Preparation of supported zeolite films and layers: Processing of zeolite suspensions and in situ growth from homogeneous solutions

The influence of microstructure on the properties of zeolite films and means of controlling the former (film thickness, crystal orientation) are the theme of this report. Firstly, the formation of thin silicalite films from regrowth of nanocrystalline silicalite/alumina composite films is presented. The crystallites at the intergrown top layer are oriented with their straight channels parallel to the substrate film. The membranes show H₂/N₂ selectivities of about 60 at 150 °C. This high selectivity is attributed to the orientation of the separating layer. Secondly, the formation of oriented multilayers of zeolite L crystallites by alternating dipping of a glass substrate in a bohemite and a `plate-like' zeolite L suspensions is illustrated. Finally, continuous films of zeolite NaA are prepared on various substrates (glass, porous and nonporous alumina) using in situ growth from homogeneous solutions. The films exhibit good adhesion to the substrates. The films prepared on porous alumina disks show He/N₂ and O₂/N₂ selectivities of 10 and 0.4 respectively at 120 °C.