From molecular oxo-hydroxo Ce clusters to crystalline CeO2

Due to their applications in catalysis, energy storage or biomedicine, many studies report synthesis and characterizations of CeO2 NPs and intensively use X-ray sources for characterization. In this study, we report a comprehensive interpretation of X-ray measurements on CeO2 models with atomically resolved structure, namely oxo-hydroxo polynuclear Ce complexes. A set of Ce clusters with growing size (0.6 nm to 1.2 nm) and nuclearity (from 6 to 38 Ce atoms) were synthetized and characterized by single crystal XRD. The samples were then analyzed using HEXS and HERFD technics and compared to larger CeO2 NPs and bulk CeO2. Both spectroscopic methods reveal consistent trends as the particle grows or shrink from the set of molecular Ce-{n} clusters up to bulk CeO2. HEXS reveals a broadening in distribution for the short Ce-oxygen bonds for the small clusters. Concomitantly, the HERFD performed at the Ce LIII edge indicates a gradual splitting of the cerium 5d states as the particles become more CeO2 like. From the crystallographic determination of the clusters structure, atomically resolved Ce LIII edge simulation were undertaken. These simulations allow to isolate structural and electronic properties for individual Ce sites within clusters and evidence the great difference between surface and core Ce atoms. It also shows how a combination of simulations from different sites results in the accurate reproduction of the corresponding experimental data. This approach based on clusters atomic sites was then successfully extended to model larger CeO2 NPs Ce LIII edge HERFD spectra. By linking atomically resolved structures to nanoparticles and bulk material using crystallography, X-ray technics and simulation, this work extends the knowledge on cerium oxide nanomaterial and supports a better understanding and predictability of their crystalline and electronic structure