Barium Oxynitride Electride as Highly Enhanced Promotor for Ruthenium Catalyst in Ammonia Synthesis: Comparative Study with Barium Oxide

Abstract Barium oxide is a conventional promoter for various transition‐metal (TM) catalysts in ammonia synthesis. Ba‐promoted Ru catalysts are widely used for ammonia synthesis under mild reaction conditions. However, the promotion mechanism, including the active factor, remains unclear. In this study, the excellent promotion effect of barium oxynitride is reported, which creates anionic electrons in the lattice, forming an electride (BaO x N y :e − z ) with the same rocksalt structure as BaO. The BaO x N y :e − z enhances the ammonia synthesis activity of the supported Ru catalyst by 40–100 fold compared with the BaO promotor. This study reveals that a low‐work‐function electron formed in the BaO lattice plays a pivotal role in the electronic promotion effect in catalytic ammonia synthesis, suggesting that BaO x N y :e − z formed near the surface during the ammonia synthesis reaction is an active species for the promotion effect of conventional BaO.