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 welldispersed CuPd nanoalloys having the sizes of 7.6-7.9 nm in diameter are encapsulated in carbonshell 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 A° 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.