In the present paper we extend the exact solution previously obtained for the heterogeneous catalytic reaction 2A + B2 → 2AB on small domains, to arbitrary lattice sizes () and calculate the average number of reactive steps necessary to poison the lattice first, . We determine as a function of through Monte Carlo simulations previously contrasted with the exact solution in lattices. We show that follows a power law with , without appreciable transient behaviors, and a scale factor () dependent on the two parameters of the model, the sticking coefficient probability and the desorption probability . The dependence of on both and is determined.