Copper-exchanged in to zeolites containing large, medium and small pores were studied for selective catalytic reduction (SCR) of NO with NH3 in the presence and absence of decane. Cu/ZSM-5 and Cu/ERI exhibited higher NOx conversion compared to Cu/FER and Cu/MOR. On the other hand NOx conversion over Cu/FER was more stable in the presence of decane compared to Cu/MOR and Cu/ZSM-5 catalysts. Fresh and used Cu/zeolite catalysts were analyzed by H-2-TPR, NH3-TPD, ESR and TGA. Copper species with different reducibility and isolated Cu2+ ions in different coordinations were identified by H-2-TPR and the ESR techniques respectively. The initial NOx conversion activity of Cu/zeolites seems to depend on the number of isolated Cu2+ species, which were affected by the zeolite structure. Whereas, the catalysts resistance to hydrocarbon poisoning depended on the pore geometry of the zeolites. During NH3-SCR, the presence of large pores and cages in the zeolite lead to hydrocarbon deposit and retention by the zeolites which blocks the active sites and also decreases the active intermediates needed for NOx conversion. Cu/ZSM-5 with higher number of isolated Cu2+ species showed higher initial NOx conversion compared to other Cu/zeolite catalysts. Cu/FER on the other hand with small pore and cage diameter with one-dimensional channel structure showed higher hydrocarbon poisoning resistance. (C) 2010 Published by Elsevier B.V.