Phenomenological Studies on the Storage and Regeneration Process of NOx Storage Catalysts for Gasoline Lean Burn Applications

Successful system integration of NOx storage catalyst properties into engine management functions implies a profound understanding of the catalyst's performance under transient exhaust gas conditions. During lean operating conditions, this technology achieves a high level of NOx conversion by storing nitrogen oxides reversibly as nitrates. Periodically, the engine control induces a switch to rich, i.e. to reducing conditions, leading to a regeneration of the NOx storage component.

The present paper focuses on the investigations of the NOx storage as well as the regeneration process under the described transient reaction conditions for gasoline lean burn applications. In order to study the influence of NOx mass, of the amount of reduction agent offered and of specific regeneration components, experiments were conducted by means of heated exhaust gas oxygen (HEGO) sensors on a model gas as well as an engine test bench. On the basis of these results a hypothesis, following the concept of the shrinking core model, for the storage and regeneration step was derived. Moreover, the results clearly indicate that an optimized regeneration process as well as a carefully tailored catalyst formulation are important requirements for the effective system implementation of NOx storage catalysts.