Impact of Thermal and Engine Ageing on a Fully Formulated Lean NO _x Trap

Comparative study of impact of thermal aging on both surface morphology and catalyst performances was performed over fully formulated commercial lean NO_x Trap using hydrothermal (oven) and engine aging for 5 hours at 750°C and 5 hr at 800°C. Investigations show that engine aging lead to more important degradation than hydrothermal aging because of the greater structural degradations that happened after engine aging: sintering of Pt particles, reaction of support (γAl₂O₃) with the storage material and a higher drop of surface area. It follows a decrease of oxidation and storage efficiency particularly after engine aging. During lean rich cycle environment, the rich step was not efficient to remove all the stored NO_x due to storage on Ba-Bulk sites leading to accumulation of NO_x after each cycle. The observed trend after engine aging was attributed to the presence of sulfur and mainly to soot as engine aging was performed with low concentration of sulfur in fuel. Presence of soot could have an inhibiting effect on NO_x storage capacity leading to a decrease of NO_x storage capacity due to adsorption over Ba sites of the CO₂ produced by soot oxidation with formation of BaCO₃. Additionally, outlet channels are not able to compensate the NO_x storage loss due to the soot deposit in inlet channels.