论文部分内容阅读
采用ONIOM和DFT方法研究了H-ZSM-5分子筛催化环己酮肟制ε-己内酰胺的贝克曼重排反应机理.所有的构型优化使用ONIOM(B3LYP/6-31+G(d):PM3)方法进行,并在此基础上对得到的最优构型应用多种密度泛度方法,如B3LYP/6-31+G(d),PBE/6-31+G(d),M062X/6-31+G(d)和ωB97XD/6-31+G(d)进行完整46T簇模型的单点能计算.B3LYP,PBE和M062X泛函使用dftd3程序计算了额外色散校正,以考虑分子筛内部的弱相互作用.计算结果显示,经色散校正的DFT方法的计算精度被大大提高,达到一个与MP2方法相媲美的精度.反应的决速步是由第一步1,2-H转移和重排步共同决定,内部反应能垒为44.5 kcal/mol.反应速率常数表明,在293~393 K时,在H-ZSM-5上贝克曼重排反应进行得相当缓慢;当温度达到423 K时,正逆反应速率相当,反应开始发生;当达到623 K时,反应速率常数为130 1/s.
The Beckmann rearrangement reaction mechanism of cyclohexanone oxime to ε-caprolactam catalyzed by H-ZSM-5 zeolite was investigated by ONIOM and DFT methods. All the configurations were optimized using ONIOM (B3LYP / 6-31 + G (d): PM3 ) Method, and based on this, a variety of density-based methods such as B3LYP / 6-31 + G (d), PBE / 6-31 + G (d), M062X / 6 -31 + G (d) and ωB97XD / 6-31 + G (d) for the complete 46T cluster model. The B3LYP, PBE, and M062X functionalities calculate the additional dispersion correction using the dftd3 program to account for the internal Weak interaction.The calculated results show that the accuracy of the DFT method with dispersion correction is greatly improved and a precision comparable to that of the MP2 method is reached.The velocity step of the reaction is composed of the first 1,2-H transfer and rearrangement The internal reaction energy barrier is 44.5 kcal / mol. The reaction rate constants show that the Beckmann rearrangement reaction at H-ZSM-5 proceeds slowly at 293-393 K; when the temperature reaches 423 K, The forward and reverse reaction rates were comparable and the reaction started to take place. The reaction rate constant was 130 1 / s when it reached 623 K.