Size- and shape-controlled metal or metal core-shell nanoparticles (NPs) have attracted much interest from catalysis community,1-3 due to their extensive potential to achieve high stability and activity. However, the structures and the origin of their superior performances are still not well understood, due to the limitation in both experimental techniques and theoretical modeling. In this talk, we present a systematic study of Pd@Pt core-shell nanoparticles using density functional theory and a cluster model, which allows us to model NPs in realistic size and shape precisely. In our study, two experimentally observed shape, tetrahedron (Td) and truncated octahedron (Oh), and the particle size ranging from 1 nm to over 3 nm are considered. Our results show that the size and shape have a significant effect on the stability and activity of a Pd@Pt NP. For a NP with the shape of either Td or Oh, the stability of a NP increases with the size, while for a NP with the same size, the Oh NP is always more stable than the Td. In contrast, the situation becomes more complicated in term of activity. The variation in activity towards oxygen with the size follows different trend depending on the shape. With the size increased from 1 nm to bulk-like particles, a volcano-like relationship is observed for the Oh NPs and an exponential decay is obtained in the case of Td NPs. According to our DFT calculations, the observed unique behaviors in stability and activity are associated with the flexibility and surface contraction, which are strongly correlated with size and shape of a NP and have significant effects on the atomic and electronic structures of the NP. Such fundamental understanding of NPs can only be achieved by the present calculations using a fully relaxed nanoparticle model in real size and shape. Our study demonstrates the importance of modeling more realistic catalysts to draw valid conclusion when catalytic properties of NPs at nanoscale are of concerns.

Theoretical understanding of Pd@Pt core-shell nanoparticles

246th National Meeting (2013)

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