well, they do convert to oxygen. the platinum, palladium and rhodium all help to bust up the oxides of nitrogen into oxygen and nitrogen, the hydrocarbons split giving the hydrogen to the oxygen and making water. the nitrogen remians static. the carbon monoxide isnt split but rather gains an oxygen to become the non-lethal co2. if you ever get a chance to play around with a four-gas analyzer do it. old tailpipe or "sniffer" tests used co2 to determine if the probe was actually in the exhaust or not. if co2 readings were too low because of poor running it would actually go into "sample dilution" and you couldnt test it