IN-SITU FTIR STUDY OF THE FORMATION OF MCM-41

The formation of both siliceous and aluminium-containing MCM-41 has be en followed in situ using attenuated total reflectance Fourier-transfo rm infrared (ATR FTIR) spectroscopy together with a range of complemen tary techniques. Key stages in the reaction are reflected by changes i n the intensity of IR bands at 1030 and 1105 cm(-1), which are assigne d to the internal Si-O vibrations of Si(OSi)(3) and Si(OSi)(4) groupin gs (Q(3) and Q(4), respectively). Assignments were confirmed using sol id state NMR. Under the conditions of these experiments, the reaction rate is limited by the relatively slow dissolution of the silica sourc e. The resulting silicate oligomers then react more rapidly with surfa ctant cations in a co-operative assembly process to give the embryonic MCM-41 structure. Slower condensation reactions subsequently increase the product Q(4)/Q(3) ratio as further crosslinking develops. From an analysis of both the CH3 head group and CH2 in-chain IR vibrations, t he surfactant appears to be complexed or micellised at all times durin g the synthesis.