Dehydration, dehydrogenation, and condensation of alcohols on supported oxide catalysts based on cyclic (WO3)3 and (MoO3)3 clusters

Abstract

Supported early transition metal oxides have important applications in numerous catalytic reactions. In this article, we review the synthesis and activity of well-defined model WO₃ and MoO₃ catalysts that are prepared via deposition of cyclic gas-phase (WO₃)₃ and (MoO₃)₃ clusters generated by sublimation of WO₃ and MoO₃ powders. Conversion of small aliphatic alcohols to alkenes, aldehydes/ketones, and ethers is employed to probe the structure–activity relationships on model catalysts ranging from unsupported (WO₃)₃ and (MoO₃)₃ clusters embedded in alcohol matrices, to (WO₃)₃ clusters supported on surfaces of other oxides, and epitaxial and nanoporous WO₃ films. Detailed theoretical calculations reveal the underlying reaction mechanisms and provide insight into the origin of the differences in the WO₃ and MoO₃ reactivity. The catalytic activity for a range of interrogated (WO₃)₃ motifs (from unsupported clusters to nanoporous films) further sheds light onto the role structure and binding of (WO₃)₃ clusters with the support play in determining their catalytic activity.