Fig. 1. Density functional theory calculations of carbon dioxide methanation.

a Relationship between hydrogenation energy of *CO and surface *H binding energy for pure metal and metal oxide clusters on Cu surface. Red square for CoO, blue square for other oxides and grey circle for metals. The yellow dashed line is Cu baseline. b Schematic diagram of CO₂ to CH₄ on CoO cluster modified Cu surface. Tangerine for copper, violet for cobalt, red for oxygen, grey for carbon and white for hydrogen. c Hydrogenation energy of *CO for different sizes of CoO cluster. We introduced one cluster on the top of a 4-layer (5 × 2) Cu(111) surface.