Modeling Of Reaction Of NO/SO₂ With Fe₆/Fe₂ By Quantum Chemical Theory

Serious air pollution has aroused widespread concern in the world.Nitrogen oxide and sulfur dioxide are the main air pollutants,mainly from coal and petroleum fossil fuel combustion.Traditional methods of removing nitrogen oxides and sulfur dioxide often lead to secondary pollution or costly.Transition metal due to their importance in heterogeneous catalysis is of particular interest,which lead to the dependence of functional properties on cluster size both from experiment and theory.In combustion research field,a lot of research has shown that iron cluster was very effective to reduce NO and SO₂.In this paper,the mechanism of the reactions?Fe₂ and NO,Fe₆ and SO₂?were studied by the density functional theory?DFT?with the B3 LYP methods combined with the 6-311+G?d,p?basis set.The geometry optimizations of reactants,transition states,intermediates and products of the reaction systems were completely confirmed,and all the transition states were verified by the vibration analysis and the intrinsic reaction coordinate calculations at Gaussian 09 suite of programs.The topological properties of bond critical points of stationery points were received by atom in molecule theory;in the light of activation energies,parameters of stationery points,the reaction rate constant?RRC?of reactions was calculated.Meanwhile,we can reached the following conclusions:1.In Fe₆+NO system,there is a crossing point?CP?existing between the 20-et and 22-et potential energy surface?PES?,which belongs to the "Two State Reactivity"?TSR?and benefits the kinetic and thermodynamic aspects of this reaction.Before the crossing point,bond orders of stationery points on 20-et PES are more stable than the 22-et PES.After the crossing point,bond orders of stationery points on 22-et PES are more stable than the 20-et PESs',which is consistent with the results of TSR.Utilizing the classical transition state theory,the RRCs of different PESs can be fitted,the existence of crossing points can make the reaction rate constant larger.2.In Fe₂+SO₂ system,there are two crossing points?CP?existing between the septet and nonet potential energy surface?PES?,which belongs to the "Two State Reactivity"?TSR?and benefits the kinetic and thermodynamic aspects of this reaction.Before the first crossing point,bond orders of stationery points on septet PES are more stable than the nonet PES;after the first crossing point,bond orders of stationery points on nonet PES are more stable than the septet PES;after the second crossing point,bond orders of stationery points on septet PES are more stable than the nonet PES,which is consistent with the results of TSR.Utilizing the classical transition state theory,the reaction rate constants of different PESs can be fitted,the existence of crossing points can make the rate constant of reaction larger.Comparing the activation energies,bond order and reaction rate constant of two reactions at same calculation level,the Fe₂+SO₂ system may be more favorable.