Hydrogen Production From Steam Reforming Of Bio-ethanol

Hydrogen production of from Bio-ethanol is regarded as environmental benign and practically effective way to provide hydrogen for fuel cell applications. In this dissertation, Hydrogen production by steam reforming of ethanol has been investigated over ceria supported Ir and Ni catalysts. The catalytic performance of Ir and Ni catalysts supported on different metal oxides were also studied. By means of addition of probe molecules and reforming of intermediate compounds and the in situ FTIR and TEM characterization methods, etc. the reaction pathway and catalysts structure were investigated.It was proposed that ethanol steam reforming over the Ir/CeO₂ catalyst proceeded through acetaldehyde or oxametallacycle intermediate, depending on the reaction temperature. At lower temperature, the interaction between the Ir particles and the adsorbed ethoxyl species is not strong enough to abstract H atom from the nearby CH3 group, and thus acetaldehyde acts as the key intermediate. Acetaldehyde can decompose to methane and CO and/or convert to acetone through decarbonylation. At higher reaction temperature, Ir particles abstracted H atom from the adsorbed ethoxyl species and formed stable five-membered oxametallacycle intermediate (Ir-CH2CH2OO-Ce4+), which was helpful to the disruption of C-C bond and the reforming of CHx group. Long-term stability test of the Ir/CeO₂ catalyst at 650oC with stoichiometric water/ethanol molar ratio of 3showed rather stable catalytic performance for 300 hours time-on-stream with no obvious coke. But high calcination temperature weakened the interaction between Ir and CeO₂. Hence, depressed the catalytic performance of Ir/CeO₂ catalyst and altered the reaction pathway partially.Ni/CeO₂ catalyst exhibited good capability of hydrogen production from ethanol steam reforming. Larger particles of NiO and CeO₂ favored the decomposition of ethanol and/or acetaldehyde, but not the reforming of methane and ethanol to hydrogen. The coke deposited on catalyst surface affected the stability of Ni/CeO₂ catalyst severely.It was revealed that the interactions among Cu, Ni and CeO₂ greatly improved the dispersion of Ni particles, and consequently led to enhanced catalytic activities. The results also showed that Ni was effective in the cleavages C-C and C-H bonds, and thus reduced the production of oxygenates. Additionally, Ni also exhibited excellent methane reforming capability at higher temperature. Cu had good performance of water gas shift reaction, and converted CO to CO₂ at lower temperatures.