Dissertation > Excellent graduate degree dissertation topics show

A Density Functional Theory Study of the Spin-forbidden Reactivity of the Activation of CH4 by Transition Metal

Author: WangQiang
Tutor: WangYongCheng
School: Northwest Normal University
Course: Physical and chemical
Keywords: density functional theory (DFT) two-state reactivity (TSR) crossing between PES spin-obital coupling intersystem crossing probability
CLC: O621.13
Type: Master's thesis
Year: 2010
Downloads: 76
Quote: 0
Read: Download Dissertation

Abstract


Methane activation by transition metal has been a topic of growing interest during the past decade, due to economic interest in the methane conversion and chemistry. Interesting insights into the details and mechanisms of the activation process can be gained by studies of gas-phase reactions of metal ions and clusters. The activation of C-H bonds is a key step in numerous syntheic reactions and catalytic processes. Methane, as one of the most important chemicals, has been widely used in chemical synthesis, hydrogen production, and energy production. As such, methane activation has been studied extensively by both experimentalists and theorists. However, the activation of C-H bond in methane is a unique challenge among the hydrocarbons due to its large bond energy (the C-H bond energy is about 440 kJ/mol). Early investigations have shown that neutral metal atoms are often reacive under electronic excitation with small alkanes. Recent studies reveal that many transition metals including lanthanides and actinides are good C-H insertion agents in reactions with small alkanes and often form high-oxidation-state complexes with a carton-metal multiple bond following H migration.Methane activation mediated by W or Ta/ Ta- have generated new class of small insertion products and high-oxidation-state complexes with multiple carbon-metal bonds and was found to be a spin-forbidden process. According to the principle of two-state reactivity reaction, the activation of C-H bonds of methane by bare transition metal atom or cation had been examined using density functional theory to explore the reaction mechanisms.The whole paper consists of four chapters. Chapter 1 mainly reviews the progress and application of quantum chemistry as well as the development and the present situation of two-state reactivity. The second chapter summarizes the theoretical background of this thesis, mianly contained the potential energy surface, the natural bond orbital and spin-orbit coupling mechanism etc. The contents of two chapters were the basis and background of our studies and offer us with useful and reliable quantum methods.In chapter 3 and 4, the gas phase reactions of W or Ta/ Ta- with CH4 have been investigated using Density Functional Theory and the activation of the C-H bonds of the methane have been emphasized. We discuss detaily the crossing points between two PESs of different spin multiplicities in the reaction pathway to better understand the spin inversion processes involved in the reaction. Firstly, all molecular geometries on each spin were fully optimized and vibrational frequency calculations on the potential energy surface of different spin multiplicities in the reaction pathway by 6-311++G (3df, 3pd) basis set and corresponding pseudopotential. Secondlly, the intrinsic reaction coordinate (IRC) was then calculated to probe the reaction path and check if the correct transition state was located. Then, on the basis of the Hammond postulate, the crossing points (CPs) between states of different spin multiplicities has been selected by means of the procedure used by Yoshizawa et al. For the sake of comparison, the mathematical algorithm to MECPs developed by Harvey et al. had also been employed. Finally, The spin-orbit coupling is calculated between electronic states of different multiplicities at the crossing points (MECPs) to estimate the intersystem crossing probabilities, and the probability of hopping from one surface to the other in the vicinity of the crossing region is calculated by the Landau-Zener type model. The energetically more favorable channel was confirmed according to thermodynamic and dynamic date.

Related Dissertations

  1. A Density Functional Theory Study for Wn C0,± （n=1-6） Clusters,O641.1
  2. A Study for Structure and Properties of OsnN0, ± （n=1-6） Clusters,O641.1
  3. CH_3X (X = OH, Cl, Br, I) solution from DFT Study of the Reaction Mechanism,O643.1
  4. Quantum chemical calculation of several chemical reaction mechanism,O643.12
  5. Preparation and Properties Research of New Type Nano-Porphyrin,TB383.1
  6. Theoretical Studies on the Structures and Properties of High-nitrogen Heterocycle Compounds: Triazole and Tetrazine Derivatives,TQ560.1
  7. Theoretical Study on Several Transition-metal Complexes Catalyzed Reactions of Carbon Dioxide with Epoxides,O641.121
  8. Synthesis, Properties of Short-wavelength Cyanine Dyes as Well as Their Application in Biomedical Areas,O621.25
  9. Doped graphene and its electronic structure Theoretical Study,O613.71
  10. Boron ( aluminum ) azide clusters structure and Theoretical Study,O613.8
  11. Ethylene and cis 2 - butene insert two cyclopentadienyl zirconium zirconium dihydride detailed reaction mechanism of hydrogen,O643.12
  12. The Experimental and Theoretical Studies of Raman Spectra of 2,2’-bipy in Acidic Solution and 2,2’-bipy on Gold,O626
  13. A Hybrid Cylindrical Model for Characterization of MCM-41 by the GCMC Method and Density Functional Theory,O647.3
  14. Adamantane derivatives and tetrahedral alkyl structure and properties of high energy quantum chemical study,O621.13
  15. Silicon-containing three-membered ring transition metals and small molecules Theoretical Study,O643.12
  16. Amino acid dipeptide crystal structure and theoretical study of the vibrational spectra,O629.7
  17. An Experimental and Theoretical Study on the Adsorption Behaviors of Molecules on Silver Nano-particles,O439
  18. The Preparation of Noble Metal Nanoparticles and the Application in Raman Spectroscopy,O611.3
  19. Impurity gases in the adsorption behavior of palladium alloy,O561
  20. LaNi_ (4.5) Al_ (0.5) H_x crystal microscopic configuration of the hydrogen,O561.1

CLC: > Mathematical sciences and chemical > Chemistry > Organic Chemistry > Organic Chemistry general issues > Theory of organic chemistry,physical organic chemistry > Organic Chemistry Structure Theory
© 2012 www.DissertationTopic.Net  Mobile