The Extensive Ambient Oxidation of Supported, Ultrasmall Noble Metal Nanoparticles Characterized with Benchtop X-ray Diffraction

Abstract High sensitivity powder X-ray diffraction has been employed to investigate the room temperature oxidation of a series of noble metals supported on an amorphous silica, using a recently developed Rietveld analysis for ultrasmall (<2 nm) supported nanoparticles. It is found that Pt, Pd, Ir, and Rh are mostly oxidized, and the metal cores consistently exhibit lattice parameter dilation as compared with the bulk. Ru appears to exist only as oxides, while Au does not show any evidence of oxidation and exhibits lattice contraction. The results for Pt are corroborated with X-ray absorption spectroscopy and extended to examine oxidation rates in situ.