Surface Properties of Supported, Colloid-Derived Gold/Palladium Mono- and Bimetallic Nanoparticles

Mono- and bimetallic Au/Pd nanoparticles deposited on different supports (Al2O3, TiO2, SiO2) have been prepared using a colloidal route. Electron microscopy revealed a narrow particle size distribution of as-prepared nanoparticles with a mean diameter in the range of 3−4 nm. CO adsorption combined with DRIFTS measurements was employed to gain information about the available adsorption sites on these nanoparticles. On Pd nanoparticles, linear, μ2-briged, and μ3-bridged CO was observed. Upon reductive treatment of the particles, the signal for the μ2-bridged species on Pd(111) faces decreased significantly. The gold particles revealed a surprisingly strong red shift of the signal at around 2110 cm−1 after reduction, indicating a morphological change of the particles upon treatment in hydrogen. In contrast, treatment in oxygen at the same temperature did not alter the IR spectrum notably. EXAFS and DRIFTS indicated a redistribution of the constituents of the bimetallic nanoparticles upon reduction: the core−shell structure of the as-prepared particles changed to a structure with more evenly distributed constituents.