Theoretical Investigation On The Reaction Mechanism Of Small Molecules Catalyzed By NiO⁺ And Mo₂O₄^-/W₂O₄^- In Gas Phase

In recent years,it has been a constant exploration for researchers to achieve the targeted chemical bond cleavage with high selectively.With the deeper understanding of catalysts,chemists have found that transition metal oxide ions have highly selectivity and activity to alkanes,especially higher alkanes.In addition,the application of transition metal oxides as electrode materials for photoelectrochemical water splitting to produce hydrogen has also expanded the research on the catalytic reactions involved in transition metal oxides.Experimental researches have provided abundant information,but there are still a lot of shortcomings about the explanation of catalytic mechanism at the micro level.Therefore,it is very meaningful to learn about the reaction mechanism of transition metal oxide ions and small molecules,which can provide the nature of the catalytic process at the molecular level,and theoretical evidences for the experimental results.For the catalytic reaction that transition metal oxide ions participate in,the d orbital of the transition metal ions have several unpaired electrons.These electrons can easily spin flip due to spin-orbit coupling effect,which causes the change in the spin state of the entire reaction system,and the reaction proceeds in different spin states.These reactions are referred to as two-state reactions.In resent years,the research on the two-state reaction in theoretical chemistry has been focused on the probability of intersystem crossing and the transition mechanism of d orbital electrons,which can help us to have a better understanding of the two-state reaction.Furthermore,chemists also pay attention to the catalytic effect of transition metal oxide ions.Unlike experimental studies,theoretical chemistry studies compare the catalytic conversion frequencies of different catalysts by Kozuch energy span model,the goal of which is to find catalysts with higher catalytic performance and to provide guidance for the experiment.This paper is divided into four chapters.The first chapter briefly introduces the research background,research progress and the main research contents of this paper.The second chapter introduces the basic theory and calculation methods involved in this paper,which is the theoretical basis of the research.In the third chapter,the gas phase reaction of ethane catalyzed by NiO⁺was studied.The Gaussian09 program was used to combine B3LYP method with 6-311++G?3df,3dp?&SDD basis set to optimized the stationary points on doublet,quartet energy surfaces.The atoms in molecules?AIM?,electron localization function?ELF?and density of states?DOS?are used to study the properties of the chemical bonding evolution along the reaction pathways.Two possible reaction pathways were identified,which lead to the formation of ethanol?path 1?,ethylene and water?path 2?.The proportion of products is discussed by Curtin-Hammett principle,and the result shows that the path 2 is the main reaction channel and the water and ethylene are the main products.There was spin crossings between doublet and quartet surface.We estimated the spin-orbit coupling constant at the minimum energy crossing points?MECP?with the help of GAMESS packages,and the weighted average with statistical concepts was introduced to estimate<P_ISC>,which is 0.12 and 0.11,respectively.The high<P_ISC>probability in the vicinity of the crossing indicates that the intersystem crossing will be very efficient between the quartet and doublet state,which makes the reaction occurs along the doublet surface.We also analyzed the crossing and spin inversion about MECP-a.It turns out to show that the?single electron on the d_xyy orbital will complete the leap from the d_xyy orbital to the d_yzz orbital to make the reaction shifted from quartet to doublet.In the fourth chapter,the reaction mechanism of Mo₂O₄^-/W₂O₄^-catalyzed H₂O and CO was studied.The theoretical calculation at the UM06/TZVP&SDD level was performed to optimized all the transition states and intermediates.The initial reaction sites were predicted using Multiwfn package.A variety of analytical methods were used to analyze the bonding properties at the critical stable point and the interaction of the frontier orbit,and we found that the interaction between two molecules in the initial complex is considered to be an electrostatic interaction.Finally,The catalytic effect of Mo₂O₄^-/W₂O₄^-was estimated by citing the energetic span model by Kozuch.It was shown that the Mo₂O₄^-have a higher catalytic effect towards H₂O and CO.At the same time,in order to eliminate the calculation error and provide a theoretical support for experimental research,we also calculated the ratio of catalytic effect of the two catalysts.It was found that the catalytic conversion frequency using Mo₂O₄^-should be 8.85×10²times than that of W₂O₄^-.