Why it is S-rich around Mo atom in the nitrogenase: A DFT investigation

Inspired by nitrogenase which can covert nitrogen (N-2) to ammonia in mild condition, we designed a series nitrogen reduction reaction (NRR) catalysts which Mo embedded on double vacancies graphene (GR) with nonmetal atoms X (X = C, N, B, P, S) doped (MoX4/GR) were used to imitate the active center of nitrogenase. By means of density functional theory (DFT) computations, it is found that MoS4/GR catalyze NRR through alternating mechanism possesses low limiting potential of -0.29 V among designed systems. The high NRR activity of MoS4/GR is attributed to its inherent properties, i.e. the d(z)(2) orbital features which indicate stronger overlap with the empty p orbitals of N-2 Back-donation phenomenon between Mo and N-2, small work function and excellent electrical conductivity are beneficial to the electron transfer. Our work provides a model to explain why Mo atom is coordinated with S atoms in the nitrogenase rather than C, N, P, and B which also exist in the organism of the nitrogenase.