In　this　work,　we　study　the　water-gas　shift　(WGS)　reaction　catalyzed　by　alpha-MoC(100)　supported　typical　platinum　group　metal　(PGM)　single　atoms　(Rh-1,　Pd-1,　and　Pt-1)　and　Au-1　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　Rh-1,　Pd-1,　and　Pt-1　can　serve　as　single-atom　promoters　(SAPs)　to　improve　the　WGS　performance　of　surface　Mo　atoms　on　alpha-MoC(100).　The　enhanced　activity　originates　from　the　fact　that　SAP　modifies　the　electronic　structure　of　Mo　active　sites.　Comparatively,　the　Au-1　species　not　only　acts　as　an　SAP　but　also　directly　participates　in　the　catalysis　as　a　single-atom　player.　The　additional　experiments　with　singleatom　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.