Credit: © 2006 Wiley

Metals are often used as catalysts in chemical reactions as they provide low-energy pathways for the conversion of reactants into products. The right catalyst can make a sluggish reaction go faster or even enable a transformation that would otherwise not happen. It has been known for quite some time that for any given metal the catalytic properties depend on the size — and, therefore, surface area — of the individual particles. Researchers are now investigating the role that particle shape can play.

Seung Uk Son and co-workers from Sungkyunkwan University and the Korea Basic Science Institute in Korea have studied how the catalytic properties of rhodium nanoparticles are influenced by their shape1. They found that tetrahedral nanoparticles were much more active catalysts for hydrogenation reactions (the addition of hydrogen to organic compounds) than spherical Rh particles of roughly the same size. Moreover, the tetrahedral catalysts were much more selective than their spherical counterparts, favouring more strongly one particular compound in the mixture of products that can be formed.

The catalytic performance of the nanoparticles is rationalized by considering the structure of the surface atoms. It is thought that the faces of the tetrahedral nanocrystals comprise solely the more active (111) lattice planes, whereas the spherical catalysts have both (111) and the less active (100) planes exposed.