Carbon Support Effects on Bimetallic Pt−Ru Nanoparticles Formed from Molecular Precursors

Abstract

We describe the preparation, structural characterization, and support interactions experienced by two different compositions of Pt−Ru nanoparticles supported on several carbons (carbon black, fullerene soot, and desulfurized carbon black). The bimetallic nanoparticles, obtained by reduction of the neutral molecular precursors PtRu 5 C(CO) 16 and Pt 2 Ru 4 (CO) 18 (the latter of which lacks a central “stabilizing” carbide core) at elevated temperatures in a hydrogen atmosphere, show a structural homology, exhibiting exceptionally narrow size and compositional distributions. A detailed structural picture of the nanoparticles has been deduced on the basis of in-situ extended X-ray absorption fine structure (EXAFS), scanning transmission electron microscopy (STEM), energy-dispersive X-ray analysis (EDX), and X-ray absorption near edge structure (XANES). These techniques reveal that the bimetallic nanoparticles have Pt/Ru compositions of 1:5 and 2:4, respectively, and average diameters lying between 1.0 and 1.5 nm. The local metal coordination environments reveal a nonstatistical distribution of the two metals in the nanoparticles. Specifically, Pt shows a marked preference for segregation to the particle surfaces under an H 2 atmosphere. The data also reveal a difference in the structural environment of the nanoparticles when formed on the fullerene soot support. Interactions between Ru and low- Z atoms are revealed through XANES, which, taken collectively with the other data presented, leads us to propose a possible Ru−C compound formation on this latter support phase.