Disclosing the structure of hybrid Au-CuO bimetallic nanoparticles and their role in selective alcohol oxidation

Hybrid nanoparticles systems have caught great interest in catalysis over the past decade. The modifications induced by the interactions among metals and other metals/oxides at the nanoscale could lead to new materials with enhanced and unforeseen catalytic properties. Recently, former bimetallic catalysts based on Au/Cu pairs have been extensively investigated since the addition of CuOx to Au NPs proves to be effective to promote activity and selectivity in several catalytic reactions. We report here the synthesis of Au-Cu bimetallic nanoparticles by simultaneous cocondensation of Au and Cu vapor with acetone vapor, according to the metal vapor synthesis (MVS) technique (3,4). The AuCu NPs where deposited on carbon (Vulcan XC-72R) by impregnation at 25°C, obtaining hybrid Au-CuO/C catalysts. Three systems with different metal ratios (i.e. Au:Cu 1:10; 4:1 and 17:1) were synthesized, together with the corresponding monometallic ones. HR-TEM, STEM-EELS maps and XAFS analysis revealed the presence of Au-CuO core-shell-like heterostructure having tailored size distributions (mean diameter < 4.5 nm). Their catalytic performances in the liquid-phase selective benzyl alcohol oxidation. A positive marked effect was observed alongside the Au core-coverage degree: i) high Au/Cu molar ratios (i.e. 13/1, 4/1) -which showed an incomplete CuO shell that partially covers the Au core- showed the highest catalytic activity; ii) in presence of a complete CuO shell (i.e. Au1Cu17/C), the catalytic activity was inhibited. The results showed the possibility to fine-tune the catalytic behaviors of Au catalysts using nanostructured modifiers as shell-like CuO hybrid systems and how this approach could be successfully applied to other metal pairs and chemical reactions.