what do catylist converters in cars actually do and where else are they used and are they expensive?

Question: what do catylist converters in cars actually do and where else are they used and are they expensive?
- Keywords:
  car,
  catalytic convertor,
  expensive
Asked by blue to Adam, Eloise, Iona, Jarrod, Yip on 20 Jun 2016.
- Jarrod Hart answered on 20 Jun 2016:
  
  Nice question right up my alley.
  
  A catalytic converter is a sort of sponge covered in platinum.
  
  The most important job it does is to help complete the combustion of the fuel that was not properly burnt in the car engine – which creates smog – is also a very nasty invisible gas that comes out of engines called carbon monoxide, which can kill people. The catalyst tries to convert these all to carbon dioxide (also a pollutant, and probably causing global warming, so cars that burn fuel are still not very good for us).
  
  ‘Cats’ are mainly used in cars and trucks, but they are also used in special heaters and burners in industry.
  
  They were first used in the smoke stacks in smoggy cities like Los Angeles, but now there are cheaper ways to reduce the factory smoke, such as having cleaner gas, or by using ‘scrubbers’, which are a curtain of water spray to wash the smoke…
- Iona Strawson answered on 20 Jun 2016:
  
  I’d go with Jarrods answer – catalytic converters are no where near my alley.

Question: what do catylist converters in cars actually do and where else are they used and are they expensive?