No wonder why clusters are important. These days a cluster means a tinier nanoparticle. You can actually count the atoms. Herzing et al. (Kiely group at Lehigh) showed us how a cluster can unravel mysteries of the catalysis world.
Gold clusters with 10 atoms (~0.5 nm) on iron oxide (FeOOH and Fe2O3) are found to oxidize CO 100% at 25 oC. Though gold (Au) is known to catalyze oxidation reaction in good yields, the unusual observation was that the smaller wasn't always the better. In fact atomic gold or monolayer gold was doing poorly as compared to bilayer clusters of 10 atoms. The article was well written and the discussions are satisfactory, however, the technique they relied on left some suspicion on several of us. The "High-magnification aberration-corrected STEM-HAADF images" were the basis of their arguments and it's very tricky to get reliable data (see the earlier post here).