CHEMISTRY 2000 Topics of Interest #8: “Green” Crystals – Cleaning up N 2 O Emissions

“Laughing Gas” is No Laughing Matter Nitrous oxide (N 2 O; colloquially known as “laughing gas”) is a greenhouse gas emitted by many chemical plants. As well as contributing to climate change, it also reacts with the ozone layer. Researchers recently developed technology to remove N 2 O from chemical plant exhausts as it is emitted: The exhausts are passed over a catalytic membrane which converts the N 2 O into N 2. As an added bonus, the oxygen atoms from N 2 O are used to convert CH 4 into “synthesis gas”, a mixture of H 2 and CO that can be used to make a wide variety of chemicals. Effectively, the waste N 2 O is “recycled” rather than emitted. H. Jiang et al Angew. Chemie Int. Ed. (2009) DOI: /457639d. As reported in Nature (2009) 457 p. 639

“Laughing Gas” is No Laughing Matter The membrane consists of a crystal lattice containing barium, cobalt, iron, zirconium and oxygen atoms (BaCo x Fe y Zr [1-(x+y)] O 3-  ). It takes the form of hollow fibres that exhausts can be passed through: H. Jiang et al Angew. Chemie Int. Ed. (2009) 48 pp As reported in Nature (2009) 457 p. 639

“Laughing Gas” is No Laughing Matter This is an example of how we can use oxidation-reduction chemistry (or “redox” chemistry) to our advantage. The oxidation half-reaction produces “synthesis gas” from methane and oxide ions while the reduction half-reaction breaks the undesirable N 2 O into harmless N 2 gas and more oxide anions: Gas mixtures containing as much as 50% N 2 O reacted fully with the membranes. H. Jiang et al Angew. Chemie Int. Ed. (2009) 48 pp As reported in Nature (2009) 457 p. 639 reduction oxidation