NiW HIDS catalysts supported on alumina-modified SBA-15 were prepared using acidic solutions of ammonium metatungstate and nickel nitrate. Using this method of preparation the integrity of the SBA-15 support was preserved. The results showed that aluminum incorporation into the support framework leads to higher dispersion of the WS2 phase and gives rise to the formation of Bronsted acid sites, which in turn increase the contribution of the isomerization-direct desulfurization (ISOM-DDS) pathway of 4,6-DMDBT HIDS. The higher activity displayed by the Al-modified catalysts in the HDS of 4,6-DMDBT seems to be related to the presence of Bronsted acid sites in the sulfided NiW/Al-SBA15(x) catalysts, to a higher dispersion of the WS2 phase and to the increased number of coordinatively unsaturated sites (CUS) present in the sulfided catalysts. (C) 2009 Elsevier B.V. All rights reserved.