分子筛催化cis-2-丁烯的双键异构反应机理的DFT研究

基于含有两个Si和一个Al的分子筛3T簇模型, 利用密度泛函方法(DFT)研究了分子筛催化1-丁烯双键异构为cis-2-丁烯的反应机理. 在B3LYP/6-31G(d,p)计算水平上对反应各驻点进行了全优化, 并计算了反应的活化能. 研究发现, 分子筛上的酸性OH基团首先通过物理吸附靠近1-丁烯的双键, 形成了π配位复合物后, 丁烯双键的端基C原子逐渐抽取这个质子, 同时相邻酸性位的一个O原子也抽取丁烯碳链上的一个H原子, 形成吸附态的cis-2-丁烯, 最后通过脱附形成产物, 使分子筛复原, 反应按照协同反应机理发生. 计算得到的表观活化能是55.9 kJ/mol, 与实验结果接近.

DFT Study on the Double Bond Rearrangement Mechanism of cis-2-Butene Catalyzed by 3T Cluster Model of Zeolite

Using density functional theory, the rearrangement of butene double bond catalyzed by a 3T cluster model of zeolite was investigated. At the B3LYP/6-31G(d,p) level, the complete geometry optimization and the activation energy calculation were performed. It was found that the OH group of acidic site of zeolite adsorbed the double bond of 1-butene with formation of a π-complex, then the side C atom of the double bond of butene drew this proton simultaneously, and the neighboring O atom of the cluster abstracted a hydrogen atom from the butene to yield adsorbed cis-2-butene, lastly restoring the zeolite active site. The whole reaction process showed a concerted mechanism. The calculated apparent activation barrier was 55.9 kJ/mol in agreement with experimental data.