Template‐Free Synthesis of Highly b‐Oriented MFI‐Type Zeolite Thin Films by Seeded Secondary Growth

Highly b‐oriented, closely packed, MFI zeolite films are prepared on seeded stainless‐steel plates using organic template‐free, secondary growth solutions, containing aluminum sulfate as a crystallization agent. The number of a‐oriented twin crystals is significantly reduced, and even eliminated, simply by restricting the pH value of the secondary growth solution to the narrow range of 11.1–11.3. Values of pH can be adjusted through the controlled addition of (NH4)2SO4 or H2SO4 to secondary growth solutions of the composition (1 SiO2:0.57 NaOH:137.5 H2O:0.0050 (Al2(SO4)3⋅18 H2O)) or by simply decreasing the molar composition of NaOH with no extra additives. Thin films: The effect of compositional constraints on the synthesis of highly b‐oriented MFI zeolite films on stainless‐steel plates using secondary growth solutions, free of organic template, was investigated. The number of twin crystals can be significantly reduced, and even eliminated, simply by restricting the pH value of the secondary growth solutions to the narrow range of 11.1–11.3.