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 particulate matter from the engine’s emissions.

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 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 number 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.

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 prone to theft.

Data obtained by inews from 25 of the UK’s 45 police forces revealed over 20,000 instances of catalytic convertors theft happened in 2020. That figure is likely much higher if all forces are counted for.

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.