In this paper we consider a modification of Ziff, Gulari and Barshad's
(1986) model of oxidation of carbon monoxide on a catalyst surface in
which the reactants are mobile on the catalyst surface. We find regio
ns in the parameter space in which poisoning occurs (the catalyst surf
ace becomes completely occupied by one type of atom) and another in wh
ich there is a translation invariant stationary distribution in which
the two atoms have positive density. The last result is proved by expl
oiting a connection between the particle system with fast stirring and
a limiting system of reaction diffusion equations.