Supported transition-metal phosphides (CO2P/SiO2, MOP/SiO2, WP/SiO2, CoMoP/SiO2, and NiMOP/SiO2) were prepared by means of pore-volume impregnation of a silica support. The metal oxide/phosphate precursors were reduced either in pure H-2 or in a flow of 4.8% H-2 in Ar. The materials obtained were characterized by CO chemisorption, powder X-ray diffractometry, and P-31 MAS NMR spectroscopy. The catalysts were tested in the hydrodenitrogenation of o-methylaniline at 643 K and 3 MPa in the presence and absence of H2S. All the materials were active in this reaction, MoP/SiO2 displaying the highest catalytic activity. In the presence of H2S, all the catalysts lost some activity. (C) 2003 Elsevier Inc. All rights reserved.