Tiny gold clusters can help clean car exhaust

September 6th, 2008 - 2:26 pm ICT by IANS  

Washington, Sep 6 (IANS) Researchers are exploiting gold’s exceptional ability to catalyse a wide variety of chemical reactions, including conversion of the poisonous pollutant carbon monoxide into carbon dioxide at room temperatures. That process, in industrial terms, could potentially improve the effectiveness of catalytic converters that clean automobile exhaust and breathing devices, protecting miners and firefighters.

For this purpose, nanoclusters - gold atoms bound together in crystals smaller than a strand of DNA - are the size most treasured.

Using a pair of scanning transmission electron microscopy (STEM) instruments, researchers at the National Institute of Standards and Technology (NIST), Lehigh University and Cardiff University in Britain for the first time achieved state-of-the-art resolution of the active gold nanocrystals absorbed onto iron oxide surfaces.

In fact, the resolution was sensitive enough to even visualise individual gold atoms. Studies have suggested that there is a critical size range at which gold nanocrystals supported by iron oxide become highly active as catalysts for carbon monoxide oxidation.

However, the theory is based on research using idealised catalyst models made of gold absorbed on titanium oxide. The STEM imaging technique allows the researchers to study the real iron oxide catalyst systems as synthesised, identify all of the gold structures present in each sample, and then characterise which cluster sizes are most active in carbon monoxide conversion.

The research team discovered that size matters a lot - samples ranged from those with little or no catalytic activity (less than one percent carbon monoxide conversion) to others with nearly 100 percent efficiency.

Their results revealed that the most active gold nanoclusters for the conversion are 40 times smaller than the common cold virus and contains about 10 gold atoms. This finding is consistent with the previous surface science studies done on the gold-titanium oxide models.

The work was published in the Friday edition of Science.

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