Facile N≡N Bond Cleavage by Anionic Trimetallic ClustersV3-xTaxC4– (x = 0-3): A DFT Study

Activation of N 2 on anionic trimetallic V 3- x Ta x C 4 - ( x = 0-3) clusters was theoretically studied with density functional theory. For all studied clusters, after adsorption of N 2 on one of the metal atoms (denoted as Site 1), N 2 transfers on clusters to form a coordination of end-on: side-on: side-on on three metal atoms, with which N 2 is dissociated. The whole reaction is exothermic and has no global energy barriers, indicating that the dissociation of N-N can be realized under mild conditions. The reaction process can be divided into two processes: N 2 transfer (TRF) and N-N dissociation (DIS). For V-series clusters, which has a V atom on Site 1, the rate-determining step is DIS, while for Ta-series clusters with a Ta on Site 1, TRF may be the rate-determining step or has close energy barriers to those of DIS. The overall energy barriers for heteronuclear V 2 TaC 4 - and VTa 2 C 4 - clusters are lower than those for homonuclear V 3 C 4 - and Ta 3 C 4 - , showing that the doping effect is beneficial for the activation and dissociation of N 2 . In particular, V-Ta 2 C 4 - has low energy barriers in both TRF and DIS, and it has the highest N 2 adsorption energy and a high reaction heat release. Therefore, a trimetallic heteronuclear V-series cluster, V-Ta 2 C 4 - , is suggested to have high reactivity to N 2 activation, and can be served as a prototype for designing related catalysts at a molecular level.