In this work, gamma-alumina acidity was modified by adding different boron proportions and used as a support for CoMo and NiMo catalysts. Catalysts were tested in simultaneous reactions of dibenzothiophene (DBT) and o-xylene under typical hydrotreating conditions. It was found that catalysts are able to develop simultaneous hydrodesulfurization (HDS), cracking and isomerization reactions when boron was added to the alumina support. On the other hand, it was also found that capacity of catalysts to develop the C-aromatic-CH3 bond scission directly correlates with total acidity, and this correlation is not dependent upon the active phase (CoMo or NiMo). Activity in HDS is not substantially affected when the boron content in the catalyst is low. In some cases HDS activity is enhanced. It was also shown that it is possible to obtain information concerning the behavior of catalysts for deep HDS of refractory compounds, using simple and not expensive model molecules. (C) 2007 Elsevier B.V. All rights reserved.