Growth of CuPd nanoalloys encapsulated in carbon-shell

Preparation of nanostructured copper-palladium (CuPd) alloys is getting more attention because specific catalytic properties can be tuned by controlling their composition, size, and shape. Thus, a better understanding especially in the formation mechanism of the CuPd nanoalloys is of great importance in designing the catalysts. Growth of CuPd nanoalloys encapsulated in carbon-shell (CuPd@C) was, therefore, studied by in situ synchrotron small-angle X-ray scattering during temperature-programed carbonization (TPC) of the Cu²⁺- and Pd²⁺-β-cyclodextrin complexes. A rapid reduction of Cu²⁺ and Pd²⁺ with nucleation is found at the temperatures of <423 K, followed by coalescence at 453–573 K. The well-dispersed CuPd nanoalloys having the sizes of 7.6–7.9 nm in diameter are encapsulated in carbon-shell of 1.4–1.8 nm in thickness. The refined extended X-ray absorption fine structure spectra indicate that the bond distances of the first-shell Cu–Pd are 2.61–2.64 Å with the coordination numbers of 5.1–5.6. A homogeneous CuPd alloy at the Cu/Pd atomic ratio of 1 is observed. Note that at the high Cu/Pd ratio, Cu is enriched on the CuPd nanoalloy surfaces, attributable to the relatively low surface free energy of Cu.