Rapid Aging of Diesel Lean NOx Traps by High-Temperature Thermal Cycling 2007-01-0470
In the present study, a bench-flow reactor is used to perform lean/rich thermal cycling on model “Ba+K” LNT catalysts at temperatures of 700, 800, 900 and 1000°C using simulated diesel exhaust gases. Deterioration of NOx performance is measured and the deactivation mechanisms of thermally-aged “Ba+K” LNTs are identified using characterization techniques such as TEM, XRD and EPMA. Results indicate that the deterioration is minimal at 700 and 800°C, however, at aging temperatures exceeding 800°C the severity of thermal aging depends on aging temperature as well as number of aging cycles. From the characterization studies four deactivation mechanisms have been identified: the loss of dispersion of PGM, NOx storage components and oxygen storage components due to sintering, the reactions between the NOx storage components and other washcoat components to form less efficient NOx storage media, the transformation of gamma-alumina to other forms, and the migration of potassium from the washcoat to the cordierite substrate.