Synthesis of acidic Al-MCM-48: influence of the Si/Al ratio, degree of the surfactant hydroxyl exchange, and post-treatment in NH 4F solution

Abstract

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 NH 4F solution. The solid structures were analyzed by XRD, N 2 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 AlO 5F species) aluminum for nonfluorinated and fluorinated catalysts, respectively.