DFT Study On The Mechanism Of Dehydrogenation Of Cyclohexane Catalyzed By NiTi~+ And FeTi~+ In Gas Phase

The catalytic dehydrogenation reaction of alkanes by transition metal ions has captured the attention of scientists in recent years because of its wide application in hydrogen energy.So far,there has been a great deal of theoretical exploration and experimental studies on the catalytic reaction of alkanes using transition metal ions as catalysts.Studies have shown that the catalytic performance of dimers of transition metal ions is stronger than that of mononuclear transition metal ions due to the synergistic effect between transition metal atoms.Based on Schwarz's experimental research basis,we have theoretically studied the catalytic reaction of cyclohexane by homonuclear transition metal ions.For example,C-H and C-C bonds of cyclohexane can be activated by the homonuclear dimer ions Ni₂⁺,Ti₂⁺,V₂⁺,Cr₂⁺and Mn₂⁺,and there is a competitive reaction between C-H and C-C bonds.However,different transition metal ions have different catalytic activities.Since the dehydrogenation mechanism of some heteronuclear transition metal ions still remain yet unclear,this thesis carries out a systematic study on the catalytic dehydrogenation process of cyclohexane by heteronuclear transition metal ions NiTi⁺and FeTi⁺.This thesis uses B3LYP method based on Density Functional Theory?DFT?to perform the quantum chemistry calculation and studies the catalytic reaction mechanism of cyclohexane by NiTi⁺and FeTi⁺.It obtains the optimized geometries of reactant,transition state,intermediate and product and relevant configuration parameters through the geometry optimization.Then it draws out the relevant quartet state and doublet state potential energy surfaces and obtains relevant thermodynamic parameters.By comprehensively analyzing the reaction mechanism of these data,this thesis provides a theoretical basis for the further experimental researches.This thesis is divided into five chapters.The first chapter discusses the development and current status of quantum chemistry,reviews the research progress of C-H and C-C bonds activation of alkanes by transition metal ions,and finally summarizes the research work of this thesis.The second chapter introduces the theory,calculation method and calculation basis of quantum chemistry.The third chapter conducts the theoretical research on the dehydrogenation mechanism of cyclohexane activated by NiTi⁺in the quartet state and doublet state,and analyzes the reaction characteristics involved in the reaction mechanism.The research analysis indicates that the dehydrogenation of cyclohexane activated by NiTi⁺is carried out on the mixed potential energy surface curves of the double and quadruple states.When NiTi⁺catalyzes cyclohexane to eliminate the first member hydrogen,there exist two reaction mechanisms in this reaction:one is to continue the activation of C-H bond,and the other is to activate C-C bond.By studying the two pathways in detail,it can be concluded that the scission of C-C bond requires higher energy,so the main pathway of this reaction is C-H bond activation of cyclohexane.The fourth chapter systematically studies the dehydrogenation mechanism of cyclohexane activation by FeTi⁺in the doublet state and quartet state.According to the potential energy surface,it is found that when FeTi⁺catalyzes cyclohexane to eliminate the first member hydrogen,the competitive reaction of cyclohexane of C-H and C-C bonds also takes C-H bond activation of cyclohexane as the main reaction pathway.The fifth chapter gives a summary and outlook of the thesis.