Hydrogen Production from Steam Reforming of Ethanol over Ir/CeO_2 Catalysts

摘要

Ethanol could be converted into hydrogen-rich gas stream by steam reforming according to the stoichiometric reaction, C_2H_5OH + 3H_2O → 3CO_2+6H_2. Depending on the catalysts and reaction conditions, however, undesirable side reactions, like ethanol dehydration to ethylene, ethanol dehydrogenation to acetaldehyde, and acetaldehyde decarbonylation of acetaldehyde to acetone, often took place and thus greatly affected the selective production of hydrogen [1-3]. Moreover, the oligomerizations of the intermediate compounds, like acetone and ethylene, have been regarded as the potential precursors of coke formation. Many studies [1-5] showed that acetaldehyde, ethylene and acetone might form at relatively low temperature, before the formation of hydrogen and CO_2, and thus ethylene and acetaldehyde were often considered as the important reaction intermediates for the formation of H_2 and CO_2. At higher temperatures, steaming of methane and reversible water gas shift become the major reactions which influence the production of hydrogen and also the stability of the catalyst due to coke deposition as usually observed in the reaction of methane steam reforming process. Apparently, the challenge is to develop novel catalysts exhibiting attractive activity for ethanol steam reforming with high yield of hydrogen and acceptable resistance to coke formation. The active metal must be capable of breaking the C-C bond in ethanol molecule at temperatures as low as possible, and also must facilitate the conversions of methane and CO into CO_2 and hydrogen efficiently. Meanwhile, the support also should have significant capability for water activation to generate reactive oxygen species and to release hydrogen, but would not favor ethanol dehydration reaction to ethylene. Therefore, the selective production of hydrogen from ethanol steam reforming is critically dependent on the choice of both the active metal and the support.