Verification of framework and extra- framework aluminum species in AlMCM-41

Framework and extra-framework aluminum species in mesoporous aluminum-containing MCM-41 materials was studied by diffuse reflectance spectroscopy (DRS) employing acetylacetone as a probe agent. A room temperature synthesis method was used for preparation of purely siliceous MCM-41 and for aluminum-containing MCM-41 materials. Samples with Si/Al ratios of 50, 20, 10 and 5 were synthesized. The treatment of the as-synthesized and calcined aluminum-containing MCM-41 samples with acetylacetone shows a distinct band at ≈ 290 nm. This band is assigned to six coordinated aluminum atoms in the structure. The 290-nm band is disappeared following the successive ethanol washing of the acatylacetonetreated surfactant-containing samples but its intensity is reduced in acatylacetone-treated calcined samples. The persisted intensity of 290-nm band in the acatylacetone-treated calcined samples after ethanol washing can be assigned to framework aluminum.