Fig. 2.

Possible mechanisms for N₂ reduction to NH₃. (Top) Dissociative mechanism typically associated with the Haber–Bosch process in which the N–N triple bond is cleaved during an initial step of the mechanism. (Bottom) Chatt‐type sequential mechanisms can proceed through distal, alternating, and hybrid pathways in which the N–N triple bond is progressively weakened via sequential hydrogenation (depicted using addition of pairs of H for simplicity). Variations include an initial reduction by multiple electrons, but without complete cleavage of the N–N triple bond [34], or reduction of N₂ by a reaction other than hydrogenation [118].