CO and CO2 methanation over Ni catalysts supported on alumina with different crystalline phases

The effect of alumina crystalline phases on CO and CO2 methanation was investigated using alumina-supported Ni catalysts. Various crystalline phases, such as alpha-Al2O3, theta-Al2O3, delta-Al2O3, eta-Al2O3, gamma-Al2O3, and kappa-Al2O3, were utilized to prepare alumina-supported Ni catalysts via wet impregnation. N-2 physisorption, H-2 chemisorption, temperature-programmed reduction with H-2, CO2 chemisorption, temperature-programmed desorption of CO2, and X-ray diffraction were employed to characterize the catalysts. The Ni/theta-Al2O3 catalyst showed the highest activity during both CO and CO2 methanation at low temperatures. CO methanation catalytic activity appeared to be related to the number of Ni surface-active sites, as determined by H-2-chemisorption. During CO2 methanation, Ni dispersion and the CO2 adsorption site were found to influence catalytic activity. Selective CO methanation in the presence of excess CO2 was performed over Ni/gamma-Al2O3 and Ni/delta-Al2O3; these substrates proved more active for CO methanation than for CO2 methanation.