Catalytic Hydrodeoxygenation of Guaiacol over Palladium Catalyst on Different Titania Supports

Pd catalysts supported on TiO 2 with different crystalline phases were prepared with formaldehyde as reducing agent and examined for hydrodeoxygenation (HDO) of guaiacol. Their properties were characterized by N 2 adsorption, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Compared to the carbon-supported Pd catalysts, TiO 2 -supported Pd catalysts exhibited higher C–O bond scission ability, which may be attributed to the presence of partially reduced titanium species originating from the reduction of Ti 4+ by spillover hydrogen from Pd at 200 °C on the surface of TiO 2 . Guaiacol was hydrogenated on Pd sites to give 2-methoxycyclohexanol, which diffused to partially reduced titanium species and subsequently reacted with hydrogen from Pd to generate cyclohexane. Anatase TiO 2 -supported Pd catalyst gave the highest HDO activity of guaiacol among the Pd catalysts supported on three types of TiO 2 (anatase, rutile, and their mix, P25), suggesting that more partially reduced titanium species are in favor of the HDO reaction because anatase is facile to reduce by H 2 at 200 °C. Higher selectivity of cyclohexane for Pd/TiO 2 reduced at 500 °C than that reduced at 200 °C further confirmed that the enhanced C–O bond scission ability of Pd/TiO 2 is mainly attributed to the partially reduced titanium species on the surface of TiO 2 .