Wouldn't it be good if we could make useful chemicals from carbon dioxide? German chemists are a step closer to making this goal a reality by greatly improving the reactivity of a catalyst to convert carbon dioxide into formic acid, an industrially important chemical.

Carbon dioxide could be a valuable precursor for the synthesis of organic chemicals, but there's a problem - it's just not very reactive. Processes have already been developed to convert carbon dioxide into methanol, but efficiently making formic acid from carbon dioxide has proved elusive. Matthias Driess and colleagues from the Technical University of Berlin have now found that incorporating lithium into a known zinc cluster compound greatly improves the rate of conversion of carbon dioxide into formate.

Zinc oxide is known to catalyse reactions of water-gas (an industrially available mixture of carbon dioxide and hydrogen), but little is known about how it works at the molecular level. Therefore, Driess took zinc-oxygen cluster compounds known as cubanes, and used them as model compounds, studying their reactions with pure carbon dioxide by infra-red spectroscopy.

The simplest cubane they tested, with four zinc-hydride groups, took three days to react with carbon dioxide. The same reaction was complete within minutes when one of the zinc hydride groups was replaced with a lithium-tetrahydrofuran unit, said Driess. His team are now hoping to use these cubanes to make heterogeneous catalysts capable of selectively converting water-gas to formic acid derivatives, he says.

The work is described as a 'milestone' by Hansjörg Grützmacher, an inorganic chemist at ETH Zürich, Switzerland, who said that the research 'gives insight at an unprecedented molecular level into the water-gas shift reaction promoted by zinc oxide - truly a reaction of immense importance.'

David Barden