Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 114, Issue 35, Pages 15061-15067Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp1058947
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Funding
- Crown Property Bureau under National Science and Technology Development Agency
- National Nanotechnology Center
- Thailand Research Fund
- Commission of Higher Education
- Ministry of Education (National Research University of Thailand (NRU))
- Kasetsart University Research and Development Institute (KURDI)
- Graduate School Kasetsart University
- Austrian Ministry of Science BMWF of the Uni-Infrastrukturprogramm of the research platform Scientific Computing at LFU Innsbruck
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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 Bronsted acid site.
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