Non-thermal plasma-assisted NO_x storage and reduction over cobalt-containing LNT catalysts

Based on their high NO oxidation capacity (NOC) and NO_x storage capacity (NSC), cobalt-containing LNT catalysts of the type Co/Ba/Al and Pd/Co/Ba/Al were tested under NO_x storage-reduction (NSR) conditions, as well as in an H₂-plasma assisted NSR process. For comparison purposes, a traditional Pt/Ba/Al catalyst was tested under the same conditions. The Co/Ba/Al catalyst exhibited similar catalytic properties to those of the Pt/Ba/Al catalyst when an H₂-plasma was employed in the rich phase to assist reduction of the stored NO_x. However, the NO_x removal efficiency was greatly depressed by the presence of H₂O and CO₂ in the feed. Notably, the addition of Pd to the Co/Ba/Al sample greatly lessened the inhibiting effects of H₂O and CO₂ on plasma-assisted cycle-averaged NO_x conversion, this being due to the excellent NO_x storage performance of the Pd/Co/Ba/Al sample even in the presence of H₂O and CO₂. The results of the present study show that by combining the high NO_x storage capacity of Pd/Co/Ba/Al in the lean phase with non-thermal plasma-assisted activation of the reductant in the rich phase, high NO_x conversion can be obtained over a broad temperature window of 150-350 °C.