In this study, the reaction mechanism for the high temperature selective catalytic reduction of NO by NH3 over a W/TiO2 catalyst was investigated. A systematic mechanistic pathway for the reaction was proposed based on the results of transient response analysis (TRA), infrared spectroscopy (IR), temperature programmed reaction (TPR) and O-2 shut-off tests. These experimental results showed that during the initial SCR reaction step, ammonia was adsorbed first and activated at Lewis acid sites (W=O), and then was decomposed into N-2 and H2O by gaseous NO+O-2. During the redox reaction, gaseous oxygen was involved in the reaction, whereas the effect of catalytic lattice oxygen was very slight (WO3 -> WO2.9x). Therefore, these findings provide important information to better understand the mechanism responsible for high temperature SCR. (C) 2012 Elsevier Ltd. All rights reserved.