The regulating effects of cobalt addition on the catalytic properties of silica-supported Ni-Co bimetallic catalysts for CO2 methanation

Co-modified Ni/SiO2 samples were prepared by the wet co-impregnation method and characterized by X-ray photoelectron spectroscopy (XPS), hydrogen-temperature programmed reduction (H-2-TPR), and X-ray diffraction (XRD) techniques. The obtained materials were used as the catalysts for the carbon dioxide methanation reaction. Methanation activities of Ni-Co/SiO2 catalysts were significantly dependent on Co/Ni molar ratios. The increase of Co loading led to the remarkable increase of CO2 conversions at temperature range from 250-350 A degrees C. The methanation activities of bimetallic catalysts were also significantly dependent on Co/Ni molar ratios from XPS results. Based on the XRD characterization, a relationship between activities and NiCo species was observed. These NiCo species showed the typical TPR peaks at high temperatures. The higher the temperatures of these species over bimetallic catalyst were, the lower the catalytic activities were observed. In addition, the decrease of both NiCo(111) lattice constants and particle sizes corresponded the increase of catalytic activities in tested samples. A possible mechanism based on those NiCo species is proposed.