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Redox-mediated conversion of atomically dispersed platinum to sub-nanometer particles

Abstract

The stability and the conversion of atomically dispersed Pt2+ species to sub-nanometer Pt particles has been investigated as a function of the Sn concentration in Pt‒CeO2 films by means of synchrotron radiation photoelectron spectroscopy, resonant photoemission spectroscopy, and angle-resolved X-ray photoelectron spectroscopy in combination with density functional calculations. The deposition of Sn onto the Pt‒CeO2 films triggers the reduction of Ce4+ cations to Ce3+ yielding Sn2+ cations. Consecutively, the redox coupling between the Ce3+ and Pt2+ species triggers the reduction of Pt2+ species yielding sub-nanometer Pt particles. The onset of reduction of Pt2+ species is directly related to the concentration of Ce3+ centers which, in turn, is controlled by the concentration of Sn2+ cations in the Pt‒CeO2 film. On average, formation of 6 Ce3+ centers corresponding to the adsorption of 3 Sn atoms gives rise to the reduction of one Pt2+ species. The analysis of the depth distribution of Sn atoms in the Pt‒CeO2 films revealed preferential adsorption of Sn2+ at the surface followed by diffusion of Sn2+ ions into the bulk at higher Sn coverages. Density functional modeling suggested that adsorption of three Sn atoms in the vicinity of the Pt2+ species results in a rearrangement of the local coordination accompanied by substantial destabilization of the Pt2+ species relative to the adsorption of Pt0 atoms. The formation of sub-nanometer Pt particles is coupled with re-oxidation of two Ce3+ centers per one Pt2+ species reduced. Annealing of the Pt‒CeO2 films in the presence of metallic Sn also leads to reduction of the Pt2+ species due to thermally triggered oxidation of metallic Sn residues followed by diffusion of Sn2+ into the bulk. Annealing of the Pt‒CeO2 films to temperatures above 600 K results in a loss of Sn yielding sub-nanometer Pt particles supported on nearly stoichiometric and Sn-free CeO2 films.

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Publication details

The article was received on 12 Mar 2017, accepted on 08 Apr 2017 and first published on 10 Apr 2017


Article type: Paper
DOI: 10.1039/C7TA02204B
Citation: J. Mater. Chem. A, 2017, Accepted Manuscript
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    Redox-mediated conversion of atomically dispersed platinum to sub-nanometer particles

    Y. Lykhach, A. Figueroba, T. Skála, T. Duchoň, N. Tsud, M. Aulická, A. Neitzel, K. Veltruská, K. C. Prince, V. Matolín, K. M. Neyman and J. Libuda, J. Mater. Chem. A, 2017, Accepted Manuscript , DOI: 10.1039/C7TA02204B

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