碳源甲基苯热裂解机理的密度泛函动力学研究  

DFT Kinetic Study of the Pyrolysis Mechanism of Toluene Used for Carbon Matrix

作　　者：王惠[1] 杨海峰[1] 翟高红[2] 文振翼[2] 冉新权[1] 史启桢[1] 罗瑞盈[3] 杨延清[4] 

机构地区：[1]西北大学化学系,西安710069 [2]西北大学现代物理研究所,西安710069 [3]北京航空航天大学,北京100083 [4]西北工业大学材料科学系,西安710072

出　　处：《化学学报》2001年第1期17-21,共5页Acta Chimica Sinica

基　　金：国家自然科学基金 ( 5 9682 0 0 70 );陕西省教委专项基金 ( 99JK10 0 )资助课题

摘　　要：在热力学研究的基础上 ,用UB3LYP/3 - 2 1G 方法对甲苯热裂解机理进行了动力学研究 .计算得到了甲苯的5种热裂解路径的活化能 .用过渡状态理论 ,计算得到了这些路径在 2 98～ 12 2 3K温度范围内的速率常数 .动力学计算结果表明 :甲苯在热解温度低于 963K时的主反应路径为甲苯热裂解生成苄基自由基的反应 ,其速控步的活化能ΔEθ0 ≠ =40 2 .2 7kJ/mol;当温度高于 963K达 12 2 3K左右时 ,主反应路径转为苯环上脱甲基生成苯基和甲基自由基的路径 ,该路径的活化能ΔEθ0 ≠ =45 6.91kJ/mol.Based on the thermodynamic data, the pyrolysis mechanism of the carbon matrix toluene used for carbon material was studied by dynamic computation using the UB3LYP/3-21G* method in the Gaussian 98 program package. The transition states were found by the QST2 method and were proved by IRC calculations. The activation energies of the five reaction paths were calculated, and the rate constants from 298-1 223 K were obtained by the transition states theory. The dynamic calculation results show, when the pyrolysis temperature of toluene is lower than 963 K, the main reaction path is the breaking of the C-H bonds of the methyl on the benzene ring. The reaction is completed via the process: reactant --> intermediate --> product, with reactant --> intermediate as rate - control step and activation energy DeltaE(0)(theta not equal) = 402.27 kJ/mol. When temperature is higher than 963 K, but below 1 223 K, the main reaction paths is the one that produces benzene radical and methyl radical. The corresponding activation energy is DeltaE(0)(theta not equal) = 456.91 kJ/mol. This mechanism is in accord with the experimental result.

关 键 词：碳/碳复合材料 碳源甲基苯 热裂解机理 反应动力学 密度泛函 

分 类 号：O625[理学—有机化学]