Electronic and chemical properties of supported Au nanoparticles

Oxidation and reduction behaviors of An nanoparticles with different sizes on highly ordered pyrolytic graphite (HOPG) and silica were studied using X-ray photoelectron spectroscopy (XPS). For Au nanoparticles smaller than similar to 6 nm in diameter, we found a novel oxygen species formed in An nanoparticles, which is absent in larger particles and Au bulk crystals. This new oxygen species is attributed to the subsurface oxygen: for a complete understanding of the structures of catalytically active Au, the new oxygen species should be taken into account. In this context, it is worth mentioning that the subsurface oxygen species has been suggested to play an important role in heterogeneous catalysis. With decreasing An particle size, a positive core level shift can be observed, which can be mostly attributed to the final state effects. Increase of the number of undercoordinated atoms with decreasing particle size is evidenced by a reduced splitting between 5d(3/2) and 5d(5/2) states and a band narrowing. Our results on electronic structures of Au nanoparticles on silica are compared to those on other substrates such as zirconia and titania to shed light onto the metal-support interactions. (c) 2006 Elsevier B.V. All rights reserved.