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Abstract:
ZSM-5 was synthesized by different methods with a gradually decreasing water content ending in a reaction mixture with absolutely dry reagents in form of a powder in the complete absence of a solution phase. Amorphous precursors obtained by drying SiO2*Al2O3 gels at 650°C were transformed into zeolites in the presence of dried NH4F and TPABr. The reaction products were characterized by XRD, REM, TG/DTA, MAS NMR and Electron Micropobe. Pure ZSM-5 or Silicalite-1 was obtained in all cases. Some water is probably formed as a reaction product, but the maximum water pressure is appreciably below the saturation pressure at the given reaction conditions. To explain the formation of a zeolite, we suggest a vapor phase mass transfer process with SiF4 as the mobile species between the solid phase which contains the amorphous Si/Al-precursor and the formed zeolite.
