The　synthesis　of　ammonia　via　the　Haber-Bosch　process　using　Fe-derived　catalysts　requires　harsh　reaction　conditions.　It　is　hence　meaningful　to　develop　catalysts　for　low-temperature　synthesis　of　ammonia　for　industrial　application.　Herein　for　the　first　time,　we　report　that　with　the　synergy　between　LaN　and　Ru/ZrH2,　NH3　can　be　synthesized　via　a　dual-path　mechanism.　The　LaN-promoted　Ru/ZrH2　catalyst　shows　exceptionally　high　NH3　synthesis　rate　(up　to　305　mmol(NH3)　g(Ru)(-1)　h(-1))　at　350　degrees　C　under　1　MPa　and　remarkable　durability　(tested　for　200　h).　The　outcomes　of　isothermal　surface　reaction　and　a　suite　of　N-15(2)　and　D-2　isotopic　labeling　experiments　reveal　that　the　N-3　of　LaN　reacts　with　Hions　to　produce　NH3,　leaving　behind　N　and　H　vacancies.　The　initial　state　of　Ru/xLaN/ZrH2　can　be　restored　by　having　the　N　and　H　entities　replenished　under　the　atmosphere　adopted　for　NH3　synthesis.　Moreover,　based　on　the　results　of　N-2　reaction　order,　nitrogen　K-edge　NEXAFS,　in　situ　XPS　as　well　as　in　situ　DRIFTS　analyses　under　a　25%N-2-75%　D-2　atmosphere,　it　is　reckoned　that　the　direct　dissociation　of　N-2　does　not　occur　on　the　LaN-promoted　Ru/ZrH2　catalyst　while　N-2　hydrogenation　takes　place　via　an　associative　pathway　under　mild　conditions.　For　the　hydrogenation　of　N-2,　an　appropriate　amount　of　LaN　would　induce　a　synergic　effect　on　the　Ru　active　sites,　leading　to　facile　activation　and　hydrogenation　of　N-2　to　*N2H2.　Nonetheless,　an　excess　amount　of　LaN　would　result　in　blocking　of　Ru　sites,　consequently　hindering　the　formation　of　*N2H2　and　decreasing　the　catalytic　activity.　Following　the　associative　and　chemical　looping　pathways,　the　LaN-promoted　Ru/ZrH2　catalyst　bypasses　the　bottleneck　of　N-2　direct　dissociation,　making　the　synthesis　of　NH3　at　mild　conditions　possible.　(c)　2020　Elsevier　Inc.　All　rights　reserved.