The dynamics of the selective catalytic reduction (SCR) reaction over a commercial V2O5-WO3/TiO2 catalyst is investigated by concentration programmed surface reaction (CPSR), i.e. a modified transient response method based on linear temporal evolution of the reactant feed concentrations. The adsorption-desorption of the reactants NH3 and NO and their surface reaction are addressed independently. The data confirm that over the investigated catalyst NH, is stored on the catalyst surface, and that the reaction occurs between adsorbed NH3 and gaseous or weakly adsorbed NO. H2O significantly inhibits the SCR reaction, but this effect is not due to competition with NH3 for the adsorption on the surface acid sites at any surface coverage. A slight inhibiting effect of adsorbed NH3 on the SCR reaction is also evident. The whole set of data is quantitatively described according to a dynamic kinetic model which superimposes the surface reaction of NO reduction to the NH3 adsorption-desorption processes, and accounts for NH3 oxidation at high temperatures. It is also shown that the transient SCR-DeNO(x) data, as well as the related kinetic analysis, approach steady-state data in the limit of slow variations.