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, C2H5COOH, to an alkane, C2H6, in a model of pyrophillite with all isomorphic substitution of aluminum ill the tetrahedral layer. We model it 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 it counterion ill decarboxylation reactions. We employ it 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 oil the reaction, the effect of Al substitution, and the role of Na counterions. The results show that all uncharged system with a sodium counterion is most feasible for catalyzing the decarboxylation reaction ill an Al-substituted pyrophillite and, also, that analysis of the orbitals is a better indicator of a reaction than charge alone.