Photoassisted selective catalytic reduction (photo-SCR) of NO with ammonia under various operating conditions was investigated with a TiO2-coated annular photoreactor at room temperature. Effects of UV irradiance, inlet concentrations of O-2, NO, NH3 and H2O, and retention time of inlet stream on the NO reduction efficiency and N-2 selectivity were discussed in this study. The experimental results indicated that more than 70% of NO molecules could be reduced by photo-SCR with the retention time more than 4 min. N-2 selectivity was found to be decreased due to the generation of NO2 and N2O molecules in the photo-SCR with specific operating conditions. Both NO reduction efficiency and N-2 selectivity were decreased for NO reduction by the photo-SCR with the presence of water molecules because of the competitive adsorption of water and NH3 molecules on the active sites of TiO2. The reaction behavior of the NO reduction by the photo-SCR was adequately described by Eley-Rideal kinetics. (C) 2010 Elsevier B.V. All rights reserved.