The work presents the development of a model for the prediction of oxidation of NO within a diesel oxidation catalyst used in a heavy engine. The model has been calibrated using a stationary data set that varies across the engine map and has been validated through several driving cycles. Two different approaches were studied for the development of the model: one based on conversion tables and the other based on global kinetics. The latter was chosen for its greater precision. The developed model consists of a set of differential-algebraic equation system to predict the evolution of species concentration along the length of the catalyst but, to reduce complexity, the energy balance equation was not considered, instead the measurements of 3 thermocouples were used to estimate the temperature distribution.