A Monte Carlo study is made of the reduction reaction of NO by CO over a uniform surface and on disordered substrates, some of them fractals, assuming a Langmuir-Hinshelwood mechanism and using experimental kinetics parameters proposed in the literature in the case of Rh as the catalyst. There is good agreement in the pressure and temperature intervals studied between the simulations and the analytic solutions of the mechanism for a uniform substrate. For nonuniform surfaces, in which the kinetics mechanism cannot be solved, MC simulations were used. The production and surface coverage diagrams and their extreme values are analyzed for the different systems, with a scaling seen for maximum CO2 and N-2 production with the fraction of blocked sites in substrates from percolation clusters. The effect of structural sensitivity, temperature, reaction order, and selectivity for N2O, of special interest for experimental work, was also studied.