title: Quantitative depth profiling of Ce(3+) in Pt/CeO2 by in situ high-energy XPS in a hydrogen atmosphere.
abstract: The redox property of ceria is a key factor in the catalytic activity of ceria-based catalysts. The oxidation state of well-defined ceria nanocubes in gas environments was analysed in situ by a novel combination of near-ambient pressure X-ray Photoelectron Spectroscopy (XPS) and high-energy XPS at a synchrotron X-ray source. In situ high-energy XPS is a promising new tool to determine the electronic structure of matter under defined conditions. The aim was to quantitatively determine the degree of cerium reduction in a nano-structured ceria-supported platinum catalyst as a function of the gas environment. To obtain a non-destructive depth profile at near-ambient pressure, in situ high-energy XPS analysis was performed by varying the kinetic energy of photoelectrons from 1 to 5 keV, and, thus, the probing depth. In ceria nanocubes doped with platinum, oxygen vacancies formed only in the uppermost layers of ceria in an atmosphere of 1 mbar hydrogen and 403 K. For pristine ceria nanocubes, no change in the cerium oxidation state in various hydrogen or oxygen atmospheres was observed as a function of probing depth. In the absence of platinum, hydrogen does not dissociate and, thus, does not lead to reduction of ceria.
authors.affiliation: Laboratory of Radio- and Environmental Chemistry, Paul Scherrer Institute, Switzerland. markus.ammann@psi.ch.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Kato
authors.forename: Markus
authors.initials: M
authors.lastname: Ammann
authors.forename: Thomas
authors.initials: T
authors.lastname: Huthwelker
authors.forename: Cristina
authors.initials: C
authors.lastname: Paun
authors.forename: Markus
authors.initials: M
authors.lastname: Lampimäki
authors.forename: Ming-Tao
authors.initials: MT
authors.lastname: Lee
authors.forename: Matthäus
authors.initials: M
authors.lastname: Rothensteiner
authors.forename: Jeroen A
authors.initials: JA
authors.lastname: van Bokhoven