Quantification of Primary Versus Secondary C-H Bond Cleavage in Alkane Activation: Propane on Pt

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Science  02 Aug 1991:
Vol. 253, Issue 5019, pp. 542-545
DOI: 10.1126/science.253.5019.542


The trapping-mediated dissociative chemisorption of three isotopes of propane (C3H8, CH3,CD2CH3, and C3D8) has been investigated on the Pt(110)-(1 x 2) surface, and both the apparent activation energies and the preexponential factors of the surface reaction rate coefficients have been measured. In addition, the probabilities of primary and secondary C-H bond cleavage for alkane activation on a surface were evaluated. The activation energy for primary C-H bond cleavage was 425 calories per mole greater than that of secondary C-H bond cleavage, and the two true activation energies that embody the single measured activation energy were determined for each of the three isotopes. Secondary C-H bond cleavage is also preferred on entropic grounds, and the magnitude of the effect was quantified.