Selective Reduction of Carboxylic Acids to Aldehydes with Promoted MoO3 Catalysts

Selective activation of renewable carboxylic acids onpromoted molybdenum oxides to form alcohols and aldehydes is reported.A combination of reaction kinetics, temperature-programmed reduction(TPR), and X-ray photoelectron spectroscopy (XPS) reveals that theactivity scales with the concentration of Mo5+active sites and is a strongfunction of surface hydrogen coverage. The addition of a very small loading(0.05 wt %) of Pt drastically increases rates of selective deoxygenation atlower temperatures (<350 degrees C) but diminishes rates at elevatedtemperatures due to over-reduction of the support. Here, it is reportedthat the incorporation of Pt clusters on MoO3decreases the apparentactivation barrier for acid conversion by over 32 kJ/mol, which highlightsthe significant role of site regeneration facilitated by hydrogen splitting andspillover. Ourfindings suggest that the rate-determining step for convertingpentanoic acid shifts upon introducing Pt clusters from formation/regeneration of oxygen vacancies to H addition to the carbonyl carbon.