Formation and Thermal Stability of Au2O3on Gold Nanoparticles: Size and Support Effects

Abstract

Gold nanoparticles with two different size distributions (average sizes of ∼1.5 and ∼5 nm) have been synthesized by inverse micelle encapsulation and deposited on reducible (TiO 2 ) and nonreducible (SiO 2 ) supports. The thermal and chemical stability of oxidized gold species formed upon cluster exposure to atomic oxygen have 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 demonstrates that (a) low-temperature (150 K) exposure to atomic oxygen leads to the formation of surface as well as subsurface gold oxide on Au nanoparticles, (b) the presence of the reducible TiO 2 substrate leads to a lower gold oxide stability compared to that on SiO 2, possibly because of a TiO 2 oxygen vacancy-mediated decomposition process, (c) heating to 550 K (Au/SiO 2 ) and 300 K (Au/TiO 2 ) 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 O 2 from preoxidized Au clusters deposited on SiO 2 depends on the cluster size, with smaller clusters showing stronger O 2 binding.