A systematic isotopic study over Pt/BaO/Al2O3 powder catalyst was carried out using temporal analysis of products (TAP) to elucidate the role of the Pt/BaO interface and spillover processes during NOX storage and reduction. The sequential pre-nitration of Pt/BaO/Al2O3 using NO and (NO)-N-15 followed by reduction with H-2 results in the preferential evolution of N-15-containing species during initial H-2 pulses. The evolution shifts toward unlabeled N-containing species in later H-2 pulses. The data suggest that NOX storage proceeds radially outward from the Pt crystallites and that some mobility of the stored NOX species exists. The evolution of N-2 and (NN)-N-15 during (NO)-N-15-H-2 pump-probe on a pre-nitrated (using unlabeled NO) catalyst confirms the involvement of spillover processes at the Pt/BaO interface. The evolution of nitrogen takes place by NO decomposition as well as by the reaction of stored NOX with H-2 to form adsorbed N and eventually N-2. A significant fraction of N-2 is also produced via NH3 serving as an intermediate. The results suggest that the local gradients at the Pt/BaO interface in the stored NOX are important and that these should be taken into account in NSR catalyst design and modeling. (C) 2009 Elsevier Inc. All rights reserved.