[mechman600]

Catalytic converters don't get dirty and require "self cleaning" of any sort, your
900 miles of driving has little to do with anything other than getting somewhere far away. When the cat is cold, the nastiness that leaves the engine just flows on through out the tail pipe without turning into "friendly" things. Above ~500F when the cat is "lit", the nastiness the catalyzed into nice things like CO2 and H2O.