New insights into the performance of ceria–zirconia mixed oxides as soot combustion catalysts. Identification of the role of “active oxygen” production

Soot combustion experiments with O2 and with O2 + NOx mixtures were performed with model and real soot samples and with a Pt-catalyst and several Ce–Zr catalysts. It was demonstrated that all the Ce–Zr catalysts tested are more effective for soot combustion (due to the important production of active oxygen), than the Pt-catalyst is, even though the noble metal yielded the highest NO2 production level. A synergetic effect was observed between the NO2-assisted and active oxygen-assisted soot combustion for the Ce–Zr catalysts studied. The contribution of the active oxygen generated by these mixed oxides to soot combustion, with regard to the NO2-assisted combustion, becomes more important as soot combustion temperature increases (because of the decrease of soot reactivity). The properties of the Ce–Zr catalysts affect significantly their active oxygen production capacities.