Soot oxidation over NO x storage catalysts: Activity and deactivation

Abstract

Soot oxidation activity and deactivation of NO x storage and reduction (NSR) catalysts containing Pt, K, and Ba supported on Al 2O 3, are studied under a variety of reaction conditions. K-containing catalysts decrease soot oxidation temperature with O 2 alone and the presence of Pt further enhance the activity due to synergetic effect. The active species responsible for synergism on Pt/K–Al 2O 3 are unstable and cannot be regenerated. Soot oxidation temperature decreases by about 150 °C with NO + O 2 exhaust feed gas and under lean conditions NSR system acts as catalysed soot filter (CSF). The reactions that are mainly responsible for decreasing soot oxidation temperature are: (i) soot oxidation with NO 2 followed by NO recycles to NO 2, and (ii) soot oxidation with O 2 assisted by NO 2. Only a part of the stored NO x that is decomposed at high temperatures under lean conditions is found to be useful for soot oxidation. NO x storage capacity of NSR catalysts decreases upon ageing under soot oxidising conditions. This will lead to a decreased soot oxidation activity on stored nitrate decomposition. Pt/K–Al 2O 3 catalyst is more active, but least stable compared with Pt/Ba–Al 2O 3.