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Researchers devise new way to cleave nitrogen

Wed, 12/16/2009 - 12:54pm
Cornell University
Hafnium complex with cleaved nitrogen

Donald J. Knobloch
A representation of the hafnium complex Paul Chirik and colleagues created after breaking the nitrogen-nitrogen bonds with carbon monoxide while simultaneously creating useful nitrogen-carbon and carbon-carbon bonds. The silver is hafnium, black is carbon, red is oxygen and blue is nitrogen.

Prescription drugs, nylon stockings and common fertilizers all have something in common -- bonded atoms of nitrogen and carbon. But any chemist knows creating these bonds is no easy task, as nitrogen in its natural state is paired (N2) and contains a strong triple bond nearly impossible to break.

Cornell chemist Paul Chirik and colleagues have devised a new way to break this tough nitrogen-nitrogen bond in the lab and simultaneously create carbon-nitrogen bonds. They fast-tracked the process by skipping the usual energy-intensive, fossil fuel-burning step of creating ammonia, a noxious compound of nitrogen and hydrogen that's produced in a high-temperature, high-pressure process in large industrial plants all over the world.

Their breakthrough is reported online in the Dec. 13 edition of the journal Nature Chemistry.

The research team, which also included first author and graduate student Donald J. Knobloch and research associate Emil Lobkovsky, made a complex of nitrogen and the metal hafnium. With the hafnium adding electrons to the nitrogen and loosening the strong triple bond, they then added carbon by dousing the complex in the gas carbon monoxide -- a key breakthrough -- and electrons from the carbon finished breaking up the nitrogen bonds in a process called cleavage. The carbon then bonded with the nitrogen without any special temperature or pressure requirements.

The scientists' next challenge is to turn this into a catalytic process -- in other words, to find an easy way to recycle the hafnium by removing it from the nitrogen after the desired chemical reaction is complete. They did it this time by adding a drop of hydrochloric acid, which also left them with a small amount of the common fertilizer oxamide. That method, however, is tedious and not reproducible for industrial purposes, Chirik noted.

The work showed that nitrogen -- which makes up nearly 80 percent of Earth's atmosphere -- and carbon can be bonded without the hassle and expense of making ammonia.

"We are living in this sea of nitrogen, but we can't do much with it except for make ammonia out of it," Chirik said. "And I think we as a society, in order to move forward, can't be lazy and just use oil. We're going to have to figure out ways to develop new chemistry to use what's around us better."

The research was funded by the Chemical Sciences Division of the U.S. Department of Energy and the Frasch Foundation, administered by the American Chemical Society.

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