Which catalytic converters are used to …

A catalytic converter is a large metal box, bolted to the underside of your car, that has two pipes coming out of it. One of them (the converter's "input") is connected to the engine and brings in hot, polluted fumes from the engine's cylinders (where the fuel burns and produces power). The second pipe (the converter's "output") is connected to the tailpipe (exhaust). As the gases from the engine fumes blow over the catalyst, chemical reactions take place on its surface, breaking apart the pollutant gases and converting them into other gases that are safe enough to blow harmlessly out into the air. The catalytic converter sits between the engine and the tailpipe, but it doesn't work like a simple filter: it changes the chemical composition of the exhaust gases by rearranging the atoms from which they're made:

i.Molecules of polluting gases are pumped from the engine past the honeycomb catalyst, made from platinum, palladium, or rhodium.
ii. The catalyst splits up the molecules into their atoms.
iii. The atoms then recombine into molecules of relatively harmless substances such as carbon dioxide, nitrogen, and water, which blow out safely through the exhaust.