title: Direct atomic-scale observation of redox-induced cation dynamics in an oxide-supported monolayer catalyst: WO(x)/alpha-Fe(2)O(3)(0001).
abstract: For the case of one-third of a monolayer of tungsten grown by atomic layer deposition on a hematite alpha-Fe(2)O(3)(0001) surface, we report direct atomic-scale observations of the structural and chemical changes that occur as this model interfacial system evolves from the as-deposited state to the oxidized state, then to the reduced state, and finally back to the oxidized state. In situ X-ray standing-wave atomic images relative to the hematite lattice show dramatic (but redox-reversible) changes to the W cation locations with respect to the occupied and unoccupied Fe surface sites. These structural changes are concurrent with X-ray photoelectron spectroscopy chemical shift changes, where W is observed to go from the 6+ to 5+ oxidation state. These novel observations of redox-induced cation dynamics in an oxide-supported catalyst are explained by models that account for W incorporation at the interface in Fe sites with various coordination schemes. Our proposed structure models are supported by our X-ray absorption fine structure measurements.
authors.affiliation: Department of Materials Science and Engineering, Institute for Catalysis in Energy Processes, and DND-CAT, Synchrotron Research Center, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: Zhenxing
authors.initials: Z
authors.lastname: Feng
authors.forename: Chang-Yong
authors.initials: CY
authors.lastname: Kim
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Elam
authors.forename: Qing
authors.initials: Q
authors.lastname: Ma
authors.forename: Zhan
authors.initials: Z
authors.lastname: Zhang
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Bedzyk