Post-synthesis alumination of SBA-15 in aqueous solution: A versatile tool for the preparation of acidic Al-SBA-15 supports

Al-SBA-15 supports were prepared by post-synthesis alumination in aqueous solution of a pure silica SBA-15 material. The effects of the aluminium concentration [Al], and of the hydrolysis ratio h = [TMAOH]/[Al] on the speciation of aluminium ([Al(H2O)6]3+, [Al13O4(OH)24(H2O)20]7+, aluminium polymers) in the solution were examined. Depending on h and [Al], samples with various Si/Al ratios and acidities were obtained. The effects of h and [Al] on the characteristics of the final material were assigned to the speciation of the aluminium in the alumination solution: a correlation between the species present in solution and the Si/Al ratio in the final materials leads us to propose that [Al13O4(OH)24(H2O)20] is the most reactive and effective species toward grafting on the silica surface.