Tackling the Activity Trend of Metal-Loaded Metal Nitride Catalysts for NH₃ Synthesis by a First-Principles Microkinetic Study

Ammonia (NH₃) is one of the most widely produced chemicals globally, primarily synthesized through the Haber-Bosch process, which requires high temperatures and pressures. Dual-site catalysts can activate N₂ and H₂ at spatially separated sites, enabling efficient NH₃ synthesis under milder conditions. Despite the rapid experimental progress of the dual-site catalysts (e.g., Ni-LaN), the feasibility and design of dual-site catalysts are challenged recently. Herein, the different metal-loaded metal nitride catalyst models are employed, and their activity map for NH₃ synthesis is explored by the first-principles microkinetic simulation. The optimum active region of this type of dual-site catalyst is identified in terms of the formation energy (E_v) of nitrogen vacancy (N_vac) on metal nitride and the adsorption energy (E_H) of hydrogen atom on metal cluster, with E_v and E_H ideally located around ≈1.50 and ≈-0.30 eV, respectively. This offers a framework for designing effective metal-loaded metal nitride catalysts for NH₃ synthesis. Importantly, this trend aligns with and rationalizes the current experimental observations of metal-loaded metal nitride reported for NH₃ synthesis. This theoretical work provides significant insights into NH₃ synthesis on dual-site mechanism, and provides a rational direction for designing metal-loaded metal nitride catalysts.