diagram
of the model as a function of the partial pressure of CO in the gaseous phase,
and of the relative adsorption probabilities. For the case where there is no
site with affinity only to O2 adsorption, we found that the non physical
O-poisoned state disappears. This feature can not be seen in the usual ZGB
model.
