A series of molybdenum phosphide catalysts with initial Mo/P ratios varying in a narrow range of 0.90-1.10 was prepared by temperature-programmed reaction; characterized by X-ray diffraction, BET, elemental analysis, X-ray photoelectron spectroscopy, and CO chemisorption measurements; and tested for the hydrogenation of acetonitrile at different pressures (0.1-1.0 MPa) and temperatures (473-513 K). The catalysts exhibited attractive catalytic activity, especially at a H-2 pressure above 0.2 MPa. The surface composition of the MoP catalysts could be fine-tuned by the initial Mo/P ratio, which consequently led to different surface properties (e.g., CO uptakes) and catalytic behaviors. Catalysts with high initial Mo amount gave high selectivity to the primary amine, ethylamine, whereas those with high initial P amount created more condensed amines, diethylamine and triethylamine. (C) 2007 Elsevier Inc. All rights reserved.