Abstract
Abstract The type and concentration of hydroxyl groups present on MCM-41 were investigated by infrared spectroscopy as a function of the Si/Al ratio and the pore size. The purely siliceous samples contained the highest concentrations of weakly acidic silanol groups. On aluminum-containing MCM-41 samples additionally Bronsted and strong Lewis acid sites were observed. Their concentration increased with increasing aluminum content, while that of the weakly acidic silanol groups decreased. For MCM-41 samples prepared with C 12 TMABr, higher concentrations of weakly acidic hydroxyl groups and strong Lewis acid sites, and lower concentrations of Bronsted acid sites, were observed compared with MCM-41 prepared with C 16 TMABr. Comparison of the spectroscopic data with the results of a structure simulation revealed that the internal surface of MCM-41 is only partially covered with hydroxyl groups.
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