AVS 52nd International Symposium
    Surface Science Thursday Sessions
       Session SS2-ThA

Paper SS2-ThA7
Variable (T@sub g@, T@sub s@) Measurements of Alkane Dissociative Sticking Coefficients

Thursday, November 3, 2005, 4:00 pm, Room 203

Session: Gas-Surface Reaction Dynamics
Presenter: K.M. DeWitt, University of Virginia
Authors: K.M. DeWitt, University of Virginia
L. Valadez, University of Virginia
K.W. Kolasinski, University of Virginia
I. Harrison, University of Virginia
Correspondent: Click to Email
A novel technique for measuring nonequilibrium dissociative sticking coefficients, S(T@sub g@, T@sub s@), with well-defined gas temperature, T@sub g@, and surface temperature, T@sub s@, is described, along with its application to activated dissociative chemisorption of CH@sub 4@ and C@sub 2@H@sub 6@ on Pt(111). Microcanonical unimolecular rate theory (MURT) is employed to analyze the sticking coefficients and to extract transition state characteristics. The MURT allows the S(T@sub g@, T@sub s@) sticking to be directly compared to other molecular beam and thermal equilibrium sticking measurements. Interestingly, measured S(T@sub g@ = 300 K, T@sub s@) for CH@sub 4@ on Pt(111) are several times larger than recent thermal equilibrium measurements, S(T@sub g@ = T@sub s@), on supported Pt nanocrystallite catalysts [J. M. Wei, E. Iglesia, J. Phys. Chem. B 108, 4094 (2004)]. This is a surprising result that runs contrary to the popular notion that dissociative chemisorption should be enhanced at the coordinatively less saturated defect sites that should be more prevalent on the ~2 nm diameter Pt nanocatalysts than on a flat Pt(111) surface.