Anomalous small- and wide-angle X-ray scattering and X-ray absorption spectroscopy for Pt and Pt–Ru nanoparticles

Abstract

We have characterized the structures of two kinds of catalytic nanoparticles of Pt and Pt–Ru, using anomalous small-angle X-ray scattering (ASAXS), anomalous wide-angle X-ray scattering (AWAXS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. With several X-ray energies near the Pt LIII edge, the AWAXS data reveal a face-centered cubic (f.c.c.) crystalline structure for Pt nanoparticles supported on carbon black, whereas the ASAXS data characterize the monometallic nanoparticles as polydisperse spheres with a mean size of 23 A and a size distribution of 20%. With similar X-ray energies, ASAXS and AWAXS data for the Pt–Ru nanoparticles indicate that they have a mean size of ~29 A and a slightly Pt-rich core that can be characterized by an f.c.c. crystalline structure similar to that of the pure Pt nanoparticles. The coordination numbers of the bimetallic nanoparticles extracted from the EXAFS data, collected at the Pt LIII edge and Ru K edge, also reveal a consistent structure of largely, but not completely, intermixed Pt and Ru atoms in the nanoparticles.