Take two reactive substances. Add them together… nothing happens. Now, add a tiny bit of magic powder. A miracle occurs! The reaction takes place. This is the mystery of catalysis. What is at stake is both fundamental – understanding the mechanisms that rule catalytic activity – and industrial – synthesizing better catalysts. In collaboration with a team of the Max Planck Institute in Stuttgart, we have shown that the morphological transformations of catalyst nanoparticles are linked to the reactions they catalyze.
Among the metals that have a catalytic activity, rhodium is well known for its role in the reduction of NOx, oxidation of CO, etc.… Recent results have shown that the catalytic activity of nanoparticles might be linked to the presence of a metal-oxide layer at the surface. It was also known that these particles changed shape in the presence of a gaszeous atmosphere. Take a look at a clean rhodium particle (A). It has a truncated octahedron shape under ultra high vacuum conditions. Now, expose it under ultra-high vacuum to a 2.10-5 mbar oxygen atmosphere. Its shape changes to as shown in (B).
During oxidation, the upper  facet and the  vertical facets widen. Atoms from the upper surface migrate towards the tilted facets ( facets on the figure). When this particle is reduced with CO, the particle changes back to its initial shape. These experiences should allow for a better understanding of catalysis as driven by nanoparticles under real conditionsin real situation.
Further reading: P. Nolte, et al., Science 321 (2008) 1654
Maj : 20/02/2014 (981)