Rapid Aging of Diesel Lean NOx Traps by High-Temperature Thermal Cycling

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 NO_x 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, NO_x storage components and oxygen storage components due to sintering, the reactions between the NO_x storage components and other washcoat components to form less efficient NO_x storage media, the transformation of gamma-alumina to other forms, and the migration of potassium from the washcoat to the cordierite substrate.