Concentration of Ce3+ and oxygen vacancies in cerium oxide nanoparticles

Temperature variations of the electron magnetic resonance (EMR) spectra and magnetization measurements are used to show that Ce3+ ions in concentration similar or equal to 18% are present in 3 nm CeO2 nanoparticles supported on silica aerogel. It is argued that the presence of Ce3+ implies the defect structure CeO2-x for ceria nanoparticles due to oxygen vacancies. This transformation of Ce4+ to Ce3+ driven by oxygen vacancies may be the key to understanding the catalytic properties of ceria.