Recent trends in the synthesis of high-silica zeolites

Abstract

Novel zeolites continue to be synthesized using organic structure directing agents in combination with unconventional choices of inorganic conditions. The latter include synthesis in concentrated fluoride media, synthesis in concentrated hydroxide media, synthesis in the presence of germanium, and synthesis with high concentrations of boron. Post-synthetic treatments of germanosilicates with the ADOR method have resulted in fully intact zeolites that cannot be obtained through direct synthesis. Unusual compositions of known frameworks have been obtained through topotactic condensation of layered precursors. Coupled with the appropriate choice of inorganic conditions, the use of new SDA molecules has also produced materials with known frameworks but with amazingly small crystal dimensions that are less than 10 nm. The preparations of once “exotic” materials are now being performed with commercially available or easily prepared organic structure directing agents. In some instances methods have been found to prepare high-silica zeolites from seeded preparations in the absence of an organocation. Methods to target zeolite catalysts for a particular reaction have been realized by identifying structure directing agent molecules that are a mimic of the transition state of the reaction.