Synthesis of ZSM-5 zeolites using palygorskite as raw material under solvent-free conditions

Zeolites have extensively been applied in gas adsorption and separation, catalysis, and ion exchange thanks to their numerous interesting features. However, the synthesis of zeolites usually requires solvents, which often lead to water pollution, loss of silicon and aluminium components, and low synthesis efficiency. In this account, ZSM-5 zeolites were synthesized from natural clay palygorskite (PAL) by acid leaching, followed by thermal treatment under solvent-free conditions. The as-obtained ZSM-5 zeolites exhibited high crystallinity and mesoporous structure. The NMR spectra of ZSM-5 zeolites confirmed the presence of aluminium element derived from the acid-treated PAL (APAL) existed in zeolite framework. Thus, PAL was simultaneously employed as silica and aluminium sources for zeolite preparation. The Si/Al molar ratio of ZSM-5 zeolites could be adjusted by adding NaAlO2, but against growth of ZSM-5 zeolites, resulting in formation of analcime. On the other hand, long thermal treatment for 72 h caused the dissolution of ZSM-5 zeolite crystals and formation of analcime. Overall, calcination could enhance the activity of APAL and crystallinity of ZSM-5 zeolites, and solvent-free synthesis of zeolites from clay might efficiently reduce the cost of zeolites.