The NOx storage-reduction catalysis under oxidizing conditions in the presence of SO2 has been investigated on Pt/Ba/Fe/Al2O3, Pt/Ba/Co/Al2O3, Pt/Ba/Ni/Al2O3, and Pt/Ba/Cu/Al2O3 catalysts compared with Pt/Ba/Al2O3, Pt/Fe/Al2O3, Pt/Co/Al2O3, Pt/Ni/Al2O3, Pt/Cu/Al2O3 and Pt/Al2O3 catalysts. The NOx purification activity of Pt/Ba/Fe/Al2O3 catalyst was the highest of all the catalysts investigated in this paper after an aging treatment. That of the aged Pt/Ba/ColAl(2)O(3) and Pt/Ba/Ni/Al2O3 catalysts was essentially the same as that of the aged Pt/Ba/Al2O3 catalyst, while that of the aged Pt/Ba/Cu/Al2O3 and Pt/Cu/Al2O3 catalysts was substantially lower than the others. The Fe-compound on the aged Pt/Ba/Fe/Al2O3 catalyst has played a role in decreasing the sulfur content on the catalyst after exposure to simulated reducing gas compared with the Pt/Ba/Al2O3 catalyst without the Fe-compound. XRD and EDX show that the Fe-compound inhibits the growth in the size of BaSO4 particles formed on the Pt/Ba/Fe/Al2O3 catalyst under oxidizing conditions in the presence of SO2 and promotes the decomposition of BaSO4 and desorption of the sulfur compound under reducing conditions. (C) 2001 Elsevier Science B.V. All rights reserved.