Catching Catalyst Particles In Action

Analytical methods for probing catalytic nanocrystals while they mediate chemical reactions can uncover insights that lead to better catalysts. Designing those methods, however, remains a formidable challenge. Two teams of researchers have taken a step in that direction by demonstrating techniques for monitoring catalyzed oxidation and reduction reactions. In one case, Paul Mulvaney and coworkers of the University of Melbourne, in Australia, combined an analytical technique known as dark field microscopy with surface plasmon spectroscopy to directly measure the single-particle reaction rates of the fundamental steps of ascorbic acid oxidation by dissolved oxygen on gold nanoparticles (Nat. Nanotechnol., DOI:10.1038/nnano.2008.246). The particles hasten the reaction by serving as electron reservoirs that transfer charge from ascorbic acid to oxygen. In the other study, Andreas Stierle of the Max Planck Institute for Metal Research, in Stuttgart, Germany, and coworkers combined X-ray diffraction and transmission electron microscopy to probe oxidation-induced shape changes to the surfaces of rhodium nanoparticles supported on magnesium oxide (Science 2008, 321, 1654). They found that crystal morphology changes, which can be reversed by CO exposure, are driven by the formation of an oxygen-rhodium-oxygen surface oxide film that stabilizes the nanoparticles.