Tuning the composition and dimensionality of transition metal carbides as possible catalysts for green chemistry related reactions
[eng] Transition metal carbides (TMCs) have acquired a wide potential as a green chemistry catalysts. Their relatively high abundance and their catalytic performance makes them great candidates to replace scarce and pollutant catalysts as Pt, as well as promising catalysts to generate and store clea...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2023 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/194844 |
| Acceso en línea: | https://hdl.handle.net/2445/194844 http://hdl.handle.net/10803/687854 |
| Access Level: | acceso abierto |
| Palabra clave: | Carburs Compostos de metalls de transició Química verda Captura i emmagatzematge de diòxid de carboni Hidrogenació Carbides Transition metal compounds Green chemistry Carbon sequestration Hydrogenation |
| Sumario: | [eng] Transition metal carbides (TMCs) have acquired a wide potential as a green chemistry catalysts. Their relatively high abundance and their catalytic performance makes them great candidates to replace scarce and pollutant catalysts as Pt, as well as promising catalysts to generate and store clean fuels. Moreover, a new synthesised family of 2D materials called MXenes, derived from the TMCs, has attracted an increasing attention due to its vast reactivity and potential applications. This thesis aims to evaluate possible applications for the TMCs and MXenes to face nowadays climate and energy problematics, as the CO2 atmosphere mitigation or clean hydrogen production for its usage as a fuel, through density functional theory calculations. First, we explore the CO2 capture, storage, and activation potential of doped TMCs using TiC as a textbook. When the TiC is doped with early transition metals the electron transfer produced upon the CO2 adsorption appear to be the leading feature, as more electrons where transferred, higher the adsorption energy. However, when replacing the Ti for a variety of elements across all the periodic table this tight relation is lost. Instead, we observed that the main effect does not come from the electronic structure perturbations but from the distortion that the dopant generates into the surface atomic structure. A simple descriptor is proposed that would allow predicting the effect of the dopant on CO2 adsorption energy in transition metal carbide surfaces without the need for DFT calculations. The MXenes are evaluated regarding its potential for hydrogen related reactions both in gas-solyd systems and electrochemical processes. In gas-solid systems, W2N, Fe2C and Mo2C presented the necessary intermediate hydrogen coverage under current reaction conditions to be promising catalyst candidates for further hydrogenation reactions, while the rest of the MXenes where fully passivated. In electrochemical systems, we also studied systematically the surface coverage of the MXenes in aqueous solution. We detailed how to construct the so-called Pourbaix diagrams, useful tool for a proper surface analysis, and show how the most thermodynamic favourable surface in a gas-solid environment could not be the most stable surface under electrochemical conditions. Finally, based on the construction of theoretical Tafel plots, we disclosed the mechanism of the Hydrogen Evolution Reaction (HER) over V2C. |
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