La/ZSM-5分子筛上1-己烯活化的理论研究  

Theoretical study of 1-hexene activation over La/ZSM-5 zeolite

作　　者：李延锋[1] 朱吉钦[1] 刘辉[1] 贺鹏[1] 王鹏[2] 田辉平[2] 

机构地区：[1]北京化工大学化工资源有效利用国家重点实验室,北京100029 [2]中国石油化工股份有限公司石油化工科学研究院,北京100083

出　　处：《北京化工大学学报（自然科学版）》2011年第3期6-11,共6页Journal of Beijing University of Chemical Technology(Natural Science Edition)

基　　金：国家“973”计划(2010CB732301)

摘　　要：基于54T团簇模型,采用ONIOM分层计算方法,研究了1-己烯分子与镧改性ZSM-5分子筛的相互作用,并详细描述了1-己烯分子在镧改性ZSM-5分子筛上的催化活化反应机理。计算结果表明,1-己烯与镧改性ZSM-5分子筛之间没有发生π配位吸附,只存在更加微弱的物理吸附,从而导致了镧改性ZSM-5分子筛烯烃吸附能力的降低。镧物种酸性中心的O—H键在活化能作用下通过极性分解直接发生质子迁移使1-己烯被质子化,经过碳正离子过渡态,形成稳定的烷氧基活化产物,从而使1-己烯被活化。计算得到的1-己烯的活化能垒是160.64 kJ/mol,这为文献中报道的镧改性ZSM-5分子筛的烯烃吸附能力和催化活性降低提供理论支持,有助于探究镧改性前后ZSM-5分子筛催化性能改变的原因。Theoretical investigations of the interaction of 1-hexene with an La-modified ZSM-5 zeolite,and the mechanism of the activation reaction of 1-hexene on the surface of the La-modified ZSM-5 zeolite have been carried out using density functional theory and the ONIOM method with 54T cluster models simulating the local structures of the zeolite materials.The study includes the geometry optimization and characterization of the reactant,product,and transition state,and the calculation of the activation energies for the process.It was found that there was no π-complex formed,but instead a weaker interaction of the alkyl group and the zeolite framework or acidic center present in the adsorption complexes.The activation of 1-hexene proceeds via heterolytic O—H bond cleavage in the La species,in which case,the acidic proton of the La species transfers to one carbon atom of the double bond of the 1-hexene,while the other carbon atom of the double bond of the 1-hexene bonds with the oxygen of the La species,yielding a stable alkoxy activated product.The calculated activation barrier for the activation of 1-hexene is 160.64 kJ/mol.The results can explain the experimental phenomena observed during the course of the catalytic cracking of olefins over the La-modified ZSM-5 zeolite.

关 键 词：分子筛 镧改性 密度泛函理论 1-己烯 活化 

分 类 号：O641[理学—物理化学]