A simple lattice gas model for the reaction of CO and NO on an Na modified surface of a square lattice is studied using Monte Carlo Simulation technique. The crucial property of the model is Na-induced dissociation of NO, which triggers the catalytic reaction. Some interesting features are added to the phase diagram when the range of Na-induced NO dissociation is studied in the nearest and next nearest neighborhood. The moment CO partial pressure departs from zero, the continuous production of CO2 and N2 starts. This production remains continuous until a point where the catalytic activity stops and the surface is poisoned with a combination of CO, N and O. The value of poisoning point depends upon the value of Na concentration on the surface. Model of the simulation and method is described in easy way to implement it and can be compared with the given results which become the basic tool for simulation of catalytic reactions.