Zenonos, Christianna; (2003) Synthesis and characterisation of metal substituted microporous materials. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The work described in this thesis is concerned with the synthesis and characterisation of a variety of metal substituted microporous materials. The majority of this work is experimental, however computational techniques are also used in the characterisation work. The synthesis of the ZSM-5 material was carried out under hydrothermal conditions, with and without the use of a template. XRD, N2 adsorption, SEM, NMR, TGA-MS and DRIFT FTIR techniques were used to characterise the materials in detail. The results obtained from the suite of techniques used suggest that the ZSM-5 materials prepared by this method is phase pure, crystalline and furthermore have a high number of acid sites and thus can be used for acid catalysed reactions. Transition metal ions were incorporated into a dealuminated zeolite β by grafting and then this was converted to a specific zeolite (TS-1). XRD studies support the formation of the MFI structure and XAS measurements, that were used to study the local geometry, support the formation of tetrahedral Ti centres in the calcined and dehydrated materials. IP calculations were also carried out and the results obtained were compared with those obtained from experimental methods. The location and characterisation of the N'N'-diisopropylethylamine template within the microporous aluminophosphate structure, AIPO4-18, using experimental and computational methods was also carried out. We show how such a combined approach enables the accurate structure resolution of the complex structure. The geometry and number of the N'N'-diisopropylethylamine molecules appear to be the same as that reported for TEAOH in AIPO4-18. The synthesis and characterisation of Fe substituted AIPO4-18 and AIPO4-5 was carried out. These materials were studied using XRD, SEM, EXAFS, Mossbauer spectroscopy, TGA-MS and IP calculations. XAS results combined with Mossbauer spectroscopy studies reveal that Fe is present, in the as-prepared catalyst, in the 3+ oxidation state in the FAPO-5 structure and as a mixture of 2+ and 3+ oxidation states in the FAPO-18 structure. Combined XAS/XRD measurements reveal that upon removal of the organic template the Fe ions are present in the 3+ oxidation state in a tetrahedral coordination environment in both catalysts; this is consistent with results determined by the computational calculations.

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