NOx storage-reduction process was studied using lean/rich cycling condition over Pt/BaO/Al2O3 model catalyst, with a special attention to the ammonia emission. The NOx reduction selectivity strongly depends on the hydrogen conversion introduced during the rich pulses. NH3 is emitted while hydrogen is not fully converted. It was concluded that the NH3 formation rate via the NOx reduction by H-2, is higher than the NH3 reaction rate with NOx to form N-2. The effect of H2O and CO2 on the reduction step was also examined and results were explained mainly taking into account the reverse water gas shift reaction. Fe addition in Pt/BaO/Al2O3 leads to a strong deactivation of the catalyst, probably due to interaction between iron and platinum. Mn is a poison for the reduction step at 200 and 300 degrees C, but it significantly enhances the NOx reduction at 400 degrees C (conversion and selectivity). Mn favors the NOx reduction with ammonia, even if the introduced hydrogen is not fully converted. (C) 2011 Elsevier B.V. All rights reserved.