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Synthesis and Structural Studies of Heteroatom Substituted Aluminophosphates and Related Materials.

Muncaster, Gavin; (2003) Synthesis and Structural Studies of Heteroatom Substituted Aluminophosphates and Related Materials. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

The aim of this work has been to employ a range of techniques to study some of the factors that affect the synthesis and structure of microporous aluminophosphate materials. Using these results we aim to gain a greater insight into which factors may be altered to produce a specific microporous framework, or materials with a particular framework composition or catalytic properties. To this end we have employed a range of powerful X-Ray techniques, which require a synchrotron radiation source to perform a variety of experiments. The synchrotron based studies have been complimented by various laboratory techniques such as nuclear magnetic resonance, thermal gravimetric analysis and infra-red spectroscopy. In particular Microcrystal Diffraction facilities at the Daresbury Synchrotron Source has been used to collect high quality diffraction data on single crystals as small 10x10x20μm in size. This has given us detailed information on the location of the template species within the as-prepared aluminophosphate materials. Further to this a newly developed heating unit was used to perform in situ, high temperature single crystal study tracking the breakdown of the organic template species, to study in detail any changes to the aluminophosphate framework which occur during this process of calcination. Further complimentary studies were performed using techniques including standard laboratory single crystal diffraction, FTIR and TGA. Solid State NMR studies have been preformel on a range of Silicon and Zinc substituted aluminophosphate materials to study the stabilising effect of substituting silicon into the framework. This allows us to study the environment of the different heteroatom species within the framework and investigate whether this is related to the resultant stability of the materials upon calcination. Energy Dispersive X-Ray Diffraction (EDXRE) performed on station 16.4 at the Daresbury Synchrotron source, using a specially designed hydrothermal cell, was employed to study the effect of altering the initial pH of a range of aluminophosphate (and heteroatom substituted aluminophosphate) reaction gels with regards to the final product produced. The technique allows us to collect diffraction data with a time resolution of approximately 1 minute, and as a result we can follow, in situ, the formation of any crystalline products from the reaction gel. A relatively new 3-element detector was used in the experiments providing us with the ability to study a large d-spacing range simultaneously. Using this extra data we are able to identify subtle differences in the products forming which previously have been very difficult to record. Finally we have re-investigated the crystal structure of the Cobalt containing heteropolytungstate material K5[CoW12 040].20H2O. This is one of only a few materials that contain tetrahedral CoIII ions co-ordinated to 4 oxygen atoms. We have obtained accurate information on the Co-O bond distances that can be used as a model for investigating the structural properties of CoIII ions substituted into an aluminophosphate framework. In tum this model can be applied to the appropriate data and used to estimate the amount of oxidisable CoII ions in as-prepared CoAlPO materials and thus the potential for REDOX catalysis.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Synthesis and Structural Studies of Heteroatom Substituted Aluminophosphates and Related Materials.
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest
Keywords: Pure sciences; Aluminophosphates
URI: https://discovery.ucl.ac.uk/id/eprint/10102910
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