2024-03-28T22:02:32Zhttps://www.tdx.cat/oai/requestoai:www.tdx.cat:10803/3926462017-09-20T15:10:16Zcom_10803_183col_10803_22730
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Aerogels catalítics de Co-Si sobre monòlits ceràmics per a produir hidrogen mitjançant la reformació d'etanol
[Barcelona] :
Universitat Politècnica de Catalunya,
2016
Accés lliure
http://hdl.handle.net/10803/392646
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Domínguez Escalante, Montse,
autor
1 recurs en línia (238 pàgines)
Tesi
Doctorat
Universitat Politècnica de Catalunya. Institut de Tècniques Energètiques
2016
Universitat Politècnica de Catalunya. Institut de Tècniques Energètiques
Tesis i dissertacions electròniques
Llorca, Jordi, ,
1966-
supervisor acadèmic
TDX
Hydrogen is an energy vector; it is not a direct energy source. It is an energy carrier. Hydrogen can be used to feed fuel cells (an electrochemical device), thus increasing the efficency of energy transfer as the amount of energy lost in form of heat is less compared to classic thermal machines (combustion engine). It is necessary to obtain hydrogen from other compounds as it is not present in molecular form in our planet. Hydrogen storage requires energy expenses, and generating hydrogen on demand is more efficient. Bioethanol is a renewable resource as it can be obtained easily by biomass fermentation. This Thesis focuses on the study of ethanol steam reforming as a method to obtain hydrogen from bioethanol. Ethanol steam reforming was selected as it extracts hydrogen from both compounds of bioethanol, ethanol and water, increasing the amount of hydrogen produced: CH3CH2OH+3H2O->6H2+2CO2 (ESR). Ethanol steam reforming is an endothermic reaction with several competitive secondary reactions. These secondary reactions produce a decrease in hydrogen yield and also some byproducts (mainly CO), which poison some fuel cells (PEM type). A catalyst is needed to perform this reaction with high selectivity at low temperature. Cobalt talc dispersed in silica aerogelscoating ceramic honeycombs and Co talc-coated ceramic honeycombs were selected as catalysts for ESR at 300-500 °C. The addition of small amounts of Fe and K to the aerogel-dispersed catalyst was also studied. Honeycombs coated with Co talc dispersed in aerogels exhibit a selectivity to ESR of 93.4% at 400 °C. The addition of Fe to the catalysts increased this value up to 95.8% at the same temperature, thus reducing CO selectivity to 3.3% (this data was recorded during long-term experiments with a duration of 75 hours). No previous treatment was performed on the catalytic monoliths. Functionalized monoliths (before and after reaction tests) were characterized by several techniques, including SEM, FIB, TEM, DRX, FTIR, XPS and magnetism. In situ XPS experiments were conducted after ESR at different temperatures. Characterization results revealed that Co talc is partially reduced to Co(0) under reaction conditions. Honeycombs coated with Co talc dispersed in silica aerogels presented a fast activation response, reaching an ethanol conversion of 90% at 312 °C, only 8 °C after reaching an ethanol conversion of 10%; this fact is related to Co talc and the excellent mass transfer of aerogel. Finally, the catalysts were tested in a high pressure reactor and in a catalytic membrane reactor (for hydrogen separation)using a non-diluted feed stream. Honeycombs coated with Co talc dispersed in silica aerogel show good catalytic properties (conversion, selectivity, fast response) for on-site, on-demand hydrogen production from bioethanol to feed a PEM cell.
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