Structural characterization of carbon-supported bimetallic AuCu nanoparticles derived from metal vapors

Bimetallic nanoparticles have caught great interest in catalysis over the past decade. The electronic or structural modifications of the active sites arising from interactions among metals at the nanoscale can result in a material with enhanced catalytic properties. Recently, bimetallic catalysts composed of Au and Cu have been widely studied in heterogeneous catalysis; the addition of Cu is an attractive way to promote activity and selectivity of Au-based catalysts in different catalytic reactions (1,2). We report here the synthesis of AuCu bimetallic nanoparticles by the simultaneous co-condensation of Au and Cu vapors with acetone, according to the solvated metal atom (SMA) technique (Figure 1) (3). The AuCu nanoparticles where then supported on carbon by direct impregnation. Samples containing three different metal ratios (i.e. Au:Cu 1:10; 4:1 and 17:1), as well as the corresponding monometallic systems, were prepared. The fine structure and the analytical local composition of the unsupported AuCu nanoparticles were investigated by corrected TEM and STEM analysis combined with energy filtered maps and EDX measurements. The structural features of the corresponding carbon-supported systems having a total metal loading (Au+Cu) of 1 wt.% were then characterized by HRTEM and X-ray absorption fine structure (XAFS) spectroscopy. Interestingly, nor nanoparticles aggregation nor structural modifications occurred during the deposition step. The catalytic performances of the 1%wt AuCu/C catalysts with different Au:Cu ratio were evaluated in both oxidation and hydrogenation of glycerol, highlighting the different role of Cu in modifying the activity/selectivity with respect to the monometallic counterparts