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

A coverage-dependent, mean-field microkinetic model of catalytic NO oxidation, NO+0.5O(2)-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-O and O=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 q 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 <= theta <0.4 ML and to be controlled by equilibrium between gas-phase NO and NO2 and chemisorbed O, O-2 dissociative adsorption (O-2(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.