International Journal of Hydrogen Energy, Vol.40, No.27, 8485-8497, 2015
Hydrogen generation over 30Co(x)V(y)/70SBA-15 mesoporous materials well-balanced by Co and V co-doping
This study examined hydrogen generation by ethanol steam reforming (ESR) over metal-doped SBA-15, Co/SBA-15, Co and V co-doped SBA-15, and V/SBA-15. The changes in the oxidation state of cobalt species during activation through a H-2-TPR experiment before ESR were investigated. The materials were pre-reduced by a H-2-treatment at 550 degrees C. A small quantity of cobalt oxide species remained in the reduced CoV (30 wt.%) co-doped SBA-15 (70 wt.%) but it was not observed in the 30Co/70SBA-15. The catalytic performance varied according to the molar ratio of the loaded metals, Co and V. The 30Co(1)V(1)/70SBA-15 showed a significantly higher reforming reactivity and the efficiencies decreased in the order of 30Co(1)V(1)/70SBA-15 > 30Co(2)V(1)/70SBA-15 > 30Co/70SBA-15 > 30Co(1)V(2)/70SBA-15 > 30V/70SBA-15 because of the synergy between cobalt and vanadium ions. H-2 production was maximized to 95% over 30Co(1)V(1)/70SBA-15 at a reaction temperature of 700 degrees C, CH3CH2OH:H2O of 1:3 and GHSV (gas hourly space velocity) of 6000 h(-1). At the end of activation, metallic cobalt was detected in all the materials. The cobalt oxide species might interact more strongly with the vanadium ions in the material, which results in the formation of a more cobalt vanadium composite and larger amount of Co2+. The presence of Co2+ in the reduced material might help equilibrate the steps of ethanol activation and carbon oxidation, resulting in stable materials. Moreover, vanadium oxides appear to provide oxygen to cobalt species, resulting in increases in hydrogen production and the suppression of CO generation. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.