The behavior of a series of CeO 2 catalysts in soot combustion reaction was investigated by HRTEM and XPS. It is shown that nanodomains of reduced ceria in the form of Ce 6 O 11 develop during reaction under oxygen-containing atmosphere, supporting the idea that the reaction between CeO 2 and carbon particulate results in the formation of a reduced ceria phase. The fact that oxygen-deficient cerium oxide particles are not in contact with soot, whereas regular CeO 2 particles are also found in contact with particulate, may suggest that reaction with soot implies the extraction of oxygen from the CeO 2 fluorite lattice, confirming the importance of redox mechanism in ceria-catalyzed soot oxidation.