NO reduction belongs to the most important reactions in environmental and industrial catalysis. In this study the NO reduction accompanied by the simultaneous oxidation of CO over a platinum catalyst is investigated on the basis of ab-initio calculations. The whole reaction cycle is broken up into several reaction steps (CO and NO adsorption, NO dissociation, N-2 desorption, CO oxidation, CO2 desorption). Each of these subprocesses is characterized by calculating transition state, adsorption/activation energy, prefactor, and rate constant, so that finally a consistent picture of the overall reaction on an atomistic scale is obtained. NO dissociation is found to be rate limiting with an activation barrier of EOact0 = 1.21 eV and a prefactor of v = 2.1 . 10(12) ML . s(-1); N-2 desor on is an essentially barrierless process, while the CO oxidation step itself can be described by an activation energy of E-act(0) = 0.83 eV and a prefactor of v = 2.0 . 10(12) ML . s(-1).