A range of ethers, alcohols and alkanes were compared as reducing agents for NOx over a Cu-ZSM-5 lean NOx catalyst. The nature of the reducing agent was found to determine the degree of NOx reduction. Methanol and DME were virtually inactive as reductants over this catalyst, while higher ethers and alcohols showed high NOx conversion. A detailed study was performed to investigate the differences. Among the studied variables, the chemical structure of the reductant was found to be especially important. Despite having a lower reducing capacity than DME, ethylene glycol was active for NOx reduction. It is concluded that a C-C bond in the reducing agent is required for lean NOx reduction over Cu-ZSM-5. The absence of this bond in DME and methanol explains their low activity for NOx reduction over this catalyst. (C) 2011 Elsevier B.V. All rights reserved.