Hydrothermal Synthesis Approach in the Presence of Fluoride Source

4 Hydrothermal Synthesis Approach in the Presence of Fluoride Source 

Hydrothermal synthesis of microporous compounds in the presence of fluoride source refers to the hydrothermal or solvothermal crystallization of aluminosilicate zeolites or microporous aluminophosphate such as AlP04-n series in the presence of a fluoride source. The successful introduction of fluoride ion into the hydrothermal or solvothermal synthesis of microporous materials paves the way for the introduction of other complex-ion or chelation agent s to the hydrothermal crystallization of microporous compounds. 

Heteroatoms (B, Al, Fe, Ga, and Ti) may be incorporated into the framework of high-silica and all-silica materials in the presence of fluoride as well, giving rise to active acid catalysts. Usually, transition metal ions will hydrolyse to form hydroxide or oxide precipitates in a high-pH solution. Therefore, there is a limitation to the content of transition metals in heteroatom-substituted zeolites. However, this limitation can be significantly increased by using fluoride during the synthesis because fluoride can coordinate to the transition metal atoms to form stable complex, which will help transition metal atoms incorporate into the framework of zeolites. 

Usually, the sources of fluoride are NH4F, NH4HF2, or HF. Sometimes, a framework element compact fluoride such as (NH4)SiF6, A1F3 H20, or NH4BF4 could be used as a fluoride source as well. The synthesis of heteroatom-substituted silicalite-I and ZSM-5 are described below as two typical examples  

Product perfect single crystals (95 x 80 pm), analysed composition Si960192 F4(TPA)4. 

---