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

Abstract

This article presents a systematic study of the formation and thermal stability of Pt oxide species on sizeselected Pt nanoparticles (NPs) supported on SiO 2 , ZrO 2 , and TiO 2 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. PtO 2 species are formed on all supports investigated after O 2 -plasma exposure. A two-step thermal decomposition (PtO 2 f PtO f Pt) is observed from 300 to 600 K upon annealing in UHV. The stability of oxidized Pt species was found to be enhanced on ZrO 2 under annealing treatments in O 2 . Strong NP/support interactions and the formation of Pt-Ti-O alloys are detected for Pt/TiO 2 upon annealing in UHV above 550 K but not under an identical treatment in O 2 . Furthermore, thermal treatments in both environments above 700 K lead to the encapsulation of Pt by TiO x . 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 SiO 2 , ZrO 2 , and TiO 2 after in situ ligand removal with atomic oxygen at RT. However, annealing in UHV at 1000 K leads to NP flattening on ZrO 2 and to the diffusion of Pt NPs into TiO 2 . The stronger the nature of the NP/support interaction, the more dramatic is the change in the NP shape (TiO 2 > ZrO 2 > SiO 2 ).

Thermodynamic properties of Pt nanoparticles: Size, shape, support, and adsorbate effects

“…56 Such a vibrational confinement gap 63 is in turn determined by the NP size and shape. 63 For example, Pt 44 (S2) has the smallest <x 2 > th and the widest phonon gap (5.7 meV), and Pt 33 (S4) has the largest <x 2 > th and smallest gap (~2.5 meV) 56 . This apparently small difference in the VDOS is critical, as seen by the visible deviation of the <x 2 > th and (σ 2 d ) th of Pt 33 with respect to the rest of the samples in Figs.…”

“…Further details on the sample preparation method and synthesis parameters can be found in Refs. 28,38,[41][42][43][44] and Table I. Table I.…”

Electrochemical Oxidation of Size-Selected Pt Nanoparticles Studied Using in Situ High-Energy-Resolution X-ray Absorption Spectroscopy

“…The polymer shells were then removed using an ultrahigh vacuum oxygen plasma source (SPECS, GmbH), which leaves behind oxidized platinum NPs. 20,38 2.2. Sample Characterization.…”

Structure control of silica-supported mono and bimetallic Au–Pt catalysts via mercapto capping synthesis

“…As listed in Table 2 and also shown in Fig. 6a, the curve fitting routine allowed to simulate the spectrum of the calcined sample Pt0 with two Pt 4f components, one at 72.2 eV due to PtO and the other at 74.0 eV due to PtO 2 [29,30]. The spectrum of the Pt5 was fitted with only the PtO component, however, given the broadness of the peak the presence of the other oxide component may not be completely ruled out.…”