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What is a Catalytic Converter?

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Updated 11 Oct 2019

Jonathan Nash

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The catalytic converter is part of a vehicle’s exhaust system, located in the exhaust pipe between the manifold and the muffler.

It is designed to convert the harmful, noxious compounds and gases that are created during the combustion process - including hydrocarbons from unburnt fuel, carbon monoxide and oxides of nitrogen – into less noxious elements such as nitrogen, oxygen, carbon dioxide and water.

It gets its name because it utilises a catalyst – a combination of metals including platinum, palladium and rhodium – that, when heated, cause chemical reactions that convert those harmful compounds.

From the outside, the catalytic converter doesn’t look like much, just a boxy lump in the exhaust pipe.

On the inside, however, there’s some clever stuff going on.

And that clever stuff is not just isolated to the converter but is linked into other systems in the car to ensure that emissions from the tailpipe are cut to the minimum possible.

Inside, the converter has a dense, honeycomb ceramic structure that is lined with the catalyst material.

The honeycomb design means there is a very large surface area packed into a small space allowing for more catalyst material to react with the noxious compounds and gases flowing through it.

The ceramic material also helps to keep the converter hot – a requirement for the reactions to be at their most effective.

There are actually two reactions taking place inside the converter.

Reduction catalysts work to remove oxygen from the nitrogen oxides atoms, resulting in Nitrogen (the stuff that makes up 78% of our atmosphere) and oxygen.

An oxidation catalyst reaction also takes place, which converts carbon monoxide and hydrocarbons to carbon dioxide and water.

Knowing the catalytic converter is working at its best is where the link to other systems in the car come into play.

Placed before and after the converter are oxygen sensors that are connected to the car’s ECU.

The sensors measure the amount of oxygen in the exhaust and the ECU monitors that data and can adjust the fuel/air mixture in the engine’s combustion chamber accordingly.

It’s all very clever stuff and while no system is perfect, the catalytic converter has certainly played a major role in making the motor car a cleaner machine.

It’s an important piece of kit and quite robust but it can be damaged, including via excessive unburnt fuel in the exhaust.

This can cause the catalysts to reach extremely high temperatures and reduce the converter’s efficiency.

A replacement is an expensive item, so it pays to keep your car serviced regularly and to act quickly if you notice any changes in the way your car performs.

Keeping the catalytic converter in good health means you’ll be doing your bit to save the planet as well as saving some of your hard-earned cash.

Remember, AutoGuru makes it super easy to book car servicing and repairs online.

See instant quotes and great reviews from a range of great mechanics, no more calling around or endless hours of searching!

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Written By

Jonathan Nash

Jonathan has been writing about the auto industry for years and is particularly interested in the high-tech innovations sweeping the industry.

He’d love to own a Tesla Model S, but also adores anything with a V8 under the bonnet. 

He has yet to decide between an EV or a Mustang for his next ride.