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An extensive theoretical study has been carried out to determine barriers for the proton exchange reactions of C2-C4 alkanes in ZSM-5. It was found that cluster size and cavity structure are very important for predicting this barrier. A decrement of up to 20 kcal/mol was observed when employing the periodic model instead of using the small cluster model. Effects of basis set quality and electron correlation to the activation energy are positive and in combination could contribute up to 8 kcal/mol. An extrapolation scheme for estimating the reaction barrier that takes into account effects of cluster size, basis set quality, and electron correlation has been proposed. The regioselectivity and the chain length were discussed.

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