Direct atomic-scale observation of redox-induced cation dynamics in an oxide-supported monolayer catalyst: WO(x)/alpha-Fe(2)O(3)(0001).
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.
Feng
Zhenxing
Z
Department of Materials Science and Engineering, Institute for Catalysis in Energy Processes, and DND-CAT, Synchrotron Research Center, Northwestern University, Evanston, Illinois 60208, USA.
Kim
Chang-Yong
CY
Elam
Jeffrey W
JW
Ma
Qing
Q
Zhang
Zhan
Z
Bedzyk
Michael J
MJ