Influence of the reduction state in the bulk and at the surface on the behavior of MoO3 catalysts in the reaction of 2-butanol (dehydration versus oxidation) in the presence of oxygen

The reaction of 2-butanol (dehydration to butenes versus total oxidation to CO2 and water) in the presence of oxygen is used as a probe of the influence of the reduction state of MoO3-based catalysts on their behavior. Two different behaviors are revealed depending on the extent of the reduction and on the manner by which this reduction is accommodated by the catalysts. Reduction accommodated through the stabilization of bulk Mo sub-oxide phases is detrimental in terms of exchangeability of oxygen atoms. Such catalysts preferentially promote the dehydration of 2-butanol on Brönsted sites, but do not succeed to oxidize it efficiently. In other words, they do not succeed to transfer oxygen atoms into hydrocarbons through the MVK mechanism. At the opposite, a slight reduction localized at the catalyst surface through the presence of Mo5+ species increases the exchangeability of surface lattice oxygen atoms. This makes the corresponding catalysts highly efficient in the oxidation of 2-butanol, and most generally in oxidation reaction proceeding through the MVK mechanism.