title: High resolution mapping of surface reduction in ceria nanoparticles.
abstract: Surface reduction of ceria nano octahedra with predominant {111} and {100} type surfaces is studied using a combination of aberration-corrected Transmission Electron Microscopy (TEM) and spatially resolved electron energy-loss spectroscopy (EELS) at high energy resolution and atomic spatial resolution. The valency of cerium ions at the surface of the nanoparticles is mapped using the fine structure of the Ce M(4,5) edge as a fingerprint. The valency of the surface cerium ions is found to change from 4+ to 3+ owing to oxygen deficiency (vacancies) close to the surface. The thickness of this Ce(3+) shell is measured using atomic-resolution Scanning Transmission Electron Microscopy (STEM)-EELS mapping over a {111} surface (the predominant facet for this ceria morphology), {111} type surface island steps and {100} terminating planes. For the {111} facets and for {111} surface islands, the reduction shell is found to extend over a single fully reduced surface plane and 1-2 underlying mixed valency planes. For the {100} facets the reduction shell extends over a larger area of 5-6 oxygen vacancy-rich planes. This finding provides a plausible explanation for the higher catalytic activity of the {100} surface facets in ceria.
authors: EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium. stuart.turner@ua.ac.be
authors: Stuart
authors: S
authors: Turner
authors: Sorin
authors: S
authors: Lazar
authors: Bert
authors: B
authors: Freitag
authors: Ricardo
authors: R
authors: Egoavil
authors: Johan
authors: J
authors: Verbeeck
authors: Stijn
authors: S
authors: Put
authors: Yvan
authors: Y
authors: Strauven
authors: Gustaaf
authors: G
authors: Van Tendeloo