The influence of the zeolite structure on the catalytic properties for the reduction of NO with propane and propene was studied. A relation between concentration and strength of acid sites and the activity of Ni-exchanged ZSM-5, MOR, and MCM-22 was found. Ni/ZSM-5, which contains a high concentration of strong acid sites, is the most active catalyst for the NO reduction with propane. Using propene as reductant Ni/ZSM-5 and Ni/MCM-22 rapidly deactivate due to the acid site-catalyzed formation of carbonaceous deposits, while Ni/MOR is less affected by the deposits formed because of its larger pore size. (C) 2003 Elsevier Inc. All rights reserved.