HZSM-5分子筛上乙烯芳构化过程中C4至C6中间体的反应机理  

Reaction Mechanism of Ethylene Aromatization over HZSM-5 Zeolite: From C4 to C6 Intermediates

作　　者：曹亮[1] 周丹红[1] 邢双英[1] 李新[2] 

机构地区：[1]辽宁师范大学化学化工学院功能材料化学研究所,辽宁大连116029 [2]中国科学院大连化学物理研究所催化基础国家重点实验室,辽宁大连116023

出　　处：《催化学报》2010年第6期645-650,共6页

基　　金：国家自然科学基金(20073058)

摘　　要：应用量子力学和分子力学联合的ONIOM2(B3LYP/6-31G(d,p):UFF)方法,采用包含分子筛孔道结构的78T簇模型,对HZSM-5分子筛上乙烯芳构化过程中C4至C6中间体的反应历程进行了研究,探讨了分子筛的酸催化机理和择形催化作用.结果表明,作为乙烯二聚产物的表面正丁基烷氧络合物(C4)直接与乙烯作用得到正己基烷氧络合物(C6),在分子筛孔穴尺寸的限制下,很难实现碳链的折叠环化.按照间歇反应历程,丁基烷氧络合物先发生C–O键断裂,脱质子生成1-丁烯,然后在酸性位上再与乙烯加成,在分子筛表面生成3-甲基戊基烷氧络合物.该烷氧络合物脱除质子给分子筛,同时环化生成甲基环戊烷,后者再与分子筛酸性质子共同脱除氢分子,生成不稳定的碳正离子中间体,然后重构成环己烷正离子.丁基烷氧络合物脱质子的活化能为158.42kJ/mol;1-丁烯与乙烯加成反应的活化能为130.71kJ/mol;3-甲基戊基烷氧络合物脱氢环化生成甲基环戊烷的活化能为122.06kJ/mol.由于孔穴的限域作用,五员环的甲基环戊烷是重要的中间体.The ONIOM2（B3LYP/6-31G（d,p）：UFF） method based on the 78T cluster model was used to study the reaction mechanism of C4 to C6 intermediates during the ethylene aromatization over HZSM-5 zeolite.The catalytic mechanism of acidic zeolite and the effect of zeolite pore size on the shape selectivity for the products was discussed.The results indicated that the n-butoxide,which is the intermediate product of ethylene dimmerization,reacted with ethylene to form n-hexane alkoxide,but it was difficult to carry out further cyclization because of the restriction of the pore size of ZSM-5 zeolite.However,along the stepwise pathways,n-butoxide was transformed into n-butene through deprontonation and then reacted with ethylene to form 3-methylpentane alkoxide intermediate,which then formed methylcyclopentane through cyclization and deprotonation.The methylcyclopentane released a hydrogen molecule by the aid of zeolite acidic proton and formed the unstable methyl-cyclopentane carbonium,which then generated the cyclohexane carbonium through reconfiguration.The calculated activation energy was 158.42 kJ/mol for n-butoxide deprontonation,130.71 kJ/mol for the oligomerization of 1-butene and ethylene,and 122.06 kJ/mol for the cyclization of 3-methylpentane alkoxide.As a result of the confinement of zeolite pore,the five-member ringed methylcyclopentane was formed as a crucial intermediate.

关 键 词：密度泛函理论 乙烯 芳构化 HZSM-5分子筛 反应机理 禁闭效应 

分 类 号：O643.32[理学—物理化学]