Here,　we　studied　Al　or　B　atom-doped　carbon　nitride　(g-C3N4　and　C2N)　as　catalysts　for　H-2　activation　and　acetylene　hydrogenation　using　density　functional　theory　calculations.　The　Al　or　B　could　be　assembled　with　the　surface　N　atoms　of　carbon　nitride　to　form　diverse　frustrated　Lewis　pairs　(FLPs).　The　results　show　that　Al-N　FLPs　had　lower　barriers　of　H-2　activation　in　comparison　with　B-N　FLPs.　The　heterolytic　H-2　dissociation　catalyzed　by　Al-N　FLPs　led　to　the　formation　of　Al-H　and　N-H　species.　The　Al-H　species　were　highly　active　in　the　first　hydrogenation　of　acetylene　to　C2H3*,　yielding　a　mild　barrier,　while　in　the　second　hydrogenation　step,　the　reaction　between　C2H3　and　the　H　of　N-H　species　caused　a　relatively　high　barrier.　Electronic　structure　analysis　demonstrated　the　electron　transfer　in　the　heterolytic　H-2　cleavage　and　explained　the　activity　differences　in　various　FLPs.　The　results　suggest　that　Al　with　the　surface　N　of　carbon　nitride　can　act　as　an　FLP　to　catalyze　the　H-2　activation　and　acetylene　hydrogenation,　thus　providing　a　new　strategy　for　the　future　development　of　noble　metal-free　hydrogenation　catalysts.