NiMo/(X)SiO2-Al2O3 catalysts were synthesized with various SiO2 contents (X = 0, 10, 25 and 50 wt%) using the pH-swing method. In order to find the Optimum SiO2 content, the catalysts were evaluated in the hydrodesulfurization of 4,6-DMDBT, hydrogenation of naphthalene and hydrodenitrogenation of carbazole. Kinetic parameters of Langmuir-Hinshelwood type equations for all the reaction systems were estimated. FTIR analysis of CO adsorption for the sulfided catalysts shows that the amount of coordinatively unsaturated Mo sites promoted by nickel (CUS-NiMoS) follows the order NiMo/10ASA > NiMo/25ASA > NiMo/OASA. This tendency agrees with the results obtained in catalytic activity. (C) 2007 Elsevier B.V. All rights reserved.