Achievement of complete CO removal at low temperature can avoid exothermic CO2 methanation at high temperatures. As a simple solution, an increase in the amount of exposedactive species can enhance the CO methanation activity. Indeed, addition of a noble metal (such as Ru67,68 and Pt69) to Ni-containing mixed oxide catalysts boosted CO methanationat low temperature because H2 spillover from the noble metal enhanced the reducibility of the Ni species, as will be seen in section 5.1. The other answer is the control of CO adsorption and dissociation, since adsorption and dissociation on an active metal surface are key steps for CO methanation. It is considered that the electron density (ED) of the surface directly influences the activity of CO methanation.