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:H2O: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 greater than or equal to 0.64, (a, b)-oriented films at 0.64 > OH-/Si > 0.5 or at 0.2 greater than or equal to OH-/Si > 0.1, and b-oriented films at 0.5 greater than or equal to 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.