Hydrogen Production from Ethanol Through Steam Reforming on Ni-based Catalysts

Abstract

Biomass is an alternative and promising source for the sustainable production of energy and commodities such as hydrogen. For this, biomass can be converted into bioethanol through fermentation/hydrolysis that is reliably converted into hydrogen through steam reforming (SRE), and the performance of the most used catalysts for this process (Ni-based) is determined by the support components and preparation methods. In this work, three Ni-based catalysts have been compared for the SRE at 500 ºC, steam/ethanol molar ratio of 3 and a low space time of 0.025 h-1 in a fluidized-bed reactor: The catalysts tested were obtained upon reduction at 850 ºC of a NiO/Al2O3 obtained by wetness impregnation (Ni-WI) and two spinel precursors (NiAl2O4 and NiMgAl2O4) prepared by co-precipitation (Ni-S and NiMg-S, respectively). The Ni-S and Ni-WI catalysts have similar performances with high ethanol conversion but unstable H2 yield over time on stream, whereas the NiMg-S catalyst has a higher and more stable H2 yield even with lower ethanol conversion, which proves differences in the prevailing reaction routes for the catalysts. The NiS and Ni-WI catalysts prompt the ethanol dehydration to ethylene (C2H4) on acid sites (which increases ethanol conversion) followed by its decomposition to carbon and H2, which are prevailing routes over SR reactions, thus producing significant amount of carbon deposits, although both carbon and H2 yield decrease suddenly after certain time on stream (TOS) due to deactivation of the C2H4 decomposition reaction. Conversely, the presence of MgO in the support of the NiMg S catalyst neutralizes the acid sites and favors the ethanol steam reforming and ethanol dehydration to acetaldehyde (C2H4O), that is decomposed into CH4 and CO. An overall significant amount of carbon is also deposited upon NiMg-S catalyst (from CO and CH4 precursors) but it allows a stable behavior of the catalyst due to its filamentous nature.