The kinetics and the mechanism of the catalytic reduction of nitrogen oxides (NOx) by hydrogen were studied over a modified alumina-based palladium monolith. Nitrogen, nitrous oxide, ammonia, and water were detected as reaction products. Transient experiments yielded information about the surface reaction mechanisms. The dissociation of NO is the crucial step, dominating the overall reaction behaviour and that it depends on temperature and on the partial pressure of H-2. A transient kinetic model based on elementary reaction steps was developed for a stoichiometric mixture of (NO + H-2)/Ar. The model was based on the transient plug flow concept. The parameters of model were determined by regression analysis. The comparison of model simulations with the experimental data revealed that the model was able to describe the transient NO reduction kinetics.