Structural Characterization of Carbon-Supported Platinum−Ruthenium Nanoparticles from the Molecular Cluster Precursor PtRu₅C(CO)₁₆

Abstract

We describe the preparation and structural characterization of carbon-supported Pt−Ru nanoparticles with exceptionally narrow size and compositional distributions. The supported bimetallic particles are obtained by reduction of the neutral molecular carbonyl cluster precursor PtRu5C(CO)16 with hydrogen. A detailed structural model of the nanoparticles has been deduced on the basis of studies by in situ extended X-ray absorption fine structure spectroscopy (EXAFS), scanning transmission electron microscopy, microprobe energy-dispersive X-ray analysis, and electron microdiffraction. These experiments show that the bimetallic nanoparticles have a Pt:Ru composition of 1:5 and an average diameter of ca. 1.5 nm and adopt a face-centered cubic closest packing structure. These results demonstrate a marked sensitivity of the metal particle structure to nanoscale size effects inasmuch as the thermodynamically stable phase for bulk alloys of this composition is hexagonal close-packed. The local metal coordination environment, revealed by multiple scattering analysis of the EXAFS data, shows the presence of a nonstatistical distribution of different metal atoms in the nanoparticles. Specifically, Pt shows a marked preference for segregation to the particle surfaces under an ambient H2 atmosphere. Oxidation of the alloy particle in O2 produces an outer metal oxide layer surrounding a metal-only core. This oxidation is easily reversed by exposing the nanoparticles to H2 at room temperature.

Catalysis on singly dispersed bimetallic sites

“…In situ X-ray absorption spectroscopy (XANES) measurements were performed at the beamline X18B at the National Synchrotron Light Source, Brookhaven National Laboratory. The samples were made by pressing the powders into circular pellets using hydraulic press and transferred onto a sample holder of a Nashner-Adler in situ cell 31 .…”

Size and composition for 1–5nm Ø PtRu alloy nano-particles from Cu Kα X-ray patterns

“…Significant efforts have been devoted to their theoretical understanding, as well as synthesis and characterization [2][3][4][5][6][7][8][9][10].A sn o single investigation method provides the required detailed structural information on bi-metallic nano-particles, the combination of several analytical methods is needed. Those methods include X-ray absorption spectroscopy (XAS) [3,4], nuclear magnetic resonance (NMR) [5], infrared spectroscopy [6,7], X-ray photoelectron spectroscopy (XPS) [8] and X-ray diffraction (XRD) [9][10][11]. We wish here to develop further the application of XRD because of the apparent simplicity of its application.…”

The structural evolution and diffusion during the chemical transformation from cobalt to cobalt phosphide nanoparticles

“…11,14,15 Surface structure and coordination number at the surface can be determined for nanoparticles if the interior is assumed to have bulklike coordination values. 15,16 EXAFS has been used successfully to characterize structures in nanoparticle metal and bi-metallic clusters made through gas-phase synthesis on supports, 11,[17][18][19][20] and metal and semiconductor nanoparticles made through solution-phase chemistry. 15,16,[21][22][23][24][25] The use of EXAFS to characterize chemical transformations in nanoparticles (NPs) is relatively rare.…”