Editing Nitrogen fixation (section)

== Industrial processes ==

=== Historical ===
A method for nitrogen fixation was first described by [[Henry Cavendish]] in 1784 using electric arcs reacting nitrogen and oxygen in air. This method was implemented in the [[Birkeland–Eyde process]] of 1903.<ref>{{cite journal| title= The Manufacture of Nitrates from the Atmosphere by the Electric Arc—Birkeland-Eyde Process | vauthors = Eyde S | journal= Journal of the Royal Society of Arts| volume= 57| issue = 2949 | year= 1909| pages= 568–576 | jstor=41338647}}</ref> The fixation of nitrogen by lightning is a very similar natural occurring process.

The possibility that atmospheric nitrogen reacts with certain chemicals was first observed by [[Desfosses]] in 1828. He observed that mixtures of [[alkali metal]] oxides and carbon react with nitrogen at high temperatures. With the use of [[barium carbonate]] as starting material, the first commercial process became available in the 1860s, developed by Margueritte and Sourdeval. The resulting [[barium cyanide]] reacts with steam, yielding ammonia. In 1898 [[Adolph Frank|Frank]] and [[Nikodem Caro|Caro]] developed what is known as the [[Frank–Caro process]] to fix nitrogen in the form of [[calcium cyanamide]]. The process was eclipsed by the [[Haber process]], which was discovered in 1909.<ref>{{cite journal |title=Die Umwandlungsgleichung Ba(CN)<sub>2</sub> → BaCN<sub>2</sub> + C im Temperaturgebiet von 500 bis 1000&nbsp;°C |trans-title=The conversion reaction Ba(CN)<sub>2</sub> → BaCN<sub>2</sub> + C in the temperature range from 500 to 1,000&nbsp;°C | vauthors = Heinrich H, Nevbner R | journal = Z. Elektrochem. Angew. Phys. Chem. | volume = 40 | issue = 10 | pages = 693–698 | year = 1934 | url = http://onlinelibrary.wiley.com/doi/10.1002/bbpc.19340401005/abstract |url-access=subscription | access-date = 8 August 2016 | doi = 10.1002/bbpc.19340401005 |s2cid=179115181 | archive-url = https://web.archive.org/web/20160820203326/http://onlinelibrary.wiley.com/doi/10.1002/bbpc.19340401005/abstract | archive-date = 20 August 2016 | url-status = live }}</ref><ref>{{cite book | url = {{google books |plainurl=y |id=87XQAAAAMAAJ}}| title = Fixed nitrogen | vauthors = Curtis HA | year = 1932}}</ref>

=== Haber process ===
{{Main|Haber process}}
[[File:THC 2003.902.022 D. C. Bardwell Study of Nitrogen Fixation.tif|thumb|right|Equipment for a study of nitrogen fixation by [[alpha ray]]s (Fixed Nitrogen Research Laboratory, 1926)]]
The dominant industrial method for producing ammonia is the [[Haber process]] also known as the Haber-Bosch process.<ref>Smil, V. 2004. Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production, MIT Press.</ref> Fertilizer production is now the largest source of human-produced fixed nitrogen in the terrestrial [[ecosystem]]. Ammonia is a required precursor to [[fertilizer]]s, [[explosive]]s, and other products. The Haber process requires high pressures (around 200 atm) and high temperatures (at least 400&nbsp;°C), which are routine conditions for industrial catalysis. This process uses natural gas as a hydrogen source and air as a nitrogen source. The ammonia product has resulted in an intensification of nitrogen fertilizer globally<ref>{{Cite journal| vauthors = Glibert PM, Maranger R, Sobota DJ, Bouwman L |author-link1=Patricia Glibert |author-link2=Roxane Maranger |date=2014-10-01|title=The Haber Bosch–harmful algal bloom (HB–HAB) link|journal=Environmental Research Letters|volume=9|issue=10|pages=105001|doi=10.1088/1748-9326/9/10/105001|bibcode=2014ERL.....9j5001G|s2cid=154724892 |issn=1748-9326|doi-access=free}}</ref> and is credited with supporting the expansion of the human population from around 2 billion in the early 20th century to roughly 8 billion people now.<ref>{{Cite journal| vauthors = Erisman JW, Sutton MA, Galloway J, Klimont Z, Winiwarter W |date=October 2008|title=How a century of ammonia synthesis changed the world |journal=Nature Geoscience|language=en|volume=1|issue=10|pages=636–639|doi=10.1038/ngeo325|bibcode=2008NatGe...1..636E|s2cid=94880859 |issn=1752-0908}}</ref>

=== Homogeneous catalysis ===
{{Main|Abiological nitrogen fixation}}
Much research has been conducted on the discovery of catalysts for nitrogen fixation, often with the goal of lowering energy requirements. However, such research has thus far failed to approach the efficiency and ease of the Haber process. Many compounds react with atmospheric nitrogen to give [[dinitrogen complex]]es. The first dinitrogen [[Complex (chemistry)|complex]] to be reported was [[pentaamine(dinitrogen)ruthenium(II) chloride|{{chem|Ru(NH|3|)|5}}({{chem|N|2}})<sup>2+</sup>]].<ref>{{cite journal | title = Nitrogenopentammineruthenium(II) complexes | vauthors = Allen AD, Senoff CV | journal = J. Chem. Soc., Chem. Commun. | issue = 24 | pages = 621–622 | year = 1965 | doi = 10.1039/C19650000621 }}</ref> Some soluble complexes do catalyze nitrogen fixation.<ref name=Peters>{{cite journal | vauthors = Chalkley MJ, Drover MW, Peters JC | title = Catalytic N<sub>2</sub>-to-NH<sub>3</sub> (or -N<sub>2</sub>H<sub>4</sub>) Conversion by Well-Defined Molecular Coordination Complexes | journal = Chemical Reviews | volume = 120 | issue = 12 | pages = 5582–5636 | date = June 2020 | pmid = 32352271 | pmc = 7493999 | doi = 10.1021/acs.chemrev.9b00638}}</ref>