Photocatalysis　transfers　CO2　molecules　into　hydrocarbons　and　aligns　with　the　principles　of　photosynthesis.　In　addition　to　the　efficiency,　reaction　selectivity　is　another　important　concern　in　photocatalysis　and　is　generally　dependent　on　the　kind　of　co-catalysts　that　provide　an　active　site.　In　the　present　study,　the　role　of　the　co-catalyst　is　focused　on,　and　the　Cu　and　Co　species,　as　well　as　the　bimetallic　CuCo　species,　are　applied　for　the　photocatalytic　CO2　reduction　reaction.　Based　on　the　in-situ　investigation,　the　role　of　the　co-catalyst　of　the　Cu/TS1　is　dominated　by　the　HCOO*　intermediate　during　the　CO2　reduction　reaction,　resulting　in　the　formation　of　HCOOH　as　the　main　product.　The　role　of　the　bimetallic　1Cu2Co/TS1　is　alternatively　dominated　by　*COOH　intermediate,　resulting　in　the　formation　of　CO　as　the　main　product.　The　density　functional　theory　(DFT)　is　applied　to　simulate　the　pathway　of　the　CO2　reduction　reaction.　From　these　results,　the　present　study　has　shown　the　importance　of　the　physicochemical　properties　of　co-catalysts　in　determining　the　selectivity　for　the　photocatalytic　CO2　reduction　reactions.　©　2025　Elsevier　B.V.