Metal-support　interactions　strongly　affect　the　catalytic　performances　of　ceria-supported　metal　catalysts,　and　hydrogen　treatment　at　high　temperature　is　important　for　the　preparation　of　catalysts　that　show　strong　metal-support　interaction　(SMSI).　With　SMSI,　the　proportion　of　metal　species　existing　in　the　form　of　a　metallic　state　is　lowered,　consequently　hindering　the　performance　of　a　metal　catalyst　for　a　reaction　that　requires　metallic　sites.　Here　we　show　that　CO　activation　of　a　Ru/CeO2　catalyst　not　only　enhances　the　reduction　degree　and　exposure　of　Ru　species　but　also　increases　Ce3+　concentration,　oxygen　vacancy　(OV),　and　active　oxygen,　resulting　in　the　formation　of　electron-enriched　RuÎ-　species　and　RuI-OV-Ce3+　sites.　As　a　result,　a　Ru/CeO2　catalyst　after　CO　activation　shows　high　ammonia　synthesis　activity,　and　the　ill　effect　of　hydrogen　poisoning　is　effectively　alleviated.　These　findings　are　important　for　the　design　of　supported　metal　catalysts　that　afford　metallic　species　as　active　sites.　©