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Article

DFT-Based Characterization of the Multiple Adsorption Modes of Nitrogen Oxides on Pt(111)

Rachel B. Getman^† and William F. Schneider*^†^‡

Department of Chemical and Biomolecular Engineering and Department of Chemistry and Biochemistry, University of Notre Dame, 182 Fitzpatrick Hall, Notre Dame, Indiana 46556

J. Phys. Chem. C, 2007, 111 (1), pp 389–397

DOI: 10.1021/jp064841p

Publication Date (Web): December 10, 2006

†

Department of Chemical and Biomolecular Engineering.

To whom correspondence should be addressed. Phone: (574) 631-8754. Fax: (574) 631-8366. E-mail: wschneider@nd.edu.

‡

Department of Chemistry and Biochemistry.

Abstract

Pt is the most common catalyst for NO oxidation to NO₂, a key reaction in NO_x remediation chemistry. In this work, density functional theory calculations and plane-wave supercell models are used to calculate the energies, charge distributions, and vibrational spectra of the stable and metastable states of adsorbed NO, NO₂, and NO₃ on Pt(111), the most likely active metal face for this catalytic oxidation. NO, NO₂, and NO₃ are all strong electron acceptors and bind to the Pt(111) surface via charge donation from the surface. NO and NO₂, in particular, exhibit a variety of adsorption geometries, the most favorable at low coverage being those that maximize surface−adsorbate charge transfer through binding to multiple surface Pt. At low coverage, the order of binding energies is NO > NO₃> NO₂, and the oxidation of adsorbed NO to NO₂ is endothermic by 0.78 eV. Higher surface coverages favor migration of NO and NO₂ to lower-coordination surface sites due to competition for metal d charge density. These changes in surface binding configurations, along with the general decrease in surface−adsorbate bond energies associated with higher surface coverages, both tend to energetically promote NO conversion to NO₂ and are important in describing this catalytic chemistry.