Chapter 5: Mechanism and Kinetics of NOx Storage

Book chapter, 2018

In this chapter, experimental studies and kinetic models are presented to elucidate the fundamental mechanisms for NOxstorage on the NOxstorage and reduction (NSR) catalysts. A well-accepted reaction pathway for NOxstorage includes, as an initial step, the oxidation of NO to NO2under lean conditions, and subsequently storage on the NOxstorage sites in the form of nitrites or nitrates. NO can also be stored directly in the presence of NO and oxygen, in the so-called nitrite route. However, the NOxstorage process is largely influenced by the primary gas components in the exhaust stream, such as CO2, H2O and SO2. In particular, significant attention has been focused on sulphur poisoning and the interaction of SO2with different NSR components due to its large potential of harming NSR catalyst activity. Finally, a kinetic model describing in detail the sulphur poisoning over a commercial LNT catalyst is discussed. The model can well describe the gradual deactivation of the catalyst during sulphur exposure.