Emissions control

Catalytic converters

Catalytic converters are specialist devices mounted in the exhaust system to minimise the emission of harmful pollutants.

Your car produces gases such as carbon dioxide, carbon monoxide, hydrocarbons and nitrogen oxides which can be poisonous or carcinogenic. The converter substrate creates a chemical reaction between these gases converting them to other relatively harmless gases. Oxygen sensors in the exhaust also help reduce emissions by adjusting the fuel mixture.

Operating between 400 – 800°C, a catalytic converter can reduce your vehicle’s emission of carbon monoxide, nitrogen oxides and hydrocarbons by up to 90%.

Check out our range of catalytic converters for petrol or diesel engines: OE replacement units, Euro-compliant universal cats, high flow performance models and diesel particulate filters.

Call our team to discuss the right catalytic converter solution for your vehicle.

Photo of two catalytic converters

How a catalytic converter works

Diagram of how a catalytic converter works

The ceramic catalytic converter substrate has a grid structure coated in precious metals.
Precious metals in the coating react with exhaust fumes which pass through the porous substrate. This reduces harmful emissions.

The process

Active materials

Alumina, Cerium Oxide

Rare earth stabilisers

Platinum, Paladium and Rhodium

Exhaust gas in

· HC  =  Hydrogen
· CO  =  Carbon Monoxide
· NOX  =  Nitrogen Oxide

Major reactions

· CO  +  ½O2  =  CO2
· H4C2  +  3O  =  2CO2  +  2H2O
· CO  +  NOX  =  CO2  +  N2

Exhaust gas out

· H2O  =  Water
· CO2  =  Carbon Dioxide
· N2  =  Nitrogen

Converter Shape 51 mm 57 mm 63 mm 76 mm
Non OBD2 Oval CAT200 CAT250
Round CAT200R CAT250R
Euro 3 pre-cats Round C37304 C37305 C37306
Euro 3 Oval C99004HM C99005HM C99006HM
Round C99204HM C99205HM C99206HM CAT300U
Euro 4 pre-cats Round C5137304 C5137305 C5150005
Euro 4 Oval C51004 C51005 C51006 C51009
Oval with O2 boss C51064 C51065 C51066 C51069
Round C51204 C51205 C51206
Round with O2 boss C51354 C51355 C51356
Euro 5 Oval with O2 boss C45004 C45005
Round with O2 boss C46004 C46005

This listing is our base range of universal catalytic converters only. Our range of direct-fit catalytic converters continues to grow as product becomes available. These model specific parts are listed as exhaust components in our muffler and pipe catalogue.


A diesel particulate filter (DPF) removes soot from the exhaust gas of diesel engines. DPFs, like catalytic converters, work to reduce vehicle emissions, but instead of letting exhaust gases flow through it like a catalytic converter, the blocked ends of the DPF substrate force the exhaust gas through the substrate walls, where the soot particles are deposited. This results in cleaner exhaust gas going out.

Contact our sales team today to find out more about the range of DPFs we stock.

Photo of a cut open diesel particulate filter