A CeO2-Ag catalyst with a 'rice-ball' morphology, consisting of Ag particles in the center surrounded by fine CeO2 particles, exhibits exceptional catalytic performance for soot oxidation by O-2 below 300 degrees C. The reaction mechanism over this catalyst was studied by O-2 temperature-programmed desorption (O-2-TPD), O-18/O-16 isotopic exchange (IE) reaction, and electron spin resonance (ESR) techniques. It is speculated that adsorbed oxygen species on the Ag surface migrate to the CeO2 surface via the Ag/CeO2 interface to form O-n(x-) species (at least partly O-2(-)) and further migrate onto the soot particles. Due to morphological compatibility of the moderately large Ag particles (ca. 30-40 nm) and the extremely large interfacial area with the CeO2 particles, the formation and migration rates of the oxygen species on the CeO2-Ag catalyst are efficiently promoted, resulting in its distinguished catalytic performance and relative insensitivity to the contact mode of the soot-catalyst mixture. (C) 2011 Elsevier Inc. All rights reserved.