DFT-Based Coverage-Dependent Model of Pt-Catalyzed NO Oxidation

Authors

  • Rachel B. Getman,

    1. Department of Chemical and Biomolecular Engineering, University of Notre Dame, 182 Fitzpatrick Hall, Notre Dame, IN 46556 (USA), Fax: (+1) 574-631-8366
    2. Current Address: Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL 60208 (USA)
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  • William F. Schneider

    1. Department of Chemical and Biomolecular Engineering, University of Notre Dame, 182 Fitzpatrick Hall, Notre Dame, IN 46556 (USA), Fax: (+1) 574-631-8366
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Abstract

A coverage-dependent, mean-field microkinetic model of catalytic NO oxidation, NO+0.5 O2⇌NO2, at a Pt(111) surface has been developed, based on large supercell density functional theory (DFT) calculations. DFT is used to determine the overall energetics and activation energies of candidate reaction steps as a function of surface coverage. Surface coverage is found to have a significant but non-uniform effect on the energetics, pathways, and activation energies of reaction steps involving formation or cleavage of ON[BOND]O and O[DOUBLE BOND]O bonds, and inclusion of this coverage dependence is essential for obtaining a qualitatively correct representation of the catalysis. Correlations are used to express all reaction parameters in terms of a single coverage variable θ and steady-state solutions to the resultant mean-field models are obtained in the method of DeDonder relations. At conditions representative of NO oxidation catalysis, the surface coverage is predicted to be 0.25≤θ<0.4 ML and to be controlled by equilibrium between gas-phase NO and NO2 and chemisorbed O. O2 dissociative adsorption (O2(g)→2O*) is rate limiting in the model. The DFT-based mean-field model captures many features of the experimentally observed catalysis, and its short-comings point the way toward more robust models of coverage-dependent kinetics.

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