Valence states of nanocrystalline Ceria under combined effects of hydrogen reduction and particle size.

This study reveals that the Ce4+ to Ce3+ ratio in CeO2 nanoparticles (<20 nm) increases with increasing temperature under a hydrogen atmosphere. Such anomalous behavior is due to the physical effect of nanoparticle sizes on increasing the oxidation state of Ce ions in CeO2, which is stronger than the chemical effect of hydrogen reduction. This discovery offers an effective way to independently control the specific surface area and Ce3+ concentration of CeO2 nanoparticles. [ABSTRACT FROM AUTHOR]