| Chapter 1:The concept and character of gas was briefly introduced, the reaction mechanism and research progresses have been reviewed about gas explosion and its catalytic oxidation via transition metal.Chapter 2:The reaction mechanism of gas explosion has been clarified and gas explosion process has been analyzed thermodynamically. The thermodynamic formula of gas explosion limits have been derived with irreversible thermodynamic parameters, and have been used to analyze various affecting factors of gas explosion limits. The first law of thermodynamics has been used to predict the danger of gas explosion. To calculate the explosion limits of methane under certain conditions, and compared the results with literature values, relative deviation of the lower limit and the upper limit were about 0-6.1% and -1.9%-11%, respectively. Finally, combining various factors, the chemical thermodynamic forewarning system of gas explosion has been established to provide a more comprehensive theory basis for gas prevention and control.Chapter 3:The hydrogen-abstraction reaction mechanisms of methane and hydrogen with oxygen have been investigated systematically using the complete active space second-order perturbation (CASPT2) approach, a multireference method. The research results show that the hydrogen abstraction reaction mechanisms were similar between the two systems CH4+O2 and H2+O2 through the analysis of reaction potential energy curves, geometric structure and electronic configuration. Oxygen may be involved in reaction in the two forms:triplet 3∑g- and the first electronic excited singlet 1△g. Under Cs symmetry, the singlet 1△g will be divided into two forms: 1△g- and 1△g+. Then there are three reaction pathways, the corresponding electronic states are 3A", 1A" and 1A'.The 3A" reaction proceeds to products via a transition state and a van der Waals complex. The 1A" pathway is similar with the A" one, and its activation barrier is lower than that of the 3A" pathway, so that the 1A" pathway should be important in the hydrogen abstraction reactions in singlet oxygen-rich cases. The 1A' pathway, however, dissociates directly to the radicals, and is distinct from the 1A" pathway though their reactants are degenerate in energy.Chapter 4:The catalytic activation mechanism of C-H bond in methane via Pd, Pt, Ag three transition metal atoms have been investigated with density functional method.The research was carried out mainly from the perspectives of the relevant intermediates and transition states on reaction potential energy curves, and the corresponding energy changes, reaction rate constants. The activation processes of C-H bond via Pd and Pt are similar:forming atom-molecule complex, then through the respective transition state generating products. However, large differences in energy, activation energy and absorbing energy required are about 13.4 kcal/mol and 8.6 kcal/mol for activation of CH4 via Pd. But the Pt atom participated in the activation reaction in two low energy state of triplet (d9s1,3D3) and singlet state (d10, 1S0). A salient feature is the crossing of two potential energy curves at the Pt-C distance of 2.685 A. The crossing takes place at a very low energy 3.6 kcal/mol above the complex Pt(3D)CH4, the energy released of the whole reaction is about 34.4 kcal/mol. The activation of C-H bond via Ag may have two reaction courses, judging from the rate constant, it is possible that the Ag atoms abstract H atom of CH4 dissociated directly to CH3 and AgH, the reaction need to absorb energy of 52.1 kcal/mol. Comparing the activation energy, enthalpy and rate constants of activation reaction via Pt, Pd, Ag, it can be obtained that the catalytic performance of three atoms was Pt> Pd> Ag. The above results can provide a theoretical guide to find high-quality, highly efficient catalyst.
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