Atomically Dispersed Mn Synergized With LiBaH 3 on MgO Enables Efficient Ammonia Synthesis via an H − Assisted N 2 Dissociation Mechanism

ABSTRACT Ammonia is an essential chemical feedstock and a promising hydrogen energy carrier, motivating the development of efficient ammonia synthesis catalysts. However, scaling relations fundamentally limit conventional transition metal‐based catalysts, rendering strongly N 2 ‐binding metals such as Mn ineffective due to sluggish hydrogenation. Herein, we demonstrate that atomically dispersed Mn (Mn 1 ) anchored on the ternary hydride LiBaH 3 (LiBaH 3 ─Mn 1 ) enables efficient ammonia synthesis via an H − ion‐assisted N 2 dissociation mechanism. The MgO supported LiBaH 3 ─Mn 1 catalyst (LiBaH 3 ─Mn 1 /MgO) exhibits an ammonia synthesis rate two orders of magnitude higher than that of manganese nitride and exceeds the benchmark Cs─Ru/MgO catalyst by a factor of 2.5 at 400°C, representing a state‐of‐the‐art performance among group 4–7 transition metal–based catalysts. Mechanistic investigations reveal that Mn 1 serves as the active site for N 2 adsorption, while H − ions from LiBaH 3 further activate the adsorbed *N 2 through a reductive protonation process to form *N 2 H intermediates. Subsequent N─N bond cleavage of *N 2 H yields surface nitride (Mn─N) and imide (*NH) species on the LiBaH 3 ─Mn 1 surface. This H − ion‐assisted N 2 dissociation pathway fundamentally overcomes the intrinsic limitations of bulk Mn, transforming it into an efficient metal for ammonia synthesis.