Concentration of surface hydroxyl groups on MCM-41

The type and concentration of hydroxyl groups present on MCM-41 were invest igated by infrared spectroscopy as a function of the Si/Al ratio and the po re size. The purely siliceous samples contained the highest concentrations of weakly acidic silanol groups. On aluminum-containing MCM-41 samples addi tionally Bronsted and strong Lewis acid sites were observed. Their concentr ation increased with increasing aluminum content, while that of the weakly acidic silanol groups decreased. For MCM-41 samples prepared with C(12)TMAB r, 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 spectrosco pic data with the results of a structure simulation revealed that the inter nal surface of MCM-41 is only partially covered with hydroxyl groups. (C) 1 999 Elsevier Science B.V. All rights reserved.