Role of clay minerals in oil-forming reactions.

Mineral-catalyzed decarboxylation reactions are important in both crude oil formation and, increasingly, biofuel production. In this study we examined decarboxylation reactions of a model fatty acid, propionic acid, C(2)H(5)COOH, to an alkane, C(2)H(6), in a model of pyrophillite with an isomorphic substitution of aluminum in the tetrahedral layer. We model a postulated reaction mechanism (Almon, W. R.; Johns, W. D. 7th International Meeting on Organic Geochemistry 1975, Vol. 7) to ascertain the role of Al substitution and a counterion in decarboxylation reactions. We employ a periodic cell, planewave, ab initio DFT computation to examine the total energies and the frontier orbitals of different model sets, including the effects of charge on the reaction, the effect of Al substitution, and the role of Na counterions. The results show that an uncharged system with a sodium counterion is most feasible for catalyzing the decarboxylation reaction in an Al-substituted pyrophillite and, also, that analysis of the orbitals is a better indicator of a reaction than charge alone.