Low temperature selective catalytic reduction (LT-SCR) of NO+NO2 mixture with NH3 was investigated over TiO2, SiO2 and activated carbon in a conventional flow type fixed-bed reactor at 100 degrees C under atmospheric pressure. The effects of gas composition such as presence of SO2 and NH3 and the ratio of NO2/NO in the feed-stream on the LT-SCR have been studied. The presence of SO2 and O-2 was essential for the selective removal of NO with NH3 over TiO2. The presence of SO2 contributed to the oxidation of NO to NO2 over TiO2. If NO2 existed with NO in the reaction system, the presence of SO2 was not necessary for the removal of NO over TiO2. The following two reactions were suggested to occur over TiO2: NO+NO2 + 2NH(3) -> 2N(2) + 3H(2)O (1) and 2NO(2) +2NH(3) -> N-2 + NH4NO3 + H2O (2). The reaction (2) occurred on all three catalysts, however the reaction (1) did not proceed significantly over SiO2. (C) 2009 Elsevier B.V. All rights reserved.