Density　functional　theory　calculations　were　carried　out　to　investigate　the　mechanism　of　CO2　and　CO　methanation　over　pure　Cu(100)　and　Co–Cu　bimetallic　catalysts.　The　most　favorable　pathways　for　the　CO2　and　CO　hydrogenation　were　obtained.　For　the　Cu(100)　surface,　the　barriers　of　the　rate-limiting　step　for　the　HCOO*　and　CO*　hydrogenation　were　122.52　kJ/mol　and　106.14　kJ/mol.　Because　the　barrier　(77.34　kJ/mol)　for　the　H2CO*　hydrogenation　is　more　than　the　desorption　energy　of　54.80　kJ/mol,　H2CO　gas　was　the　main　product　from　the　hydrogenation　of　CO2　and　CO　on　a　pure　Cu(100)　surface.　For　the　Co4/Cu(100)　surface,　the　optimal　pathways　for　the　CO2　and　CO　methanation　were　the　same　as　those　on　the　Cu(100)　surface.　The　rate-limiting　step　for　CO2　and　CO　methanation　is　the　H2COO*　(barrier　of　103.57　kJ/mol)　and　H2CO*　hydrogenation　(barrier　of　107.80　kJ/mol).　Compared　to　the　mechanism　of　CO2　and　CO　over　Cu(100),　the　Co　dopant　can　modify　the　rate-limiting　step　and　decrease　the　activation　barrier.　Particularly,　the　barrier　for　the　H2COH　decomposition　was　changed　from　100.96　kJ/mol　to　69.81　kJ/mol　(CO2　pathway)　and　61.26　kJ/mol　(CO　pathway).　Furthermore,　the　co-adsorbed　OH*　group　affects　the　hydrogenation　pathway　of　some　intermediates　rather　than　electronic　structures.　©　2019　Elsevier　B.V.