A novel "double-template" method has been developed to hydrothermally synthesize high silica MFI-type zeolite crystal with preferentially oriented growth alog ac-plane. The reactant system for the synthesis is SiO2-Na2O-n-propylamie (n-PrNH2)-N-ethyl- hexamethylene tetrammium bromide (EtHMTA^+)-NaF-H20. SEM images show that almost all as-synthesized single crystals of the zeolite are in flat and thin form with (010) plane parallel to the test plate. The XRD patterns show that the intensity of (0k0)(k=2n) peaks is much stronger than that of any other peaks, indicating that the as- synthesized crystals are b-axis perferentially oriented on the test plate. The fraction of b-axis orientation of the crystals is strongly dependent on the ratio ofthe two templatesused in the reactant, n- PrNH2 and EtHMTA^+. The optimal molar ratio of n-PrNH2 toEtHMTA^+ IS 0. 7: 0.3 for the preferentially oriented growth of MFI-type zeolite crystals.

Key words: ORIENTED GROWTH, ZEOLITE, CRYSTALS, SILICON DIOXIDE, SODIUM OXIDE, QUATERNARY AMMONIUM COMPOUNDS, SODIUM FLUORIDE, SCANNING ELECTRON MICROSCOPES, X-RAY DIFFRACTION ANALYSIS, ORIENTATION