Design of microporous materials: A novel generation of solid acids

Abstract

ZSM-5 zeolite materials were synthesized under acidic conditions using a fluoride-mediated route. Our approach consisted in changing the nature of the silica source in the starting synthesis gel via two different pathways: (i) polymeric silica having different surface specific areas (aerosils 130, 200 and 300); and (ii) dissolution-recrystallization of a thin silica upper layer of a silicon carbide substrate. The zeolites were characterized by XRD, SEM, and H/D exchange titration methods. 27Al MAS NMR analysis revealed that all aluminum was present in a tetrahedral coordination, thus being present inside the zeolite framework. A complete self-transformation of aerosils 130, 200 and 300 sources into highly crystalline ZSM-5 material was achieved, thus leading to a star-like morphology for the MFI crystals. Hence, this study reports the first observation of this unusual star-like morphology for zeolite crystals. It is therefore possible to synthesize zeolites having properties tailored at the microscopic level. Finally, these structured materials were both active and selective catalysts in the conversion of methanol-to-gasoline (MTG process). © 2008 Académie des sciences.