Selective hydrodeoxygenation of cyclic vicinal diols to cyclic alcohols over tungsten oxide-palladium catalysts

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 WO_x 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 WO _x-Pd/C and WO_x-Pd/ZrO₂, respectively. The WO_x-Pd/ZrO₂ catalyst was reusable without significant loss of activity if the catalyst was calcined as a method of regeneration. Characterization of WO_x-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.