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 Onx- species (at least partly O2-) 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.

A CeO2–Ag catalyst with ‘rice-ball’ morphology exhibits exceptional performance for soot oxidation. The moderately large Ag particles (>30 nm) and large interface with small CeO2 particles result in the formation of active oxygen species on the Ag surface and migration to soot particles.Figure optionsDownload high-quality image (442 K)Download as PowerPoint slideHighlights
► A CeO2–Ag catalyst has a unique morphology composed of Ag and CeO2 particles.
► The reaction mechanism for soot oxidation by O2 over this catalyst was studied.
► Active oxygen species for the reaction are formed on the Ag surface.
► They migrate to the CeO2 surface via the Ag/CeO2 interface and onto soot particles.
► The morphology of this catalyst is optimal for their formation and migration.