Detailed Kinetic Modeling Study of NOx Oxidation and Storage and Their Interactions over Pt/Ba/Al₂O₃ Monolith Catalysts

Abstract

The concept of nitrogen oxide storage-reduction (NSR) is a promising aftertreatment technology for reducing NOx emissions from lean-burn engine exhaust. The present work focuses on the first two steps of the overall NSR mechanism, namely, NO to NO2 oxidation and NOx storage. The governing storage mechanisms are mainly elucidated on the model catalysts such as Pt/Ba/Al2O3. A unique detailed NO oxidation kinetic model over Pt/Al2O3 was conceived based on literature data and validated over a wide range of experimental conditions. This detailed mechanism was then globalized to obtain a Langmuir−Hinshelwood rate expression, which resulted in a reduced CPU cost in reactor computations. The global oxidation model predicts various experimental NO and NO2 profiles well. Further, a detailed kinetic model for NOx storage over Ba/Al2O3 was developed and validated against different experimental data. Finally, the detailed oxidation and storage schemes were successfully coupled and species spillover between the noble metal and the storage material was accounted for. The experimental NO and NO2 profiles obtained from the NOx storage experiments over Pt/Ba/Al2O3 could be reproduced by the detailed coupled model. Reaction pathway analyses and sensitivity studies were performed to provide a more comprehensive insight into the system behavior.