Agote Aran, Miren;
(2019)
Identification of Structure-activity Relationships in Molybdenum and Iron containing Zeolites used in Methane Dehydroaromatisation and NOx Reduction.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
In order to design an optimal catalyst, it is important to correlate different chemical species with their activity. This thesis is focused on structure-activity relationship studies of M/zeolite catalysts (where M = Mo or Fe) for methane dehydroaromatisation (MDA) and selective catalytic reduction with ammonia (NH3-SCR). MDA is of great industrial interest as it converts methane directly into light hydrocarbons and aromatics - precursors for the chemical industry. Mo-containing medium pore H-ZSM-5 zeolite is a promising catalyst; nonetheless, the rapid material deactivation compromises its commercialisation. In order to shed light on the MDA catalyst working mechanism, the evolution of Mo species in Mo/H-ZSM-5 has been investigated by means of synchrotron-based X-ray absorption/diffraction techniques under operando and in situ conditions. The results reveal that in contact with methane, initial tetrahedral Mo-oxo species attached to the zeolite are fully carburised to MoxCy which show to be highly active for MDA. Evidences of detachment of MoxCy from the zeolite and subsequent sintering bring new insights regarding catalyst deactivation. The effect of zeolite acidity and topology on MDA has been also investigated by comparing the performance of catalysts based on Silicalite-1 (a pure siliceous analogue of the H-ZSM-5 presenting no Brønsted acidity) and small pore H-SSZ-13. These studies reveal that Brønsted acidity is not necessary for the aromatisation to occur and puts the traditionally accepted bifunctional mechanism into question. Mo/H-SSZ-13 presented different product distribution due to the shape selectivity of small pores towards lighter hydrocarbons. Finally, NH3-SCR is a process used to reduce NOx into N2 and H2O; among others, Fe/zeolites present good catalytic performance. High energy resolution fluorescence detected X-ray absorption and X-ray emission spectroscopic experiments under in situ standard NH3-SCR conditions were performed to determine that octahedral isolated species on Fe/H-ZSM-5 showed greater activity.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Identification of Structure-activity Relationships in Molybdenum and Iron containing Zeolites used in Methane Dehydroaromatisation and NOx Reduction |
| Event: | UCL |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10065691 |
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