Theoretical Investigation For The Cycle Reaction Of Small Molecules Catalyzed By Transition Metal

Because they can provide fundamental information about catalytic bondactivation a large number of studies both experimental and theoetical have beendevoted to the reactions of transition metal atoms or ions with small molecules.Many of these studies concentrated on the activation of hydrocarbons （CH₄, C₂H₄,CH₃OH…）. And wide attention was also given to remove some importantpollutants of the atmosphere （N₂O, CO₂, NO₂, CO and NO,）. The theoreticalapproaches to these reactions also indicated that the transformations of spinmultiplicities occur frequently in thermal reactions. Namely, the reactions did notobey “spin conservation law”. Usually, more than one state is involved inreaction process, which ensures the whole reaction always proceeds on thelow-energy potential energy surface （PES）. Such a phenomenon is called“two-state reactivity （TSR）”.In the thesis, In the thesis, based on “two-state reactivity （TSR）”theory,the gas phase reactions of H₂O with CH₄catalyzed by Pt⁺（²D,⁴F） generation of water gasand CO oxidation by O₂over FeO_1–3which were selected as representativesystems of the activation of C-H bonds of hydrocarbons by bare transition-metalcations and activate the strong O–O bond by Transition metal oxides, have beenexamined by using density functional theory （DFT） and CCSD （T） methods withcorresponding basis sets to explore the reaction mechanisms. The Gaussian03andGamess program package were performed in this thesis.The whole thesis consists of four chapters, Chapter1and Chapter2describethe progress and application of quantum chemistry as well as the development andthe present situation of TSR/MSR, and briefly introduce elementary theory andquantum chemistry computation methods. The contents of the two chapters are thebasis and background of our studies and offered us with useful and reliablequantum methods.The chapter3, The two-state reaction of H₂O with CH₄catalyzed by Pt⁺（²D,⁴F） generation of water gas has been investigated at the density functionallevel of theory using the hybrid exchange correlation functional B3LYP and thecoupled cluster with single, double and perturbative triple excitations CCSD（T）. The important analysis and explanation of minimum energy reaction potentialenergy surfaces were done using molecular orbital theory and natural bondingorbital （NBO）. The energetic span （δE） model coined by Kozuch was applied inthis cycle. The turnover frequency （TOF）-determining transition state （TDTS） andTOF-determining intermediate （TDI） were confrmed. Finally, utilizing theturnover frequency（TOF） evaluate cycle reaction.The chapter4, Carbon monoxide （CO） and oxygen （O₂） catalyzed by smallneutral iron oxide clusters (FeO_1–3) was investigated at the density functional levelof theory using the Becke–Perdew–Wang functional （BPW91）. Three reactionpathways along with singlet, triplet and quintet states were calculated for ascertainthe presence of some spin inversion during the catalytic cycle. The catalytic cyclewas found to be “two state reactivity” resulting from the crossing among themultistate energetic profiles. Where after, a series of crossing points （CPs）involving the structures and energy values has been located and the spin inversionbehaviors by which the reaction system can hop from one PES to another byeffective spin-orbital coupling have been inspected. Finally, the energetically morefavorable channel was confirmed according to thermodynamic and dynamic data.In order to evaluate the performance of catalyst, the energetic span modeldeveloped by Kozuch was implemented here, whereas this model is not suitablefor handling the diabatic reaction. To this end, we taking into consideration thedifferent spin states of the system. A kinetic assessment is carried out with anexpansion of the energetic span model, including the spin-crossing effects. Thisapproximation enables one to measure the efficiency of catalytic cycle includespin-crossing effects by quantum mechanically compute.