Molecular sieve films and zoned materials

Sammanfattning: Molecular sieve films and colloidal particles may have great potential for further utilization in novel technological sophisticated applications such as structured catalysts, sensors and membranes. The work presented in this thesis concerns the synthesis molecular sieve films and the crystallization of zoned MFI materials for novel catalyst and sensor applications. The seeding method developed at the division has been modified for the preparation of MFI and FAU type films on a variety of steel substrates ranging from ordinary carbon steel to highly corrosion resistant stainless steel. The films were characterized by SEM, XRD and gas adsorption techniques. The results revealed that the type of steel did not affect the film morphology, the thickness or the preferred orientation of the crystals, whereas the thermal stability was dependent on the steel. Films on various stainless steel supports were stable during calcination, whereas films on carbon steel supports peeled off upon rinsing after calcination because a relatively thick magnetite/hematite film formed. Pre-calination of carbon steel improved the zeolite film stability upon calcination. Zoned MFI materials (colloidal zoned MFI crystals and zoned films) were synthesized in this work in order to improve the catalytic performance of MFI. A two-step crystallization method was developed to prepare zoned MFI materials, in which precursor ZSM-5 colloidal particles or film were grown in a silicalite-1 synthesis solution directly or after acid treatment. It was shown that zoned MFI materials did not form when the ZSM-5 surface had a high aluminum content. In this case, polycrystalline aggregates or a sandwich film formed due to secondary nucleation. After reducing the aluminum content to half by acid treatment of ZSM-5, secondary nucleation of new silicalite-1 crystals was inhibited and zoned MFI material was obtained.