High-Loading Nickel Phosphide Catalysts Supported on SiO₂-TiO₂ for Hydrodeoxygenation of Guaiacol

High-loading Ni_xP_y catalysts supported on SiO₂-TiO₂ binary oxides with different Si/Ti atomic ratios were prepared by liquid-phase phosphidation using triphenylphosphine (PPh₃) and valued for the hydrodeoxygenation (HDO) of guaiacol. The samples synthesized were characterized by N₂ adsorption, X-ray diffraction (XRD), transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and ammonia temperature-programmed desorption. The XRD and XPS results showed that the Ni₂P/Ni₁₂P₅ mixed phase was formed when SiO₂-TiO₂ binary oxides were employed as supports, whereas only Ni₂P and Ni₁₂P₅ phases were produced on SiO₂ and TiO₂ single oxides, respectively. XPS analysis showed that TiO_2-x species were generated on the surface of the catalyst during the reduction of the precursor, and the electron transfer occurred from TiO_2-x species to the Ni_xP_y surface. TiO_2-x species on the Ni_xP_y surface would contribute to the high HDO activity of guaiacol on Ni_xP_y catalysts because the presence of TiO_2-x species promoted the adsorption of guaiacol and activation of the C-O bond in the guaiacol molecule. HDO reaction of guaiacol on Ni_xP_y catalysts dramatically followed the hydrogenation path owing to the high hydrogenation activity of Ni_xP_y catalysts.