Catalytic converters

What is a catalytic converter?

A catalytic converter is an exhaust emission control device. Its purpose is to convert gaseous pollutants resulting from the operation of the internal combustion engine into less harmful elements in order to protect the environment and public health.

It is increasingly common for a vehicle to have more than one catalytic converter to comply with regulations. Some catalytic converters are directly attached to the exhaust manifold; others may even include a silencer and the exhaust pipe. Be it because it plays a key role in keeping vehicle emissions below regulatory limits, or because of the increasing wave of theft, the automotive catalytic converter is one of the most talked-about vehicle components today.

How does a converter work and why is it used to reduce emissions?

By definition, a catalyst is an agent that takes part in a chemical reaction by increasing its speed, but without intervening directly, so that its mass remains unchanged. It could be compared to a group of spectators cheering on the cyclists in a race and giving them strength only by their encouragement.
The main pollutant exhaust gases from combustion are carbon monoxide (CO), unburned hydrocarbons (HC) and nitrogen oxides (NOx).
Their presence in the air is linked both to human health harms (increased chances of cancer and respiratory failure), as well as to atmospheric and biodiversity degradation. When passing through the channels of the ceramic substrate of the catalytic converter, the presence of the precious metals activates different chemical reactions (oxidation and reduction), which recombine the particles in the gases so that they come out of the exhaust pipe reconverted. More specifically:

• Carbon monoxide (CO) combines with oxygen (O2) to form CO2. This is an oxidation process.
• Hydrocarbons (HC) combine with oxygen (O2) to form a mixture of CO2 and water vapour (H2O). This is an oxidation process.
• Nitrogen oxide (NOx) combines with carbon monoxide (CO) to form a mixture of CO2 and nitrogen. This is a reduction process.

It is important to note that for these reactions to take place, the catalytic converter requires an operating temperature of over 450 degrees Celsius. In turn, the reactions themselves release more residual heat, so a good clue to diagnose whether a catalyst is working properly or not is to measure the temperature at the inlet and outlet. If it is hotter at the outlet, the catalyst is probably working properly.

Are catalytic converters for diesel and petrol vehicles the same?

Broadly speaking, yes. Emissions from both a diesel catalytic converter and a petrol catalytic converter are similar, and need to be treated to comply with current regulations. However, the higher oxygen content due to the compression ratio of diesel engines means that nitrogen oxide cannot be reduced sufficiently. Hence, because they only act on CO and HC through the oxidation process, catalytic converters on diesel vehicles are said to be ‘two-way’ catalysts, whereas those on petrol vehicles would be ‘three-way’ catalytic converters. In order to prevent nitrogen oxides from escaping freely through the exhaust, they are treated by the exhaust gas recirculation circuit and, in more modern vehicles, the selective reduction catalytic converter. The latter is a special device that requires a urea-based reducing agent so that the reduction processes can be activated and completed.

At Kat Europe we have a wide range of car catalytic converters to cover the needs of over 90% of the European vehicle fleet, with the best price in the market and fast and efficient delivery. If you have any questions about how your catalytic converter works or how to find the correct catalytic converter for your vehicle, please do not hesitate to contact us or consult our help centre.