Selective catalytic reduction (SCR) of NO with NH3 on an activated coke supported V2O5 (V2O5/AC) catalyst was studied at 200 A degrees C by in-situ diffuse reflectance infrared Fourier transform spectroscopy. Results indicate that NH3 is adsorbed in the forms of coordinated NH3, NH4 (+) and -NH2. V2O5 promotes formation of -NH2. NO is oxidized to NO2 in the presence of O-2. -NH2 and NO2 are the intermediates of the SCR reaction.