Rice straw char and sewage sludge char were applied as catalysts for selective catalytic reduction between 50 and 250 degrees C using ammonia as the reducing agent. Each char was activated physically, using water vapor, or chemically, using KOH. The characteristics of the prepared catalysts were analyzed through elemental analysis, N-2 adsorption-desorption, FT-IR, NO-TPD, NH3-TPD, and NOx removal efficiency. The physically activated chars showed characteristics similar to those of the non-activated chars, whereas the chemically activated chars exhibited increased specific surface areas, pore volumes, NO adsorption capacities, NH3 adsorption capacities, and oxygen functional group amounts, leading to higher NOx removal efficiency. When the catalysts were impregnated with 3 wt% manganese, NOx removal efficiency significantly increased. In particular, the NOx removal efficiency was highest when the chemically activated chars were impregnated with manganese. (C) 2009 Elsevier B.V. All rights reserved.