TiO₂-Modified Pd/SiO₂ for Catalytic Hydrodeoxygenation of Guaiacol

TiO₂-modified Pd/SiO₂ catalysts (Ti_xPd/SiO₂) have been prepared using wet impregnation and characterized with N₂ adsorption, X-ray diffraction, transmission electron microscopy, and temperature-programmed reduction. Their catalytic performance was examined for hydrodeoxygenation (HDO) of guaiacol as a model component of bio-oil. A smaller Pd particle size was obtained by the addition of TiO₂, which may contribute to the high conversion of guaiacol on Ti_xPd/SiO₂. A strong interaction between TiO₂ and Pd occurred when the catalysts were reduced with H₂ at 500 °C. TiO_x covered on Pd particles can coordinate the oxygen atom in hydrogenation intermediates and activate the C-O bond that could contribute to the significantly enhanced deoxygenation activity. The results suggest that the catalytic HDO proceeds through hydrogenation of the benzene ring of guaiacol on Pd sites to form 2-methoxycyclohexanol, followed by deoxygenation on the sites at a reduced TiO_x-Pd interface to generate cyclohexane.