Theoretical Study Of The Mechanism For The Cycle Reaction Of N₂O And CH₄Catalyzed By Fe⁺, Co⁺, Ni⁺to Yield CH₃OH In The Gas Phase

Catalytic cycles are ubiquitous in chemistry and biology. The efficiency ofcatalytic cycles is measured by their turnover frequency （TOF）, which is defined ascycles per time and catalyst concentration. How one can conceptualize an efficientcatalytic cycle is the main concern of the present contribution that seeks to combinethe insights of quantum chemistry with a kinetic model. In2006, Kozuch proposedthe energetic span model, which can calculate TOF using the Gibbs free energy ofintermediates and transitions. This model has provided chemists a method to controland design better catalysts, nevertheless it is just fit for single-state reactivity. As weall know, there would appear intersystem crossing between tow potential energysurfaces when transition metals participated in the reaction. Therefore the energeticspan model coined by Kozuch should be corrected in order to deal with diabaticreactions.In this thesis, the gas phase cycle reaction of N₂O and CH₄catalyzed by Fe⁺, Co⁺and Ni⁺to yield CH3OH have been examined using density functional theory （DFT）,CCSD methods with corresponding basis sets. The Gaussian03, Games, and NBOprogram package were performed.The whole thesis consists of four chapters. Chapter1and Chapter2describe theprogress and application of quantum chemistry as well as the development and thepresent situation of TSR, and briefly introduce elementary theory and quantumchemistry computation methods. The contents of the two chapters are the basis andbackground of our studies and offered us with useful and reliable quantum methods.In chapter3, the mechanism of the gas phase reaction between N₂O and CH₄catalyzed by Fe⁺to yield CH3OH has been investigated on the B3LYP and CCSD（T）levels of theory. The potential energy surfaces （PESs） were characterized in detailusing molecular orbital theory and natural bonding orbital （NBO）. Crossing pointsbetween the different potential energy surfaces and the possibility of spin inversionwere discussed based on calculation of spin-orbit coupling （SOC）. The energeticspan model developed by Kozuch was corrected in order to deal with non-adiabatic reactions. Finally, we calculated the turnover frequency （TOF） of the catalytic cycleand found the TOF determining transition state （TDTS） and the TOF determiningintermediate （TDI） using the treated energetic span model.In chapter4, the mechanism of the gas phase reactions between N₂O and CH₄catalyzed by Co⁺and Ni⁺to yield CH3OH has been compared. The potential energysurfaces （PESs） were characterized in detail using molecular orbital theory andnatural bonding orbital （NBO）. We find the low-energy pathways of these two cyclereactions between N₂O and CH₄catalyzed by Co⁺and Ni⁺to yield CH3OH aresurprisingly similar to that of the cycle reaction catalyzed by Fe⁺we considered inchapter3. Then, we used the energetic span model that is suitable for two-statereactivities to compare the efficiency of the three catalysts for the cycle reaction.