A Theoretical Study of the Mechanism of the Hydride Transfer Reaction between Alkanes and Alkenes Catalyzed by an Acidic Zeolite

Density functional theory has been used to study the mechanism of the hydride transfer between alkanes and alkenes catalyzed by an acidic zeolite. The (C3H7−H−C3H7)+, (t-C4H9−H−t-C4H9)+, and (C3H7−H−t-C4H9)+ carbonium ion intermediates through which hydride transfer reactions proceed in the gas phase have been localized adsorbed on the catalyst surface, and they have been characterized, like in the gas phase, as reaction intermediates. However, they are about 25 kcal/mol less stable than separated reactants, and consequently, it will be difficult to detect them experimentally. The complete reaction path for the zeolite-catalyzed hydride transfer between propane and propene has been calculated, and it has been found that the (C3H7−H−C3H7)+ carbonium ion intermediate directly decomposes into propane and propene, and not into propane and a covalent alkoxide as previously reported. The activation barrier was calculated assuming this mechanism is in very good agreement with the only available estimation of this value. It has also been shown that the geometries and energies provided by the B3PW91 and B3LYP functionals are equivalent and in very good agreement with the MP2 values and that increasing the basis set size does not significantly alter the results.