Zeolite Synthesis in the Presence of Fluoride Ions
1989; American Chemical Society; Linguagem: Inglês
10.1021/bk-1989-0398.ch013
ISSN1947-5918
AutoresJ.L. Guth, H. Kessler, J. M. Higel, J.M. Lamblin, Joël Patarin, A. Seive, J.M. Chézeau, Raymond Wey,
Tópico(s)Inorganic Fluorides and Related Compounds
ResumoReplacement of OH- by F- makes it possible to obtain zeolites in media where pH values can be lowered to acidic ones. Under such conditions MFI-, FER-, MTT-, MTN- and TON-structure type materials could be prepared. This route is especially suited for high-silica materials synthesis, but partial substitution of silicon by BIII, AlIII, GaIII, FeIII, GeIV and TiIV has been possible too. The ease of substitution decreases with increasing stability of the corresponding fluorocomplezes in the solution. As the supersaturation of crystallizing species is lower for fluoride-containing media, the number of phases that could be obtained is smaller (fewer metastable phases), but crystallization is more regular (formation of large crystals with less defects). The choice of templates is therefore more critical. The new medium enables the incorporation of elements sparingly soluble in alkaline solutions (e.g., FeIII) or of cations such as NH4+, Co2+. Finally the presence of F in the materials leads to catalytic properties modifications which will be discussed.
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