Developing　high-performance　Fe-based　ammonia　catalysts　through　simple　and　cost-efficient　methods　has　received　an　increased　level　of　attention.　Herein,　we　report　for　the　first　time,　the　synthesis　of　two-dimensional　(2D)　FeOOH　nanoflakes　encapsulated　by　mesoporous　SiO2　(mSiO2)　via　a　simple　solution-based　method　for　ammonia　synthesis.　Due　to　the　sticking　of　the　mSiO2　coating　layers　and　the　limited　spaces　in　between,　the　Fe　after　reduction　retains　the　2D　morphology,　showing　high　resistance　against　the　sintering　in　the　harsh　Haber-Bosch　process.　Compared　to　supported　Fe　particles　dispersed　on　mSiO2　spheres,　the　coated　catalyst　shows　a　significantly　improved　catalytic　activity　by　50%　at　425　°C.　Thermal　desorption　spectroscopy　(TDS)　reveals　the　existence　of　a　higher　density　of　reactive　sites　for　N2　activation　in　the　2D　Fe　catalyst,　which　is　possibly　coupled　to　a　larger　density　of　surface　defect　sites　(kinks,　steps,　point　defects)　that　are　generally　considered　as　active　centers　in　ammonia　synthesis.　Besides　the　structural　impact　of　the　coating　on　the　2D　Fe,　the　electronic　one　is　elucidated　by　partially　substituting　Si　with　Al　in　the　coating,　confirmed　by　29Si　and　27Al　magic-Angle　spinning　nuclear　magnetic　resonance　(MAS　NMR).　An　increased　apparent　activation　energy　(Ea)　of　the　Al-containing　catalyst　evidences　an　influence　on　the　nature　of　the　active　site.　The　herein-developed　stable　2D　Fe　nanostructures　can　serve　as　an　example　of　a　2D　material　applied　in　catalysis,　offering　the　chance　of　a　rational　catalyst　design　based　on　a　stepwise　introduction　of　various　promoters,　in　the　coating　and　on　the　metal,　maintaining　the　spatial　control　of　the　active　centers.　©