Hydrogen augmentation of biogas through dry reforming over bimetallic nickel-cobalt catalysts supported on titania

Abstract

The nickel and cobalt bimetallic catalysts (with 11 wt% metals content) supported on Titania were synthesized through wet-impregnation approach and investigated for biogas reforming. The catalysts were characterized using BET analysis, X-ray diffraction (XRD), Field-emission Scanning Electron Microscope (FESEM), and H2-temperature programmed reduction (H2-TPR) techniques. The H2-TPR analysis revealed that bimetallic catalysts have sturdy metal-support synergy which restrains the metallic sintering. The catalytic activity for biogas reforming was explored under ambient pressure condition with temperature varying from 650 to 900 ˚C and GHSV range of 24,000 to 72,000 ml/g/h with CH4/CO2 ratio of 1.5. The experimental results revealed that the catalytic performance is strongly dependent on the appropriate Ni/Co ratio for bimetallic catalysts. The bimetallic catalyst (7 wt.%) Ni-(4 wt.%) Co/TiO2 showed better catalytic activity and stability due to the synergistic effects of Ni and Co. The Ni/Co ratio could be fine-tuned to enhance pore textural properties, which assisted the metal particle distribution and led to reduction in metallic particle size, increment in activity, and retardation to coke deposition. At 900 °C, (7 wt.%) Ni-(4 wt.%) Co/TiO2 catalyst showed 87.13% CH4 and 92.6% CO2 conversion with 41.1% H2 production. The bimetallic catalysts also withstand the catalytic performance during 15 h of continuous reforming as an insignificant decrease was observed in the activity. XRD characterization of spent catalyst shows the re-oxidation of cobalt metal in single metal catalyst. Moreover, with addition of oxygen the increase in catalyst activity was obtained in terms of reactant conversion and hydrogen selectivity.