DFT kinetic study of the pyrolysis mechanism of toluene used for carbon matrix

Based on the thermodynamic data, the pyrolysis mechanism of the carbon matr ix toluene used for carbon material was studied by dynamic computation usin g the UB3LYP/3-21G* method in the Gaussian 98 program package. The transiti on states were found by the QST2 method and were proved by IRC calculations . The activation energies of the five reaction paths were calculated, and t he rate constants from 298-1 223 K were obtained by the transition states t heory. 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 --> i ntermediate as rate - control step and activation energy DeltaE(0)(theta no t 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 a nd methyl radical. The corresponding activation energy is DeltaE(0)(theta n ot equal) = 456.91 kJ/mol. This mechanism is in accord with the experimenta l result.