b-Oriented MFI membranes prepared from porous silica coatings

The preparation of b-oriented MFI films from porous silica layers was investigated and optimized. The alumina supported silica membranes were immersed in a concentrated TPAOH solution. Finally b-oriented and well-intergrown MFI crystal films were produced by carrying out an in situ hydrothermal synthesis using a synthesis solution 1 SiO2:0.05 TPAOH:37.5–169 H2O:0.15 NaOH. The main function of the silica is twofold, it serves as a nucleation layer for the silicalite-1 and provides a smooth surface for the oriented crystal growth into a continuous layer. Prolonged synthesis duration leads to the formation of a secondary layer with increasing a-orientation.