The methanation reaction converting CO into CH4 at ca. 400 °C is proposed to take place on uncoordinated surface sites (e.g. step-edges) of Ru catalysts because of the higher measured reactivity of stepped vs. flat single crystal metal surfaces. However, the reaction mechanisms occurring at step-edges remain unclear due to the limitations in modelling high temperatures processes by the common evaluation of potential energy surfaces by density functional theory calculations. Here, we show using ab initio molecular dynamics simulations on CO-covered Ru flat and stepped surfaces models at 400 °C that hydrogen-transfers favoured at elevated temperatures are crucial for both CO activation and CHx (x = 1, 2, 3) hydrogenation steps of the methanation reaction, especially at step-edges.