Ga-ZSM-5催化MTO生成初始烯烃反应机理研究

摘要

DFT-GGA was applied to study the mechanisms of the formation of the first C—C bond and the initial olefins over Ga-ZSM-5 in the MTO process.We determined the stable config-urations of reactants,intermediates,and products as well as the corresponding activation barriers and reaction energy of the numerous reactions involved in such a process.Here,two different kinds of mechanisms were proposed for the formation of dimethyl ether,one involving an associa-tive interaction and another occurring via a dissociative pathway.A critical intermediate of the methoxymethyl cation was theoretically verified.Furthermore,1,2-dimethoxyethane is the first intermediates containing a C—C bond and ethene is the first alkene product in the MTO process.%采用密度泛函理论广义梯度近似方法(DFT-GGA)研究了 Ga-ZSM-5分子筛上 MTO反应过程中第一个 C—C 键及初始烯烃生成的反应机理.选用周期性模型,系统地研究了生成初始烯烃的整个反应体系,确定了各个反应物、过渡态及产物的最稳定构型,同时也确定了各个反应所涉及的反应能垒和反应热.结果表明:二甲醚生成反应可按照分步和协同机理进行.在生成初始 C—C 键过程中,理论上证实了一个关键性的反应中间体,即甲氧基甲基阳离子,1,2-二甲氧基乙烷是第一个包含 C—C 键的反应中间体,生成的初始烯烃为乙烯.