Structural and electronic properties of cubic CeO_2: Unpaired electrons in CeO_2

摘要

The high performance of cerium dioxide (CeO_2) as support for Au in catalysis relies on its ability to anchor Au clusters and transfer charge to the gold nanoparticles. These two processes are governed by oxygen vacancy formation. To study the localization and the mobility of the electrons left behind by the vacancy from the relaxed oxygen, an experimental and theoretical study is hereby reported. CeO_2 powder was synthesized by the polyacrylamide gel method and its microstructure wascharacterized by X-ray diffraction and high resolution scanning electron microscopy. We have determined the presence of only the fluorite cubic phase in our samples andthe formation of acicular particles of ～1 μm in length. In the electron spin resonance study, we observed that the unpaired electrons are quasi free. A single-line paramagnetic signal is observed that exhibits spin characteristics with a g-value of 2.0039 at room temperature. This compares well to the value of 2.0023 determined for free electrons. In addition, we have conducted a theoretical study using a density functional theory cluster approach and calculate the electron spin density of CeO_2 clusters. We find that spin density clouds are localized around the cerium ions.