Well, the passive layer is not necessarily a pure one with just one oxidation state of iron in the oxide form. There may be other oxidation states. For instance, the layer could be made up of a mixture of Fe2O3, Fe3O4 or FeO. There could also be other impurities which could prevent efficient binding of whatever be the layer you're trying to bind onto the metal
And could you also please tell us why you're applying the layer? I mean, is the application of Fe2O3 your primary objective in this 'activation' process you mentioned?