Molecular sieve films and zoned materials : synthesis and characterization

Sammanfattning: Molecular sieve films and colloidal particles have great potential for utilization in novel, technological sophisticated applications such as structured catalysts, sensors and membranes. The work in this thesis mainly concerns the synthesis of molecular sieve films and the crystallization of zoned MFI materials. Films are also evaluated in an FTIR-ATR application. A previously developed preparation method has been adapted for the preparation of MFI and FAU type films on various steel types and crystals (Si, ZnS, ZnSe and Ge) for ATR spectroscopy. The films were characterized by SEM, XRD and gas sorption. The type of substrate did not affect the film morphology, the thickness or the preferred orientation of the crystals in the film, whereas the thermal stability was dependent on the substrate. Zeolite (MFI) coated ATR crystals were investigated using ATR-FTIR spectroscopy to detect low amounts of organic molecules in a gas flow. It was demonstrated that these novel materials could be used as a sensor with high sensitivity. The sensor offers the possibility to study both the adsorbate and the adsorbent, and can be used for in-situ studies of sorption, diffusion and reaction in zeolites. The sensor combines the strengths of IR spectroscopy with the high sensitivity of zeolite coated ATR elements. Zoned (epitaxial) MFI materials in the form of colloidal crystals and films were also synthesized in this work. The materials were characterized by SEM, TEM and XRD. A two-step crystallization method was developed, in which acid treated precursor colloidal particles or films of ZSM-5 were grown in a silicalite-1 synthesis solution. It was shown that zoned MFI materials did not form when the ZSM-5 surface had high aluminum content. In this case, polycrystalline aggregates or a sandwich film formed due to secondary nucleation. After acid treatment of ZSM-5, which reduced the surface aluminum content to half, zoned MFI material was obtained by epitaxial growth.