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 H₂ 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.