Effect of External Electric Field on Nitrogen Activation on a Trimetal Cluster.

Efficient nitrogen (N) fixation and activation under mild conditions are crucial for modern society. External electric fields (F) can significantly affect N activation. In this work, the effect of F on N activation by Nb clusters supported in a sumanene bowl was studied by density functional theory calculations. Four typical systems at different stages of N-N activation were studied, including two intermediates and two transition states. The impact of F on various properties related to N activation was investigated, including the N-N bond length, overlap population density of states (OPDOS), total energy of the system, adsorption energy of N, decomposition of energy changes, and electron transfer. The sumanene not only functions as a support and protective substrate, but also serves as a donor or acceptor under different F conditions. Negative F is beneficial to N-N bond activation because it promotes electron transfer to the N-N region and improves the d-π* orbital hybridization between metals and N in the activation process. Positive F improves d-π* orbital hybridization only when the N-N is nearly dissociated. The microscopic mechanism of F's effects provides insight into N activation and theoretical guidance for the design of catalytic reaction conditions for nitrogen reduction reactions (NRR).