(639d) In-Situ Promotion of Coupled Oxidation and Reduction Cycles over Metal Catalysts

Catalytic oxidation and reduction are critical routes in the selective conversion of bio- as well as petroleum-based feedstocks into chemicals and fuels. Nature and biology often carry out similar oxidation and reduction reactions by uniquely coupling both cycles. External reagents often act as co-catalysts to efficiently transfer hydrogen as protons or hydride species and selectively carry out such transformations. Similar coupled oxidation and reduction cycles are also at the heart of most electrochemical systems. These reactions are typically carried out via efficient proton-coupled electron transfer reactions. In most heterogeneous catalyzed oxidation and reduction systems, oxygen and hydrogen, respectively are used directly and the coupling of these cycles is not considered. Recent efforts, however, have shown that heterogeneous catalytic oxidation and reduction reactions can be significantly enhanced by the presence of co-catalysts that can efficiently transfer hydrogen. Herein we examine the oxidation of alcohols by active and selective co-catalysts formed via the in-situ reduction of an unsaturated carbonyl or molecular oxygen. Such systems show considerably enhanced activities and selectivities. Similarly, we discuss the reduction of oxygen to form hydrogen peroxide over metal catalysts and show how hydroxyalkyl or alkoxide intermediates formed via the oxidation of alcohol can actively carry out the reduction of oxygen. Finally, we discuss how the activity and selectivity for these catalytic reduction and oxidation systems can be further improved by the design of 3D nanoscale environments that self-assemble into enzyme-like cavities to promote their reactivity