A mechanistic study on soot oxidation over CeO2–Ag catalyst with ‘rice-ball’ morphology

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 O2 below 300 °C. The reaction mechanism over this catalyst was studied by O2 temperature-programmed desorption (O2-TPD), 18O/16O 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 image species (at least partly image) 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.