分子筛催化甲苯歧化SE1反应机理的分子模拟研究

应用分子模拟半经验量子力学Mopac 6．0-AM1近似计算方法分析了分子筛催化甲苯歧化反应的S_E~1反应历程,确定了反应历程中的反应态、过渡态和产物态,得到了反应活化能和反应热等相关信息,对内禀反应坐标的计算进一步验证了反应过程中的能量变化。计算结果表明,分子筛催化的甲苯歧化反应沿S_E~1反应历程可通过两步基元反应完成；质子由分子筛向甲苯分子转移的过程为反应的快速步骤,其活化能达到428．54 kJ·mol~(-1),需要在高温下进行；甲苯歧化总反应的热效应很小,与实验数据相吻合。

Molecular simulation research on SE1 reaction mechanism of toluene disproportionation in catalysis over zeolite

Molecular simulation techniques(Mopac 6.0-AM1 semi-empirical quantum mechanics method)were used to analyze the re- action related to S_E~r mechanism of toluene disproportionation catalyzed by acidic zeolite cluster model.The corresponding reactant state, transition state and product state were confirmed,activation energy and reaction heat were obtained according to them.The intrinsic re- action coordinate was used to identify the energy variation connected to each transition structure.Simulation results prove that toluene disproportionation can complete through two-steps elementary reaction along S_E~1 reaction mechanism.The difference in activation energy between p-xylene,m-xylene and o-xylene is little.The transfer process of proton between zeolite and toluene molecule is rate-determi- ning step of reaction.Product selectivity is not controlled by disproportionation reaction mechanism.The calculated activation energy is 428.54 kJ(?)mol~(-1)of proton exchange and toluene disproportionation reaction has to take place in higher temperature.Whole toluene disproportionation is a micro-thermal effect reaction.Simulation results show great agreement with experimental data.