Synthesis, characterization and catalytic evaluation of NiMo HDS catalysts supported on pure and alumina-modified SBA-15 were carried out. For the synthesis of supported-NiMo catalysts, a molybdenum precursor acidic solution and aqueous nickel nitrate solution were used. Mo/SBA-15 catalyst was prepared as reference with an aqueous ammonium heptamolybdate solution. In this case, the support structure is partially destroyed since the heptamolybdate anions react with the pore walls. In contrast, when an acidic solution is used, the formation of a different molybdenum precursor (presumably MoO2Cl2), which does not react easily with silica is favored. The catalytic activity test showed that aluminum incorporation in the support framework enables the 4,6-DMDBT HDS reaction mainly by direct desulfurization pathway, probably due to previous isomerization of the molecule by Al-SBA-15 (x) acid sites. (C) 2007 Elsevier B.V. All rights reserved.