Catalysts Transform While Molecules React: An Atomic-Scale View.
We explore how the atomic-scale structural and chemical properties of an oxide-supported monolayer (ML) catalyst are related to catalytic behavior. This case study is for vanadium oxide deposited on a rutile α-TiO2(110) single-crystal surface by atomic layer deposition (ALD) undergoing a redox reaction cycle in the oxidative dehydrogenation (ODH) of cyclohexane. For measurements that require a greater effective surface area, we include a comparative set of ALD-processed rutile powder samples. In situ single-crystal X-ray standing wave (XSW) analysis shows a reversible vanadium oxide structural change through the redox cycle. Ex situ X-ray photoelectron spectroscopy (XPS) shows that V cations are 5+ in the oxidized state and primarily 4+ in the reduced state for both the (110) single-crystal surface and the multifaceted surfaces of the powder sample. In situ diffuse reflectance infrared Fourier transform spectroscopy, which could only achieve a measurable signal level from the powder sample, indicates that these structural and chemical state changes are associated with the change of the V═O vanadyl group. Catalytic tests on the powder-supported VOx revealed benzene as the major product. This study not only provides atomic-scale models for cyclohexane molecules interacting with V sites on the rutile surface but also demonstrates a general strategy for linking the processing, structure, properties, and performance of oxide-supported catalysts.
‡Electrochemical Energy Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Zhenxing
Z
Feng
§Energy Systems Division, Argonne National Laboratory, Argonne, Illinois 60439, United States.
Junling
J
Lu
§Energy Systems Division, Argonne National Laboratory, Argonne, Illinois 60439, United States.
Hao
H
Feng
Peter C
PC
Stair
§Energy Systems Division, Argonne National Laboratory, Argonne, Illinois 60439, United States.
Jeffrey W
JW
Elam
Michael J
MJ
Bedzyk
X-ray standing wave; atomic-layer deposition; infrared spectroscopy; oxidative dehydrogenation; redox activity; titanium dioxide; vanadium oxide