Formation and Thermal Stability of Platinum Oxides on Size-Selected Platinum 
Nanoparticles: Support Effects

Ono, Luis K.; Yuan, B.; Heinrich, H.; Roldan Cuenya, Beatriz

doi:10.1021/jp1086703

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Formation and Thermal Stability of Platinum Oxides on Size-Selected Platinum Nanoparticles: Support Effects

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Ono, L. K., Yuan, B., Heinrich, H., & Roldan Cuenya, B. (2010). Formation and Thermal Stability of Platinum Oxides on Size-Selected Platinum Nanoparticles: Support Effects. The Journal of Physical Chemistry C, 114(50), 22119-22133. doi:10.1021/jp1086703.

Cite as: https://hdl.handle.net/21.11116/0000-0006-D1D0-2

Abstract

This article presents a systematic study of the formation and thermal stability of Pt oxide species on size-selected Pt nanoparticles (NPs) supported on SiO₂, ZrO₂, and TiO₂ thin films. The studies were carried out in ultrahigh vacuum (UHV) by temperature-dependent X-ray photoelectron spectroscopy (XPS) measurements and ex situ transmission electron microscopy and atomic force microscopy. The NPs were synthesized by inverse micelle encapsulation and oxidized in UHV at room temperature by an oxygen plasma treatment. For a given particle size distribution, the role played by the NP support on the stability of Pt oxides was analyzed. PtO₂ species are formed on all supports investigated after O₂-plasma exposure. A two-step thermal decomposition (PtO₂ → PtO → Pt) is observed from 300 to 600 K upon annealing in UHV. The stability of oxidized Pt species was found to be enhanced on ZrO₂ under annealing treatments in O₂. Strong NP/support interactions and the formation of Pt−Ti−O alloys are detected for Pt/TiO₂ upon annealing in UHV above 550 K but not under an identical treatment in O₂. Furthermore, thermal treatments in both environments above 700 K lead to the encapsulation of Pt by TiO_<i>x</i>. The final shape of the micellar Pt NPs is influenced by the type of underlying support as well as by the post-deposition treatment. Spherical Pt NPs are stable on SiO₂, ZrO₂, and TiO₂ after in situ ligand removal with atomic oxygen at RT. However, annealing in UHV at 1000 K leads to NP flattening on ZrO₂ and to the diffusion of Pt NPs into TiO₂. The stronger the nature of the NP/support interaction, the more dramatic is the change in the NP shape (TiO₂ > ZrO₂ > SiO₂).