What is a catalytic converter and how does it work?

A catalytic converter is a device fitted to your car’s exhaust system to filter out harmful substances from the engine’s emissions. It’s important for reducing pollution and improving air quality.

Since 1993, every petrol car sold in the UK has been legally required to have a catalytic converter. But how do they work, and what exactly do they filter out?

What is a catalytic converter?

A catalytic converter part of a car’s exhaust system. Sometimes known as a ‘cat’, this device reduces harmful emissions. It uses a substance that causes a chemical reaction – the catalyst. This substance reacts with the gases in the exhaust, trapping harmful pollutants that would otherwise be released into the atmosphere.

What is the purpose of a catalytic converter?

A catalytic converter is fitted to the exhaust system of your car between the engine itself and the tips. It’s there to reduce the amount of harmful emissions coming out the other end of your exhaust system.

In particular, it’s there to trap things like carbon monoxide, nitrogen dioxide and hydrocarbons.

You’ll find a catalytic converter underneath your car, close to the engine.

How does a catalytic converter work?

All types of catalytic converters work in a similar fashion. They trap those harmful substances mentioned above and transform them into less harmful substances by means of chemical reactions.

The heat from the engine warms up a honeycomb-like block inside of a catalytic converter’s metal casing. This causes the precious metals inside to trigger a chemical reaction with more harmful emissions.

Two-way catalytic converters

Early catalytic converters were ‘two-way’ systems that would use platinum and palladium to break down carbon monoxide and hydrocarbons. You won’t find two-way catalytic converters in modern cars.

Three-way catalytic converters

These work the same as two-way, albeit with the addition of rhodium to filter out oxides of nitrogen as well. These are now commonplace in petrol cars.

Which cars have a catalytic converter?

Every petrol car sold in the UK since 1993 must be legally fitted with a catalytic converter. That said, the tech has been around since the ‘70s.

This includes hybrid vehicles. That’s despite the fact they can drive on electricity alone.

Diesel cars do not use catalytic converters. Rather, they have a device called a diesel particulate filter (DPF). These are similar to catalytic converters and use a near-identical honeycomb structure. However, they focus more on trapping soot produced by a diesel engine.

You may be wondering if electric cars have catalytic converters. The answer is no, an EV does not have a catalytic converter. An electric car has no exhaust emissions to clean up, so there’s no need for one.

Why do catalytic converters get stolen?

Catalytic converters are packed with expensive and rare metals, with a very high scrap value. As such, they’re a target for thieves.

According to the British Metals Recycling Association (BMRA), there were 27,195 thefts of catalytic converters in 2023, a huge rise on the 10,049 incidents in 2013. The BMRA believes there are up to 60 organised crime groups involved in the theft of catalytic converters, part of the metal black market which costs the UK economy around half a billion pounds each year.

Catalytic converters fitted to hybrid vehicles are a particular target. With the engine itself used less in hybrid cars, the condition of these converters tends to be much better than a pure petrol car with similar mileage.

Theft is usually covered under your car’s insurance but replacing a converter can be expensive.

It’s not unheard of for cars to be deemed a write off if a convertor is stolen. It’s worth checking your policy to be sure you’re covered.

Catalytic converters FAQs

Where would you find a catalytic converter?

A catalytic converter is part of the exhaust system of a modern petrol or petrol-electric hybrid car. So, you will find it under the car, close to the engine.

How much is a catalytic converter?

Prices will vary, but £150-£900 is a good rule of thumb. Catalysts for high-end cars will generally cost more than cats for more affordable vehicles. If replacing a catalytic converter, you’ll also need to factor in the cost of labour.

Do diesel cars have catalytic converters?

They have something very similar, called a diesel particulate filter, or DPF. These remove particulate matter from the exhaust gases.

Can your car run without a catalytic convertor?

Yes, a car can run without a catalytic convertor. However, this would lead to increased emissions, more engine noise, and rough performance. In theory, the catalytic convertor can be replaced by an exhaust without a cat, but this increases emissions and is bad for the environment.

How long do catalytic converters last for?

A catalytic converter can last a long time. A lifespan of 10 years and close to 100,000 miles can be achieved. However, they won’t last indefinitely. Catalysts in cars used for stop-start journeys may not last as long as those in cars that cover a lot of motorway miles.