Cobalt-ruthenium bimetallic catalysts for dry reforming of methane
(English) The processes used nowadays for hydrogen and syngas production require more sustainable alternatives to advance in the necessary decarbonisation to fight against climate crisis. Currently, the main process is methane steam reforming (MSR) using natural gas. In this thesis, the use of dry r...
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| Formato: | tesis doctoral |
| Fecha de publicación: | 2024 |
| País: | España |
| Recursos: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/444428 |
| Acesso em linha: | https://hdl.handle.net/2117/444428 https://dx.doi.org/10.5821/dissertation-2117-444428 |
| Access Level: | acceso abierto |
| Palavra-chave: | 66 - Enginyeria, tecnologia i indústria química. Metal·lúrgia Àrees temàtiques de la UPC::Enginyeria química |
| Resumo: | (English) The processes used nowadays for hydrogen and syngas production require more sustainable alternatives to advance in the necessary decarbonisation to fight against climate crisis. Currently, the main process is methane steam reforming (MSR) using natural gas. In this thesis, the use of dry reforming of methane (DRM) is proposed as a method of producing syngas. DRM is an attractive alternative since the two reactants, methane and carbon dioxide, are gases with a high global warming potential (GWP). Moreover, they are found together in the biogas resulting from the anaerobic digestion of organic matter. In the actual state-of-the-art, Ni catalysts supported on a wide range of metal oxides have been extensively studied. However, the main disadvantage is the accumulation of carbon that causes deactivation. In Chapter 4, the application of CoRu bimetallic catalysts supported on CeO2 has been studied. The catalysts have been prepared by conventional incipient wetness impregnation and by mechanochemical methods. A screening of catalytic activity has been conducted, and in-situ characterisation (NAP-XPS and XRD) has been used to get insight into the nature and behaviour of the catalytic active sites. It has been observed how the addition of ruthenium directly impacts the reducibility of cobalt species and results in smaller nanoparticles, as demonstrated by temperature-programmed reduction (H2-TPR) and XRD, respectively. The results of NAP-XPS show how ruthenium is able to modify the metal-support interaction, evidenced by a greater Ce3+/Ce ratio in the bimetallic samples. The synthesis method influences the dispersion of Co and Ru on the surface; NAP-XPS data suggested a higher Ru concentration on the surface of the bimetallic ball-milled samples, indicating the formation of small Ru clusters during milling, as confirmed by TEM analyses. Samples prepared by mechanochemistry, both mono- and bimetallic, have higher activity and stability than those synthesised by the conventional impregnation method, achieving higher CH4 and CO2 conversions. CoRu/CeO2-BM catalyst turns out as a stable catalyst for 24 hours at 700 C and with an average H2/CO ratio close to 1. In Chapter 5, the application of the same CoRu formulation supported on a Mg-Al-O mixed oxide has been studied. For these catalysts, the effect of Ru addition and the use of different precursors has also been studied, observing an effect on the catalytic activity and stability related to a synergy between Co and Ru. Through a "Design of Experiments" approach, the impact of various parameters of mechanochemical synthesis, such as milling frequency, milling time, and precursor addition order, has been studied. It should be highlighted that the samples synthesised by mechanochemistry show a lower amount of carbon deposits, which is ascribed to the particular architecture of the catalytic active sites. Finally, in Chapter 6, characterisation under operating conditions (X-ray absorption spectroscopy and X-ray diffraction) of the main samples synthesised in the previous chapter is performed. In addition to studying dry methane reforming, a small amount of water vapour is added to the reaction to study the combined reforming of methane (CRM), where steam reforming and dry reforming occur simultaneously. It is also observed that in CRM the carbon deposition in samples prepared by mechanochemical methods is substantially lower than those synthesised by conventional impregnation. |
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