Theoretical Investigation On The Oxidation Of CH₃OH With O₂ Catalyzed By [VO₃]^- And Acetylene Cyclotrimerization Catalyzed By TiO₂,Ti In Gas Phase

Although the reactions for small molecules activated by transition metal and corresponding oxides have been comprehensively applied in global chemical industries, the catalytic mechanism is still the hotspot both in the experimental and theoretical research, especially in the reaction with hydrocarbons in the gas phase.Due to the several different arrange styles of valence electrons, transition metals and corresponding compounds have different spin states corresponding to different potential energy surfaces（PESs） during the catalyst course. Meanwhile, the reaction is likely to appear the phenomenon of spin flips in virtue of the effect of spin-orbit coupling close to crossing points（CP）, resulting in the change of spin state. The reaction may occur intersystem crossing（ISC） between PESs with different spin states, leading to the reaction accessible to a much lower energy pathway. Namely, it is extremely possible to appear “two state reactivity” even “multiple state reactivity（TSR/MSR）”. By now the machanism of TSR have being still studied extensively.The effects of each TS and IM in the minimum energy pathway of the cycle reaction could be obtained by citing the energetic span model proposed by Kozuch. And the TOF-determining transition state（TDTS） and TOF-determining intermediate（TDI）were also confirmed. Finally, an activity evaluation for the catalyst was conducted with the energetic span（δE） that has been obtained.In this paper, in accordance with density functional theory（DFT）, the oxidation of CH3 OH with O2 catalyzed by [VO₃]- and acetylene cyclotrimerization catalyzed by TiO2, Ti in gas phase were investigated theoretically. The mechanism of two different reactions were verified, respectively. Accordingly, provide a theoretical foundation for further experimental exploration.This paper is comprised of four chapters. The first chapter covers the improvement and application of quantum chemistry, the background and development of TSR/MSR besides. The second one briefly presents the theoretical principles and computational methods needed in this paper. Thereby, provides a substantial theoretical basis for the coming exploration.In the light of experimental research of Waters et al. in chapter 3, theoreticalvalidation about the reaction mechanism of catalytic cycle was in progress between singlet and triplet state, aimed at the oxidation of CH3 OH with O2 catalyzed by [VO₃]-.And the crossing points have been analyzed between the two different potential energy surfaces at length. The possibilities of spin flip in the vicinity of CPs are discussed through spin-orbit coupling calculations. The probabilities of ISC at minimum energy crossing points（MECPs）are computed by Landau-Zener formula.Finally, the turnover frequency（TOF） of [VO₃]- at 298 K has been obtained by citing the energetic span（δE） model proposed by Kozuch, and confirmed the rate-determining transition states and rate-determining intermediate for a cyclic reaction.In chapter 4, according to the theoretical research of Ma et al., select acetylene cyclotrimerization catalyzed by TiO2, Ti in gas phase as the research object. As with the above reaction, theoretical validation about the reaction catalytic mechanisms was underway between singlet and triplet state. Among the rest, there is not CP in the reaction catalyzed by TiO2, while the other owns. In succession, spin flips close to CPs are analyzed identically. The minimum energy reaction path was ascertained by calculating the probabilities of ISC nearby the CPs. The turnover frequency（TOF） of TiO2, Ti at 298 K has been severally obtained ultimately as well as confirmed the rate-determining states for every cyclic reaction, and then catalytic activities of the two different catalysts were compared.