Abdul Nasir, Jamal;
(2023)
Selective Catalytic Reduction of Nitrogen Oxides with Ammonia over Transition Metal Exchanged Zeolites.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Metal-exchanged zeolites have received considerable attention in recent years, owing to their wide range of catalytic activity, especially their application in the selective catalytic reduction (SCR) of NOx species. In this thesis, we study the NH3-SCR reaction over transition metals (Cu and Fe) exchanged zeolites (CHA and BEA) using the hybrid quantum mechanical/molecular mechanical (QM/MM) technique and where needed with input from the experiment. First, we investigate the NH3-SCR reaction mechanism on Cu-CHA zeolite and compare the reaction energies of water- and ammonia-solvated and bare Cu species. Our results indicate that physisorbed solvent coordinated to the Cu-active sites has a promoting effect on the oxidation component of the NH3-SCR cycle. In particular, we find that the formation of important nitrate species is energetically more favourable on solvated Cu sites than in the absence of solvent molecules. However, both water and ammonia molecules inhibit the reduction component of the NH3-SCR cycle. Next, we study the NH3-SCR of NOx reaction over various Fe-BEA active sites including systems with both framework and extra-framework Fe cations. The catalytically active sites are found to include Fe-FeF-BEA, Fe-AlF-BEA, and Cu-FeF-BEA, (where the subscript F indicates framework species) on which the formation and consumption of key intermediates, including nitrosamine and nitrate species were analyzed. The results obtained from this study are further compared with other zeolites including ZSM-5 and Chabazite. Finally, we study the formation of Cu-dimer species which are considered to be one of the possible species in the NH3-SCR of the NOx reaction. We find that the isolated Cu species can form dimer species in the presence of a solvent. This thesis contributes to the understanding of the reactivity of transition metals containing zeolites and offers insights for improving the efficiency of the existing zeolitic system in the NH3-SCR reaction.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Selective Catalytic Reduction of Nitrogen Oxides with Ammonia over Transition Metal Exchanged Zeolites |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2023. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/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 BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10174908 |
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