Chapter 9: Reduction of Stored NO_x with CO/H₂ and Hydrocarbons: A Spatial Resolution Analysis¹

Lean NO_x traps (LNT) are multi-function multi-component catalysts which operate in an integral and transient reactor mode to reduce NO_x in the exhaust from diesel or lean-burn gasoline engines. This chapter addresses the regeneration phase of the LNT operation, discussing various types of reductants and reactions involved. We describe how reductants of different reactivity influence catalyst functions, reactions, and overall regeneration efficiency. The presented examples highlight the importance of understanding the spatial and temporal development of key reactions and their interplay to rationalize the global performance of practical LNTs which are generally honeycomb-shaped ceramic monoliths. The emphasis is on explaining global NO_x removal performance (i.e., activity and selectivity) based on the insights gained through spatially resolved techniques, including initial distribution and redistribution of stored NO_x; oxygen storage and reduction; transformation of feed reductants; and formation and utilization of reduction intermediates. Pathways leading to N₂O and NH₃ byproduct formation as well as mitigation strategies are also discussed.