Golden opportunities

Gold nanoparticles could be a key ingredient for ‘clean’ catalysts, according to UK researchers. In a paper in Nature, the researchers claim that carbon-supported gold nanoparticle clusters can be fine-tuned to catalyse highly selective and efficient oxidation reactions, used in a wide variety of syntheses in the agro-chemical and pharmaceutical sectors.

Currently, most oxidation processes use chlorine or organic peroxides — not on the list of environmentally-friendly compounds. ‘The chemical industry would be transformed if selective oxidation of hydrocarbons could be achieved efficiently using cheap and clean oxygen from the air,’ comments Masatake Haruta, a catalyst chemist at Tokyo Metropolitan University.

The team, led by Graham Hutchings of Cardiff University and including Chris Kiely, a materials scientist from Lehigh University in Pennsylvania, and researchers from precious metal catalyst specialist Johnson Matthey, has found that gold nanoparticles can catalyse partial oxidations without solvents.

This is particularly useful for reactions to convert unsaturated hydrocarbons to epoxides and ketones, which is a key step in building simple compounds into the complex structures needed for pharmaceutical and agrochemical active ingredients. Moreover, they say, the catalysts’ selectivity can be tuned by adding trace amounts of bismuth.

The nanoparticles are 2-15nm across, and must be distributed evenly across a large surface area. However, they must also be prevented from coalescing, as larger particles have a much weaker catalytic effect.

‘We’re trying to determine the size, distribution and shape of the gold nanoparticles, and to see how these parameters relate to the measured catalytic properties,’ says Kiely. ‘We are also interested in the interaction of gold with other promotor elements, such as bismuth.’