Stability and Reactivity of Intermediates of Methanol Related Reactions and C–C Bond Formation over H-ZSM-5 Acidic Catalyst: A Computational Analysis

详细信息    查看全文

• 作者：Zhihong Wei ; Yan-Yan Chen ; Junfen Li ; Wenping Guo ; Sen Wang ; Mei Dong ; Zhangfeng Qin ; Jianguo Wang ; Haijun Jiao ; Weibin Fan
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：March 24, 2016
• 年：2016
• 卷：120
• 期：11
• 页码：6075-6087
• 全文大小：923K
• ISSN：1932-7455

文摘

On the basis of density functional theory including dispersion correction [ωB97XD/6-311+G(2df,2p)//B3LYP/6-311G(d,p)], the thermodynamics and kinetics of the reactions of CH₃OH and CH₃OCH₃ over H-ZSM-5 have been systematically computed. For the reaction of the methylated surface (CH₃OZ) with CH₃OH, CH₃OCH₃ formation is kinetically controlled and the competitive formation of CH₂O + CH₄ is thermodynamically controlled, in agreement with the observed desorption temperatures of CH₃OH, CH₃OCH₃, and CH₂O under experimental conditions. For the reaction between ZOCH₃ and CH₃OCH₃, the formation of the framework stabilized (CH₃)₃O⁺ is kinetically controlled, consistent with the NMR observation at low temperature, and the competitive formation of surface CH₃OCH₂OZ + CH₄ is thermodynamically controlled. On the basis of the thermodynamically more favored CH₂O and CH₃OCH₂OZ, there are two parallel routes for the first C–C bond formation, from the coupling of CH₃OCH₂OZ with CH₃OH and CH₃OCH₃ as well as from the coupling of CH₂O with CH₃OH and CH₃OCH₃. The most important species is the methylated surface (CH₃OZ), which can react with CH₃OH and CH₃OCH₃ to form the corresponding physisorbed CH₂═O and chemisorbed CH₃OCH₂OZ, and they can further couple with additional CH₃OH and CH₃OCH₃ to result in first C–C formation, verifying the proposed formaldehyde (CH₂O) and methoxymethyl (CH₃OCH₂OZ) mechanisms.