I could sort of see how such a thing, if it worked, could help if we were back in the early 80s and were all still running carburetors but today's injection systems do a good job of turning the fuel into a fine mist and the combustion chambers are much better about burning most of the fuel. If I understand correctly how catalytic converters work, they change harmful compounds in the exhaust into less harmful compounds through a molecular change. They change carbon monoxide to carbon dioxide, nitrogen oxides to nitrogen and oxygen, and hydrocarbons into carbon dioxide and water. As we all know, hydrocarbons are the fuel which engines burn to produce power. Now lets think about if we turn the hydrocarbons in our fuel into carbon dioxide and water BEFORE it's introduced into the engine. Seems to me like it would get less power from the fuel since we are changing the very things we get power from into compounds that the engine can't get power from. With that in mind, I would say that such a thing, if it worked, would result in LESS fuel mileage. At least that's how I see it, but I am no scientist by any means.
