On the Mechanism of CO and CO2 Methanation Over Ni/CeO2 Catalysts

The reactions of the CO and CO2 methanation in the excess of hydrogen were studied over Ni/CeO2 and Ni(Cl)/CeO2 catalysts prepared from nitrate and chloride precursors, respectively. Macrokinetic parameters of the CO and CO2 methanation over Ni/CeO2 and Ni(Cl)/CeO2 catalysts were determined. The nature of surface species during the CO and CO2 methanation over Ni/CeO2 and Ni(Cl)/CeO2 catalysts was studied by the Fourier transform infrared spectroscopy in situ technique. It was shown that the CO methanation proceeds similar ways over both Ni/CeO2 and Ni(Cl)/CeO2 catalysts via CO and H-2 chemisorption on the surface of Ni particles. The CO2 methanation over Ni/CeO2 catalyst proceeds via the CO2 adsorption on the ceria surface and stepwise hydrogenation to methane through hydrocarbonate and formate intermediates by the hydrogen spilled over from Ni particles. With the Ni(Cl)/CeO2 catalyst, this reaction pathway is locked due to the ceria surface blockage by chlorine, to inhibit the CO2 methanation and therefore provide a high efficiency of Ni(Cl)/CeO2 catalyst in preferential CO methanation in the presence of CO2.