Comprehensive Study of Surface Chemistry of MCM-41 Using²⁹Si CP/MAS NMR, FTIR, Pyridine-TPD, and TGA

Abstract

A comprehensive study was conducted on mesoporous MCM-41. Spectroscopic examinations demonstrated that three types of silanol groups, i.e., single, (SiO) 3 Si−OH, hydrogen-bonded, (SiO) 3 Si−OH-OH−Si(SiO) 3, and geminal, (SiO) 2 Si(OH) 2, can be observed. The number of silanol groups/nm 2, α OH, as determined by NMR, varies between 2.5 and 3.0 depending on the template-removal methods. All these silanol groups were found to be the active sites for adsorption of pyridine with desorption energies of 91.4 and 52.2 kJ mol -1, respectively. However, only free silanol groups (involving single and geminal silanols) are highly accessible to the silylating agent, chlorotrimethylsilane. Silylation can modify both the physical and chemical properties of MCM-41.