Hot Electron Surface Chemistry at Oxide-Metal Interfaces: Foundation of Acid-base Catalysis

Abstract

The development of catalytic nanodiodes to measure the flow of hot electrons generated at metal-oxide interfaces has proven that exothermic catalytic reactions on platinum induce a steady flux of hot electrons. Based on the simultaneous measurement of hot electrons and chemical reactions, it was found that chemicurrent is correlated with turnover frequency. It was shown that charge transport between the metal and oxide interfaces also influences the catalytic activity and product distribution of multipath reactions. Metal-oxide interfaces appear to produce ions that carry out reactions; these reactions have long been called "acid-base catalysis" by the organic chemistry community. A typical catalytic structure is a mesoporous oxide that is produced to hold metal nanoparticles. The structures provide high-surface-area oxide-metal interfaces that create the catalytic architecture for acid-base catalysis. Studies where the transition metal oxide is changed and only a single metal (i.e., platinum) is used for the nanoparticles show a tremendous amplification effect of the oxide-metal interfaces in the reactions (e.g., carbon monoxide oxidation). In this Perspective, we address the role of metal-oxide interfaces in generating a flow of charge carriers, thus implying a link between acid-base catalysis, the spillover process, and hot electron chemistry. We highlight recent studies on the amplification of catalytic activity when using Pt nanoparticles and various oxides (e.g., cobalt oxide, nickel oxide, manganese oxide, iron oxide) under CO oxidation, n-hexane isomerization, and cyclisation reactions, which imply that charge transfer between the metal and the oxide plays a key role in catalytic activity and selectivity. We suggest that catalytic nanodiodes can be used to detect hot electron flow, spillover, and charged reactive intermediates, which can improve a fundamental understanding of electronic excitation and charge flow in chemical reactions. [GRAPHICS]