High spin polarized Fe2 cluster combined with vicinal nonmetallic sites for catalytic ammonia synthesis from a theoretical perspective

Abstract

An Fe₂ catalyst combined with the vicinal nonmetallic sites may break the Brønsted–Evans–Polanyi limitation and lead to a more efficient ammonia synthesis than previously reported. Our theoretical calculations show that the Fe₂ catalyst supported on graphitic carbon nitride (Fe₂/mpg-C₃N₄) strongly favors hydrogenation of *N₂ to form *NHNH₂ species, which leads to low energy barriers for N–H formation (0.47 eV) and N–N dissociation (0.50 eV). In addition, B–N Lewis pairs constructed on the mpg-C₃N₄ serve as nonmetallic sites that enable heterolysis of the H–H bond to overcome the relatively high energy barrier of hydrogen transfer. Through a comprehensive study of Fe_n/mpg-C₃N₄ (n = 2, 3, 4) and Fe (211) catalysts, we conclude that synergistic Fe₂ catalyst shows a significant advantage due to its high spin polarization and thus can avoid harsh reaction conditions for the thermal conversion of N₂ to NH₃.