Influences of alkali metal fluoride and Si/Al ratio on preparation aluminum-rich ZSM-5 zeolite membrane without organic template

Abstract

Aluminum-rich ZSM-5 zeolite membranes are prepared on α-alumina support through organic template free precursor gels by secondary hydrothermal synthesis, microstructure of the membrane through the different Si/Al ratio and alkali metal fluoride synthesis gel are discussed in this work. Alkali metal fluorides have a significant influence on the synthesis of aluminum-rich ZSM-5 zeolite membranes without organic template, which are realized by the synergistic reaction of the “bridging” and “salting-out” effects. Sodium fluoride and potassium fluoride could produce dense and needle-like zeolites layer on the supports by an extremely low Si/Al ratio synthesis gel (Si/Al <10). When the Si/Al ratio of the initial synthesis gel is 18.52, the compact and prismatic ZSM-5 zeolites are fully covered on the supports with sodium fluoride, potassium fluoride or lithium fluoride. There are few of ZSM-5 zeolites could form on the support by cesium fluoride containing synthesis gel.