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A new catalyst composition comprised of Ni, Ru, and MgO was investigated with a focus on improving methanation performance for sub-stoichiometric H2/CO-ratio producer gas from biomass gasification. The catalyst was loaded on an alumina support by wet impregnation for testing the catalytic methanation activity for syngas (CO/H2) and producer gas (CO/CO2/H2) in a fixed-bed reactor. The optimum addition of promoters Ru and MgO to the main Ni catalyst was determined by maximizing the CO conversion and CH4 yield in the methanation reactions. The optimization experiments were conducted on a low-surface-area alumina support. With 10% Ni loading, the highest activity and stability was achieved with the addition of 1.5%MgO and 0.5-1.0% Ru as promoters. X-ray Photoelectron Spectroscopy (XPS) of Ni in pretreated Mg-Ni and Ni-Ru-Mg catalysts indicated the presence of approximately 30% of Ni in metallic state on the Al2O3 support. Bulk reduction, measured by TPR, was nearly 40% in the Mg-Ni-Ru catalysts. The MgO promoter enhanced the methanation activity, while the Ru component was mainly responsible for improvement in catalytic stability in the low H2/CO-ratio (1.82) feed gas. The effect of the presence of H2O in the feed gas showed no significant change in the methanation activity of the catalyst. The Ni-Ru-Mg catalyst showed much higher stability in comparison to a promoted Ni-based commercial catalyst. The CO in the low H2/CO-ratio feed gas was primarily responsible for catalyst deactivation due to coke formation. Experiments with high-surface-area commercial alumina supports with the Ni-Ru-Mg catalyst demonstrated CO conversion activity comparable to a commercial catalyst but eliminated deactivation due to coke formation at the low H2/CO-ratio producer gas commonly found in the gasification of biomass. |
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