(327f) Optimizing Hierarchical Structures of BEA and FAU Type Zeolites By Post-Synthetic Modifications

Hierarchical zeolites have received extensive attention during the past decade for their potential to provide improved catalytic performance in reactions involving bulky molecules. Different approaches have been proposed to engineer different levels of porosity in zeolites. In particular, the top-down route by post-synthetic leaching of zeolites is a convenient and cost-effective approach for the creation of mesoporosity and concurrent preservation of microporosity, which is favorable for commercial zeolite production. It has been demonstrated that hierarchical structures can be obtained by an appropriate treatment in alkaline solutions for MFI type zeolites in a wide range of Si/Al ratios.  In this work, the generation of mesopores in less stable BEA and FAU type zeolites is optimized by a series of different post-synthetic modifications, including traditional and modified alkaline leaching, fluoride etching and sequential fluorination-desilication operation. The material properties of these hierarchical zeolites as characterized by XRD, N₂/Ar physisorption, NH₃-TPD, SEM, TEM and NMR will be discussed. The effectiveness of different treatments as evaluated by comparing product yields, crystallinity, mesopore formation and micropore/acidity preservation under optimized conditions will be presented.