Catalysts made of small particles of metals such as platinum are widely used in the chemical and refining industries, as well as in catalytic converters in automobile tailpipes. Now researchers at the University of California, Davis, studying irridium catalysts just four atoms in size have found some unexpected behavior that could open the way for a new class of nano-sized catalysts.

By directly observing the steps in chemical reactions, the researchers found that modifying the support material under catalytic nanoparticles had a dramatic effect, said UC Davis chemical engineer Bruce Gates, who led the research team. Previously, the support material was thought of as little more than something to hold the catalyst in place, Gates said. The results are published in the Feb. 7 issue of Nature.

Gates, with graduate students Andrew Argo, Felix Lai and undergraduate Josip Odzak, made nanoclusters of four irridium atoms each -- one atom sitting on three in a tiny pyramid -- on different support materials. Significantly, they were able to make their catalysts nearly uniform. They used the irridium nanoclusters to react propene and hydrogen to form propane gas.

To their surprise, they found that changing the support material changed the efficiency of the catalyst up to ten-fold. They also found that the catalytic nanoclusters and the support were chemically bonded to each other, so that the support had a marked effect on the catalyst.

Understanding how solid catalysts work has been a difficult challenge for chemists, Gates said. By using the new theory and experimenting with different arrangements of nanocluster catalysts and support materials, scientists and engineers would be able to design new catalysts for specific functions, Gates said.