How a catalytic converter works; The Ultimate Guide (2022)

Did you know that there is a component on your vehicle that contains a noble metal that is worth 10 x the price of gold? Would you be surprised if I would refer to it as the unsung hero of your vehicles exhaust system.

This component I am discussing is the vehicles catalytic converter. The catalytic converter is a component of the exhaust system that reduces the number of harmful emissions that are released from the tailpipe of vehicles.

This article is going to go through everything you need to know about how a catalytic converter works.

The catalytic converter was invented around the year 1950. It was invented by Eugene Houdry who was granted a United States patent for the device.

Even though it was invented in the 1950’s it took some time to reach the automotive market. In fact, if we turn back the clocks we see when the introduction of the catalytic converter occurred, we will find 1975 as the year for widespread adoption of this technology. 

In 1975 many vehicles came with a catalytic converter as standard equipment. However, it was not until release of new emissions regulations in the United Stats in 1981 that they were made mandatory.

Why wasn’t the catalytic converter released earlier?

The catalytic converter did not see widespread adoption earlier than 1975 due to the use of tetraethyl lead in fuels. The tetraethyl lead that was used in leaded fuels was toxic to catalytic converters.

This lead in the fuel would coat the internal surfaces of the catalyst inside of the catalytic converter. This would render the catalyst ineffective and cause a reduction or complete failure of the catalytic converter.

This effect is more widely known in the industry as catalytic converter “poisoning”.

In 1975 unleaded fuel was becoming more available for the general public. Because of its accessibility manufacturers were now able to install these emissions fighting component onto vehicles without fear of “poisoning”.

What creates vehicle emissions?

Gasoline contains over 150 different hydrocarbons. Fuel is mixed with air inside of the combustion chamber than the mixture is burned. After the combustion process there is a large amount of chemical by products from this process.

The gases that are released during this process can be harmful while others can be safe.

Nitrogen (N2)

Nitrogen is released which is simple nitrogen gas. This gas can be considered harmless as the air we breath on an everyday basis contains 78% nitrogen.

Water (H20)

H20 or more commonly knows as water. However, I wouldn’t suggest you try drinking the water that is coming out of the tailpipe of your vehicle.

Harmful Gases

Carbon Dioxide (CO2)

This gas is crated during the combustion process. Oxygen that is in the air combines with the carbon of the fuel and combines to create Carbon Dioxide.  Carbon dioxide is a greenhouse gas and is a leading cause of climate change.

Sulphur Oxides and Nitrogen Oxides (NOx)

These gases are very harmful when they reach our atmosphere. They can combine when in our atmosphere to create acid rain as well as smog. If you cannot picture smog, think of it as fog that is created by air pollution.

Carbon Monoxide (CO)

Carbon monoxide is one of the most immediate dangers in exhaust gases. Carbon monoxide when absorbed into our bodies can displace oxygen. This can cause the oxygen in our blood to deprive our vital organs of the oxygen that it requires.

While these are the major pollutants that are released from the exhaust system there are many others.  Particulates, unburnt fuel as well as volatile organic compounds are only some these compounds that are released.  

If you have ever been walking down the street and had a vintage vehicle drive past you, you can understand why a change had to be made. Thankfully the catalytic converter was around to solve the problem.

How does a catalytic converter work?

A catalytic converter works but using a catalyst to reduce harmful tailpipe emissions. A catalyst is a substance that is very unique. It can cause a further chemical reaction or accelerate a chemical reaction without changing itself.

A catalytic converter is a unique component in the exhaust system. While it looks like a large tube from the outside, when you peel back the outer layer the magic of what is inside is revealed.

Inside of this metal casing is a densely packed ceramic honeycomb structure. The honeycomb structure is used because it increases the surface area inside of the catalytic converter. This structure is than coated with a combination of noble metals that act as a catalyst.

Noble metals are unique as they can stand up to the harshest conditions that are present in the exhaust system. They can stand up to acids, corrosion, and even oxidation.

The noble metals that are used in modern day catalytic converters are Platinum (Pt), Palladium (Pd, and Rhodium (Rh).

Some new catalytic converter designs are using gold. Although this may seem like an expensive material to use. Rhodium for example, has traded at 10x the value of gold at various times in history.

Gold is being used for its unique characteristics. It has been found that it has potential to increase the oxidation process which could lead to a reduction of pollutants by up to 40%.

Infographic of how a catalytic converter works
Infographic of how a catalytic converter works

Chemical Reactions

Inside of the honeycomb structure there is two beds where unique chemical reactions occur. These beds are known as the reduction bed and the oxidation bed.

