Pt-Pd Bimetallic Catalysts: Structural and Thermal Stabilities of Core-Shell and Alloyed Nanoparticles

Atomic-level understanding of structural characteristics and thermal behaviors of nanocatalysts is important for their syntheses and applications. In this article, we present a systematic study on structural and thermal stabilities of Pt-Pd bimetallic nanoparticles with core shell and alloyed structures by using atomistic simulations. It was revealed that the Pd-core/Pt-shell structures are the least structurally stable, while the inverted Pt-core/Pd-shell nanoparticles are more stable than the alloyed ones when the Pt percentage exceeds 42% or so. The origin for this order was clarified through analysis of atomic energy distribution in these structures. Furthermore, the core-shell structures exhibit enhanced thermal stability as compared to the alloyed ones for Pt composition more than about w30%. The diverse melting behaviors of bimetallic nanoparticles, associating with their thermally driven structural evolutions under the heating process, were characterized by the measurement of the Lindemann index In addition, the analyses of diffusion behavior and atomic distribution suggest that the minimization of surface energy tends to form Pd surface segregation. This study is of considerable importance not only to experimental preparation of Pt-Pd nanocatalysts but also to design of bimetallic (even multimetallic) nanostructures of high catalytic activity and excellent stability.