Synthesis of low-silica CHA zeolite chabazite in fluoride media without organic structural directing agents and zeolites

• Chabazite was prepared in fluoride media without OSDAs.
• Fluoride specie in gel played the positive effect on the formation of chabazite.
• The fluoride ion was verified to exist in the zeolite channels.

The fluoride route was adopted for the preparation of chabazite (Si/Al = 2.5–3.5) in the absence of organic structural directing agents (OSDAs). The crystallization kinetics of the fluoride-derived chabazite and the effects of gel SiO2/Al2O3 ratio, gel F−/SiO2 ratio, fluoride source and synthesis temperature on the morphology and composition of crystals were investigated. A certain amount of the specific fluoride source (NH4F) dominated the crystallization of CHA phase in the competitive growth of MER/CHA phases. The fluoride-derived chabazite by in situ synthesis had a particle size of 15–20 μm. Seeded-in-gel synthesis increased the crystallization rate and resulted in the smaller crystals with higher BET surface area and microspore volume. The location of fluoride ion in zeolite framework and the role of fluoride salts on chabazite crystallization were also demonstrated.

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