The Honda CVCC was able to pass California (the strictest) emissions in the early 70's WITHOUT a cat. Federal laws immediately went into effect, because a cat MUST use heat to power it, thus dropping mileage, meaning more gas usage.
I am not knocking the use of cats to control harmful emissions, BUT the truth is that natural gas can burn without the use of a cat, INDOORS even, without doing anything other than increasing CO2 levels, just CO2 and water are the byproducts.
The gasoline that is in today's vehicles is a less clean mixture than that of 50 years ago, except for no lead. The problem is 50 year old engines weren't designed to burn it efficiently.
Even fuel-injected engines still spray wet gas, not vapor. Only the vapor part burns. Once someone releases plans to the world on how to run an engine solely on gasoline vapors THEN we eliminate our dependence on foreign oil, and not before.
376milespergallon.com
It CAN be done, we just don't have it in mass production on a current safety standards vehicle.