Sulfur poisoning is a durability issue for Cu/SAPO-34 selective catalytic reduction (SCR) catalysts. In this study, the impact of SO2 on the SCR performance, and the sulfur poisoning mechanism itself, was investigated. SO2 inhibited SCR activity at low temperature (<300 degrees C), while at higher temperatures no evident effect was observed. Temperature programmed desorption data show significant SO2 desorption starting at 300 degrees C, thus the lack of impact noted at high temperature. Low temperature deactivation is primarily caused by the formation of ammonium sulfate species, with some contribution from competitive adsorption between SO2 and NOR, which is considered a key step in the standard SCR reaction, possibly through the formation of metal sulfate species. However, the surface sulfur species decomposed under high temperature thermal treatment in an O-2/N-2 mixture, such that activity was reattained. (C) 2014 Elsevier B.V. All rights reserved.