Adsorption and desorption of NO and NO2 on Cu-ZSM-5

✍ Scribed by Joël Despres; Manfred Koebel; Oliver Kröcher; Martin Elsener; Alexander Wokaun

• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 210 KB
• Volume: 58
• Category: Article
• ISSN: 1387-1811
• DOI: 10.1016/s1387-1811(02)00627-3

✦ Synopsis

The interaction of NO x from lean exhaust gases with copper-exchanged ZSM-5 has been studied by combined adsorption and temperature-programmed desorption. Experiments with NO at 200 °C show that this molecule cannot be stored on Cu-ZSM-5. On the other hand, NO 2 may be stored over a wide temperature range from both dry and humid feeds. Therefore, in order to obtain storage of NO, NO must first be oxidized to NO 2 . However, the oxidation reaction is inhibited by water in the exhaust gas.

The adsorption of nitrogen dioxide involves a disproportionation reaction yielding two stored nitrate species and one molecule of NO released to the gas phase:

Water in the feed gas competes with the formation of nitrates, thus lowering significantly the amount of NO 2 stored on Cu-ZSM-5. NO has also a negative effect on the storage of NO 2 . This effect is due to its reaction with the stored nitrates, causing a considerable shift in the equilibrium of the above reaction back to NO 2 .