Preferentially oriented growth of MFI-type zeolite crystals

A novel "double-template" method has been developed to hydrothermally synth esize high silica MFI-type zeolite crystals with preferentially oriented gr owth along ac-plane. The reactant system for the synthesis is SiO2-Na2O-n-p ropylamine (n-PrNH2)-N-ethyl-hexamethylene tetrammium bromide (EtHMTA(+))-N aF-H2O. SEM images show that almost all as-synthesized single crystals of t he 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 mu ch stronger than that of any other peaks, indicating that the as-synthesize d crystals are b-axis preferentially oriented on the test plate. The fracti on of b-axis orientation of the crystals is strongly dependent on the ratio of the two templates used in the reactant, n-PrNH2 and EtHMTA(+). The opti mal molar ratio of n-PrNH2 to EtHMTA+ is 0.7:0.3 for the preferentially ori ented growth of MFI-type zeolite crystals.