Polyhedral CeO2 Nanoparticles: Size-Dependent Geometrical and Electronic Structure

Ceria-based materials have many interesting applications including catalysis, fuel cells, and biology. The size- and shape-dependent changes in the catalytic properties of nanoceria are often attributed to stabilization Ce3+ defects on the nanopartide surface. In this paper, we have performed a systematic analysis of the structure of polyhedral CeO2 nanoparticles of 2-10 nm, under ambient conditions, using a combination of transmission electron microscopy, X-ray diffraction, and X-ray spectroscopy at Ce K- and L-edges. We reveal that under ambient conditions Ce3+ concentration does not depend on the size; however, the unit cell parameter and the pseudo Debye-Waller factors systematically change due to size-dependent surface contribution. The presence of Ce3+ traces relates to the use of Ce3+ precursors during synthesis. Exposure of nanoparticles to an intense beam of X-ray radiation causes reduction of Ce4+ ions, the extent of which is size-dependent.