物理化学学报 >> 2012, Vol. 28 >> Issue (07): 1630-1636.doi: 10.3866/PKU.WHXB201204171

理论与计算化学 上一篇    下一篇

HZSM-5分子筛上乙基叔丁基醚合成反应的理论研究

李军男, 蒲敏, 粟勇, 何静, EVANS David G.   

  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
  • 收稿日期:2011-12-01 修回日期:2012-03-26 发布日期:2012-06-07
  • 通讯作者: 蒲敏 E-mail:pumin@mail.buct.edu.cn

Theoretical Study on the Synthesis of Ethyl Tertiary Butyl Ether over HZSM-5 Zeolite

LI Jun-Nan, PU Min, SU Yong, HE Jing, EVANS David G.   

  1. State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, P. R. China
  • Received:2011-12-01 Revised:2012-03-26 Published:2012-06-07
  • Contact: PU Min E-mail:pumin@mail.buct.edu.cn

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Brönsted 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25.14 kJ·mol-1.

关键词: 乙醇, 异丁烯, HZSM-5分子筛, ONIOM, 乙基叔丁基醚

Abstract:

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 Brönsted acidic sites leads to the formation of a π-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 HZSM-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.

Key words: Ethanol, Isobutene, HZSM-5 zeolite, ONIOM, Ethyl tertiary butyl ether

MSC2000: 

  • O641