Controlling Crystal Orientation in Zeolite MFI Thin Films by Direct In Situ Crystallization

A systematic study was carried out on the synthesis of oriented continuous zeolite MFI thin films on stainless steel substrate by direct in-situ crystallization, and clear correlation was obtained between crystal orientation in the zeolite film and the composition of the synthesis solution. Within the synthesis system of TPAOH:NaOH:TEOS:H 2 O:NaCl, OH - /Si and Na + /TPA + ratios play a critical role in controlling crystal orientation. For sodium-free or low sodium syntheses, only random-oriented films are formed at OH - /Si ≥ 0.64, ( a, b )-oriented films at 0.64 > OH - /Si > 0.5 or at 0.2 ≥ OH - /Si > 0.1, and b -oriented films at 0.5 ≥ OH - /Si > 0.2. For a given OH - /Si ratio, addition of Na + leads to change of crystal orientation from b -oriented, to ( a, b )-oriented, to ( a, b, c )-oriented, and eventually to random-oriented.