Flow reactor experiments were performed to study the effect Of SO2 + O-2 and SO2 + H-2 exposures on the NOx storage performance of Pt/BaO/Al2O3 and BaO/Al2O3 catalysts. In addition, Pt/SiO2 samples were used to study the interaction between Pt and SO2 under the two exposure conditions. For BaO/Al2O3 the two SO2 exposure conditions caused similar deactivation of the NO, storage capacity, whereas for Pt/BaO/Al2O3 the decline in the NOx storage capacity was faster during the SO2 + H-2 exposure than for SO2 + O-2 exposure. The presence of Pt enhances the adsorption Of SO2 for both SO2 exposure conditions. Quantitative analysis of sulfur showed that exposure to SO2 + O-2 caused higher accumulation of sulfur in Pt/BaO/Al2O3 samples in comparison with SO2 + H-2 exposure. Thus there is no correlation between the total amount of adsorbed sulfur in the samples and the reduction of the NOx storage capacity, probably because of the adsorption of sulfur on sites not necessarily important for the NOx storage process. (c) 2005 Elsevier Inc. All rights reserved.