Acidic and adsorptive properties of SBA-15 modified by aluminum incorporation

In this work, Al-SBA-15 samples with different Si/Al ratios were synthesized; Al was incorporated in the mesoporous SBA-15 structure either using the direct synthesis method, with tri-block copolymer P123 as surfactant, or by the post-synthesis method. The porous solids were characterized using different techniques, such as: XRD, pore size distribution, 27Al MAS NMR, and XPS. Acidic properties were estimated by adsorption and titration microcalorimetry, respectively. Ammonia and pyridine were used as probe molecules in the first case, while aniline in n-decane was used in the second one. FT-IR of pyridine adsorption and XPS of ammonia adsorption completed the characterization of acid properties. The increase of acidity with the incorporation of aluminum was evidenced; lower Si/Al ratios led to higher acidity of the sample. Microcalorimetry was also used to test the adsorption properties of these mesoporous materials toward pollutants such as methyl ethyl ketone, propionaldehyde and acetonitrile (in gas phase) and nicotine (in aqueous phase). The ketone was better retained in comparison to the other two molecules. Regarding nicotine, its adsorption was strongly influenced by the aluminum content in the solids; the higher the quantity of aluminum, the lower the adsorption of nicotine.