NH3 formation and utilization in regeneration of Pt/Ba/Al2O3 NOx 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, 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 (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 NOx 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.
Journal: Applied Catalysis B: Environmental - Volume 91, Issues 1–2, 7 September 2009, Pages 144–151