What is a Catalytic Converter?

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To really understand what a Catalytic Converter is – and more importantly what it does – we unfortunately have to start with something of a history lesson- don’t worry, we’ll keep it brief!

The recent Volkswagen emissions scandals have brought the issue of car emissions back into the public conscience in a big way. But this is not the first time they have made headlines.

What is a Catalytic Converter?

Of course it was suspected for a long time that the emissions from vehicle exhausts could have a harmful impact both on humans directly and also on the wider environment.

The United States was the first country to recognize this and to bring in laws and regulations designed to limit this potential damage. One of the first of such laws was issued by the then newly formed Environmental Protection Agency.

The law stated that all Gasoline powered vehicles built from 1975 onwards must be fitted with a converter. The US was very much a pioneer in this field, creating the first mass market use of converters in the world. Other countries were remarkably slow to adopt the technology, the UK as an example did not make converters a legal requirement in new cars until 1991.

What is a Catalytic Converter Made of?

There are a number of materials used in a Catalytic Converter. The basic structure of the converter as viewed from the outside is an enclosed structure, often box shaped or a long tube.

It is an integral part of the vehicle exhaust system, usually located closer to the engine block than to the exhaust outlet pipe itself at the other end of the system. This is because exhaust gases formed whilst the engine is operating must all pass through the converter before they are allowed out into the wider atmosphere.

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The appearance of the interior of the convertor will depend on the age of the device itself. Most modern models will be passageways of closely formed metal mesh. Picture a honeycomb made of metal, and you will not be far off. Older models are full of ceramic beads instead of the honeycomb design.

The purpose of either the honeycomb or the beads is to slow the passage of exhaust gases through the converter. This allows them more time to interact with the Catalyst material, which is painted all over the surface areas inside the converter.

These catalyst materials are usually a very thin layer of a metal such as Platinum or Rhodium. If you’ve ever been in a jewelry store, you’ll know that Platinum is a precious metal with a pretty high value. The typical converter will contain anywhere up to 9 grams of platinum, so that should explain why they can be so expensive to replace!

What does it do?

The basic function of the Catalytic Converter is to remove potentially dangerous compounds from the exhaust gases before they can be expelled into the air. There are three compounds the converter works to remove, which are:

  • Hydrocarbons – This compound is basically left over gasoline that has not been burnt by the engine. If released into the atmosphere it can build up and cause dangerous clouds of smog to form.
  • Nitrogen Oxide – The sheer heat in the engine whilst it is running forces oxygen and nitrogen molecules to be compounded together, which in turn causes Nitrogen Oxide to be formed. This compound is also very bad for the environment, as it can pool at cloud level, until it falls to the earth as acid rain.
  • Carbon Monoxide – this compound is also formed by the heat of the engine during operation. In this case, carbon monoxide is formed as a byproduct of gasoline being burnt in the engine. This gas is extremely dangerous and is poisonous to oxygen breathing mammals – including us humans.
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How Does it Do it?

The clue is in the name of the device!

Basically, it uses “Catalysts” (the metals such as platinum) to “Convert” the dangerous compounds into less harmful ones. Essentially, the compounds react with the catalyst materials, changing their molecular makeup and converting them from one compound into another.

So for example, extremely harmful carbon monoxide, after it comes into contact with the catalyst, is changed into Carbon Dioxide. Nitrogen Oxide is split back into its original states so it can be expelled as simple nitrogen and oxygen whilst the Hydrocarbons are turned into Carbon Dioxide and water.

So whilst people still talk about the potential health effects of the chemicals found in emissions, without the catalytic convertor they would be far, far more dangerous.

What Are the Downsides?

The main downside to a converter is that by restricting the otherwise free flow of the exhaust gases, they can have a negative impact on the overall engine performance. In tests however, it’s been shown that an old fashioned converter, for example a model with ceramic beads, can lead to a performance reduction of only 3% – a modern, honeycomb style converter will only lower engine performance by closer to 1%.

The converter itself has a pretty long life span, but it doesn’t last forever. It needs sporadic servicing and checks that it is not becoming clogged or otherwise ineffective. A clogged converter will further affect performance, and an old one will be less efficient at catalyzing compounds as the catalyst itself ages.

Because of the high temperatures it operates at, the converter can be damaged by sudden temperature changes. For example, sudden immersion in water – such as driving through a pool or very deep puddle – can dramatically and instantly lower the temperature of the converter, causing the internal honeycomb structure to crack.

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Many Petrolheads who want to squeeze every ounce of power from their cars will consider removing the Catalytic Converter. This is frankly a bad idea as:

1) it will barely have any effect at all on the engine performance, especially if you are using a modern model, and

2) it is illegal.

The converter performs a vital function protecting you and your passengers from breathing in extremely harmful compounds and it also helps to protect the wider environment from smog and acid rain.

It is therefore an essential piece of kit that should be just as looked after – and well serviced – as any other key component in your car.

Originally posted 2023-10-17 13:50:25.

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