A kinetic model is presented which considers the catalytic reduction of NO to N-2 by hydrocarbons in oxidizing atmosphere (NO-HC-O-2) as the sum of two simultaneous competitive reactions: the red-ox reaction between NO and hydrocarbon (NO-HC) and the hydrocarbon oxidation (O-2-HC). The model is developed for alkenes employed as reductants and noble metal catalysts. The ratio of the kinetic constants of the two reactions can be considered as a selectivity index in evaluating the ability of a catalyst to favor the desired NO reduction with respect to the undesired O-2-HC oxidation.