A series of phosphorus promoted gamma-Al2O3 Supported NiMo carbide catalysts with 0-4.5 wt.% P, 13 wt.% Mo and 2.5 wt.% Ni were synthesized and characterized by elemental analysis, pulsed CO chemisorption, BET surface area measurement, X-ray diffraction, near-edge X-ray absorption fine structure, DRIFT spectroscopy of CO adsorption and H-2 temperature programmed reduction. X-ray diffraction patterns and CO uptake showed the P addition to NiMo/gamma-Al2O3 carbide, increased the dispersion Of beta-Mo2C particles. DRIFT spectra of adsorbed CO revealed that P addition to NiMo/gamma-Al2O3 carbide catalyst not only increases the dispersion of Ni-Mo carbide phase, but also changes the nature of surface active sites. The hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activities of these P promoted NiMo/gamma-Al2O3 carbide catalysts were performed in trickle bed reactor using light gas oil (LGO) derived from Athabasca bitumen and model feed containing quinoline and dibenzothiophene at industrial conditions. The P added NiMo/gamma-Al2O3 carbide catalysts showed enhanced HDN activity compared to the NiMo/gamma-Al2O3 catalysts with both the feed stocks. The P had almost no influence on the HDS activity of NiMo/gamma-Al2O3 carbide with LGO and dibenzothiophene. P addition to NiMo/gamma-Al2O3 carbide accelerated C-N bond breaking and thus increased the HDN activity. (C) 2007 Elsevier B.V. All rights reserved.