Dehydrogenation of a reactor system of one or more vertically oriented flow reactors equipped with a system for introducing a catalyst extender into the inlet of the reactor. A vertically oriented radial flow reactor comprises inner and outer reactor tubes having perforated wall members extending longitudily of the reactor and defining an annulus containing a dehydrogenation catalyst. A supply line to the reactor is equipped with a rotation vane. An injection nozzle comprising a coaxial flow tube extends into the supply line downstream of the vane. The coaxial flow tube has an interior chamber and an annular chamber surrounding the interior chamber and extending into the supply line along with the interior chamber. The interior chamber is connected to a catalyst extender source and the annular chamber is connected to a source of a carrier gas which is effective to disperse the extender within feedstock flowing into the reactor.