Expanding the synthesis field of high silica zeolites.

Aluminosilicate zeolites are synthesized under hydrothermal conditions in basic/alkaline medium in the pH range between 9 and 14. Here we report the synthesis of MFI-type zeolite in acidic medium. The critical parameter determining the zeolite formation in acidic medium was found to be the isoelectric point (IEP) of gel particles. MFI-type zeolite was synthesized above the isoelectric point of the employed silica source, where the silica species exhibit a negative charge and the paradigm of zeolite formation based on the electros tatic interaction with the posit iv ely charged template retained. No zeolite formation is observed below the isoelectric point of silica. The impact of aluminum on the zeolite formation is also studied. The results of this study will serve to extend the zeolite synthesis field of high silica zeolites to the acidic medium and thus open new opportunities to control the zeolite properties.