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.
- Carboxylic acid