The NOx storage reduction (NSR) process is commonly envisaged for the NOx treatment of exhaust gas from lean-burn engine vehicles. NOx are firstly stored on the catalyst, which is periodically submitted to a reducing mixture for few seconds in order to reduce the stored NOx into N-2. The on-board reducer is coming from the gasoline/diesel fuel and, in fact, the NSR catalyst is submitted to a mixture of hydrocarbons, CO and H-2 with various compositions depending on the lean/rich step. In this study, the influence of each reducer (C3H6, CO and H-2) is evaluated separately, with a special consideration to the N2O selectivity. It is demonstrated that the N2O can be emitted during both lean and rich periods, with varying ratio depending on the considered reducer and the temperature of gas. For instance, at 300 degrees C, a high N2O selectivity is observed when C3H6 is used, and near half of the N2O emission occurs during the storage phase in lean condition. (C) 2012 Elsevier B. V. All rights reserved.