The nature of H-2 regeneration of a model Pt/Ba/Al2O3 LNT catalyst was investigated with specific focus on intra-catalyst formation and utilization of NH3 and its role in catalyst regeneration. In situ measurements of the transient intra-catalyst species (H-2, NH3, N-2, NOx) distributions at different temperatures were used to detail the reaction evolution along the catalyst axis. Comparison of the species transients identifies unique individual natures for the reductant (H-2), inert product (N-2) and intermediate-reductant product (NH3) which readily explain the conventional effluent species sequence as an integral effect. The data demonstrate that NH3 is created on similar timescales as the N-2 product inside the catalyst, but consumed as aggressively as H-2 reductant along the catalyst. This spatiotemporal NH3 behavior experimentally confirms that Intermediate-NH3 regeneration pathway is active. Analysis at 200 and 325 degrees C indicates equivalent local NOx storage, H-2 consumption and regeneration effectiveness, but differing NH3/N-2 ratio, suggesting a temperature-dependence of partitioning between Direct-H-2 and Intermediate-NH3 regeneration pathways. Further experimental and numerical work is needed to more clearly understand the partitioning between the possible regeneration pathways. Nevertheless, the experimental data show that intermediate NH3 plays a significant role in LNT catalyst regeneration. (C) 2009 Elsevier B.V. All rights reserved.