Single atoms confuse understanding of catalysis

Ars Technica : Catalysts reduce the amount of energy required in a wide range of chemical reactions. Without them, much of the modern chemical manufacturing process would not be cost-effective. How most catalysts work is still not well understood, however, and a new discovery has further confused the issue. Generally speaking, increasing the surface area of a catalyst increases the efficiency of the reaction. To catalyze the reaction of water and carbon monoxide, an international team of researchers doped iron oxide with a range of very low concentrations of iridium. On the pieces of iron oxide in which single atoms of iridium were separated from others, the reaction rate was much higher than on the pieces where the iridium atoms clumped together. And on the pieces with a mix of clumps of atoms and single atoms, the single atoms were responsible for up to 75% of the reactions. The difference in surface area between the single atoms and clumps of atoms does not explain the variation in efficiency, and no other explanation seems forthcoming.