Spatially Separated Activation-Conversion Nitride Catalysts for Accelerated Ammonia Synthesis

Ammonia synthesis is a cornerstone of the modern chemical industry and emerging energy technologies, yet its catalytic efficiency remains fundamentally limited by the intrinsic linear scaling relationships. Here, we address this challenge by constructing a triphase heterostructure comprising a Ni₂Mo₃N host integrated with Mo₂N domains and metallic Ni nanoparticles via a solid-solution reaction. Mechanistic studies reveal that metallic Ni activates H₂ and supplies spillover hydrogen to the Ni₂Mo₃N host, thereby promoting surface hydrogenation and generating nitrogen vacancies within the host lattice. These vacancies drive lattice nitrogen migration from the Mo₂N reservoir to the host, simultaneously creating surface vacancies on Mo₂N that serve as efficient N₂ activation centers. Through this spatially separated activation-conversion pathway, the catalyst effectively decouples conflicting elementary steps, achieving a high ammonia synthesis rate of 32.5 mmol·g_Ni2Mo3N^-1·h^-1 at 500 °C under 1.0 MPa, which is nearly three times that of the Ni₂Mo₃N reference and superior to most reported Mo-based catalysts. This work establishes a general design paradigm for constructing tandem catalytic architectures based on a spatial-synergy strategy, providing a viable route to overcome the intrinsic Sabatier limitation imposed by scaling relationships.