Soot combustion experiments with O(2) and with O(2) + 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 NO(2) production level. A synergetic effect was observed between the NO(2)-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 NO(2)-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. (C) 2010 Elsevier B.V. All rights reserved.