Two-dimensional　molybdenum　carbide　(2D-Mo2C)　is　thought　to　be　promising　for　catalytic　hydrogenation　of　CO2　to　CH4,　but　little　is　known　about　its　catalytic　reaction　mechanism.　In　this　work,　we　investigate　the　hydrogenation　of　CO2　to　CH4　on　2D-Mo2C　using　density　functional　theory.　Our　calculations　show　that　Mo　on　the　surface　can　efficiently　decompose　CO2　to　CO　and　O,　and　also　H2　to　H.　The　hydrogenation　of　CO　produces　CHO　that　is　readily　deoxygenated　to　CH,　and　CH　is　selectively　hydrogenated　to　produce　CH4.　Interestingly,　the　embedded　Ir1　on　2D-Mo2C　can　act　as　a　single-atom　promoter　to　improve　the　performance　of　CO2　methanation,　while　on　the　other　hand　maintaining　its　high　selectivity　for　CH4.　This　work　provides　insight　into　the　mechanism　of　2D-Mo2C-catalyzed　CO2　methanation　reactions　and　suggests　a　strategy　to　improve　the　performance　of　such　catalysts　through　single-atom　promoters.　©　2022　Hydrogen　Energy　Publications　LLC