Synthesis of a zeolitic thin layer by a vapor-phase transport method: Appearance of a preferential orientation of MFI zeolite

Zeolitic membranes were synthesized on a porous alumina support by the vapor-phase transport method using one of two alumina sources: aluminum sulfate and sodium aluminate. By choosing the appropriate period and temperature for drying the aluminosilicate gel on the alumina support, MOR, FER and MFI could be synthesized. MOR was formed when the water content in the dry gel was high. As the water content decreased, FER and MFI were formed sequentially. Preferential formation of MFI was achieved by treating the dry gel at 373 K. The temperature at which the support was dipped in the parent gel also influenced the type of zeolite formed, although the effect of drying conditions was more pronounced. A similar trend was found for both aluminum sulfate and sodium aluminate. When the alumina source was sodium aluminate and the aluminosilicate gel was treated at 373 K, a preferentially oriented MFI membrane could be synthesized, as the (a00) and (0b0) crystal faces were oriented in parallel to the surface of porous alumina support. The uniform and dense morphology of the dry gel seems to account for the appearance of the orientation. (C) 1997 Elsevier Science B.V.