Adsorption and Tautomerization Reaction of Acetone on Acidic Zeolites: The Confinement Effect in Different Types of Zeolites

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• 作者：Bundet Boekfa ; Piboon Pantu ; Michael Probst ; Jumras Limtrakul
• 刊名：Journal of Physical Chemistry C
• 出版年：2010
• 出版时间：September 9, 2010
• 年：2010
• 卷：114
• 期：35
• 页码：15061-15067
• 全文大小：377K
• 年卷期：v.114,no.35(September 9, 2010)
• ISSN：1932-7455

文摘

The adsorption and tautomerization reaction of acetone in H-FER, H-ZSM-5, and H-MCM-22 zeolites has been studied using full quantum calculations at the M06-2X/6-311+G(2df,2p) level of theory. The combination of a large quantum cluster and this meta-hybrid density functional results in reasonably accurate adsorption energies of −26.9, −28.1, and −23.9 kcal/mol for acetone adsorption in H-FER, H-ZSM-5, and H-MCM-22, respectively. Due to the acidity of the zeolite and the framework confinement effect, the tautomerization of acetone proceeds through a much lower activation barrier than in the isolated gas phase or in the presence of water molecules alone. The activation energies are calculated to be 24.9, 20.5, and 16.6 kcal/mol in H-FER, H-ZSM-5 and H-MCM-22, respectively. The endothermic reaction energy decreases with increasing of the zeolite pore sizes and amounts to 22.7, 17.6, and 15.9 kcal/mol for the reaction in H-FER, H-ZSM-5 and H-MCM-22, respectively. In addition, the adsorbed acetone enol is found to be highly unstable in the zeolite framework and readily reverse-transforms to adsorbed acetone with a very small activation energy. The activity trend and relative stabilities of the adsorbed keto and enol forms are well correlated with the interactions within the Brønsted acid site.