CoMo catalysts supported on sodium-doped amorphous aluminosilicates (ASA) with different Si/(Si + Al) ratios were prepared. The catalytic performance of these catalysts in the HDT of synthetic FCC naphtha was compared with the one of a CoMo catalyst supported on pure alumina, as well as with another one supported on sodium-modified alumina. The catalysts results were also compared with the ones of CoMo catalyst supported on ASA without sodium. The catalysts were characterized by XRF, XRD, Raman, as well as their textural and acid properties. The sodium introduction simultaneously with the variation of the Si/(Si + Al) ratio conducts to obtain a catalyst (15% Si/(Si + Al), 3 wt.% Na) with, on the one hand, an Mo oxide species distribution with an important participation of beta-CoMoO4 crystalline species and, on the other hand, a selective formation of weak Bronsted acid sites. As a consequence of this especial balance between the acid properties and the oxidic Mo-surface-species distribution, this catalyst presented an activity similar to the one of the CoMo/Al2O3, but with improvements in the selectivity to HDS. Additionally, it was also encountered that when CoMo catalysts supported on materials of predominantly acidic nature are used, the linear olefins inhibit more the HDS activity than the branched ones, whereas the contrary effect was encountered when supports of a predominantly basic nature are used. (C) 2012 Elsevier B.V. All rights reserved.