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Nanosheets Catalyze Nitrogen Fixation

Sustainability: Oxygen vacancies in BiOBr layered catalyst help split nitrogen and water to reduce energy demand for making ammonia

by Stephen K. Ritter
May 4, 2015 | A version of this story appeared in Volume 93, Issue 18

A research team in China has invented a light-harvesting layered semiconductor nanosheet that could one day significantly reduce the energy required for chemically reducing nitrogen to ammonia. Converting N2 to NH3 via the iron-catalyzed Haber-Bosch process is one of the most important industrial chemical reactions. But splitting N2 and preparing hydrogen via steam reforming of methane at high temperature and pressure make it one of the most energy-intensive processes. Lizhi Zhang of Central China Normal University and coworkers designed a layered BiOBr catalyst with oxygen vacancies that is ideal for binding N2 molecules. When the researchers shine visible light on the nanosheet surface the semiconductor generates electrons to reduce adsorbed N2 while at the same time it oxidizes water solvent molecules to generate H+ and O2. Overall, the process couples nitrogen and hydrogen to make NH3 at room temperature and atmospheric pressure with better efficiency than previously reported semiconductor systems (J. Am. Chem. Soc. 2015, DOI: 10.1021/jacs.5b03105). “Although photocatalytic reduction is unlikely to replace the Haber-Bosch process at present,” the researchers write, “this study might open up a new vista.”

A BiOBr layered photocatalyst splits water and fixes nitrogen to make ammonia.
Credit: J. Am. Chem. Soc.
A layered BiOBr photocatalyst binds N2 in oxygen vacancy sites as part of a low-energy nitrogen-fixing process.


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