The kinetics of the catalytic reduction of NO by CO on Rh(111) was simulated by using a lattice-gas model and a Monte Carlo algorithm. These simulations were designed to incorporate some new experimental results, which reveal that the formation of a N-NO intermediate is necessary for molecular nitrogen production. The steady-state phase diagram for the overall NO reduction reaction was studied in terms of several parameters representing different reaction schemes. It was found that, under the assumptions made in the model, an Eley-Rideal mechanism which includes a NO(gas)+N(ads)-->N-2(gas)+O(ads) step is absolutely necessary to be able to sustain a steady-state catalytic regime.