Nanoporous Gold: Understanding the Origin of the Reactivity of a 21st Century Catalyst Made by Pre-Columbian Technology

Nanoporous gold (np-Au), a three-dimensional nanoporous bulk material, is made by selective corrosion of Ag from Ag-Au alloys, a technique already applied by the pre-Columbian cultures of South America. Nanoporous gold is actually a Au-rich Ag-Au alloy which, specifically the Ag0.03Au0.97 composition, combines high reactivity and selectivity for a wide variety of oxidation reactions, from simple CO oxidation to complex oxygen-assisted coupling reactions. Its catalytic reactivity is surprising because np-Au is a nonsupported Au catalyst with relatively large feature sizes on the order of tens of nanometers, thus breaking the generally accepted notion that gold must be in the form of small particles (about a few nanometers) to be an active catalyst. The ease of sample preparation in combination with high reactivity, selectivity, and long-term stability suggests that nanoporous gold has the potential to bring Au catalysis closer to practical applications. In this perspective, we provide a critical review of the current understanding of the origin of the high catalytic activity of nanoporous gold in context of morphology and surface composition.