Nanocatalysts Reveal Structure Sensitivity

A combined molecular-beam and quantum-simulation study that explores the catalytic behavior of tiny platinum clusters calls into question a well-established precept regarding the influence of structure on the reactivity of solid catalysts (Nat. Commun. 2016, DOI: 10.1038/ncomms10389). Years of experiments have shown that platinum-catalyzed hydrogenation of ethylene to ethane does not depend on the surface structure of the platinum crystallites. This archetypal “structure-insensitive” reaction has long stood in contrast to structure-sensitive reactions, for example, ammonia synthesis on iron crystals. These classifications have influenced strategies for enhancing catalyst performance. Now, a team led by Ueli Heiz of the Technical University of Munich and Uzi Landman of Georgia Tech has shown that ethylene hydrogenation is indeed sensitive to the structure of platinum particles, if those particles lie at the low end of the nanoscale regime. By studying size-selected platinum clusters composed of nine to 13 atoms, they found that the nine-atom cluster does not catalyze ethylene hydrogenation but the larger particles do catalyze the reaction with activity that increases with cluster size. Calculations show how the number of atoms dictates cluster geometry, which controls the clusters’ electronic properties underpinning surface catalysis.