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

An Fe 2 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 Fe 2 catalyst supported on graphitic carbon nitride (Fe 2 /mpg-C 3 N 4 ) strongly favors hydrogenation of *N 2 to form *NHNH 2 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-C 3 N 4 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-C 3 N 4 ( n = 2, 3, 4) and Fe (211) catalysts, we conclude that synergistic Fe 2 catalyst shows a significant advantage due to its high spin polarization and thus can avoid harsh reaction conditions for the thermal conversion of N 2 to NH 3 . Compared to other Fe n ( n > 2) clusters, Fe 2 cluster catalysts combined with vicinal nonmetallic sites are expected to be an ideal catalyst for ammonia synthesis with a lower N-H formation (0.47 eV) and N-N dissociation (0.50 eV) energy barrier at the same time.