hi
only british and American cars have got a catalytic converter in em...as per their requirement specifications otherwise the cars cant come on road...it is kinda cartridge that is wasted after 50,000km and needs replacement after that...the cylincers have a chamber in it to purify the poisonous gases....
the sensor you are talking about is called a Lambda sensor...
it has nothin to do with the catalytic converter...it only adjusts Fuel and air ratio by sensing thru waste gases and inlet manifolds.
an ideally tuned car has more oxygen being produced and less carbon monoxide and also sulphur and other petroleum producrs
i was only talking abt Petrol cars