CHEMISTRY 2000

1. CHEMISTRY 2000 Topics of Interest #8: “Green” Crystals – Cleaning up N2O Emissions

2. “Laughing Gas” is No Laughing Matter • Nitrous oxide (N2O; 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 N2O from chemical plant exhausts as it is emitted: • The exhausts are passed over a catalytic membrane which converts the N2O into N2. • As an added bonus, the oxygen atoms from N2O are used to convert CH4 into “synthesis gas”, a mixture of H2 and CO that can be used to make a wide variety of chemicals. • Effectively, the waste N2O is “recycled” rather than emitted. H. Jiang et al Angew. Chemie Int. Ed. (2009) DOI: 10.1038/457639d. As reported in Nature (2009) 457 p. 639

3. “Laughing Gas” is No Laughing Matter • The membrane consists of a crystal lattice containing barium, cobalt, iron, zirconium and oxygen atoms (BaCoxFeyZr[1-(x+y)]O3-). It takes the form of hollow fibres that exhausts can be passed through: H. Jiang et al Angew. Chemie Int. Ed. (2009) 48 pp. 1-5. As reported in Nature (2009) 457 p. 639

4. “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 N2O into harmless N2 gas and more oxide anions: • Gas mixtures containing as much as 50% N2O reacted fully with the membranes. reduction oxidation H. Jiang et al Angew. Chemie Int. Ed. (2009) 48 pp. 1-5. As reported in Nature (2009) 457 p. 639