On Three-Fold Coordinated Si Sites in Mesoporous MCM-41 Catalysts

Abstract

Si-NMR, gas adsorption and SAXS results are discussed to determine if the geometry and the electronic properties of Si sites, present in the MCM-41walls, are more similar to three- than to four-fold coordinated sites. The features of Si-MCM-41, SBA-15, Y zeolite and silica (SiO2), characterized by several techniques, are compared. It is shown that the pre-polymer geometries are similar to those of the zeolite secondary building units, but, in the organization-polymerization step, the generation of partially saturated or quite stressed structures is favored.