Silica-supported Au-CuO_x hybrid nanocrystals as active and selective catalysts for the formation of acetaldehyde from the oxidation of ethanol

The selective oxidation of ethanol with molecular O₂ is increasingly becoming an important process to develop fine chemicals because it can be obtained from renewable biomass feedstock while reducing the demand on fossil fuels. We have synthesized silica-supported Au-Cu alloy nanoparticles, and through an oxidative dealloying process, we have developed Au-CuO _x hybrid catalysts for the selective oxidation of ethanol into acetaldehyde. Using a combination of XRD, XPS, and HR-STEM experiments, we have confirmed that the active catalyst is a Au core with a thin CuO_x shell. Oxidation of the AuCu/SiO₂ alloy catalyst at 300 °C was found to produce the most active and stable catalyst for ethanol conversion (∼90%) with the highest selectivity (∼80-90%) at a reaction temperature of 200 °C for 50 h on-stream. TEM and XRD results show that Au-CuO _x/SiO₂ catalysts calcined at 300 and 500 °C are also more resistant to sintering during pretreatment and catalytic conditions than pure gold supported on silica. Furthermore, the silica-supported Au-CuO _x catalysts (calcined at 300 and 500 °C) were also found to be more active and selective in the dehydrogenation of ethanol to form acetaldehyde. It is likely that the increased interfacial contact between the Au and CuO_x forms the most active site on the catalyst and is responsible for the enhanced catalytic properties when compared with pure Au/SiO₂.