Catalysts for heavy oil hydrocracking require an enhanced mesoporosity (higher pore diameters) and a moderate acidic function (mild acidity) to treat the bulky molecules present in this kind of feedstock and to yield middle distillates (MD). In this work, we have synthesized five different kinds of mesoporous silica based on SBA-15 by modifying some of the variables of their synthesis with the aim at enhancing mesoporosity. NH4F and 1,3,5-trimethylbenzene (TMB) were used to modify the mesostructured arrangement in SBA-15. TMB modified SBA-15 materials exhibited the highest textural properties (2.16 cm(3) g(-1) and 17 nm) in comparison to NH4F modified silica (1.90 cm(3) g(-1) and 10.8 nm) and pristine SBA-15 silica (1.03 cm(3) g(-1) and 12 nm). The acidity of the SBA-15 based materials was modified by a post-synthesis "grafting procedure" to Si/Al molar ratios of 10, 25, and 40. SBA-15 based materials modified with both Al and TMB were used as supports for Fe-W sulfides. These catalysts were tested in the hydrocracking of phenanthrene. In general, all of the catalysts supported on Al-SBA-15 based materials were selective to the ring opening reaction of phenanthrene in contrast to the results obtained over a commercial Ni-Mo/gamma-Al2O3 catalyst. Such trend was associated to the presence of Bronsted acid sites on the surface of the Al modified supports as shown Al-27 MAS NMR analysis. (C) 2015 Elsevier B.V. All rights reserved.