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Influence of the synthesis of Fe-MFI for partial methane oxidation

Milne, Kirstie 2020. Influence of the synthesis of Fe-MFI for partial methane oxidation. PhD Thesis, Cardiff University.
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Iron-containing MFI-type zeolites have been shown to be active catalysts for a range of oxidative transformations. Even though much research has been devoted to these materials in the past, correlations between the choice of zeolite synthesis procedure and catalytic performance are not well explored. Moreover, the impact of catalyst composition on the ultimate catalytic performances of Fe-MFI zeolites is far from understood. However, evidence from zeolite research suggests that these parameters can affect the properties of these materials, which could have implications on catalytic performance. Herein, this thesis aims to better understand the effect of Fe-MFI synthesis and composition on the catalytic performance of these materials for aqueous phase partial methane oxidation. Aqueous phase partial methane oxidation, which utilises hydrogen peroxide as the oxidant, was chosen as a model reaction for the study of the effect of Fe-MFI hydrothermal synthesis on catalytic performance. Initial work focused on the correlation of the SiO2/Al2O3 ratio and Fe content in hydrothermally synthesised catalysts to the catalytic performance of Fe-MFI zeolites for partial methane oxidation. Batch reaction testing was performed at 50 °C to determine turnover frequencies (TOF), and Fe-selective spectroscopic probes, such as DRUV-vis and resonance Raman spectroscopy, were utilised to link the nature of Fe3+ speciation with catalytic performance. In addition to this, the effect of each step of Fe-MFI preparation was studied, to determine the extent of Fe3+ speciation throughout the different preparation steps. Secondly, the effect of crystallisation time and temperature on the hydrothermal synthesis process were explored, to understand whether crystallisation parameters influenced catalytic performance of partial methane oxidation. In the later stages of the thesis, a new procedure for the preparation of Fe-MFI zeolites was explored. Typically, Organic Structure Directing Agents (OSDAs) are used during crystallisation of Fe-MFI zeolites, and such compounds are thought to be critical to the success of zeolite crystallisation. Yet, use of OSDAs requires extra processing methods to remove the OSDA prior to catalytic studies, which adds synthetic complexity, produces CO2 on thermal degradation, and may impact catalytic performance. Furthermore, the presence of the OSDA complicates spectroscopic studies of the synthesised catalyst. In this thesis, an adapted synthesis method, utilising seeding techniques, was developed, resulting in the synthesis of a highly active catalyst for aqueous phase methane oxidation without need of an OSDA.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 5 February 2021
Last Modified: 05 Feb 2022 02:30

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