The　development　of　efficient　oxides-supported　bimetallic　catalysts　is　critical　for　ammonia　synthesis　or　other　catalytic　reactions.　Herein,　the　design　of　ceria-supported　Co-Mo　bimetallic　catalysts　with　different　properties　is　performed　by　changing　Mo　addition　to　enhance　the　ammonia　synthesis　activities.　It　is　found　that　the　reduction　of　ceria　and　molybdenum　oxide　would　be　boosted　by　Co　species,　but　the　reduction　of　the　bimetallic　catalyst　would　be　inhibited　by　the　aggregated　molybdenum　oxide　for　the　catalyst　with　Co　and　Mo　simultaneous　addition.　On　the　contrary,　this　ill　effect　of　molybdenum　oxide　on　the　reduction　of　the　bimetallic　catalyst　can　be　effectively　alleviated　by　the　subsequent　addition　of　Mo　species　to　ceria-supported　Co　catalyst,　resulting　in　enhancement　of　the　proportion　of　Co　metal,　Ce3+　and　low-valent　Mo　species,　as　well　as　surface　enrichment　of　Co　species.　In　such　cases,　the　amount　of　the　adsorbed　hydro-gen　and　nitrogen　species　would　increase,　and　hydrogen　species　preferentially　desorbs　following　a　path-way　of　H-2　formation.　As　a　result,　the　catalyst　obtained　by　the　separate　addition　of　Co　and　Mo　shows　2.5-fold　more　active　than　its　counterpart　with　the　simultaneous　addition　of　Co　and　Mo　species.　These　findings　provide　a　valuable　insight　in　designing　reducible　oxide-supported　bimetallic　catalysts　in　ammonia　syn-thesis　or　other　hydrogen-involved　reactions.　(c)　2022　Elsevier　Inc.　All　rights　reserved.