Silica-supported nickel phosphide (Ni2P/SiO2) catalysts have been prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), elemental analysis, X-ray photoelectron spectroscopy (XPS), and O-2 chemisorption measurements. Ni2P/SiO2 catalysts were synthesized from oxidic precursors by reduction in either flowing H-2 or a H2S/H-2 mixture. XRD and TEM analysis of a 25 wt% Ni2P/SiO2 catalyst confirmed the presence of Ni2P crystallites dispersed on the surface of the silica support. XPS analysis of a passivated 30 wt% Ni2P/SiO2 catalyst indicated the presence of two kinds of Ni species, as well as phosphide and phosphate species at the catalyst surface. Thiophene hydrodesulfurization (HDS) activities were measured for Ni2P/SiO2 catalysts with a wide range of Ni2P loadings (5-35 wt%) and after different pretreatments. A 30 wt% Ni2P/SiO2 catalyst, when pretreated only by degassing in flowing He, was nearly 15 and 3.5 times more active than sulfided Mo/SiO2 and Ni-Mo/SiO2 catalysts, respectively, after 100 h on-stream. The HDS activities of the Ni2P/SiO2 catalysts correlated well with their O-2 chemisorption capacities, allowing calculation of a turnover frequency of 0.017 +/- 0.002 s(-1). Based on XRD measurements of tested catalysts as well as catalysts subjected to H2S/H-2 treatments at increasing temperatures, silica-supported Ni2P shows excellent stability under HDS conditions. (C) 2003 Elsevier Science (USA). All rights reserved.