CO oxidation on colloidal Au_0.80Pd_0.20-Fe _xO_y dumbbell nanocrystals

We report a colloidal synthesis of Au_0.80Pd_0.20- Fe_xO_y dumbbell nanocrystals (NCs) derived from Au _0.75Pd_0.25 NCs by metal oxide overgrowth. We compared the catalytic activity of the two types of NCs in the CO oxidation reaction (CO + 1/2O₂ → CO₂), after they had been dispersed on an alumina nanopowder support. In both cases, the surface active sites were identified by means of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The enhanced catalytic performance of the dumbbell NCs (Au_0.80Pd_0.20-Fe_xO_y) catalyst over that of the initial Au_0.75Pd_0.25 NCs could be correlated to the presence of the epitaxial connection between the Fe_xO _y and the Au_0.80Pd_0.20 domains (as the main factor). Such connection should result in an electron flow from the metal oxide (Fe_xO_y) domain to the noble metal (Au _0.80Pd_0.20) domain and appears to influence favorably the nature and composition of the catalytically active surface sites of the dumbbells. Our experiments indicate indeed that, when the metal alloy domain is attached to the metal oxide domain (that is, in the dumbbell), surface Pd species are more active than in the case of the initial Au_0.75Pd _0.25 NCs and also Au^δ- sites are formed that were not present on the initial Au_0.75Pd_0.25 NCs.