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Issue 39, 2008
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A first-principles investigation of the effect of Pt cluster size on CO and NO oxidation intermediates and energetics

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Abstract

As catalysis research strives toward designing structurally and functionally well-defined catalytic centers containing as few active metal atoms as possible, the importance of understanding the reactivity of small metal clusters, and in particular of systematic comparisons of reaction types and cluster sizes, has grown concomitantly. Here we report density functional theory calculations (GGA-PW91) that probe the relationship between particle size, intermediate structures, and energetics of CO and NO oxidation by molecular and atomic oxygen on Ptx clusters (x = 1–5 and 10). The preferred structures, charge distributions, vibrational spectra, and energetics are systematically examined for oxygen (O2, 2O, and O), CO, CO2, NO, and NO2, for CO/NO co-adsorbed with O2, 2O, and O, and for CO2/NO2 co-adsorbed with O. The binding energies of oxygen, CO, NO, and of the oxidation products CO2 and NO2 are all markedly enhanced on Ptx compared to Pt(111), and they trend toward the Pt(111) levels as cluster size increases. Because of the strong interaction of both the reactants and products with the Ptx clusters, deep energy sinks develop on the potential energy surfaces of the respective oxidation processes, indicating worse reaction energetics than on Pt(111). Thus the smallest Pt clusters are less effective for catalyzing CO and NO oxidation in their original state than bulk Pt. Our results further suggests that oxidation by molecular O2 is thermodynamically more favourable than by atomic O on Ptx. Conditions and applications in which the Ptx clusters may be effective catalysts are discussed.

Graphical abstract: A first-principles investigation of the effect of Pt cluster size on CO and NO oxidation intermediates and energetics

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Publication details

The article was received on 28 Mar 2008, accepted on 20 Jun 2008 and first published on 11 Aug 2008


Article type: Paper
DOI: 10.1039/B805179H
Citation: Phys. Chem. Chem. Phys., 2008,10, 6009-6018
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    A first-principles investigation of the effect of Pt cluster size on CO and NO oxidation intermediates and energetics

    Y. Xu, R. B. Getman, W. A. Shelton and W. F. Schneider, Phys. Chem. Chem. Phys., 2008, 10, 6009
    DOI: 10.1039/B805179H

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