  We present kinetic Monte Carlo simulations exploring the nonequilibrium phase
diagram of a modified Ziff-Gulari-Barshad (ZGB) dynamic lattice-gas model for
the catalytic oxidation of carbon monoxide (CO) on a surface. The modified
model includes the simultaneous presence of contaminants in the gas phase, CO
desorption, CO diffusion, and strong repulsion between adsorbed oxygen (O)
atoms; all of which have been observed in experimental systems. We find that
the strong O-O repulsion produces higher reaction rates, albeit in a reduced
reactive pressure window. In systems with impurities, the CO$_2$ production
rate is greatly reduced, but this effect is mitigated by CO desorption and
diffusion. CO desorption has the effect of widening the reactive pressure
window, while CO diffusion has the effect of increasing the reaction rate. In
some parameter regimes the presence of impurities destroys the discontinuous
transition between the reactive and high CO coverage phases.
