Synthesis of acidic Al-MCM-48: influence of the Si/Al ratio, degree of the surfactant hydroxyl exchange, and post-treatment in NH4F solution

Al-MCM-48 mesostructures with different Al contents (Si/Al = 40, 30, and 20) have been prepared with hydroxyl-exchanged cetyl-trimethylammonium bromide as the template and a post-synthesis treatment in NH4F solution. The solid structures were analyzed by XRD, N2 adsorption, DRIFT, SEM, HREM, and 27Al and 29Si MAS NMR. Moreover, surface acidity was determined with the use of pyridine (Py) and 2,6-dimethylpyridine (DMPy) as probe molecules. The catalytic activity of Al-MCM-48 materials in isopropylbenzene dealkylation was compared with those of the microporous H-Y and ZSM-5 zeolites and that of a commercial silica-alumina catalyst (Harshaw, Si235, 13 wt% alumina). For these solids, the catalytic activity was related to the tetrahedral or octahedral (probably AlO5F species) aluminum for nonfluorinated and fluorinated catalysts, respectively.