Car catalytic converter: what it is for, operation and faults

El catalyst of a vehicle with a combustion engine is responsible for reducing the harmful gases resulting from burning the fuel. Actually, his full name is catalytic converter and there are several main types depending on whether they are for diesel or gasoline.

We tell you their history, what they are for, how they work and how much they cost. In addition to the symptoms that reveal that there is a fault in the catalytic converter.

Brief history of the catalyst

The first prototype of a catalytic converter for these purposes was developed in France and was first patented by Eugene Houdry. This mechanical engineer founded the Oxy-Catalyst company in the United States, which he first developed catalysts for chimneys and later for forklifts, which used a low-grade unleaded gasoline. Later, he developed a catalytic converter for automobiles which he patented in 1956.

Catalysts spread across the US in the 70s

Following the Engelhard Corporation improvements that culminated in 1973. , appeared the first catalyst intended for mass production. By 1975 almost every car in the United States had one installed to comply with its Environmental Protection Agency regulations.

Since then, the catalysts have been improving both in effectiveness and efficiency, up to variants such as selective reduction catalysts (SCR) that use AdBlue. Although these are used as an add-on, and do not exclude the conventional catalytic converter.

What is the catalyst for?

The catalytic converter converts harmful gases into less harmful or harmless ones.

A catalyst reduces the harmful gases generated in an internal combustion engine. Without it we would be much more exposed to the following harmful gases:

  • With a rich mix (more fuel than air) incomplete combustion occurs, generating:
    • Unburned hydrocarbons (HC): are carcinogenic and irritate the respiratory tract and eyes. As for the environment, they can create acid rain and photochemical fumes.
    • carbon monoxide (CO): in low doses it produces headache, shortness of breath and coordination, dizziness, irritability, confusion and memory gaps. In high doses it causes death without the affected person realizing it, hence they call it the silent killer.
  • With a lean mix (more air than fuel) oxides of nitrogen are produced, which are represented by the formula NOx. They have carcinogenic variants and cause irritation of the respiratory tract and, as a consequence, bronchopulmonary conditions and respiratory problems.

The gases removed by the catalyst can be deadly

The Lambda Sensor, as important as the catalytic converter or more

The Lambda Sensor is an element that allows the correct adjustment of the air and fuel mixture at all times. In gasoline engines it is 14,7 parts of air for each part of gasoline (14,5 in diesel).

Without it, the engine would release many more gases like those mentioned above and the capabilities of the catalyst would be greatly exceeded. We recommend the article Lambda sensor: what it is, how it works, breakdowns, cleaning, price..., to find out how it works and if your car has any fault related to it.

However well this probe performs, it is currently impossible to maintain a perfect mix at all times. For this reason, cars need one or more catalytic converters to eliminate these harmful gases.

How does a catalyst work?

Use of materials in the catalyst

A catalyst works thanks to metals such as platinum, rhodium, zirconium or palladium, which have catalytic properties. That is, the ability to accelerate a chemical reaction. Each is dedicated to a different type of noxious gas:

  • El Platinum accelerates the oxidation of unburned hydrocarbons to convert them into carbon dioxide and water. The chemical formula is as follows: CxH2x+2 + [(3x+1)/2] O2 -> xCO2 + (x+1) H2O.
  • El born accelerates the reduction of nitrogen oxides to nitrogen and oxygen: 2NOx -> xO2 + N2 and the oxidation of carbon monoxide to carbon dioxide: 2CO + O2 -> 2CO2. They are also used zirconium o palladium, which are cheaper but less efficient.

Do not forget other catalyst material. These metals are arranged on a ceramic structure of cordierite, which supports the high temperatures of the exhaust gases.

Catalyst Shape

As you can see, the catalyst uses certain metals in the solid state to convert gases. Which leads to an obstacle: how to make a gas come into contact with these materials as much as possible, without losing too much speed. For this reason, the ceramic structure of the catalyst is in the form of a matrix with longitudinal channels. A system similar to hydrogen car fuel cell which, by the way, also uses platinum as a catalyst. Although in his case the distribution of the gas is much finer, with a much more intricate structure.

These longitudinal channels allow the gases to pass without stopping too long but to come into contact with as many walls as possible. Hence, they have more than 70 tubes per cm2.

In addition, modern cars often use two or even three catalytic converters in order to eliminate harmful gases as much as possible to comply with the Euro 6 (at the date of this article) and Euro 7 anti-pollution regulations in 2025.

Wrapping around this catalyst matrix is ​​a heat shield and metal layer. Otherwise, the heat accumulated in it could damage the vehicle or the surfaces where it is parked. Without it, a fire could easily start.

The working temperature of a catalyst

For metals with catalytic properties to work at their maximum efficiency, a conventional catalyst has to be above 500ºC. This is why at least one of the engine's catalytic converters is usually close to the engine exhaust manifold, which is where the gases still have a very high temperature.

Thanks to this, the catalyst is heated before and it takes less time to start eliminating harmful gases. If we could see a catalyst working through its protective layers, we would see that the ceramic matrix and the metals in it are red hot.

Knowing this, you will understand that a cold engine releases more harmful gases than one that has been running for a while now. Anecdotally, Toyota had to deal with this emissions problem in the development of the Prius. Switching off the heat engine in favor of the electric one caused the catalytic converter not to reach the correct operating temperature on many occasions. For this reason, they had to devise a system that would take the heat from the combustion engine to the catalytic converter by other means.

universal catalyst

Catalyst of a gasoline car

These catalysts are usually triple pathway. That is, they have the three catalyzing systems described above: platinum for remove unburned hydrocarbons and rhodium, zirconium or palladium for remove NOx and CO.

