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A New Possibility for Manufacturing Environmental-Friendly Fertilizer

For the first time ever, a catalyst capable of extracting nitrogen from the air and converting it to ammonia under natural conditions has been developed. Unlike the previously existing human methods of producing ammonia, no input of high temperature or pressure was necessary in this case. Previously, only nature could perform this exceptional feat.

This scientific breakthrough was accomplished by researchers at the Northwestern University and published in the Journal of the American Chemical Society.

With light energy as the only fuel driver of the process, this new method promises to gift the world a more environmental-friendly fertilizer. Ammonia is normally the critical ingredient in fertilizer.

The lead-researcher in this study, inorganic chemist Mercouri G. Kanatzidis, termed the process they used in their study as a “big-deal” reaction due to its ability to work under just ambient natural conditions to turn nitrogen into ammonia. For over 60 years, nitrogenase, which is the biological enzyme responsible for catalyzing the same reaction in nature, has intrigued scientists. They have now successfully mimicked nature's process.

Mercouri G. Kanatzidis is a Charles E. & Emma H. Morrison Chemistry Professor at Weinberg College of Arts and Sciences.

The natural process is known as nitrogen fixation, and is what is relied upon by plants for nutrition and growth. Plants cannot access nitrogen in its elemental form straight from the air. Because of this, nature reduces it to a form like ammonia that acts as a nutrient for plants.

The new method catalyzes this crucial reaction using light. Due to the abundance of solar energy, this process provides an appealing alternative to the Haber-Bosch Process, which is the industrial standard for mass production of ammonia. Currently, up to 1% of the global energy supply is used to fuel Haber-Bosch.

At present, while the Northwestern method is only proof of a concept, it is nevertheless an impressive scientific discovery. With three single covalent bonds that are extremely difficult to break, nitrogen is very stubborn when it comes to interacting with other molecules.

Professor Kanatzidis and his group were able to navigate around this "stubbornness" by using a chalcogel. This is an interesting material that scientists had created earlier. Similar to a sponge, this material is porous and offers a large surface area of reactive sites enabling nitrogen to react as it flows through it. The chalcogel made was a cluster of the key elements found in nitrogenase, i.e. iron, molybdenum and sulphur (FeMoS). These are responsible for the reduction of nitrogen.

In addition to surface area, the chalcogel possessed another advantage of being black in color. This enables it to absorb light in abundance, energy that the scientists thought that may be able to be tapped. Rather than sunlight, nitrogenase acquires its energy from other sources. The FeMoS co-factor present in the chalcogel binds to nitrogen, reducing them by eight electrons. Just as it happens in nature, two ammonia molecules and a single hydrogen molecule are formed.

On attaining these early positive results, the researchers then conducted some control experiments so as to confirm if the ammonia produced had indeed been generated from the nitrogen they used and not any other source.

According to Professor Kanatzidis, the chalcogel they made is a very robust material that can be used for longer. Contrarily, the nitrogenase in biological systems needs to regenerate itself every 6-8 hours. However, the catalyst is roughly 1,000 times slower than nitrogenase.

Professor Kanatzidis explained that nitrogenase had 2-3 billion years to evolve, adding that the researchers were happy that the chalcogel was able to reduce nitrogen much the way nitrogenase does. He termed theirs as a fantastic beginning point for further research to figure out how it works and how its working speed could be enhanced, something which the group has already made some progress on.

 

Image credit: mattwalker69 via Flickr

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