In　this　work,　we　study　the　water-gas　shift　(WGS)　reaction　catalyzed　by　α-MoC(100)　supported　typical　platinum　group　metal　(PGM)　single　atoms　(Rh1,　Pd1,　and　Pt1)　and　Au1　via　density　functional　theory　calculations.　The　adsorption　energies　of　key　reaction　intermediates　and　the　kinetic　barriers　of　the　proposed　rate-determining　step　in　the　WGS　were　systematically　investigated.　It　is　found　that　Rh1,　Pd1,　and　Pt1　can　serve　as　single-atom　promoters　(SAPs)　to　improve　the　WGS　performance　of　surface　Mo　atoms　on　α-MoC(100).　The　enhanced　activity　originates　from　the　fact　that　SAP　modifies　the　electronic　structure　of　Mo　active　sites.　Comparatively,　the　Au1　species　not　only　acts　as　an　SAP　but　also　directly　participates　in　the　catalysis　as　a　single-atom　player.　The　additional　experiments　with　single-atom　catalyst　performance　and　kinetic　studies　confirm　the　theoretical　calculation　conclusions.　This　study　can　provide　a　basis　to　further　develop　efficient　WGS　catalysts　by　tuning　the　activity　of　the　substrate　with　intercalation　of　SAPs.　©　2021　American　Chemical　Society.