This is so because gasoline engines release less NOx than the diesels and the catalyst alone can reduce them Enough. Although due to advances in anti-pollution, more modern cars may have other types of catalytic converters.

catalytic converter of a diesel car

In diesel engines, conventional catalysts are two-way. That is, they only take care of the removal of unburned hydrocarbons and CO. The NOx was left in the hands of gas recirculation systems such as the EGR valve, which returned them to the combustion chamber to burn completely.

There is also the NOx accumulator catalyst, which has an important role in the systems' fight to make diesel even cleaner and to meet future emission limits, which will be even stricter than now. It is placed behind the oxidation catalyst and the particulate filter and has a special layer that collects nitrogen oxides from the exhaust gases.

Two different types of operation are distinguished in the NOx storage catalytic converter: In normal operation (Lambda > 1), NO is first oxidized to NO2 and then, with the formation of nitrate (NO3), accumulates in the catalytic converter to an oxide alkali metal (eg barium oxide).

Diesel engine catalysts

Same as particulate filter the real challenge for the NOx storage catalyst is the regeneration, that is, the periodic emptying of the accumulator. For accumulator regeneration, oily conditions must be created in the exhaust gases (Lambda < 1). Under these service conditions there is so much reductant (carbon monoxide, hydrogen or various hydrocarbons) that the nitrate bond is suddenly released and the noble metal catalyst is converted to non-toxic nitrogen (N2). The duration of the charge is about 30 to 60 seconds, depending on the point of service and the regeneration lasts between 1 and 2 seconds.

Many temperature and pressure sensors are required to detect the need for regeneration. The catalyst accumulator can reduce NOx emissions by up to 85%.

However, the current diesel cars they also have a SCR catalyst (selective reduction catalyst). It is the one used with the additive of AdBlue, which is nothing more than urea that is sprayed into the exhaust gases, before they reach this catalyst. This initiates a chemical reaction that breaks down NOx into N2 and H2O, much more efficiently than older systems.

Cars with AdBlue have SCR catalytic converters.

Catalyst faults and their symptoms

Most failures of a catalytic converter are due to some previous problem in the engine. For example, excess fuel in the exhaust system (too rich mixture) due to bad spark plugs, incorrect timing or damaged oxygen sensor. What this causes is that the catalytic converter reaches too high a temperature, which melts metallic components and breaks the ceramic matrix.

It can also happen that oil or antifreeze enters the exhaust system, due to damaged gaskets, seals of Válvulas spoiled or piston rings worn. This causes the accumulation of soot in the catalytic converter.

The symptoms of a failed catalytic converter are:

  • Rotten egg smell caused by the sulfur in gasoline, which during combustion turns into hydrogen sulfide. As the conversion of gases does not take place due to a damaged catalyst, the hydrogen sulfide arrives outside.
  • Power loss, because the exhaust system is partially obstructed by the catalytic converter. If this obstruction is due to the fact that the materials are melting and breaking, you will have to replace the catalytic converter and detect what is the fault in the engine that has caused it. If it is only obstruction by dirt you can try to clean it.
  • Emissions test failed. Needless to explain about it, because the catalyst does not convert harmful gases and the test indicates that it does not work. In Spain, it is the Technical Inspection of Vehicles (ITV).

With a damaged catalyst you will not pass the ITV

  • rattling noise under the car when it is idling or moving. It is caused by parts of the broken ceramic matrix inside the catalyst, which are moved by the exhaust gases. Be careful because if these pieces reach the muffler, the exhaust system can become more obstructed.
  • Consumption increase. This is not a symptom of a bad catalytic converter, but it is a symptom of a rich fuel mixture that tends to break down the catalytic converter. That is why it is a symptom to be taken into account.
  • Engine fault light on. If the car's sensors detect that the gas conversion is not taking place properly, the control unit will turn on this warning light. Although as it also serves for many other faults, it is a symptom that by itself does not indicate the failure of the catalytic converter. You can connect the car to an OBD Reader to see what error code it has registered to know what the specific problem is.

Watch out for blockages in the exhaust system, because they raise the temperature of the exhaust manifold and other pipes and can cause much more serious damage to the car.

A system is clogged exhaust can overheat

Although engine failure is the most common cause of catalytic converter failure, there are also models that have recurrent catalytic converter problems due to design or manufacturing defects.

The price of a catalyst

As you have seen throughout the article, there are several types of catalysts. So their prices can vary a lot from one model to another. However, replacing a catalytic converter with a new one is usually between the 600 and the 1.000 euros for passenger cars. In any case, that figure can be higher if other catalysts are involved in addition to the conventional one.

Also exist universal catalytic converters at a good price compatible with various models. Although you must also make sure that it complies with the Euro regulations that your car has and is homologated. Then we recommend that the assembly be done by a professional, since it is a delicate element.

Images – Frankieleon, Riley Kaminer, Duurzaam Bedrijfsleven, Gonzalo Malpartida


Follow us on Google News

A comment, leave yours

Leave a Comment

Your email address will not be published. Required fields are marked with *

*

*

  1. Responsible for the data: Miguel Ángel Gatón
  2. Purpose of the data: Control SPAM, comment management.
  3. Legitimation: Your consent
  4. Communication of the data: The data will not be communicated to third parties except by legal obligation.
  5. Data storage: Database hosted by Occentus Networks (EU)
  6. Rights: At any time you can limit, recover and delete your information.

  1.   Javier said

    And in Mexico where can I get a catalyst doc for jetta tdi 2006, apart from those that the agency sells very expensive? gpfj2@yahoo.com.mx