The dynamics of NH3 adsorption-desorption and of selective catalytic reduction (SCR) of NO with NH3 are investigated in this work over a commercial V2O5-WO3/TiO2 catalyst by transient response techniques. Linear variations in the inlet concentration of one or more reactants are imposed while analyzing the system outlet response. The transient experiments could be successfully described by a kinetic model based on: (i) a negligible NO adsorption on the catalyst surface; (ii) a non-activated NH3 adsorption; (iii) a Temkin-type NH3 coverage dependence of the desorption energy; and (iv) an Eley-Rideal mechanism for the SCR reaction with a non-linear dependence of the reaction rate on the NH3 surface coverage. The presence of low concentrations of water in the feed stream does not seem to affect the ammonia adsorption-desorption process on the surface but significantly inhibits the SCR reaction; an inhibiting effect of adsorbed NH3 on the SCR reaction is also pointed out.