Heteronuclear Trimetallic MFe₂ and M₂ Fe (M=V, Nb, and Ta) Clusters for Dinitrogen Activation

Catalysts with heteronuclear metal active sites may have high performance in the nitrogen reduction reaction (NRR), and the in-depth understanding of the reaction mechanisms is crucial for the design of related catalysts. In this work, the dissociative adsorption of N₂ on heteronuclear trimetallic MFe₂ and M₂ Fe (M=V, Nb, and Ta) clusters was studied with density functional theory calculations. For each cluster, two reaction paths were studied with N₂ initially on M and Fe atoms, respectively. Mayer bond order analysis provides more information on the activation of N-N bonds. M₂ Fe is generally more reactive than MFe₂ . The coordination mode of N₂ on three metal atoms can be end-on: end-on: side-on (EES) for both MFe₂ and M₂ Fe. In addition, a unique end-on: side-on: side-on (ESS) coordination mode was found for M₂ Fe, which leads to a higher degree of N-N bond activation. Nb₂ Fe has the highest reactivity towards N₂ when both the transfer of N₂ and the dissociation of N-N bonds are taken into account, while Ta-containing clusters have a superior ability to activate the N-N bond. These results indicate that it is possible to improve the performance of iron-based catalysts by doping with vanadium group metals.