Reduction Bed

The honeycomb structure in the reduction be is coated with a combination of Platinum and Rhodium. This bed reduces the amount of Nitrogen Oxides (NOx) that is released from the tailpipe.

It does this by removing nitrogen atoms from the nitrogen oxide molecules and creates nitrogen gas and oxygen.

Oxidation Bed

The honeycomb structure inside of the oxidation catalyst is coated with platinum and palladium. The main purpose of the oxidation be is to reduce the number of Hydrocarbons (HC) and Carbon Monoxide (CO) from the exhaust gases.

The carbon monoxide and oxygen for carbon dioxide while any unburnt fuel and oxygen create carbon dioxide and water.

When these chemical processes have occurred, the exhaust travels out the tailpipe where it is released in the atmosphere.

Are catalytic converters effective?

Yes, catalytic converters are very effective in removing harmful tailpipe emissions from a vehicle. Once a catalytic converter is brought up to operating temperature which is roughly 600°F, the process begins.

Most estimates of a catalytic converter’s efficiency are at 90% reduction. This means 90% of the most harmful hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) is reduced to less harmful gases. Carbon Dioxide (CO2), water vapour and nitrogen.


What is secondary air injection?

Like I mentioned in the above section, a catalytic converter does not start functioning until it reaches operating temperature, 600°F.

Modern day engines bring the temperature of the converter to operating temperature within minutes. Some modern vehicles but most older vehicles required some assistance to get the catalytic converter up to operating temperature as soon as possible.

Secondary Air Injection was originally used to reduce the amount of unburnt fuel that was released from the vehicle. By pumping air into the exhaust, it would allow the unburned fuel that was present to oxidize before it exited the tailpipe.

This technology had issues, if a misfire was present or the engine had improperly adjusted valves extreme heat would build up in the exhaust. If this heat continued to build up it could cause damage to the exhaust valves in the engine.

When catalytic converters were introduced, they were able to use this system to help them come up to operating temperature as fast as possible.

When the engine was cold, air would be directed into the exhaust system before the catalytic converter. This would cause any unburnt fuel to oxidize and increase the temperature. This increase in temperature would result in the catalytic converter reaching operating temperature sooner.

When the catalytic converter was warm it would be directed into the catalytic converter. This would increase the catalytic converter’s ability to reduce the number of unburned hydrocarbons that were released.

Do diesel engines have catalytic converters?

Yes, diesel engines do have catalytic converters, but they are known as Diesel Oxidation Catalysts (DOC).

Along with the name change their function is slightly different as well. The DOC is designed to convert carbon monoxide (CO) into carbon dioxide (CO2) and oxidize any unburnt diesel fuel that may be present.

Diesel engines operate differently than a gasoline engine, they use compression ignition versus spark ignition used in gasoline engines. Due to the properties of compression ignition the heat that is generated inside of the combustion chamber is very high.

Because of the high heat levels that are generated, a diesel engine can produce 10x the amount of NOx emissions.

With the high NOx levels in the exhaust they need to be treated differently. Diesel engines have a separate component known as a Selective Catalytic Reduction (SCR) catalyst.

Can I drive my vehicle with a bad catalytic converter?

Depending on how your catalytic converter failed you may be able to drive the vehicle to the repair shop. If the catalytic converter has poor efficiency, or the PCM detected the catalytic converter isn’t functioning properly than it will be no problem to drive your vehicle.

However if the honeycomb structure has failed internally inside of the catalytic converter than no. If this honeycomb structure begins to fail it can cause the catalytic converter to plug. This effectively restricts the exhaust flow through the catalytic converter preventing the engine from “breathing”.

A flashing check engine light is another indicator not to drive the vehicle any further. A flashing check engine light indicates to the driver that there is a “catalyst damaging event”

This is problem is the result of an engine misfire. The check engine light flashes to warn the driver to pull over the side of the road as soon as it is safe to do so.

This prevents any further damage to the catalytic converter which may save the vehicle owner thousands of dollars in repair costs.

How much does it cost to replace a catalytic converter?

Depending on the make and model of your vehicle a catalytic converter may cost anywhere from $500-$2500 to replace.

The main reason the price varies so much from vehicle to vehicle is the amount of noble metals that are inside of the catalytic converter. The more metals the higher the price, and possibly the greater the risk of theft.

Catalytic converter theft is a growing concern and is not to be take lightly. Check out our Catalytic Converter Theft article to learn more about how to protect yourself from this needless crime.

That about sums up everything you need to know about catalytic converters. If there is something I missed please leave a comment so we can add it to our ever-increasing knowledge base for vehicle lovers just like you.

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