Active Sites In Gold Foam Revealed

Atomic-scale imperfections in a nanoporous gold foam serve as active sites in catalytic oxidations, according to a team of researchers based in Japan, China, and the U.S. (Nat. Mater., DOI: 10.1038/nmat3391). Gold’s long-standing reputation as an inert metal has been shattered repeatedly in the past 20 years by numerous studies showing that gold nanoparticles can be highly active catalytically. Nonetheless, many details of gold’s catalytic nature remain unknown. For example, highly active gold catalysts are typically endowed with structural features no larger than 5 nm. Yet several researchers have shown that monolithic three-dimensional spongelike gold foams with channels and ligaments exceeding 30 nm catalyze several types of reactions. On the basis of electron microscopy imaging during carbon monoxide oxidation, Tohuku University’s Takeshi Fujita and Mingwei Chen and coworkers report that these foams, which are formed by using nitric acid to remove silver from gold-silver alloys, possess regions of high curvature featuring an abundance of crystal defects known as steps and kinks. The defects, which form upon exposure to CO, are dotted with catalytically active undercoordinated gold atoms and are stabilized by residual silver, they say.