Reforming of bioethanol over Ni/Al2O3 and Ni/CeZrO2/Al2O3 catalysts in supercritical water for hydrogen production
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Author list: Therdthianwong S., Srisiriwat N., Therdthianwong A., Croiset E.
Publisher: Elsevier
Publication year: 2011
Journal: International Journal of Hydrogen Energy (0360-3199)
Volume number: 36
Issue number: 4
Start page: 2877
End page: 2886
Number of pages: 10
ISSN: 0360-3199
Languages: English-Great Britain (EN-GB)
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Abstract
Bioethanol was reformed in supercritical water (SCW) at 500ฐC and 25 MPa on Ni/Al2O3 and Ni/CeZrO2/Al 2O3 catalysts to produce high-pressure hydrogen. The results were compared with non-catalytic reactions. Under supercritical water and in a non-catalytic environment, ethanol was reformed to H2, CO2 and CH4 with small amounts of CO and C2 gas and liquid products. The presence of either Ni/Al2O3 or Ni/CeZrO2/Al2O3 promoted reactions of ethanol reforming, dehydrogenation and decomposition. Acetaldehyde produced from the decomposition of ethanol was completely decomposed into CH4 and CO, which underwent a further water-gas shift reaction in SCW. This led to great increases in ethanol conversion and H2 yield on the catalysts of more than 3-4 times than that of the non-catalytic condition. For the catalytic operation, adding small amounts of oxygen at oxygen to ethanol molar ratio of 0.06 into the feed improved ethanol conversion, at the expense of some H 2 oxidized to water, resulting in a slightly lower H2 yield. The ceria-zirconia promoted catalyst was more active than the unpromoted catalyst. On the promoted catalyst, complete ethanol conversion was achieved and no coke formation was found. The ceria-zirconia promoter has important roles in improving the decomposition of acetaldehyde, the enhancement of the water-gas shift as well as the methanation reactions to give an extremely low CO yield and a tremendously high H2/CO ratio. The SCW environment for ethanol reforming caused the transformation of gamma-alumina towards the corundum phase of the alumina support in the Ni/Al2O3 catalyst, but this transformation was slowed down by the presence of the ceria-zirconia promoter. ฉ 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Keywords
Supercritical water
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