Theoretical Prediction of a New Dinitrogen Reduction Process:Utilization of Four Dihydrogen Molecules and a Zr_2Pt_2 Cluster

摘要

The mechanisms of dinitrogen reduction to hydrazine by four dihydrogen molecules and a Zr_2Pt_2,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,Zr_2Pt_2(mu-l,2-N_2),II,activates four dihydrogen molecules and produces the (mu-l-H)_2ZrPt(mu-l,2-N_2H_4)PtZr(mu-l-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 (AG=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 Zr_2Pt_2+N_2+4H_2 ->(mu-1-H)_2ZrPt_2Zr(mu-l-H)_2+N_2H_4 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 H_2 molecule.The dinitrogen reduction to hydrazine by four dihydrogen molecules and a Zr_2Pt_2 cluster is predicted to be feasible at the modern experimental conditions.