Structural study of zeolites utilizing novel electron crystallographic methods : A voyage into the world of zeolite structures
Abstract: Electron crystallography has evolved as a powerful method for structural characterization of a wide range of materials. It has two significant advantages over other methods for structure determination, e.g. X-ray diffraction. Electrons interact much more strongly with matter compared to X-rays and they can be focused by electromagnetic lenses to form images with atomic resolution. These advantages make electron crystallography a unique tool for characterization of crystalline materials suffering from small crystal size and complex or disordered structures. Zeolites are a class of microporous materials with significance in several applications. They often possess complex and disordered structures, which demand large efforts in the structure determination. Over the last years, two new electron crystallographic methods have been developed; the rotation electron diffraction (RED) and the structure projection reconstruction from a through-focus series of high resolution transmission electron microscopy (HRTEM) images. In this thesis, they will be applied for structure determination of four new zeolite structures, including EMM-25 and EMM-23 with two ordered structures, and ITQ-39 and ITQ-38 with disordered structures. Each of the structure solutions have different challenges to overcome. The high silica borosilicate EMM-25 was solved by the RED method. The aluminosilicate EMM-23 was solved by a combination of HRTEM and RED. The structure solution of two materials with disordered structures, ITQ-39 and ITQ-38, will be described. For materials containing disorders, structure projection images are of utmost importance. Furthermore, the mesoporosity inside hierarchically porous ZSM-5 crystals was studied by a combination of focused ion beam (FIB) and HRTEM imaging. The last part of this thesis explores STEM imaging for use in structure determination from 3D reconstruction.
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