The Protonation of MoO3 during the Partial Oxidation of Alcohols

Atomic force microscopy and X-ray diffraction have been used to characterize the structural evolution of the MoO3(010) surface during gas phase reactions with nitrogen-alcohol (methanol, ethanol, and 2-propanol) mixtures between 200 and 400◦C. Our results demonstrate that MoO3 intercalates H during these reactions (T≥ 300◦C) and that protonation leads to the precipitation of a well known hydrogen molybdenum bronze, HxMoO3, where 0.23≤ x≤ 0.4. The acicular precipitates of HxMoO3 form topotactically and are aligned along the 〈203〉 directions of the MoO3(010) surface plane. Identical HxMoO3 precipitates form when MoO3 (010) surfaces are reacted with atomic H produced by “spill over” from supported Pt particles. The mechanism by which MoO3 oxidizes alcohols, and the potential role of the protonated phase in this reaction, is reexamined in the context of these new observations.