Differences in the NOx storage-reduction (NSR) behavior of Pt/Ba/CeO2 and Pt/Ba/Al2O3 have been identified and traced to their different chemical and structural properties. The results show that Pt/Ba/CeO2 exhibits inferior NO, storage and, particularly, reduction (regeneration) activity compared to the Al2O3 supported catalyst. The incomplete reduction of the stored NOx-species in Pt/Ba/CeO2 seems to be caused by a faster and more profound reoxidation of Pt particles during the lean period as evidenced by in situ X-ray absorption spectroscopy. Interestingly, the reduction activity could be significantly improved by a pre-reduction step at mild conditions. Exposure of the Pt/Ba/CeO2 catalyst to reducing H-2 atmosphere in the temperature range 300-500 degrees C lead to a moderate increase of Pt particle size which beneficially influenced the regeneration activity. In contrast, pre-reduction at temperatures above 500 degrees C was unfavorable and resulted in a severe decrease of the regeneration activity, probably due to migration of the partially reduced CeO2 onto the surface of Pt particles. (c) 2007 Elsevier B.V. All rights reserved.