(184g) Surface Chemistry of Alcohols Over WO3-Based Model Catalysts

Catalytic reactions of
alcohols (ROH) over WO₃ model catalysts were studied by the
experimental techniques temperature-programmed desorption (TPD) and
reflection-absorption infrared spectroscopy (RAIRS), as well as by density
functional theory (DFT) calculations. The WO₃ model catalysts were prepared by deposition of WO₃
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.