Once thought inert, gold has been recognized during the past decade as a powerful catalyst for oxidations and other reactions. Calculations and experiments have indicated that the catalytic activity of nanosized gold clusters containing only a few atoms of the precious metal should be extremely high. But scientists haven’t had an optimal way to prepare and study them, until now. Avelino Corma of the Institute of Chemical Technology at Polytechnic University of Valencia, in Spain, and colleagues have developed a simple way to attach gold atoms or clusters of atoms to carbon nanotubes. Using the O2 oxidation of thiophenol as an example, they showed that a single gold atom has no catalytic activity, but clusters with five to 10 atoms are highly catalytic (Nat. Chem. 2013, DOI: 10.1038/nchem.1721). When the clusters reach a diameter greater than 1 nm, which is about 13 atoms, the catalytic activity drops to zero. The findings suggest that only the tiny clusters can adsorb and activate thiophenol and O2 simultaneously.