September 9, 2008
Tiny Gold Clusters Seen As Good Catalysts
U.S.-led scientists say they have, for the first time, achieved state-of-the-art resolution of active gold nanocrystals absorbed onto iron oxide surfaces.
Using two scanning transmission electron microscopy instruments, the researchers said the resolution was sensitive enough to visualize individual gold atoms.The scientists from the National Institute of Standards and Technology, Lehigh University and Cardiff University in Wales note gold has an exceptional ability to catalyze a wide variety of chemical reactions, including the oxidation of poisonous carbon monoxide into harmless carbon dioxide.
Previous studies suggested there's a critical size range at which gold nanocrystals become highly active as catalysts for CO oxidation. But that theory is based on research using idealized catalyst models made of gold absorbed on titanium oxide.
The new imaging technique allowed the researchers to study the real iron oxide catalyst systems as synthesized, identify all gold structures present in each sample and then characterize which cluster sizes are most active in CO conversion.
The study showed the most active gold nanoclusters for CO conversion are bilayers approximately 0.5-0.8 nanometers in diameter and containing about 10 gold atoms.
The study is reported in the Sept. 5 issue of the journal Science.