Exploring the complexity of nanostructured catalysts with computational chemistry methods
[eng] Heterogeneous catalysis relies on interactions with a material’s surface to lower the energy barrier of chemical reactions, thus increasing their rate. Enhancing catalytic performance typically involves nanoscale surface modifications designed to increase the density of active sites and tailor...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2025 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/223698 |
| Acceso en línea: | https://hdl.handle.net/2445/223698 http://hdl.handle.net/10803/695509 |
| Access Level: | acceso abierto |
| Palabra clave: | Química quàntica Catàlisi heterogènia Òxids metàl·lics Materials nanoestructurats Quantum chemistry Heterogeneus catalysis Metallic oxides Nanostructured materials |
| Sumario: | [eng] Heterogeneous catalysis relies on interactions with a material’s surface to lower the energy barrier of chemical reactions, thus increasing their rate. Enhancing catalytic performance typically involves nanoscale surface modifications designed to increase the density of active sites and tailor their geometric and electronic structures at the atomic level, thereby optimizing adsorption energies, reaction intermediates stabilization, and turnover frequencies. However, the structural complexity of nanostructured multi-component catalysts precludes their understanding and rational improvement. The work presented in this thesis studies different types of technologically relevant nanostructured ceria-based catalysts varying in shape, composition, size and dimensionality. Computational simulations are used to understand the effect of the interaction of different nanostructures with CeO2 surfaces and elucidate their physical and chemical properties. First, metallic Pt clusters supported on CeO2 are studied to address the effects of electron transfer between metal particles and reducible oxides (known as Electronic Metal Support Interactions - EMSI) on the chemical properties of a Pt8 cluster. A computational strategy is proposed and critically evaluated to systematically characterize the electron transfer process and the different possible resulting electronic states. The chemical properties of the different sites and electronic states of the supported Pt8 cluster are evaluated, revealing significant effects in calculated adsorption energies due to EMSI for various reactants and intermediates. Second, the structural and electronic properties of the interface between a 2D FeO monolayer and the CeO2(111) surface are investigated. Simulations reveal a corrugated interfacial geometry, structure, consistent with experimental observations of periodic nanostructures. The electronic structure analysis indicates the presence of multiple electronic states, exhibiting an intricate interplay between the Fe2+/Fe3+ - Ce4+/Ce3+ redox couples. These calculations also reveal the importance of dispersion interactions and oxygen adsorption in the stabilization of periodic FeOx 2D nanostructures. Finally, the chemical reactivity of an oxidized Pt6O9 cluster supported on CeO2 is investigated to rationalize the high catalytic activity of oxidized ceria-supported Pt particles towards the CO oxidation reaction below room temperature. Activation energies of CO oxidation on the Pt6O9 cluster suggest that both the oxidized cluster and gas-phase O2 are the main sources of O atoms for CO2 formation. A reaction mechanism is proposed for the reaction on the Pt6O9 cluster where the CeO2 support acts as a spectator for the described catalytic cycles. Kinetic Monte Carlo simulations show the proposed mechanism to be consistent with high catalytic activity of Pt oxide clusters below room temperature. |
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