HY分子筛催化己烷/环己烷质子化反应的分子模拟  

Molecular simulation of protonation of hexane/cyclohexane catalyzed by HY zeolite

作　　者：杜硕 龙军[1] 代振宇 赵毅[1] DU Shuo;LONG Jun;DAI Zhenyu;ZHAO Yi(State Key Laboratory of Catalytic Materials and Reaction Engineering,Research Institute of Petroleum,Sinopec,Beijing 100083,China)

机构地区：[1]中国石化石油化工科学研究院催化材料与反应工程国家重点实验室

出　　处：《计算机与应用化学》2019年第5期572-576,共5页Computers and Applied Chemistry

摘　　要：本文研究了己烷与环己烷质子化反应的细节,选取了336T分子筛模型,采取量子力学与分子力学(QM/MM)相结合的方法进行计算。结果表明,烷烃的质子化过程有两步基元反应,先经历CHH五配位碳正离子过渡态,生成CHC五配位碳正离子,然后CHC五配位碳正离子发生裂化得到最终的烷氧化物。在第一步基元反应中,己烷生成CHC五配位碳正离子需要克服189.4 kJ/mol的能垒,而环己烷的生成五配位碳正离子需克服293.8 kJ/mol的能垒,环己烷反应的能垒比己烷高,这主要是受分子自身结构的影响。与己烷相比,环己烷过渡态电荷转移更明显,与分子筛酸中心相互作用力更强,生成五配位碳正离子的过程较难,过渡态能垒较高。另外,环己烷的特征结构也影响了其裂化过程,使得环己烷的反应能垒125.3kJ/mol比己烷的能垒31.1 kJ/mol高。In this paper, the 336 T HY zeolite model was selected to reveal details of the protonation reaction of hexane and cyclohexane by a method of QM/MM(quantum mechanics and molecular mechanics). The results show that the protonation process of alkane can be divided into two elementary reactions. The first step undergoes the CHH pentacoordinated carbocation transition state to form a CHC pentacoordinated carbocation, and then the CHC pentacoordinated carbocation is cleaved to obtain the final alkoxy product. In the first step,Hexane undergoes 189.4 kJ/mol energy barrier to form CHC pentacoordinated carbon cations,while the energy barrier of cyclohexane to form pentacoordinated carbon cations is 293.8 kJ/mol.Influenced by the structure of the alkane molecules, the energy barrier of the cyclohexane reaction is significantly higher than that of hexane. The cyclohexane transition state charge transfer is more obvious, and the interaction with the zeolite acid center is stronger, which makes it difficult to generate pentacoordinated carbon cations. Besides, the structural characteristic of cyclohexane also affects the cleavage process, making the reaction energy barrier of cyclohexane 125.3 kJ/mol higher than the energy barrier of hexane 31.1 kJ/mol.

关 键 词：HY分子筛 质子化反应 量子力学和分子力学(QM/MM) 

分 类 号：TE621[石油与天然气工程—油气加工工程]