The unsteady-state kinetics of the selective catalytic reduction (SCR) of NO with NH3 is studied over V2O5-WO3/TiO2 model catalysts by means of the transient response method. NH3 strongly adsorbs onto the catalyst surface whereas NO does not adsorb appreciably. A dynamic mathematical model based on a Temkin-type desorption process for NH3 and a SCR reaction rate with a complex dependence on the ammonia surface coverage is well suited to represent the data.