Paper SS-TuP15
Formation and Thermal Stability of Gold Oxide and Platinum Oxide Shells on Nanoparticles: Size and Support Effects

Tuesday, October 21, 2008, 6:30 pm, Room Hall D

Gold and Pt nanoparticles (NPs) with two different size distributions (average sizes of ~1.5 and ~5 nm) have been synthesized by inverse micelle encapsulation and deposited on reducible (TiO₂) and non-reducible (SiO₂, ZrO₂) supports. The thermal stability of oxidized Au and Pt species formed upon cluster exposure to atomic oxygen has been investigated in ultrahigh vacuum using a combination of temperature-, time- and CO dosing-dependent X-ray photoelectron spectroscopy (XPS), as well as temperature programmed desorption (TPD). Our work on gold clusters demonstrates that (a) low temperature (150 K) exposure to atomic oxygen leads to the formation of surface, as well as sub-surface gold oxide, (b) the presence of the reducible TiO₂ substrate leads to a lower gold oxide stability compared to that on SiO₂, possibly due to a TiO₂ oxygen vacancy-mediated decomposition process, (c) heating to 550 K (Au/SiO₂) and 300 K (Au/TiO₂) leads to a near-complete reduction of small (~1.5 nm) NPs while a partial reduction is observed for larger clusters (~5 nm), and (d) the desorption temperature of O₂ from pre-oxidized Au clusters deposited on SiO₂ depends on the cluster size, with smaller clusters showing stronger O₂ binding. Preliminary data on the formation and thermal stability of different Pt oxide species (PtO₂ and PtO) on size-selected Pt clusters will be shown. Emphasis will be given to how the nature of the oxide support affects this stability. Furthermore, the distinct reactivity of similarly-sized, pure Pt and Au nanoparticles versus their oxidized counterparts will be discussed.