Ru-based　catalysts　have　attracted　increasing　interest　due　to　their　high　efficiency　in　NH3　synthesis,　yet　their　performance　is　limited　by　the　inability　of　single　site　to　simultaneously　activate　both　N2　and　H2　molecules.　To　overcome　this　challenge,　introducing　different　functional　sites　(e.g.,　C60　as　an　adsorption/activation　site　for　H2)　is　vital　to　achieving　highly　efficient　NH3　synthesis　under　mild　conditions.　However,　how　the　relative　positioning　of　the　second　functional　site　to　the　Ru　site　influences　the　local　environment　and　subsequent　catalytic　performance　is　still　elusive.　Herein,　we　present　a　site-selective　strategy　for　anchoring　C60　at　distinct　locations　on　a　single-site　Ru　catalyst.　Compared　to　surface-anchored　C60,　embedded　C60　substantially　modifies　the　electronic　structure　of　the　Ru　single-atom　site　and　decreases　the　work　function.　By　virtue　of　cascading　different　functional　sites,　embedded　C60　facilitates　hydrogen　spillover　to　nitrogen　species　activated　on　Ru　to　form　NH3.　In　contrast,　despite　the　high　capacity　for　H2　adsorption,　surface-anchored　C60　exhibits　sluggish　hydrogen　spillover,　which　results　in　its　inefficient　catalytic　performance.　Therefore,　the　optimal　single-site　Ru　catalyst　with　embedded　C60　achieves　a　1.4-fold　increase　in　the　NH3　synthesis　rate　compared　to　its　counterpart　with　surface-anchored　C60　at　400　°C　and　1　MPa.　This　study　sheds　light　on　optimizing　the　positioning　of　second　functional　site　in　the　design　of　high-performance　NH3　synthesis　catalysts.　©　2025