Catalytic Performance of Doped Ni₂P Surfaces for Ammonia Synthesis

Ammonia plays a crucial role in upholding the global food supply chain because it is a key ingredient in the production of nitrogen-based fertilizers. NH₃ is produced industrially from N₂ and H₂ using the Haber-Bosch process. This process is energy-intensive and requires the consumption of natural gas and coal to produce hydrogen, which leads to the generation of various greenhouse gases. The conventional transition metal catalysts used in this process, such as Fe and Ru, operate at elevated temperatures and pressure to cleave the strong N≡N bond in N₂, which is the rate limiting step, followed by sequential hydrogenation of N atoms on the catalytic surface to produce NH₃. Previous studies have indicated that reducing the activation barrier of N₂ on metal catalysts can lead to stronger binding of atomic N on the surface, ultimately inhibiting N₂ activation sites. Recently, metal phosphide catalysts have gained attention for their unique activity, selectivity, and resistance to deactivation in various catalytic reactions. In this study, we investigate the catalytic performance of Ni₂P catalyst doped with different transition metals (e.g., Ru and Fe) for ammonia synthesis using density functional theory (DFT) calculations. We also explore H-assisted N–N activation pathways involving diazene (NH–NH) and hydrazine (NH₂–NH₂) to weaken the N–N bond prior to activation.