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论文类型：期刊论文
发表时间：2011-05-16
发表刊物：CATALYSIS TODAY
收录刊物：SCIE、EI
卷号：165
期号：1
页面范围：120-128
ISSN号：0920-5861
关键字：Phenol; Tert-butylation; H-beta; Zeolite; Reaction mechanism; ONIOM
摘要：Tert-butylation of phenol with tert-butyl alcohol (TBA) over H-beta zeolite was studied using the ONIOM approach with two proposed reaction paths: stepwise and concerted mechanisms. The results obtained by the ONIOM2 (B3LYP/6-31G(d,p):UFF) method reveals that the tert-butylation of phenol preferentially occurs through a co-adsorbed, concerted mechanism without prior dehydration of tert-butyl alcohol, rather than via a stepwise mechanism through dehydration to form tert-butyl carbenium ion as the first step followed by tert-butyl cation attack on the 2- or 4-position on phenol. The kinetic difference between 2- and 4-tert-butylation is more apparent in the concerted path, where 4-tert-butylation proceeds over a lower activation barrier. Decreasing the acid site strength, via substitution of Ga for Al, reduces the H-bonding interaction between the zeolitic proton and tert-butyl alcohol and increases the apparent activation barriers, which slows the overall reaction, and also lowers the selectivity to 4-tert-butyl phenol. (c) 2010 Elsevier B.V. All rights reserved.