Mitigating the Emission of Anthropogenic CO2 by its Integrated Capture and Conversion with Amines
Carbon Dioxide (CO2) can be considered the main responsible for global warming and climate change. The excess of its emission caused by human activity is harmful to the environment and can have catastrophic consequences. Point source capture of CO2 by amines is a well-established process and can rep...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2024 |
| País: | Brasil |
| Institución: | Universidade de São Paulo (USP) |
| Repositorio: | Biblioteca Digital de Teses e Dissertações da USP |
| Idioma: | inglés |
| OAI Identifier: | oai:teses.usp.br:tde-30042025-174504 |
| Acceso en línea: | https://www.teses.usp.br/teses/disponiveis/46/46136/tde-30042025-174504/ |
| Access Level: | acceso abierto |
| Palabra clave: | Carbamate Carbamato Catalise Catalysis CH4 CO2 Electrocatalysis Eletrocatalise Formamida Formamide |
| Sumario: | Carbon Dioxide (CO2) can be considered the main responsible for global warming and climate change. The excess of its emission caused by human activity is harmful to the environment and can have catastrophic consequences. Point source capture of CO2 by amines is a well-established process and can represent the capture of more than half of the total anthropogenic emission. However, recovering the amine and pressurizing the obtained CO2 is energy intensive. The integration of capture and conversion of CO<2 can be a key strategy to relocate this wasted energy to the conversion step. Because CO2 is a stable and inert molecule, its capture and conversion is challenging and energy becomes the most important aspect of the whole process, making this strategy highly valuable. In this dissertation the integration of CO2 capture and conversion is studied using two different approaches: the N-formylation of amines by CO<2 and its following reactions, using heterogeneous high pressure thermocatalysis; and the electrochemical conversion of carbamate species in a capture solution to methane (CH4). For the N-formylation study we prepared a Au/TiO2 catalyst. A detailed characterization using STEM, XPS, and XAS, showed that Au was highly dispersed on TiO2 as small clusters and single atoms. The catalyst exhibited activity towards the N-formylation of amines. Interestingly, amines containing oxygen presented high conversion, probably due to higherinteraction with the catalyst. Employing a strong base, we found that most formamides are hydrolyzed to formic acid, recovering the initial amine. Intriguing, the formamide obtained from ethanolamine remained stable in the presence of the strong base. We found, for the first time, that CO2 can interact with most formamides slightly stabilizing it against nucleophilic attacks. However, the formamide obtained from ethanolamine specifically form a stable covalent adduct with CO2 strongly stabilizing it. For the electrochemical conversion of capture species, we found a new class of lowcost, earth-abundant Ni catalyst that converts carbamate to hydrocarbons. We demonstrated that carbamate was the active species by control experiments and 13C-NMR spectroscopy. Employing XPS, we found that Ni was specifically the catalyst of the reaction, using STEM, we demonstrated that highly dispersed single-atom Ni deposited in different substrates, including carbon nanotubes, produces CH4 with high selectivity and stability. Ni coverage calculations using XPS demonstrated that increasing in the Ni particle size was detrimental to the catalytic activity towards CH4. These claims were supported by DFT calculations, which also elucidated the mechanism of the reaction. This is the first example of carbamate conversion to hydrocarbons through electrocatalysis. We also found that by tailoring the pH gradient between the electrode and the bulk solution, the conversion of carbamate to methane is promoted. By investigating the CH4 formation and HER in different conditions, we hypothesized that at the ideal pH gradient, ammonium can reach the surface and be reduced to amine and H2. The produced amine can react with CO2 to produce carbamate inside the stern layer, overcoming the charge repulsion limitation between carbamate species and surface, and promoting its conversion. |
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