In this study the selective catalytic reduction (SCR) of NO has been investigated over H-ZSM-5 with three different reducing agents. Comparison of the reaction mechanisms using propane, ammonia and isopropylamine has been performed using in situ DRIFTS step-response experiments. The same type of surface NH species, likely organic amines, is formed in the presence of either propane or isopropylamine as reducing agent. For NH3, on the other hand, NH4+ is the dominating NH surface species during reaction. Furthermore, in the case of propane, the nature of the NOx-source, i.e. NO or NO2, is crucial for the reaction. With NO2. the reaction likely proceeds fast via direct reduction, while for NO, oxidation to NO2 is required initially. in either case NH species play a vital role in the SCR reaction and organic amines are possible key-intermediates in the SCR with saturated hydrocarbons over H-ZSM-5. (C) 2008 Elsevier Inc. All rights reserved.