摘要
采用ONIOM(B3LYP/6-31G(d,p):UFF)分层计算的方法,研究了HZSM-5分子筛上乙醇和异丁烯合成乙基叔丁基醚(ETBE)的反应机理.通过反应物在HZSM-5分子筛上吸附性质的研究发现,乙醇与分子筛酸性位相互作用形成氢键,而异丁烯则作用在Bronsted酸位上形成π配位吸附.确定反应物吸附位置后,进一步探索反应机理,结果表明:HZSM-5分子筛上乙醇和异丁烯合成乙基叔丁基醚的反应为协同反应,并且,反应物吸附顺序的不同对反应过程存在一定的影响.ETBE合成反应的最优途径以反应物同时吸附形成的复合物作为起点.在反应过程中,形成π配位的H原子向异丁烯分子中不饱和双键的端位C原子靠近,被吸附的乙醇分子中的O原子向异丁烯双键中的另一个C原子靠近,直到形成C-O键,生成ETBE.这一过程中,原有的质子H加成到异丁烯的端基C上形成C-H键,而原醇羟基中的H和B酸位附近的O原子作用形成新的酸性位.相应的协同反应的最低的反应势垒为25.14kJ·mol-1.
The formation mechanism of ethyl tertiary butyl ether （ETBE） from ethanol and isobutene catalyzed by HZSM-5 has been investigated using the ONIOM （B3LYP/6-31G（d,p）：UFF） method. The calculation results of the reactants adsorbability reveal that the interaction between ethanol and the acidic sites on HZSM-5 leads to the formation of hydrogen bonds. The interaction between isobutene and BrSnsted acidic sites leads to the formation of a E-complex. It is subsequently found that the mechanism of the ETBE formation from ethanol and isobutene catalyzed by HZSM-5 is a concerted reaction, and that the order of reactant adsorption onto H7SM-5 affected the reaction. The favorable pathway is based on the complex formed by the simultaneous adsorption of ethanol and isobutene, in which the H atom of the π-complex is transferred to the C atom of the C=C in isobutene, and the O atom of the adsorbed ethanol is transferred to the other C atom of the C=C to form the C-O bond. In this process, the proton of the acidic sites adds to the C=C bond forming the C-H bond, and the H atom of the ethanol hydroxyl interacts with acidic sites, generating a new proton. The corresponding lowest energy barrier was 25.14 kJ·mol^（-1）.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2012年第7期1630-1636,共7页
Acta Physico-Chimica Sinica
