Novel　catalysts　for　carbon　dioxide　(CO2)　reduction　into　specific　energy-rich　products　with　great　activity　and　selectivity　is　highly　desired,　which　is　closely　related　to　the　adsorption　ability　of　substrate　with　specific　intermediates　and/or　products.　In　this　work,　via　first　principles　calculations　we　have　extensively　studied　the　properties　of　two-dimensional　transition　metal　carbides　(MXenes)　for　efficient　CO2　capture　and　reduction.　Our　results　suggest　that　all　the　investigated　MXenes　exhibit　excellent　CO2　capture　abilities,　which　are　demonstrated　to　be　originated　from　the　surface　lone　pair　electrons　of　MXenes　and　can　be　described　via　the　effective　charge　numbers　of　their　transition　metal　atoms.　Then　we　highlight　that　the　activated　CO2　can　be　selectively　reduced　to　methane　(CH4)　with　a　moderate　limiting　step,　where　the　Mo2C　MXene　exhibit　higher　catalytic　efficiency　than　the　other　MXenes.　Further　analysis　on　transition　states　confirms　that　the　largest　energy　demand　during　CO2　reduction　happens　on　the　surface　regeneration　of　Mo2C　MXene,　which　is　critical　to　realize　sustainable　catalytic　activity.　The　stability　of　Mo2C　MXene　has　been　confirmed　via　phonon　dispersion　and　ab　initio　molecular　dynamics　simulations.　Our　findings　pave　the　way　of　MXenes　for　CO2　capture　and　pioneer　the　application　of　Mo2C　MXene　as　novel　CO2　reduction　catalyst.　©　2020