AVS 51st International Symposium
    Surface Science Monday Sessions
       Session SS1-MoA

Paper SS1-MoA3
Atomistic Modeling of CO Oxidation on Pd(100): Ordering of the Reactant Adlayer, Bistability of Steady States, and TPR

Monday, November 15, 2004, 2:40 pm, Room 210B

Session: Simulation and Theory of Adsorption
Presenter: D.-J. Liu, Iowa State University
Authors: D.-J. Liu, Iowa State University
J.W. Evans, Iowa State University
Correspondent: Click to Email
We develop a realistic atomistic lattice-gas model for CO-oxidation on Pd(100) under UHV conditions which describes equilibrium c(2@sq@2 x @sq@2)R45° ordering of CO(ads) on bridge sites, and both non-equilibrium c(2 x 2) and equilibrium p(2 x 2) ordering of O(ads) on four-fold hollow sites. The latter requires suitable treatment of the dissociative adsorption kinetics of O@sub 2@(gas) via an 8-site rule (reflecting strong repulsions between neighboring O) together with transient mobility. CO-CO and O-O adspecies interactions are tuned to match experimental LEED, TPD, and heat of adsorption data for the separate adspecies. Description of the interaction and reaction between CO(ads) and O(ads) is guided by DFT results and by comparison with TPR data. With this model, we map out the bifurcation diagram for the reactive steady states identifying the bistability regime and critical (cusp) point. We also relate various features of the experimental TPR spectra to details of the adspecies interactions in this system. We also discuss extension of the model to the regime of higher pressures, where oxide formation produces a clear signature in the TPD spectra for oxygen, and impacts the reaction kinetics.