In an engine with a properly-functioning catalytic convertor, what benefit is there to using any oxygenator? Such chemicals reduce fuel economy, increasing the emissions of CO2 per mile. They may make the air going into the catalytic convertor cleaner, but what's the point of doing that?
Oxygenated gas was developed in the 1970's as an alternative to catalytic convertors. If catalytic convetors were not widely used, oxygenated gas would indeed reduce polution. Using oxygenated gas on a car which already has a catalytic convertor, however, is redundant and wasteful.