Heather Abbott-Lyon - Using effusive molecular beams and microcanonical unimolecular rate theory to characterize CH4 dissociation on Pt(111)

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  Publication Details (including relevant citation   information):

  K.M. DeWitt, L. Valadez, H.L. Abbott, K.W.   Kolasinski, and I. Harrison, Journal of Physical Chemistry   B, 110,   6705 (2006).

  Abstract:

  The dissociative sticking coefficient for CH4 on Pt(111) has been   measured as a function of both gas temperature (Tg) and surface   temperature (Ts) using effusive molecular beam and   angle-integrated ambient gas dosing methods. The experimental   results are used to optimize the three parameters of a   microcanonical unimolecular rate theory (MURT) model of the   reactive system. The MURT calculations allow us to extract   transition state properties from the data as well as to compare   our data directly to other molecular beam and thermal equilibrium   sticking measurements. We find a threshold energy for   dissociation of E0 ) 52.5 ( 3.5 kJ mol-1. Furthermore, the MURT   with an optimized parameter set provides for a predictive   understanding of the kinetics of this C-H bond activation   reaction, that is, it allows us to predict the dissociative   sticking coefficient of CH4 on Pt(111) for any combination of Ts   and Tg even if the two are not equal to one another, indeed, the   distribution of molecular energy need not even be thermal.   Comparison of our results to those from recent thermal   equilibrium catalysis studies on CH4 reforming over Pt   nanoclusters (~2 nm diam) dispersed on oxide substrates indicates   that the reactivity of Pt(111) exceeds that of the Pt   nanocatalysts by several orders of magnitude.

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