Why are cars fitted with a catalytic converter?

Created by Jonathan Fry, Modified on Tue, 1 Apr at 9:45 PM by Jonathan Fry

UK cars, like those in many other countries, are fitted with catalytic converters primarily to reduce harmful emissions and comply with environmental regulations. The UK has strict laws, influenced by both its own policies and former EU standards (still largely followed post-Brexit), aimed at improving air quality and reducing pollution from vehicles.

A catalytic converter is a device in the exhaust system of a car that transforms toxic gases produced during combustion into less harmful substances before they’re released into the atmosphere. Here’s what it does in simple terms:

Reduces Harmful Pollutants: Inside the engine, burning fuel creates nasty stuff like carbon monoxide (CO), nitrogen oxides (NOx), and unburnt hydrocarbons (HC). The catalytic converter uses a catalyst—usually made of precious metals like platinum, palladium, or rhodium—to trigger chemical reactions that turn these into safer outputs: carbon dioxide (CO2), nitrogen (N2), and water (H2O).
How It Works: Exhaust gases pass through a honeycomb-like structure coated with the catalyst. This setup maximizes surface area, letting the reactions happen efficiently as the gases flow out.
Why It’s Mandatory: Since the early 1990s, UK regulations (aligned with EU directives at the time) have required catalytic converters on all new petrol cars to meet emission standards, like the Euro norms. Diesel cars got them later with tweaks for their specific exhaust profiles. It’s about cutting smog, acid rain, and health risks from urban air pollution.

Without it, cars would pump out way more toxic junk, and cities would be choking harder than they already do. It’s not perfect—CO2 still gets through, and the converters can wear out—but it’s a big dent in the worst of the exhaust mess. Plus, tampering with or removing one in the UK is illegal and will fail your MOT test faster than you can say "emissions."