The selective catalytic reduction (SCR) of NOx by urea as a reducing agent was carried out over fresh and sulfated CuO/gamma-Al2O3 catalysts in a fluidized-bed reactor. The optimum temperature ranges for NO reduction on the fresh and sulfated CuO/gamma-Al2O3 catalysts were 300-350 degreesC and 400-450 degreesC, respectively. NO reduction with the sulfated CuO/gamma-Al2O3 catalyst was somewhat higher than that with the fresh CuO/gamma-Al2O3 catalyst. N2O formation increased with increasing reaction temperature. Ammonia (NH3) slip increased with increasing gas velocity and decreased with increasing reaction temperature. (C) 2003 Society of Chemical Industry.