New insights into reaction mechanism of selective catalytic ammonia oxidation technology for diesel aftertreatment applications

Mitigation of ammonia slip from SCR system is critical to meeting the evolving NH ₃ emission standards, while achieving maximum NOx conversion efficiency. Ammonia slip catalysts (ASC) are expected to balance high activity, required to oxidize ammonia across a broad range of operating conditions, with high selectivity of converting NH ₃ to N ₂, thus avoiding such undesirable byproducts as NOx or N ₂ O. In this work, new insights into the behavior of an advanced ammonia slip catalyst have been developed by using accelerated progressive catalyst aging as a tool for catalyst property interrogation. The overall behavior was deconstructed to several underlying functions, and referenced to an active but non-selective NH ₃ oxidation function of a diesel oxidation catalyst (DOC) and to the highly selective but minimally active NH ₃ oxidation function of an SCR catalyst. In particular, it was shown that different functions of the ASC degrade independently, resulting in minimal changes to NH ₃ conversion with substantial changes to product selectivity.