The effect of the intermediate activated carbon covering the alumina carrier on catalytic activity of the supported transition metal sulfides (TMS) prepared from heteropolycompounds (HPCs) in thiophene hydrodesulfurization (HDS), benzene hydrogenation (HYD) and hydrotreating (including HDS of S-containing and HYD of polyaromatic compounds) of diesel oil fractions was investigated. Carbon content on the alumina carrier varied from 0 to 3.8 wt.% It was found that the structure of carbon coating the alumina surface changes depending on the presence/absence of the active phase on the intermediate activated carbon. Total catalytic activity of the catalysts in HDS and HYD reactions was maximal for carbon content of 1-2 wt.% and fell down for catalysts with 3.8 wt% of carbon. The specific catalytic activity grew proportionally to the carbon content on the catalyst. The experimental data showed that a rise of the reaction temperature leads to a decrease in the amount of adsorbed hydrogen whose deficiency limits the formation of H(2)S. It was supposed that the intermediate carbon placed between the alumina carrier and the active phase accumulates hydrogen inside carbon pores. Besides, the intermediate C-carrier of the catalysts synthesized from Co(Ni) salts of heteropolycompounds promotes rising of stacking number in nanoslabs of the active CoMoS phase of the second type. (C) 2009 Elsevier B.V All rights reserved.