The influence of the heating rate on the degree of sulfidation and hydrodesulfurization activity of NiMo/SiO2/Al2O3 catalysts prepared with and without citric acid was analyzed. The temperature programmed sulfidation patterns of the catalysts were obtained by following the consumption of H2S at different rates of heating (1, 3 and 10 K/min). The resulting dispersion of MoS2 crystallites was observed by transmission electron microscopy, and the reducibility of the different metal species was analyzed by temperature programmed experiments. The results of catalytic activity during the HDS of 4,6-dimethyldibenzothiophene show that the use of a slow rate of heating during sulfidation (1 K/min) can increase twice the activity compared to a fast heating rate (10 K/min). The use of citric acid during catalyst preparation produces smaller MoS2 crystallites without altering the stacking, and a greater number of promoted sites, detected by FT-IR of adsorbed CO. The temperature programmed reduction of the NiMo catalyst with citric acid showed the formation of a Mo-citrate complex. (C) 2014 Elsevier B.V. All rights reserved.