Theoretical prediction of a new dinitrogen reduction process:: Utilization of four dihydrogen molecules and a Zr2Pt2 cluster

The mechanisms of dinitrogen reduction to hydrazine by four dihydrogen molecules and a Zr2Pt2, I, cluster have been extensively studied at the density functional level. It was shown that the reaction starts from the coordination of the N-2 molecule to the Zr centers of I. The resulting complex, Zr2Pt2(mu-1,2-N-2), II, activates four dihydrogen molecules and produces the (mu-1-H)(2)ZrPt(mu-1,2-N2H4)PtZr(mu-1-H)(2), X complex. The activation barriers corresponding to the first, second, third, and fourth H-2 molecules are predicted to be DeltaH = 7.0 (DeltaG = 15.6), 10.6 (19.3), 18.3 (27.4), and 25.8 (34.6) kcal/mol, respectively. The calculated dissociation energy of the hydrazine molecule from the product X is 19.2 (6.5) kcal/mol. The entire reaction Zr2Pt2 + N-2 + 4H(2) (mu-1-H)(2)ZrPt2Zr(mu-1-H)(2) + N2H4 is found to be exothermic by 52.6 (21.7) kcal/mol and proceed via a 25.8 (34.6) kcal/mol rate-determining barrier corresponding to the activation of the fourth H2 molecule. The dinitrogen reduction to hydrazine by four dihydrogen molecules and a Zr2Pt2 cluster is predicted to be feasible at the modem experimental conditions.