NH₃ formation and utilization in regeneration of Pt/Ba/Al₂O₃ NO_x storage-reduction catalyst with H₂

The nature of H₂ 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 (H₂, NH₃, N₂, NO_x) 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 (H₂), inert product (N₂) 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 N₂ product inside the catalyst, but consumed as aggressively as H₂ reductant along the catalyst. This spatiotemporal NH₃ behavior experimentally confirms that Intermediate-NH₃ regeneration pathway is active. Analysis at 200 and 325 °C indicates equivalent local NO_x storage, H₂ consumption and regeneration effectiveness, but differing NH₃/N₂ ratio, suggesting a temperature-dependence of partitioning between Direct-H₂ 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.