Abstract
The mesoporous molecular sieves Al-MCM-41 with Si/Al ratio equal to 16, was synthesized under hydrothermal conditions using cetyltrimethylammonium bromide (CTMA
+Br
−) as surfactant. The same ratio of Al-MCM-41 materials was impregnated using sulfuric acid, the materials as sulfated Al-MCM-41 (SO
4
2−/Al-MCM-41). The mesoporous materials viz Al-MCM-41 and SO
4
2−/Al-MCM-41 were characterized using several techniques e.g. ICP-AES, Nephelometer, XRD, FT-IR, TG/DTA, N
2-adsorption, solid-state-NMR, SEM and TPD-pyridine. ICP-AES studies indicated the presence of Al in the mesoporous materials. Nephelometer studies indicated the SO
4
2− presence of the SO
4
2−/Al-MCM-41. XRD studies indicated that the calcined materials of Al-MCM-41 and SO
4
2−/Al-MCM-41 had the standard MCM-41 structure. The surface area, pore diameter, pore volume and wall thickness of the mesoporous materials were calculated by BET and BJH equations, respectively. Crystallinity, surface area, pore diameter and pore volume of SO
4
2−/Al-MCM-41 decreased except wall thickness and the expelling aluminum from the Al-MCM-41 framework increased the Lewis acidity. FT-IR studies indicated that Al-ions were incorporated in the hexagonal mesoporous structure of Al-MCM-41 and sulfuric acid was impregnated into hexagonal Al-MCM-41 materials. The thermal stability of as-synthesized Al-MCM-41 materials and SO
4
2−/Al-MCM-41 materials were studied using TG/DTA. The environments of the Al-ions coordinated in the silica matrix were determined by
27Al-MAS-NMR. The morphology of Al-MCM-41 and SO
4
2−/Al-MCM-41 was determined by SEM. The total acidity of Al-MCM-41 and SO
4
2−/Al-MCM-41 materials was determined by TPD-pyridine. The catalytic results were compared with those obtained by using sulfuric acid, amorphous silica–alumina, H-β, USY and H-ZSM-5 zeolites. The SO
4
2−/Al-MCM-41 catalyst exclusively forms the product of dypnone from self-condensation of acetophenone molecules due to higher number of Lewis acid sites and has much higher yields than other catalysts except USY.