Credit: © 2008 AAAS

Catalysts composed of metal nanoparticles, dispersed across the surface of a support, lie at the heart of the synthesis of many industrial chemicals and fuels. For such catalysts, the relationship between structure and properties is delicately poised, and to date, most fundamental insights have come from studying model catalysts such as single-crystal surfaces in controlled environments. However, real catalysts are inherently more complex, and their size, shape and surface structure can also change during a reaction. Andreas Stierle and colleagues1 at the Max-Planck-Institut für Metallforschung and the Institute for Nanoscience and Cryogenics have now shown that reaction-induced changes to supported rhodium nanoparticles can be followed directly using high-resolution X-ray diffraction.

The researchers examined the rhodium nanoparticles, which were supported on a magnesium oxide surface, during oxidation and reduction reactions. By using in situ X-ray diffraction carried out using synchrotron radiation they found that the addition of oxygen led to the pyramid-shaped nanoparticles becoming flatter, a change which could be reversed by exposure to carbon monoxide. Complementary information about the nanoparticles was also obtained using transmission electron microscopy.

From their experimental results, Stierle and team showed that this reversible shape change was driven by the formation of a surface oxide of oxygen–rhodium–oxygen at the facets of the nanoparticle.