Au-Pd separation enhances bimetallic catalysis of alcohol oxidation

Abstract

In oxidation reactions catalysed by supported metal nanoparticles with oxygen as the terminal oxidant, the rate of the oxygen reduction can be a limiting factor. This is exemplified by the oxidative dehydrogenation of alcohols, an important class of reactions with modern commercial applications^1-3. Supported gold nanoparticles are highly active for the dehydrogenation of the alcohol to an aldehyde⁴ but are less effective for oxygen reduction^5,6. By contrast, supported palladium nanoparticles offer high efficacy for oxygen reduction^5,6. This imbalance can be overcome by alloying gold with palladium, which gives enhanced activity to both reactions^7,8,9; however, the electrochemical potential of the alloy is a compromise between that of the two metals, meaning that although the oxygen reduction can be improved in the alloy, the dehydrogenation activity is often limited. Here we show that by separating the gold and palladium components in bimetallic carbon-supported catalysts, we can almost double the reaction rate compared with that achieved with the corresponding alloy catalyst. We demonstrate this using physical mixtures of carbon-supported monometallic gold and palladium catalysts and a bimetallic catalyst comprising separated gold and palladium regions. Furthermore, we demonstrate electrochemically that this enhancement is attributable to the coupling of separate redox processes occurring at isolated gold and palladium sites. The discovery of this catalytic effect-a cooperative redox enhancement-offers an approach to the design of multicomponent heterogeneous catalysts.