It　is　urgent　to　develop　new　efficient　ammonia　synthesis　catalysts　using　non-precious　metals.　Herein,　the　Mo2C　species　is　introduced　into　a　carbon-supported　Mo　catalyst　by　in　situ　carburization　of　a　carbon-supported　Mo　catalyst　in　H2.　In　combination　with　the　presence　of　the　Mo2C　phase　as　well　as　the　enhancement　of　the　graphitization　degree　of　carbon　and　the　amount　of　the　low-valent　Mo　species,　the　migration　and　the　exchange　of　the　adsorbed　species　with　the　gaseous　species　are　accelerated.　As　a　result,　the　catalyst　with　carbonization　treatment　shows　higher　ammonia　synthesis　activity　than　the　sample　without　carbonization,　and　the　ill　effect　of　the　poisoning　of　reagent　gases　also　is　alleviated.　©　2022　The　Royal　Society　of　Chemistry.