Martis, M.; (2011) In situ and ex situ characterization studies of transition metal containing nanoporous catalysts. Doctoral thesis , UCL (University College London).

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Abstract

The research within this thesis has concentrated around characterization of nanoporous catalysts with metals incorporated or substituted inside the framework, and inside the cavities as small clusters, and in very low concentrations. The main objective has been to advance the understanding of the structure and active sites, and relate them to their catalytic properties through the use of combination in situ and ex situ methods and in some cases combination with optical spectroscopic techniques. Characterisation methods include synchrotron radiation based techniques, high-resolution powder diffraction (HRPD) and X-ray absorption spectroscopy (XAS), and laboratory based X-Ray Diffraction (XRD), Infrared Spectroscopy (IR), Raman Spectroscopy (RS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy TEM A combination of techniques is used to investigate cobalt substituted AlPO-18 prepared by different compositions. The determination of the nature of cobalt ions, in particular their location in the samples was carried by XAS. Additionally, a new in situ IR cell was developed which allowed to determine the nature of the redox chemistry of cobalt ions in the samples. Structural changes during calcinations and methanol to olefins reaction (MTO) were studied on transition metals substituted (Co, Zn, Si) small pore AlPO-18. Using diffraction methods it was possible to accurately determine the changes in the lattice parameters and correlate this with metal ion incorporation into the lattice, and also determine the negative thermal properties of these materials prior to catalytic reactions; the study also allowed us to follow their stability during calcination. High energy X-ray diffraction (HEXRD PDF method) measurements gave an insight into the direction of possible lattice contraction during calcination which may be related to shape-selective catalytic properties of these solids. Characterization of a series of vanadium containing ZSM-5 was carried by in situ XAS and Raman spectroscopy. The catalytic activity was very different, and detailed understanding of the vanadium environment using XAS and Raman spectroscopy provided an insight into the nature of vanadium ions in the zeolites. In the last part of the thesis, a series of platinum impregnated zeolite beta and ferrierite were characterized to understand how the nano clustered platinum metal particles (active centres) were created during activation, and the study also allowed us to estimate the size and sitting of the platinum cluster inside the zeolite lattice.

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