Ab Initio Transition State Searching in Complex Systems: Fatty Acid Decarboxylation in Minerals.

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• 作者：Dawn L. Geatches ; H. Christopher Greenwell ; Stewart J. Clark
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：March 31, 2011
• 年：2011
• 卷：115
• 期：12
• 页码：2658-2667
• 全文大小：1225K
• 年卷期：v.115,no.12(March 31, 2011)
• ISSN：1520-5215

文摘

Because of the importance of mineral catalyzed decarboxylation reactions in both crude oil formation and, increasingly, biofuel production, we present a model study into the decarboxylation of the shortest fatty acid, propionic acid C₂H₅COOH, into an alkane and CO₂ catalyzed by a pyrophillite-like, phyllosilicate clay. To identify the decarboxylation pathway, we searched for a transition state between the reactant, comprised of the clay plus interlayer fatty acid, and the product, comprised of the clay plus interlayer alkane and carbon dioxide. Using linear and quadratic synchronous transit mechanisms we searched for a transition state followed by vibrational analysis to verify the intermediate found as a transition state. We employed a periodic cell, planewave, ab initio density functional theory computation to examine total energy differences, Mulliken charges, vibrational frequencies, and the frontier orbitals of the reactants, intermediates, and products. The results show that interpretation of vibrational data, Mulliken charges and Fermi-level orbital occupancies is necessary for the classification of a transition state in this type of mixed bulk surface plus interlayer species, clay-organic system.