Complex Alternative

Another proposed system could provide a way to use CO₂ without the need for hydrogen. Raja Angamuthu and Elisabeth Bouwman at Leiden University in the Netherlands and their team have just shown how a copper-based chemical called a copper complex can help turn CO₂ into something new.

The team's yellow-coloured copper complex turns greenish-blue as it snatches CO₂ molecules from air at room temperature and normal pressure. Angamuthu and Bouwman used CO₂₂ rather than oxygen in the air, which demonstrates the process is "quite selective for CO₂", says Bouwman. labelled with a heavy carbon isotope to confirm that the copper complex reacts with CO

The team then added a lithium salt to the copper complex solution, causing insoluble lithium oxalate to precipitate. Using electrolysis they can reduce the copper to recreate the copper complex to react with more CO₂.

O'Hare finds Angamuthu and Bouwman's work interesting. "What caught my eye is the reactivity to CO₂ in the presence of oxygen," he says, which means the reaction could work in the Earth's atmosphere. But while recycling the copper is "neat", he says the end product – an insoluble salt – is not as useful as making a liquid fuel like methanol.

But the lithium oxalate is far from useless, says Bouwmann. "It can be reduced to ethylene glycol, used, for example, as coolant in freezers," she says. The oxalate can also be oxidised into oxalic acid for use in household cleaning products.

Journal references: O'Hare and Ashley's paper is published in Angewandte Chemie, DOI: 10.1002/anie.200905466; Angamuthu and Bouwman's study is in Science, DOI: 10.1126/science.1177981