Hydrodeoxygenation of Anisole over Silica-Supported Ni2P, MoP, and NiMoP Catalysts

Abstract

Ni 2 P/SiO 2, MoP/SiO 2, and NiMoP/SiO 2 with different Ni/Mo molar ratios were prepared by temperature-programmed reduction (TPR). Their structural properties were characterized by N 2 sorption, X-ray diffraction (XRD), CO chemisorption, X-ray photoelectron spectroscopy (XPS), H 2 temperature-programmed desorption (H 2 -TPD), and NH 3 temperature-programmed desorption (NH 3 -TPD). Their performances for the hydrodeoxygenation (HDO) of anisole were tested in a fixed-bed reactor. It was found that there were mainly three reactions that occurred during the HDO, i.e., the demethylation of anisole, the hydrogenolysis of phenol, and the hydrogenation of benzene. The HDO activities decreased in the sequence of Ni 2 P/SiO 2 > NiMoP/SiO 2 > MoP/SiO 2 . The NiMoP/SiO 2 catalysts with larger Ni/Mo ratios had higher activities. In the phosphides, the Ni δ+ and Mo δ+ sites bearing small positive charges acted not only as Lewis acid sites for the demethylation but also as metal sites for the hydrogenolysis and hydrogenation. The Ni δ+ site was more active than the Mo δ+ site, and there was no synergy between the Ni δ+ and Mo δ+ sites. The superior activity of Ni 2 P to that of MoP is attributed to the higher d electron density in Ni 2 P. PO−H groups, which acted as Brønsted sites and provided active hydrogen species, had less activity for the three reactions compared to the metal sites. In comparison to a conventional NiMo/γ-Al 2 O 3 catalyst, the Ni phosphide-containing catalysts had much higher activities. The catalyst deactivation due to water was preliminarily discussed. The oxidation of phosphide by water might lead to the formation of metal oxide and/or phosphate, leading to the catalyst deactivation. The high stability of Ni 2 P/SiO 2 may be related to the ligand effect of P that lowers the electron density of Ni and inhibits the Ni−O combination.