A reaction pathway for methanation of CO is often proposed.It is reported that CO methanation over supported metal catalysts proceeds via dissociation of CO on the metal and successive hydrogenation of the resultant surface carbonaceous species.33–35 Methanation of CO under CO and CO2 coexisting conditions is also considered to take place on the active metal surface.12,16 Panagiotopoulou and coauthors precisely analysed the nature of Ru species on TiO2 during CO and/or CO2 methanation using in situ DRIFT and TPD techniques.16,17 Under CO methanation conditions, the following CO species were observed: linear and bridged CO on metallic Ru (Rux–CO), multicarbonyl species on partially oxidized Ru,Ru (CO)x), and Ru–CO located at the metal–support interface IJ(TiO2)Ru–CO). The presence of Run+(CO)x may indicate the dissociative adsorption of CO.14,36 The authors concluded that hydrogenation of surface carbon produced by dissociative adsorption of CO on metal Ru (eqn (4)–(6)) was much faster than that of (TiO2)Ru–CO, and the main route for CO methanation at low temperature (