The behavior of a series of CeO2 catalysts in soot combustion reaction was investigated by HRTEM and XPS. It is shown that nanodomains of reduced ceria in the form of Ce6O11 develop during reaction under oxygen-containing atmosphere, supporting the idea that the reaction between CeO2 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 CeO2 particles are also found in contact with particulate, may suggest that reaction with soot implies the extraction of oxygen from the CeO2 fluorite lattice, confirming the importance of redox mechanism in ceria-catalyzed soot oxidation.