Insight into 100-Year-Old Haber-Bosch Process for Producing Ammonia

For the past 100 years, the Haber-Bosch process has been used to convert atmospheric nitrogen into ammonia, which is essential in the manufacture of fertilizer. Despite the longstanding reliability of the process, scientists have had little understanding of how it actually works. But now a team of chemists, led by Dr. Patrick Holland of the University of Rochester, has gained new insight into how the ammonia is formed. Their findings are published in the November 11, 2011 issue of Science. Dr. Holland calls nitrogen molecules "challenging." While they're abundant in the air around us, which makes them desirable for research and manufacturing, their strong triple bonds are difficult to break, making them highly unreactive. For the last century, the Haber-Bosch process has made use of an iron catalyst at extremely high pressures and high temperatures to break those bonds and produce ammonia, one drop at a time. The question of how this works, though, has not been answered to this day. "The Haber-Bosch process is efficient, but it is hard to understand because the reaction occurs only on a solid catalyst, which is difficult to study directly," said Dr. Holland. "That's why we attempted to break the nitrogen using soluble forms of iron." Dr. Holland and his team, which included Dr. Meghan Rodriguez and Dr. William Brennessel at the University of Rochester and Dr. Eckhard Bill of the Max Planck Institute for Bioinorganic Chemistry in Germany, succeeded in mimicking the process in solution. They discovered that an iron complex combined with potassium was capable of breaking the strong bonds between the nitrogen (N) atoms and forming a complex with an Fe3N2 core, which indicates that three iron (Fe) atoms work together in order to break the N-N bonds.
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