Direct synthesis and the morphological control of highly ordered mesoporous A1SBA-15 using urea-tetrachloroaluminate as a novel aluminum source

摘要

The synthesis of A1SBA-15 under mild acidic conditions was performed through adjusting the molar H2O/HCI ratio, which indicates the formation of Si-O-Al linkages that lead to isomorphous substitution of Si~(4+) by some Al~(3+) ions. In this paper, the direct incorporation of Al~(3+) onto a SBA-15 framework in acid mediated synthesis with a nSiA1 molar ratio of 7 was optimized using urea tetrachloroaluminate ionic liquid as a new aluminum source. The hydrothermal temperature was varied from 80 to 140 °C and the samples were denoted as A1SBA-15(UX). The conventional A1SBA-15 also was prepared using direct synthesis [A1SBA-15(D)] and post synthesis [A1SBA-15(P)] aiming to study the influence of aluminum sources and preparation conditions on their structural, textural, and physicochemical properties. The synthesized materials were characterized by N2 physisorption, XRD, FT-IR, Py-FT-IR, NH3-TPD, XRF, HRTEM and SEM. All preparation methods led to the formation of aluminum containing SBA-15 samples with different Si/Al contents. Nevertheless, depending on the preparation methods, the A1SBA-15 samples exhibited different structural, morphology, and surface characteristics, especially in terms of Bronsted and Lewis acid site content. AlSBA-15(U_(100)) had high surface area (813 m~2 g~(-1)) and high acidity. TEM images of synthesized AlSBA-15(U_(100)) showed well-ordered hexagonal arrays of uniform cylindrical channels. The effectiveness of A1SBA-15, as an acid catalyst, was studied for the esterification of acetic acid with butanol and cumene cracking. The high activity of AlSBA-15(U_(100)) is attributed to its good ordered structure and high acidity.