A NEWLY invented metal compound can loosen the chemical bonds of the nitrogen molecules that make up four-fifths of the atmosphere. The development could eventually pave the way to using this nitrogen directly, leading to cheaper pharmaceuticals and fertilisers.
Nitrogen in the air exists as N2, and is loath to react chemically because the two atoms are held together by a strong triple bond. To make the wide range of useful chemicals that contain nitrogen, it must first be converted into ammonia (NH3), using an industrial process called Haber-Bosch, in which an iron catalyst is used to crack open the triple bond of the nitrogen molecule, at high temperature and pressure. The nitrogen can then react with hydrogen, producing ammonia. Large industrial plants produce hundreds of millions of tonnes of ammonia this way every year.
But Paul Chirik and colleagues from Cornell University in Ithaca, New York, have a new way of making nitrogen reactive. They found that when N2 binds to a compound of the metal zirconium its bonds are weakened, allowing the molecules to react with hydrogen to produce ammonia (Nature, vol 427, p 527). The researchers are investigating why this happens. 鈥淗undreds of metal-nitrogen compounds have been made, but ours is the only one that reacts with hydrogen,鈥� says Chirik.
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The zirconium compound 鈥� which consists of a single metal atom attached to two carbon rings 鈥� is used up in the reaction. That would make the method too expensive to replace the Haber-Bosch process in industry.
But Michael Fryzuk, whose group at the University of British Columbia in Canada also studies N2, says the work is exciting because the reaction seems to work by a completely new mechanism. The breakthrough suggests that with further research it might be possible to use N2 directly when making chemicals, eliminating the Haber-Bosch process completely.