Cu/SAPO-34 catalysts have been reported to show much improved activities and durability for selective catalytic reduction (SCR) of NOx. In this work, we examined the nature of Cu species in SAPO-34 catalysts in order to shed light on the active site requirements. Cu/SAPO-34 catalysts, prepared by ion-exchange and precipitation methods, were characterized in detail. The results consistently indicate that Cu species exist predominantly as isolated ions at the exchange sites in the ion-exchanged sample, whereas in the precipitated sample CuO on the external surface is the dominant species. The ion-exchanged Cu/SAPO-34 was found to show superior NH3-SCR activity than the precipitated sample, suggesting that isolated Cu ions at the exchange sites are likely the active sites. (C) 2012 Elsevier Inc. All rights reserved.