Polycrystalline films of epitaxial MFI overgrowths

Films of epitaxial MFI overgrowths, i.e. ZSM-5 films covered with silicalite-1, with crystals extending from the substrate to the top surface, were synthesized using a seeding method with acid leaching between the synthesis of the MFI layers. The films were characterized by SEM, TEM, XRD and XPS. When acid leaching was omitted, secondary nucleation of silicalite-1 on the ZSM-5 film resulted in a sandwich film with discontinuous crystals. When the precursor ZSM-5 film was acid leached and the surface Si/Al ratio increased from 23 to 47, the crystals in the precursor film grew epitaxially upon treatment in a silicalite-1 synthesis mixture. It was thus revealed that reduction of the aluminum content at the external surface of ZSM-5 may be important for the successful synthesis of epitaxial MFI overgrowths. Alternatively, acid leaching may provide a cleaner surface, and facilitate epitaxial growth.