2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

DFT studiy CO Absorption Coverage on Pt(111)

B. Shan, Y. Zhao, L. Wang, J. Hyun, S. Yang and J.B. Nicholas
Nanostellar, Inc., US

DFT Pt CO adsorption oxidation catalysis diesel

CO saturation coverage on Pt (111), and the reactions at saturation coverage, are crucially important in diesel oxidation catalysis. We used density functional theory (DFT) calculations, assisted with derived empirical models and surface Monte Carlo simulations, to systematically study CO adsorption on a close-packed Pt (111) surface over a wide coverage range. At low coverage, the CO adsorption energy is almost degenerate at the revised Perdew–Burke–Erzernhof functional (RPBE) level. At higher coverage, however, strong CO lateral repulsion, from through-space repulsions and substrate-mediated metal sharing, tends to dominate the stability of adsorbed CO and alter binding preferences. Our calculated differential binding energy curve and adsorption patterns compare well with experiments. Our results indicate that the conventional notion of CO desorption being the rate determining step in CO oxidation might be true in surface science experiments, but needs a new interpretation under industrial conditions. At high coverage CO desorption energy is reduced significantly, while the O2 activation barrier dominates the apparent activation barrier. Our differential binding energy curve is consistent with the negative first-order reaction kinetics observed in experiment, which as been a long standing puzzle in the CO oxidation reaction.

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