Simultaneous removal of soot and NOx over Ir-based catalysts in the presence of oxygen

The potentiality of Ir-based catalysts for the simultaneous removal of soot and NOx in the presence of O2 is investigated by using temperature programmed reaction (TPR) technique. The behaviors of the catalysts for the soot oxidation and the NOx reduction are also separately analyzed. The results show that soot plays an important role on the NOx reduction, the formed NO2 promotes the soot oxidation, and soot and NOx can be removed simultaneously over Ir-based catalysts in the presence of O2. The simultaneous removal paths of soot and NOx over Ir catalyst are proposed that the NO2 formation by the oxidation of NO oxidizes the soot and the CO formation by the soot oxidation reduces NO. Furthermore, the adsorbed-dissociation of NO2 is a path of the NOx reduction. Comparing with Pt catalyst, Ir catalyst is a more effective catalyst for the simultaneous removal of soot and NOx. The Ir contents and support materials have some effects on the catalytic activity and 1 wt.% Ir/ZSM-5 exhibits a high level activity for the simultaneous removal of soot and NOx.