AVS 50th International Symposium
    Surface Science Thursday Sessions
       Session SS2-ThM

Paper SS2-ThM3
Methane Dissociative Chemisorption on Ni(100): Closing the Non-equilibrium Gap between Surface Science and Catalysis

Thursday, November 6, 2003, 9:00 am, Room 327

Session: Catalysis III: High vs. Low Pressures
Presenter: H.1 Abbott,
Authors: H.1 Abbott,
A. Bukoski, University of Virginia
D. Kavulak, University of Virginia
I. Harrison, University of Virginia
Correspondent: Click to Email
A simple, 3-parameter microcanonical unimolecular rate theory of gas-surface reactivity is shown to predict experimental dissociative sticking probabilities for methane dissociative chemisorption on the Ni(100) surface over roughly 10 orders of magnitude variation in both pressure and sticking - even at quantum state resolved levels of detail. Facile energy randomization within the transiently formed gas-surface collision complexes is postulated to make the pooled energy from 15 local degrees of freedom statistically available to surmount the barrier to dissociation. The apparent threshold energy for C-H bond cleavage of CH@sub 4@ incident on Ni(100) is 65 kJ/mol, down from 432 kJ/mol in the gas phase. Interestingly, this threshold energy is in quantitative accord with ab initio quantum chemistry calculations, but 15-45% smaller than calculations based on generalized gradient approximation density functional theory. More generally, some of the difficulties faced when interpreting non-equilibrium surface science experiments and comparing them with equilibrium catalysis experiments will be discussed.