A series of molybdenum carbides was prepared by the temperature-programmed carburization of MoO3, with pure CH4 or an equimolar mixture of CH4 and H-2. The resulting materials contained only Mo2C in the bulk, but the surface areas and average pore sizes depended on the heating rate and H-2/CH4 ratio employed. In general, the surface area increased with increases in the heating rate and/or H-2/CH4 ratio. The Mo carbides were mesoporous with a small amount of microporosity and the average pore sizes ranged from 27 to 52 Angstrom Oxygen uptakes corresponded to similar to 13% of the Mo on the carbide surface being accessible. The Mo carbides were very active for pyridine hydrodenitrogenation with catalytic properties that were similar to those of Mo nitrides and superior to those of commercial sulfided Co-Mo and Ni-Mo/gamma Al2O3 hydrotreatment catalysts. Pyridine hydroenitrogenation over the Mo carbides appeared to be structure-sensitive as the activity and selectivity varied with changes in the surface area. Selectivities over the carbides were significantly different from those over the Mo nitride and sulfide catalysts. While the Mo carbides produced substantial amounts of cyclopentane, the Mo nitrides and the sulfided catalysts produced mostly pentane with only trace amounts of cyclopentane. These differences have been interpreted in terms of differing bonding geometries for pyridine on the Mo carbides and nitrides.