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Breaking Nitrogen's Three-Handed Clasp

17 January 2007 (All day)
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NASA

Future fuels?
A new way to access nitrogen may lead to cheaper rocket fuels.

Nitrogen is a ubiquitous resource, comprising some 78% of the atmosphere. But most of the gas is inert, locked in molecules that don't interact with their neighbors. That's long been a problem for industry, which expends vast amounts of energy harnessing nitrogen to make fertilizers, drugs, plastics, and many other products. Now a team of researchers has taken a key step towards what could become a much cheaper approach.

Nitrogen's lack of interest in other elements stems from the strong ties it makes to its brethren. Whereas most molecules share single or double bonds between adjacent atoms, pairs of nitrogen atoms clasp one another with three bonds. Making use of those nitrogens requires first breaking this three-handed clasp. About a century ago, scientists figured out how to do this by combining nitrogen with hydrogen to make ammonia, a development that led to the production of synthetic fertilizers--among other things--and the rise of modern agriculture. But even today, manufacturing ammonia requires vast amounts of energy.

Three years ago, Paul Chirik, a chemist at Cornell University, and his colleagues devised a zirconium-based catalyst that could incorporate atmospheric nitrogen into ammonia. But for many chemical compounds, ammonia isn't an ideal starting material, so this time Chirik and his colleagues decided to see if they could get their catalysts to work some new magic. In an upcoming issue of Angewandte Chemie International Edition in English, they report their success in developing a compound centered around the metallic element hafnium that couples nitrogen with carbon dioxide.

The compound works by initially locking nitrogen in a vice between two of the hafnium complexes. This causes the nitrogen atoms to unclasp two of their bonds to one another and transfer them to the hafniums instead. After the switch, carbon dioxide molecules wedge their way in between the nitrogens and the metals. Further chemical additions allowed the researchers to create a type of hydrazine, a common starting material for making a wide range of chemical compounds, all without the need for adding excess energy.

"I think that's really cool," says Michael Fryzuk, a chemist at the University of British Columbia in Vancouver, Canada. Fryzuk and Chirik both note, however, that the current compound isn't ready for industry, as it's not instantly reusable. As opposed to common catalysts, which create a compound, cut it loose, and automatically set about creating another, the hafnium complex must be recycled and regenerated before it can continue turning out hydrazines. Still, Fryzuk notes that even this compound represents an important first step to developing a non-energy-intensive way to generate important chemicals from starting materials pulled out of thin air.

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