(5bf) Surface Chemistry of Oxide Clusters as Model Catalyst

A systematic study on (WO₃)₃ clusters as a model catalyst was performed by the experimental techniques temperature-programmed desorption (TPD) and reflection-absorption infrared spectroscopy (RAIRS), as well as by density functional theory (DFT) calculations. The model catalyst was prepared by deposition of (WO₃)₃ vapor onto the well-characterized oxide surfaces TiO₂(110) and FeO(111)/Pt(111) in ultra-high vacuum.
A series of aliphatic alcohols from methanol
to t-butanol were used to identify various partial oxidation channels
such as dehydration, dehydrogenation, and alcohol condensation. Our results indicate that the active sites
are Lewis acidic tungstyl (W=O) groups where RO-H heterolytically
dissociates into alkoxy (RO-) and hydroxyl (HO-). The alkoxy bound to W⁶⁺ undergoes
further reactions into alkene, aldehyde, and
ether. Dehydration is found to be the
dominant channel for secondary and tertiary alcohols, while the other channels
compete with dehydration in the oxidation of primary alcohols. The reaction
mechanism for each reaction channel is discussed based on DFT
calculations.

The research described in this presentation was performed in
the Environmental Molecular Sciences Laboratory, a national scientific user
facility sponsored by the Department of Energy's Office of Biological and
Environmental Research and located at Pacific Northwest National Laboratory.