1. Pt-Ru Bulk Phase Diagram

2. + H2H2 673 K ? Supported Metal NanoparticleMetal Salt Precursor Characterization of final nanoparticles: X-ray Photoelectron Spectroscopy (XPS) Scanning Transmission Electron Microscopy (STEM) Energy Dispersive X-ray Analysis (EDAX) Electron Microdiffraction Nanoscale Phase Behavior Pt/C + RuCl 3 3H 2 O Ru/C + H 2 PtCl 6xH 2 O [Pt x Ru y ]/C Ru/C + (CH 3 ) 2 Pt(COD) [Pt x Ru y ]/C

3. X-ray Photoelectron Spectroscopy (XPS) X-Ray Photoelectron Spectroscopy (XPS) probes the composition of the bulk sample. These figures show that bimetallic nanoparticles are formed upon reduction of a a metallic salt in the presence of supported nanoparticles (Ru or Pt). Binding Energy (eV) N(E)/E Ru3d Pt4f Binding Energy (eV) N(E)/E Ru3d Pt4f

4. Growth of Nanoparticles after Reduction Dark field micrograph of 10% Ru/Carbon Black (ETEK) after addition of H 2 PtCl 6, followed by reduction. Dark field micrograph of 10% Ru/Carbon Black (ETEK).

5. Particle Size Distribution: Ru + Pt/C Relative Abundance Particle Size (Å) 10 % Pt/C 10% Pt/C + RuCl 3

6. Compositional Analysis: Energy Dispersive X-ray Analysis (EDAX) Cu Ru Cu Pt Ru nanoparticle carbon support Pt Using EDAX, the composition of individual particles is probed. The figure on the left shows sample EDAX spectra for both the carbon support and a particle of ca. 80 % Ruthenium. The figure on the right shows the representative composition distribution for all bimetallic samples. Atomic Composition (at.% Ru) Relative Abundance

7. A B C A B B B B A A A C A A Hexagonal Closest Packed (hcp) Face Centered Cubic (fcc) Atomic Ordering in Solids Adapted from: http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch13/structureframe.html

8. Model XRD of Pt (fcc) 420 400 331 222 311 220 200 111 Model XRD of Ru (hcp) 20-20 10-13 11-20 10-12 10-11 0002 10-10 10-1420-22 0004 20-21 11-22 21-30 20-23 Sample X-Ray Diffraction Patterns 2  (deg) Intensity

9. Electron Microdiffraction [011] [0001] [011] 41 Å particle with a composition of 42% Ru 66 Å particle with a composition of 16% Ru 35 Å particle with a composition of 66% Ru

10. Particle Size (Å) Atomic Composition (% Ru) “Nano”-phase diagram of bimetallic particles formed on supported Pt clusters. Particle Size (Å) Atomic Composition (% Ru) Particle Size (Å) “Nano”-phase diagram of bimetallic particles formed on supported Ru clusters. Template Effects in the Binary Phase Diagram of Pt-Ru Nanoparticles

11. Binary Nano-Phase Diagram Supported bimetallic nanoparticles can be synthesized by reducing metallic salts onto pre-existing metallic nanoparticles. XPS, EDAX, and STEM provide evidence of the formation of bimetallic particles with wide size and compositional distributions. These bimetallic nanoparticles have an organized close-packed structure that shows phase-sensitive behavior across the compositional space. Microdiffraction results show template effects via the coexistence of both (fcc) and (hcp) structures within the same samples. Atomic Composition (% Ru) Particle Size (Å)