Enhanced stability of Pd-Ni 2 P/SiO 2 catalysts for phenol hydrodeoxygenation in the presence of H 2 O

Abstract This work compares the stability of Ni 2 P/SiO 2 , Pd/SiO 2 and Pd-Ni 2 P/SiO 2 catalysts during phenol hydrodeoxygenation (HDO) in the presence of H 2 O. The Pd-Ni 2 P/SiO 2 catalyst (PNP) was prepared by an in-situ reduction method in which PdCl 2 is added directly to unpassivated Ni 2 P/SiO 2 . A series of physicochemical characterizations, such as X-Ray diffraction, transmission electron microscopy, thermogravimetry, temperature programmed reduction and X-ray photoelectron spectroscopy were used. The results showed that the PNP catalyst has the highest stability among these catalyts. Phenol conversion and cyclohexane selectivity vary from 100.0% to 93.0% and from 94.2% to 83.1%, respectively with 0.1 g catalyst at 2 MPa and 493 K in four reaction cycles. Enhanced stabiltiy is attributed to Pd highly dispersed and strongly interacting with Ni 2 P on the PNP catalyst, resulting in negligible aggregation and loss of metal as well as very low carbon formation over the PNP catalyst. In contrast, the deactivation of Pd/SiO 2 results from aggregation and loss of Pd, while that of Ni 2 P/SiO 2 is due to the loss of phosphorus, phosphide oxidation and carbon deposition in the presence of H 2 O.