The catalytic functionalities of bimetallic Pt-Mo/gamma-Al(2)O(3) catalysts in hydrotreatment were studied by performing simultaneous and independent dibenzothiophene (DBT) hydrodesulfurization (HDS) and naphthalene hydrodearomatization (HDA) reactions as a function of the activating agent and the MoO(3) content. Pt-Mo/gamma-Al(2)O(3) catalysts always displayed a higher selectivity to both the direct route of desulfurization (DDS) of DBT and to HDS over HDA than the one exhibited by conventional CoMo and NiMo/gamma-Al(2)O(3). It was established that for the Pt-Mo catalytic system, the selectivity DDS to the hydrogenation route of desulfurization of DBT can be indirectly described by the selectivity HDS/HDA in simultaneous HDS-HDA catalytic tests. The model of an active phase composed of separated metallic Pt particles, PtSx species, and sulfided Mo which can either act as independent or cooperative active centers seems to be suitable to explain both the observed kinetic trends and the synergy effect between Pt and Mo. (C) 2009 Elsevier Ltd. All rights reserved.