The exhaust catalyst or catalytic converter plays an important role in a car’s exhaust system. Its purpose is to minimize pollution to better respect the environment by reducing exhaust gases.

The exhaust catalyst is also commonly called catalytic converter. It is however not to be confused with the exhaust pipe even though it is indeed a part of the exhaust system and is essential in the process of cleaning up the engine.

The exhaust catalyst is also subject to some wear and needs to be changed over the life of the vehicle. When, how, what is this piece used for? All the answers are in our file.

Exhaust catalyst: what role?

Weighing up to ten kilos, the exhaust catalyst is an exhaust system component consisting of a stainless steel shell and a ceramic core (also called honeycomb) impregnated with precious metals such as platinum or rhodium.

The main role of the exhaust catalyst is to reduce pollution in the air by reducing or destroying polluting gases through a catalysis system. For a diesel engine, the exhaust catalyst converts carbon monoxide and hydrocarbons into carbon dioxide and water (more and more it is connected to a particulate filter FAP).

On the other hand, for a petrol engine, the catalyst simply converts carbon monoxide and nitrogen dioxide into a non-polluting substance. The catalytic converter is effective at high temperatures, which explains why it is placed very close to the engine to heat up quickly and reach a good operating temperature.

How it works ?

The exhaust gases cross the tiny pores of the honeycomb which strongly resembles a filter (the goal is that a maximum of “treating” surface is in contact with the gases).

The toxic molecules are brought into contact (in the pores) with rare metals (the details will interest only seasoned chemists).

In contact with these elements, the chemical reaction causes the toxic molecules of the gases to be transformed into other elements that are much less dangerous (take out your high school physics lessons) for our health. Note that the Catalyst is often located in the same location as the DPF (known as the particle filter or dust filter).

Transformations (nothing is lost, nothing is created, everything is transformed):

Carbon monoxide is transformed into carbon dioxide
Nitrogen oxides transformed into carbon dioxide and nitrogen
Hydrocarbons transformed into water and carbon dioxide

Disadvantages of the system

The first disadvantage for the user is that he adds an additional and expensive organ… And when he finally gives up the ghost (because he is not eternal, far from it) it is quite expensive.

In addition, to function properly (like many other organs) the engine must be at the optimum operating temperature. It is therefore not 100% efficient since people making short journeys (engine not having no time to heat up) release pollutants not assimilated by the catalytic converter.

To do this, the catalyst is often brought as close as possible to the exhaust manifold and sometimes a second small catalyst (pre-catalyst) is even used at the manifold outlet.

Finally, the oil residues that accumulate over time are not evacuated by the regenerations, ending up ending the catalyst.

Exhaust catalyst: when to change it?

The catalytic converter must be changed approximately every 100,000 to 120,000 kilometers or risk ending up with a faulty component that no longer complies with the standards in force.

Indeed, a vehicle with an exhaust catalyst in poor condition can affect air quality due to a level of pollution that is far too high. Very good engine maintenance allows the catalyst to extend its life by a few additional kilometres, but must be automatically changed every 120,000 kilometers at most.

Exhaust catalyst failure

A strange smoke coming out of the exhaust or a metallic noise coming from the exhaust system are the first signs of a failing catalyst. Exhaust leaks also damage the catalytic converter. If the component were to clog, the consequences could even be serious for the vehicle since the engine could be damaged.

The exhaust catalyst is therefore an important part to monitor. A visit to a pollution bench with a specialist makes it possible to check its operating condition. This examination is also part of the checkpoints carried out during the technical inspection every two years from the four years of the vehicle’s life.

Can a catalytic converter be removed?

The elimination of the catalyst or catalytic converter is possible thanks to a tube called Tube Africa. However, the removal of the catalytic converter is strictly prohibited by law.

In addition, this removal will lead you to the categorical refusal of the vehicle during the technical inspection because of pollution since no element will then be able to filter the carbon monoxide generated by your vehicle. Namely that a new anti-pollution control appeared in January 2019.

Its structure: How is a catalyst made?

From 1 to 10 kg in general, there are two types of catalytic converters: a two-way converter (for diesel engines) or old-generation catalyst, and a three-way converter (for gasoline engines). There are also two different types of catalysis: reduction catalysis and oxidation catalysis.

Both versions of this exhaust part have an external structure, a “shell” in stainless steel (inox) which encloses a ceramic core, a brick, called a “honeycomb”. This brick, made up of hundreds of micro cells, is notably covered with precious metals such as rhodium, palladium and platinum.

It is they who will operate the chemical catalysis, which will allow the catalyst to filter the emissions of polluting gases as much as possible.