Flow reactor experiments were performed to study the effect of SO 2 +O 2 and SO 2 +H 2 exposures on the NO x storage performance of Pt/BaO/Al 2 O 3 and BaO/Al 2 O 3 catalysts. In addition, Pt/SiO 2 samples were used to study the interaction between Pt and SO 2 under the two exposure conditions. For BaO/Al 2 O 3 the two SO 2 exposure conditions caused similar deactivation of the NO x storage capacity, whereas for Pt/BaO/Al 2 O 3 the decline in the NO x storage capacity was faster during the SO 2 +H 2 exposure than for SO 2 +O 2 exposure. The presence of Pt enhances the adsorption of SO 2 for both SO 2 exposure conditions. Quantitative analysis of sulfur showed that exposure to SO 2 +O 2 caused higher accumulation of sulfur in Pt/BaO/Al 2 O 3 samples in comparison with SO 2 +H 2 exposure. Thus there is no correlation between the total amount of adsorbed sulfur in the samples and the reduction of the NO x storage capacity, probably because of the adsorption of sulfur on sites not necessarily important for the NO x storage process.