The kinetics of NH3 adsorption-desorption and of the NO + NH3/O-2 Selective Catalytic Reduction (SCR) reaction were studied in the 50-450 degreesC T-range in the presence of water over a commercial powdered V2O5-WO3/TiO2 catalyst loaded in a micro-reactor, following the temporal evolution of the outlet species concentrations by a mass spectrometer. The influence of water and oxygen feed contents was examined. Different Transient Response Techniques were applied to investigate the SCR dynamics in view of applications to vehicles. The experimental results were analysed by means of a dynamic one-dimensional heterogeneous PFR model, and fitted by multiresponse nonlinear regression to provide estimates of the rate parameters. Such parameters, as well as the relevant geometrical and morphological characteristics, were then used to simulate transient SCR runs performed over an extruded honeycomb sample of the same commercial catalyst. The satisfactory match obtained between model predictions and monolith data validates the proposed rate equations. (C) 2004 Elsevier Ltd. All rights reserved.