Microstructure of silica monolayer solid acid catalysts determined by 29Si NMR spectroscopy

Abstract

The nuclear magnetic resonance (NMR) of 29Si showed that the silica monolayer, which was prepared by chemical vapor deposition (CVD) of Si(OCH3)4 at 593 K on alumina, mainly consisted of Si(OAl)1(OSi)3 and Si(OAl)1(OSi)2(OH)1 species, in agreement with the mechanism of formation of monolayer. The Bronsted acid site is suggested to be the latter species. On the other hand, such an isolated species as Si(OAl)3(OH)1 was formed from Si(OCH3)(CH3)3. Lack of acidity on this species indicates that the acidity requires the siloxane network.