Non-Transition-Metal Catalytic System for N-2 Reduction to NH3: A Density Functional Theory Study of Al-Doped Graphene

The prevalent catalysts for natural and artificial N-2 fixation are known to hinge upon transition-metal (TM) elements. Herein, we demonstrate by density functional theory that Al-doped graphene is a potential non-TM catalyst to convert N-2 to NH3 in the presence of relatively mild proton/electron sources. In the integrated structure of the catalyst, the Al atom serves as a binding site and catalytic center while the graphene framework serves as an electron buffer during the successive proton/electron additions to N-2 and its various downstream NxHy intermediates. The initial hydrogenation of N-2 can readily take place via an internal H-transfer process with the assistance of a Li+ ion as an additive. In view of the recurrence of H transfer in the first step of N-2 reduction observed in biological nitrogenases and other synthetic catalysts, this finding highlights the significance of heteroatom-assisted H transfer in the design of synthetic catalysts for N-2 fixation.