Potassium nitrate solution referred to as alkali poison was impregnated on the Cu-SAPO-34 catalyst using incipient wetness impregnation. Cu-SAPO-34 catalyst showed a better resistance to the alkali metal poisoning compared with vanadia-based catalysts. But the NH3-SCR activities of Cu-SAPO-34 were greatly reduced at a high content of potassium (>0.5% of potassium). The transformation of the isolated Cu2+ (most active) to the square-plane copper oxide clusters (less active) arising from the potassium poisoning was considered as the main reason for the deactivation of Cu-SAPO-34 catalyst, although the Bronsted acid sites were also decreased by alkali simultaneously. (C) 2014 Elsevier B.V. All rights reserved.