The ceria-supported rhenium catalyst modified with palladium (ReO x –Pd/CeO2 (Re = 2 wt %, Pd/Re = 0.25)) is still the best catalyst for simultaneous hydrodeoxygenation. Higher Re loading amount decreased the activity. The simultaneous hydrodeoxygenation of cyclic vicinal diols occurs with high cis-stereoselectivity. ReO x –Pd/CeO2 catalysts were characterized by means of XRD, TEM, H2-TPR, XAFS, XPS, Raman, and DFT calculations. The Re species on ReO x –Pd/CeO2 (Re = 2 wt %, Pd/Re = 0.25) catalyst after reduction and after stoichiometric reaction of 1,2-hexanediol to 1-hexene were ReIV and ReVI, and the ReIV species were converted to ReVI through the stoichiometric reaction. The Re species on ReO x –Pd/CeO2 are proposed to be randomly located on the CeO2 surface, and probably only monomeric Re species have catalytic activity for simultaneous hydrodeoxygenation. This model can explain the higher activity of Re = 2 wt % catalyst than those of higher Re loading catalysts. The reaction is proposed to proceed by the tetra/hexavalent redox cycle of the Re center in the catalysis followed by hydrogenation.

Heterogeneous ReO x -Pd/CeO 2 catalyst showed excellent performance for simultaneous hydrodeoxygenation of vicinal OH groups. High yield (> 99 %), turnover frequency (300 h À1 ), and turnover number (10 000) are achieved in the reaction of 1,4-anhydroerythritol to tetrahydrofuran. This catalyst can be applied to sugar alcohols, and mono-alcohols and diols are obtained in high yields (! 85 %) from substrates with even and odd numbers of OH groups, respectively. The high catalytic performance of ReO x -Pd/CeO 2 can be assigned to rhenium species with + 4 or + 5 valence state, and the formation of this species is promoted by H 2 /Pd and the ceria support.

Gold nanoparticle cocatalyst and ceria support catalyst enabled the use of H2 as a reductant for Re-catalyzed deoxydehydration (DODH), converting vicinal diols to olefins with higher activity than homogeneous Re catalysts using non-H2 reductants and with comparable selectivity. The suitable particle size (∼10 nm) of Au in ReO x -Au/CeO2 catalyst was especially effective for activating H2 while retaining the CC bond in DODH products. Glycerol was converted to allyl alcohol in 91% yield, and the TON per Re atom reached 300. This system is applicable to other substrates such as erythritol (81% yield of 1,3-butadiene).

Hydrodeoxygenation of cyclic vicinal diols such as 1,4-anhydroerythritol was conducted over catalysts containing both a noble metal and a group 5-7 transition-metal oxide. The combination of Pd and WOx allowed the removal of one of the two OH groups selectively. 3-Hydroxytetrahydrofuran was obtained from 1,4-anhydroerythritol in 72 and 74% yield over WOx -Pd/C and WOx -Pd/ZrO2 , respectively. The WOx -Pd/ZrO2 catalyst was reusable without significant loss of activity if the catalyst was calcined as a method of regeneration. Characterization of WOx -Pd/C with temperature-programmed reduction, X-ray diffraction, and transmission electron microscopy/energy-dispersive X-ray spectroscopy suggested that Pd metal particles approximately 9 nm in size were formed on amorphous tungsten oxide particles. A reaction mechanism was proposed on the basis of kinetics, reaction results with tungsten oxides under an atmosphere of Ar, and density functional theory calculations. A tetravalent tungsten center (W(IV) ) was formed by reduction of WO3 with the Pd catalyst and H2 , and this center served as the reductant for partial hydrodeoxygenation.

Heterogeneous ReO x -Pd/CeO 2 catalyst showed excellent performance for simultaneous hydrodeoxygenation of vicinal OH groups. High yield (> 99 %), turnover frequency (300 h À1 ), and turnover number (10 000) are achieved in the reaction of 1,4-anhydroerythritol to tetrahydrofuran. This catalyst can be applied to sugar alcohols, and mono-alcohols and diols are obtained in high yields (! 85 %) from substrates with even and odd numbers of OH groups, respectively. The high catalytic performance of ReO x -Pd/CeO 2 can be assigned to rhenium species with + 4 or + 5 valence state, and the formation of this species is promoted by H 2 /Pd and the ceria support.