Nitrogen is vital to crops such as corn, wheat, rice, and sugar cane, along with many others. This nutrient often comes from ammonia in fertilizer. Producing ammonia requires vast amounts of fossil fuel, particularly natural gas. Scientists are developing catalysts that can produce ammonia with less fossil fuels. But where are we now and where should we go? Experts delineated the state of the science. Extensive studies of different types of catalysts, including detailed views of how the catalysts transform nitrogen, are pushing us toward better processes. However, scientists must translate their discoveries into new catalytic systems.
Farmers as well as industries and cleanup experts rely on industrial reactions that transform nitrogen into ammonia or other chemicals. Farmers need ammonia in their fertilizers. Industries need nitric acid to make dyes. Remediation teams need to clean up hazardous nitrogen oxide pollutants. The chemical reactions that underlie the transformations all rely on catalysts. The team's review summarizes the state of catalytic science for such reactions. Just like a nation's state of the union address, well-researched reviews summarize the progress to date and help clarify future directions.
Since 1913, ammonia has been produced via the Haber-Bosch process. The process transforms nitrogen gas into ammonia, which is packed into fertilizer. Plants use nitrogen in ammonia to grow. Mass production of ammonia-containing fertilizer changed global food production. The process breaks strong bonds in nitrogen and adds hydrogen from natural gas to create ammonia. The challenge is the amount of natural gas used and the associated release of carbon dioxide. Catalysts that could drive simple, low-energy routes to ammonia without releasing a lot of carbon dioxide would reduce the cost and environmental footprint of ammonia production. Natural catalysts in bacteria and other microbes get the job done, producing ammonia in an environmentally benign way. A team of experts reviewed the state of the science. They found that scientists have designed model catalysts that mimic some of the functions of natural catalysts. Also, researchers have achieved modest success with other types of catalysts and processes, including electrocatalysis and plasma-driven reactions. The reviewers attribute the success, in part, to a basic science understanding of how molecules interact during reactions. To benefit from such insights, the experts believe scientists and industries must translate the discoveries into catalytic systems that yield ammonia without need of natural gas or other fossil fuels.
Jingguang G. Chen
Richard M. Crooks
University of Texas at Austin
Lance C. Seefeldt
Utah State University
This article evolved from presentations and discussions at the workshop "Frontiers, Opportunities, and Challenges in Biochemical and Chemical N2 Activation" held in October 2016 in Gaithersburg, Maryland. The workshop was sponsored by the Council on Chemical Sciences, Geosciences, and Biosciences of the Department of Energy, Office of Science, Office of Basic Energy Sciences.
J.G. Chen, R.M. Crooks, L.C. Seefeldt, K.L. Bren, M. Bullock, M.Y. Darensbourg, P.L. Holland, B. Hoffman, M.J. Janik, A.K. Jones, M.G. Kanatzidis, P. King, K.M. Lancaster, S.V. Lymar, P. Pfromm, W.F. Schneider, and R.R. Schrock, "Beyond fossil fuel-driven nitrogen transformations." Science 360(2018), 873 (2018). [DOI: 10.1126/science.aar6611]