Density Functional Theory Study Of The Reaction Of Iron With NO And SO₂

In recent years, transition metal is of particular interest due to their importance inheterogeneous catalysis. The dependence of functional properties on cluster size has attacted muchattention both from experiment and theory. In combustion research field, plenty of researches haveshown that transition metal was very effective to reduce NO and SO2. In our former researches,we have found that iron mesh roll was very effective to reduce NO to N2. However, due to thecomplex of the reaction and the unstable intermediate products, experimental methods are difficultto find the intermediate products and definite reaction pathways. With the development oftheoretical chemistry and compute capability, studying chemical reactions by the densityfunctional theory (DFT) has been a significant method to understand the mechanism of chemicalreactions.In this paper, on the basis of the molecular orbital theory, the traditional transition state theoryand two-state reactivity (TSR), the system have carefully investigated using the Gaussian09program computational package. After the calculations, the information of all species(intermediates and transition states) on potential energy surfaces (PESs), the data ofthermodynamics and orbital ware obtained. In the light of that data, we can receive frequencyvibration, reaction pathway, energy barriers, activation energy, and rate constant of reaction(CRR), also the mechanism of reaction. Meanwhile, we can reach the following conclusion:1) In the reaction between iron atom and NO, there are crossing points (CPs) on the quartet/sextet PES in four reaction channels, which can lower the energy barriers of reactions, andgood for the kinetics and thermodynamics of reactions. Utilizing the classical theory oftransition metal, the CRR of single PES and PES inversed by CPs can be fitted. Theexistence of CPs can make the rate constant of reaction larger.2) In the reaction between iron dimer and NO, there are CPs existing in the two PESs, whichbelongs to the TSR. Also, CPs can lower the energy barriers of reactions, and good for thekinetics and thermodynamics of reactions. At the same mechanism of reaction, comparingthe reaction of iron atom and NO, the reaction of iron dimer and NO is more feasible.Furthermore, the activation energy of NO activated by iron dimer is lower than the iron atom’s. Besides, the rate constant of reaction of NO activated by iron dimer is larger than theiron atom’s3) SO2activated by the iron atoms is two-step reaction. At first, the iron atom separate theoxygen of the SO2, the next, the other oxygen atom is cleaved by the iron atom, result in thesulfur.The reaction of SO2activated by the iron atoms is on two PESs separately, the reactionon the quintet potential energy surface is favorable.