Reaction-Driven Restructuring of Rh-Pd and Pt-Pd Core-Shell Nanoparticles

The structure and composition of core-shell Rh{sub 0.5}Pd{sub 0.5} and Pt{sub 0.5}Pd{sub 0.5} nanoparticle catalysts were studied in situ, during oxidizing, reducing, and catalytic reactions involving NO, O{sub 2}, CO, and H{sub 2} using X-ray photoelectron spectroscopy in the Torr pressure range. The Rh{sub 0.5}Pd{sub 0.5} nanoparticles undergo dramatic and reversible changes in composition and chemical state in response to oxidizing or reducing conditions. Under oxidizing conditions the Rh atoms segregate to the shell region while in reducing atmospheres the Pd atoms diffuse to the shell region. In contrast no significant segregation of Pd or Pt atoms was found in Pt{sub 0.5}Pd{sub 0.5} nanoparticles. The distinct behavior in restructuring and chemical response of Rh{sub 0.5}Pd{sub 0.5} and Pt{sub 0.5}Pd{sub 0.5} nanoparticle catalysts under the same reaction conditions illustrates the flexibility and tunability of the structure of bimetallic nanoparticle catalysts during catalytic reactions.