Golden promise for green catalyst

Gold nanoparticles can catalyse specific oxidation reactions using air and no solvents, report UK researchers.

Graham Hutchings at Cardiff University found that oxygen from air can be used to make epoxides selectively when gold particles, supported on carbon, are used as a catalyst. Hydrogen or another co-reductant was previously needed to activate oxygen. ’We’ve shown that if you add a little bit of a peroxide initiator then you don’t need the hydrogen there at all,’ Hutchings told Chemistry World.

Hutchings’ system works at low temperatures and without extra solvent. ’You can just have the substrate itself, the molecule you want to react, as its own solvent,’ he said.

A green oxidation catalyst is likely to attract commercial interest said Hutchings: ’All the big catalyst players are waking up to the fact that gold is really capable of doing some special things.’ The catalyst will be useful for fine chemicals manufacturers to make intermediates for drugs and agrochemicals, he said.

Hutchings first realised that gold might catalyse oxidation without hydrogen three years ago, but he has not gone public until now. ’We found that, in water, hydrocarbons could be rapidly but non-selectively oxidised,’ he said. ’I didn’t think anybody would spot this,’ he added, ’I was right’. The trick was finding the conditions that gave the selectivity that would make the catalyst applicable. 

With the selectivity problem solved, Hutchings predicts that commercial success is close, with engineers now working on a flow system. He says that improving the dispersion of the gold on the support will help increase the rate of reaction, to improve yields.

Masatake Haruta, from Tokyo Metropolitan University, Japan, who first mooted the hydrogen co-reductant theory, said that there are still questions to be answered about exactly how gold particles activate molecular oxygen at such low temperatures, and how epoxidation works. ’Convincing answers to such questions would provide us with a valuable roadmap for pursuing green, sustainable chemistry,’ said Haruta. Katharine Sanderson