The NH3-SCR (selective catalytic reduction) reactions were systematically investigated over a commercial copper zeolite catalyst in view of its application to the DeNO(x), aftertreatment of exhaust gases from light- and heavy-duty Diesel engines. Catalytic activity data were collected at high space velocities in both steady state and dynamic runs over the catalyst in the form of powder, in order to derive intrinsic kinetic information in a wide temperature range. Results were also compared to those obtained over a commercial iron zeolite catalyst under similar conditions. With respect to the iron-based catalyst, the copper zeolite system showed a higher ammonia storage capacity, a higher activity in the ammonia oxidation reaction and in the Standard SCR reaction, and its DeNO(x) activity was found less sensitive to the NO2 feed content. As opposite to the iron zeolite, over the copper zeolite no inhibiting effect of ammonia on the Standard SCR reaction was observed, while formation of some N2O was detected even in the absence of NO2 in the gas feed mixture. (C) 2010 Elsevier B.V. All rights reserved.