Based on the mechanistic studies of selective CO methanation (Scheme 2), we suggest that the key for selective CO methanation is the control of interfaces between active metals and support materials (section 3). If the interface can be blocked or the perimeter can be shortened, CO2 conversion to CO will be hindered, leading to high CO methanation selectivity. As mentioned in section 5, the following solutions can prove to be quite effective in enhancing CO methanation selectivity: (i) the combination of Ru and Ni and (ii) chlorine modification. In addition, it can be necessary to choose suitable support materials and promoters, otherwise undesirable CO2 methanation will proceed (section 4).