A carbon black composite (CBC) support was synthesized and activated with HNO3 for three time periods 0.5, 2, 3 h. These samples were impregnated by ammonium heptamolybdate and carburized to prepare the molybdenum carbide active phase. Characterization of the samples by X-ray diffraction, temperature programmed reaction, CO chemisorption and surface area measurements showed that the HNO3 treatment of the carbon increased the dispersion of the active phase. This was clearly evidenced by transmission electron microscopy which showed a corresponding decrease in Mo2C particle size. The kinetic study of the hydrodenitrogenation of indole demonstrated that the catalyst activity was dependent on the active phase dispersion and the global kinetic order were found to vary between zero and one, depending or, the dispersion of the active phase on carbon support. (C) 2004 Elsevier B.V All rights reserved.