Activation energy of hydride transfer between isobutane molecules on USY zeolite. First direct experimental measurement by in situ MAS NMR using mixtures of isotopomers

In situ 13C and 1H MAS NMR study of hydride transfer between 13C and 2H isotopically labeled isobutanes on acidic zeolites enabled to estimate the activation energy of this process for the first time and allow full re-evaluation of C–H bond activation mechanism at moderate temperatures. The hydride transfer was shown to occur on the methine position of the molecule. The rates of the intermolecular H/D exchange were measured at different temperatures, and the activation energy was determined to be ca. 55 kJ/mol. These new results definitively support the carbenium mechanism for alkane activation over zeolites through a bimolecular process.