What is a catalytic converter and how does it work?

Published: 30 April 2021

► What is a catalytic converter
► How it works
► And why they’re important

Catalytic converters (or simply ‘cats’ for short) are one of the most important parts of the exhaust system of modern cars. Generally located close to the engine, the catalytic converter is tasked with breaking down the pollution coming out the end of the tailpipe.

To put it in the simplest of terms, it’s a metal box that cleans up the emissions coming out of the back of your car, but the science behind it is far more complex than that.

How does it work?

Catalytic converters contain catalysts – chemicals which speed up the process of chemical reactions, which themselves do not change during this process. Catalysts break down the harmful exhaust gases coming from the engine by separating the atoms which make up these molecules.

There are typically two different catalysts inside a common three-way catalytic converter – one which tackles nitrogen oxide by removing oxygen through a process called reduction, and the other which turns carbon monoxide into carbon dioxide by adding oxygen, called oxidation.

There is also a second oxidation reaction that happens inside the catalytic converter, which turns any unburned hydrocarbons into carbon dioxide and water.

What this all amounts to is less smoke and odour coming out of the exhausts of cars now than before catalytic converters were mandated by UK authorities.

It is also worth noting catalytic converters are one reason we must use unleaded fuel in cars today, as leaded fuel, which is no longer sold in the UK, prevents the catalysts from breaking down the pollution in the exhaust gases.

Why does it matter?

Arguably, if it weren’t for catalytic converters at play, cities would be a lot smoggier than they are, and the smog would be far more harmful to the environment and to people.

As catalytic converters play a vital role in reducing short-term air pollution, they can certainly be considered beneficial, although they aren’t without their detractors.

Some environmental concern bodies, such as the Intergovernmental Panel on Climate Change, have claimed that due to the amount of nitrous oxide they produce they are doing more long-term harm to the environment than they are good.

However, newer catalytic converters produce far less nitrous oxide than older ones, and the effect they have on reducing the emissions of hydrocarbons, carbon monoxide, and nitrogen oxides is certainly noticeable.