Structure and Mechanism of Titania-Supported Platinum–Molybdenum Catalyst for Hydrodeoxygenation of 2-Furancarboxylic Acid to Valeric Acid

Selective hydrodeoxygenation of 2-furancarboxylic acid, which can be a relatively stable platform chemical from hemicellulose, to valeric acid was investigated in detail, and the reaction has been reported to be specifically promoted by supported Pt-MoOx catalysts. The dependence of catalytic performance of Pt-MoOx/TiO2 on loading amounts of Pt and Mo showed that the highest activity is obtained at around Mo ∼ 0.5 wt % when the Pt loading amount is fixed. With enough of the catalyst that can minimize the effect of deactivation, ∼60% yield of valeric acid was obtained over all Pt-MoOx/TiO2 catalysts with Pt ≥ 1 wt % and 0.5 wt % Mo loadings. Characterization results of Pt-MoOx/TiO2 catalysts with XRD and CO adsorption showed that the Pt particles (3–5 nm, depending on Pt loading amount) were not covered with MoOx species, suggesting that MoOx species were mainly located on the TiO2 support surface. Mo K-edge XAFS results suggest that the MoOx species in Pt-MoOx/TiO2 have a Mo(IV) valence state and some of the MoIVOx species have direct bonds with the Pt atom on Pt metal particles. The number of the direct Pt–Mo bonds became smaller after catalytic use, which can be related to the deactivation. Therefore, the Pt–Mo bimetallic site can be the catalytically active site. Based on the solvent effect, reactivity trends of related substrates, and reaction orders in kinetics, a reaction mechanism is proposed where the ring is opened after addition of one hydrogen atom to the 2-position of the furan ring.