Silica-supported binary and ternary phosphides, MoP/SiO2, Ni2P/SiO2, and Ni-Mo-P/SiO2 have been prepared and characterized by X-ray diffraction (XRD), BET surface area, CO chemisorption, transmission electron microscopy (TEM), and infrared spectroscopy (IR). The hydrodesulfurization (HDS) activities of dibenzothiophene (DBT) were measured and compared at 593 K and 3.0 MPa for MoP/SiO2, Ni2P/SiO2, and Ni-Mo-P/SiO2 catalysts with different Mo and Ni loadings. The activities of the phosphides follow the order Ni2P/SiO2 > Ni-Mo-P/SiO2 > MOP/SiO2. The Ni sites in the Ni-MO-P/SiO2 catalysts play a major role in the conversion of DBT, and the activity of the catalysts increases with increasing Ni content. This is different from sulfides, nitrides, and carbides, as no synergetic effect is observed between the phosphided Ni and the Mo atoms. The surface of these phosphide catalysts is partially sulfided forming a surface phosphosulfide phase, while the bulk structure of the phosphides is maintained in the HDS reactions. (C) 2004 Elsevier Inc. All rights reserved.