(204a) Structural Evolution of Pt-Based Bimetallic Nanoparticle Catalysts During Reactions

The bimetallic catalyst is one important category of heterogeneous catalysts for numerous industrial processes and energy conversion. The development of Pt-based bimetallic catalysts is one of the main approaches to enhance activity of oxygen reduction reaction of hydrogen fuel cell technology. Surface structure and chemistry of a few Pt-base bimetallic catalysts including Rh-Pt and Pd-Pt nanoparticle catalysts were studied under different reaction conditions using ambient pressure XPS in Torr pressure range and high resolution TEM. The RhxPt1-x nanoparticles undergo reversible changes in both atomic fractions and chemical states corresponding to the switch of reaction environments between oxidizing and reducing conditions. Rh atoms in RhxPt1-x segregate to surface layers and are oxidized in oxidizing conditions while in reducing atmospheres the Pt atoms in RhxPt1-x diffuse to the surface regions and Rh atoms are largely reduced. In contrast to RhxPt1-x, no significant segregation of Pd or Pt atoms was found in PtxPd1-x nanoparticles; Pd atoms are alternatively oxidized and reduced under oxidizing and reducing conditions, whereas Pt atoms do not. The capability of restructuring nanoparticles through chemical reactions suggests the flexibility of the structure of bimetallic nanoparticle catalysts and indicates a new method for the development of new catalysts.