Editorial Cite This: ACS Sustainable Chem. Eng. 2017, 5, 9527-9527
pubs.acs.org/journal/ascecg
Sustainable Ammonia Production
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ammonia synthesis methods as well as improving how nitrogen-containing products are handled and utilized.
ore than 100 million metric tons of atmospheric nitrogen are extracted from the air every year to make ammonia,1 a key industrial intermediate to nitrogen fertilizers. Ammonia is produced by hydrogenating the very stable dinitrogen triple bond with H2 during the Haber−Bosch process, which uses extreme temperature and pressure (450 °C, 200 bar) reaction conditions. Indeed, the scale and intensity of ammonia production via Haber−Bosch accounts for 1−2% of the global energy consumption and 3−5% of the total natural gas output.2 It also presents multiple other sustainability challenges including the energy consumed to generate H2, the resulting CO2 emissions, and the energy needed for handling large unreacted synthesis gas recycles. Accordingly, there is an urgent need for alternative, more sustainable processes for ammonia production. Recognizing this as a key issue, the U.S. National Academy of Engineering (NAE) identified management of the nitrogen cycle as one of the 14 Grand Challenges for Engineering in the 21st Century.3 The U.S. Department of Energy recently held a roundtable and concluded that a scientific basis for the sustainable synthesis of ammonia remains lacking, and there is no sustainable ammonia catalyst (either heterogeneous, homogeneous, or enzyme based) that would fulfill activity, selectivity, and scalability requirements. Multiple efforts have attempted to develop low pressure and low temperature thermal processes for NH3 synthesis through electro- or photochemistry, chemical looping, and biochemical routes,2,4−7 but substantial improvements are still needed to achieve commercially viable efficiencies. Lastly, constraints in dinitrogen bond activation suggest that nitrogen management beyond ammonia synthesis is of significant importance for sustainable development as well; for example, approaches to stabilize nitrogen products, such as urea, must also be developed so that overall energy inputs can be reduced. This Virtual Special Issue (VSI) in ACS Sustainable Chemistry & Engineering was organized in an effort to report on recent advancements, from catalyst development to system wide analysis, potentially leading to general improvements in nitrogen management and sustainable ammonia synthesis more specifically. Contributions were welcomed on a wide range of scientific and engineering topics that would result in the improved sustainability of the NH3 synthesis process. These range from conceptually new ammonia synthesis methods using photocatalysis and electrochemistry to the techno-economic assessment of ammonia as a fuel vector. The current “Sustainable Ammonia Production” VSI collection features research from a diverse set of the experts in their fields (http:// pubs.acs.org/page/ascecg/vi/sustainable-ammonia-production. html). I want to use this opportunity to acknowledge the authors and reviewers of these contributions, the editorial team at ACS Sustainable Chemistry & Engineering, and specifically, Professor David T. Allen and Dr. Rhea Williams for their efforts on behalf of this VSI. The aim of the VSI is to catalyze a significant effort toward increasing the diversity and energy efficiency of © 2017 American Chemical Society
Jonas Baltrusaitis
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Lehigh University, United States
AUTHOR INFORMATION
ORCID
Jonas Baltrusaitis: 0000-0001-5634-955X Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS.
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REFERENCES
(1) Canfield, D. E.; Glazer, A. N.; Falkowski, P. G. The Evolution and Future of Earth’s Nitrogen Cycle. Science (Washington, DC, U. S.) 2010, 330 (6001), 192−196. (2) Patil, B. S.; Wang, Q.; Hessel, V.; Lang, J. Plasma N2-fixation: 1900−2014. Catal. Today 2015, 256 (Part 1), 49−66. (3) NAE Grand Challenges for Engineering. National Academy of Engineering. http://www.engineeringchallenges.org/challenges.aspx (accessed October 2017). (4) Hinnemann, B.; Nørskov, J. K. Catalysis by Enzymes: The Biological Ammonia Synthesis. Top. Catal. 2006, 37 (1), 55−70. (5) Tanabe, Y.; Nishibayashi, Y. Developing more sustainable processes for ammonia synthesis. Coord. Chem. Rev. 2013, 257 (17), 2551−2564. (6) Michalsky, R.; Avram, A. M.; Peterson, B. A.; Pfromm, P. H.; Peterson, A. A. Chemical looping of metal nitride catalysts: lowpressure ammonia synthesis for energy storage. Chem. Sci. 2015, 6 (7), 3965−3974. (7) Singh, A. R.; Rohr, B. A.; Schwalbe, J. A.; Cargnello, M.; Chan, K.; Jaramillo, T. F.; Chorkendorff, I.; Nørskov, J. K. Electrochemical Ammonia SynthesisThe Selectivity Challenge. ACS Catal. 2017, 7 (1), 706−709.
Received: October 13, 2017 Published: November 6, 2017 9527
DOI: 10.1021/acssuschemeng.7b03719 ACS Sustainable Chem. Eng. 2017, 5, 9527−9527
