Analytical TEM study of the core-shell structure of Au-Pd nano-particles prepared by sonochemical technique

Akita, Tomoki; Hase, Naoki; Taguchi, Noboru; Tanaka, Shingo; Kohyama, Masanori; Hori, Fuminobu Japan

Noble metal nano-particles are widely used for various catalytic reactions. It is important to control the structures of nano-particles in nano- or atomic-scale in order to develop new materials for catalysts. Many bimetallic nano-particles are prepared and applied for the various catalytic reactions, for example, Au-Pd bimetallic particles exhibit higher catalytic activity for hydrogenation reactions compared to Pd. The detail structure of the bimetallic nano-particle is not well understood because atomic-scale characterization is difficult. In this study, the structure of Au-Pd nano-particles prepared by sonochemical technique was investigated by an analytical TEM.
The bimetallic Au-Pd particles were prepared by sonochemical techniques. The aqueous solutions of NaAuCl₄^.2H₂O and PdCl₂^.2NaCl^.3H₂O were used as precursors. The aqueous solutions containing Au and Pd ions with sodium dodecyl sulfate (SDS) sonicated in a water bath at approximately 293 K. The structure of the Au-Pd particles was observed by the analytical TEM, JEOL JEM-3000F. TEM observation reveals that the nano-particles about 10nm in diameter are successfully prepared. The core (Au)-shell (Pd) structure was confirmed by the ADF-STEM images. The line-scan EDS analysis also reveals the core (Au)-shell (Pd) structure. The ratio of Au and Pd content was controlled by adjusting the ratio of precursor, and the thickness of Pd shell was also controlled by the ratio of Au and Pd content. Selected area electron diffraction patterns shows no diffraction rings corresponding to the lattice constant of bulk Pd. And lattice fringes observed in HRTEM images were also analyzed by FFT. The space of the lattice fringes did not coincide with the lattice constant of bulk Pd. ADF-STEM observations enabled to identify the interface between Au and Pd from the difference of the image intensity. It was revealed that Pd shell was growing on the Au particle with epitaxial relationship. These experimental results indicated that the lattice constant of Pd shell expands and coincides with the lattice constant of Au. This work was supported by the Japan Society for the Promotion of Science(JSPS-Grant-in-Aid for Scientific Research (B) 17360314)

---

back