Heather Abbott-Lyon - Dissociative chemisorption and energy transfer for methane on Ir(111)

Version 1

      Publication Details (including relevant citation   information):

      H.L. Abbott and I. Harrison. Journal of   Physical Chemistry B, 109, 10371 (2005).

      Abstract:

      A 3-parameter local hot spot model of gas-surface reactivity is   employed to analyze and predict dissociative sticking   coefficients for CH4 incident on Ir(111) under varied   nonequilibrium and equilibrium conditions. One Ir surface   oscillator and the molecular vibrations, rotations, and   translational energy directed along the surface normal are   treated as active degrees of freedom in the 14 dimensional   microcanonical kinetics. The threshold energy for CH4   dissociative chemisorption on Ir(111) derived from modeling   molecular beam experiments is E0 ) 39 kJ/mol. Over more than 4   orders of magnitude of variation in sticking, the average   relative discrepancy between the beam and theoretically derived   sticking coefficients is 88%. The experimentally observed   enhancement in dissociative sticking as beam translational   energies decrease below <10 kJ/mol is consistent with a   parallel dynamical trapping/energy transfer channel that likely   fails to completely thermalize the molecules to the surface   temperature. This trapping-mediated sticking, indicative of   specific energy transfer pathways from the surface under   nonequilibrium conditions, should be a minor contributor to the   overall dissociative sticking at thermal equilibrium.   Surprisingly, the CH4 dissociative sticking coefficient predicted   for Ir(111) surfaces at thermal equilibrium, based on the   molecular beam experiments, is roughly 4 orders of magnitude   higher than recent measurements on supported nanoscale Ir   catalysts at 1 bar pressure, which suggests that substantial   improvements in catalyst turnover rates may be possible.

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