A set of catalysts was prepared to improve the activity of the Ba-Pt/gamma Al2O3 catalyst in the NOx storage reduction (NSR), by replacing Ba with Mg or Ca, but maintaining constant the moles of alkaline-earth element in order to keep the number of storage sites constant. The catalysts were prepared by impregnating first 1.0 wt.% Pt and then the alkaline-earth cations (Ca, Mg and/or Ba) on a commercial gamma Al2O3 (Sasol, D). Tests were carried out in a wide temperature range (100-500 degrees C), thus evidencing the specific role of each different alkaline-earth element. Both the activity and the resistance to SO2 poisoning in the catalysts were different and the alkaline-earth cation with lower electronegativity registered the strongest deactivation. A new catalyst with high activity and resistance to deactivation by SO2 was obtained by co-impregnating Ba and Mg on gamma Al2O3 (1.5Mg8.5Ba-1Pt/gamma Al2O3). (c) 2006 Elsevier B.V. All rights reserved.