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O: Fachverband Oberflächenphysik

O 40: Heterogeneous Catalysis: Experiment

O 40.1: Vortrag

Dienstag, 8. März 2016, 14:00–14:15, S053

Bimetallic redox interactions in model Pt-Sn-CeO₂ catalysts for fuel cell applications — •A. Neitzel¹, Y. Lykhach¹, N. Tsud², T. Skála², M. Vorokhta², K. C. Prince³, V. Matolín², and J. Libuda¹ — ¹FAU Erlangen-Nürnberg, Germany — ²Charles University in Prague, Czech Republic — ³Elettra-Sincrotrone Trieste, Italy

We investigated bimetallic Pt-Sn interactions as a function of the oxidation state of Pt and Sn in model Pt-Sn-CeO₂ catalysts by synchrotron radiation photoelectron spectroscopy and resonant photoemission spectroscopy. The corresponding experiments involved model Sn-CeO₂ and Pt-CeO₂ mixed oxide films prepared on a stoichiometric CeO₂(111) buffer layer on Cu(111). Both systems are characterized by excellent stabilities of Sn²⁺ and Pt²⁺ upon annealing to 700 K in UHV. We found that deposition of metallic Sn⁰ on Pt-CeO₂ films initially leads to formation of Pt-Sn-CeO₂ mixed oxides. At larger amounts of Sn⁰, we observed conversion of Pt²⁺ to new species which we assign to small Pt or PtO_x particles. The following annealing of the deposit to 700 K in UHV leads to complete reduction of Pt²⁺ but does not yield Pt-Sn alloy nanoparticles. Stepwise deposition of Pt on Sn-CeO₂ films yields Pt-Sn alloy nanoparticles at the expense of Sn²⁺. Subsequent annealing of the deposit in UHV to 750 K promotes further Pt-Sn alloy formation. The surface composition of Pt-Sn-CeO₂ catalysts was probed by CO adsorption at 110 K. We found that CO adsorption at atop sites on the Pt-Sn nanoparticles is inhibited due to thermally promoted alloying.