A selective catalytic reduction system that can defrost urea aqueous solution without interruption of warm air of an engine or heating of a vehicle cabin. An oxidizing gas including ozone flows along a surface of the metal precursor layer to oxidize the metal precursor layer so that the metal oxide is formed on the substrate. The staple drivers each support a staple thereon and serve to drive the staples into forming contact with the anvil upon actuation by the actuator. The signal detector coupled to the automatic frequency controller receives the control voltage and determines whether the radio frequency signal is a frequency modulation signal according to the control voltage and a predetermined voltage range.