Deactivating effect Of SO2 on selective catalytic reduction of NO by NH3 over a CuO/Al2O3 catalyst sorbent was examined in a fixed-bed reactor. Transient experiment, DRIFT, elemental analysis, temperature-programmed techniques, and physical adsorption were used to evaluate the deactivation mechanism. Results show that SO2 greatly deactivates SCR activity of CuO/Al2O3 catalyst sorbent at temperatures of 200-300 degreesC, and the deactivation is dependent on reaction temperature. The deactivating agents are ammonium sulfate salt and copper sulfate, formed during the reaction of NO-NH3-O-2-H2O in the presence of SO2. Ammonium sulfate salt reduces the SCR reaction through pore filling and/or plugging, but can be removed by heat treatment at around 400 degreesC. Copper sulfate deactivates the SCR either by pore filling and/or plugging or by its low SCR activity compared to CuO at low temperatures. Copper sulfate decomposes at temperatures greater than 660 degreesC but can be converted back to CuO in NH3 at about 400 degreesC. (C) 2004 Elsevier Inc. All rights reserved.