What’s Inside a Catalytic Converter?

The catalytic converter is a vital component of the exhaust system in a vehicle. The function of the catalytic converter is to convert toxic exhaust fumes and gases into less toxic ones.

In other words, the catalytic converter reduces the number of hydrocarbon emissions in the exhaust fumes that are generated by the internal combustion engine. This is a very innovative procedure which requires the chemical composition of these gases to be altered before they leave the vehicle.

But have you ever wondered, “what’s inside a catalytic converter”? Let’s take a look.

Related: 5 Symptoms of a Clogged Catalytic Converter

Inside a Catalytic Converter

catalytic converter interior

Have you ever wondered what is inside a catalytic converter which makes this process successful? Imagine a metal chamber with a small set of passageways inside of it.

A lot of people compare the converter to a honeycomb because of its many tiny passageways. But this particular honeycomb is constructed from a ceramic-based composite and lots of precious metals.

As the exhaust gases go into the honeycomb of the catalytic converter, they pass through several different passageways. When this happens, a chemical reaction occurs which draws out the toxic pollutants.

Each of these passageways is coated with metallic catalysts, such as palladium, platinum, and rhodium. These metals contribute to the chemical reaction which reduces the hydrocarbons, NOx gases, and carbon monoxide in the exhaust fumes.

It is important for the catalyst materials to have the most surface area possible. That is why a honeycomb design is used for the catalyst converter.

As for these precious metals, they are quite expensive themselves. A lot of car thieves like to steal catalytic converters from vehicles just to get their hands on these pricey metals.

Related: How to Quickly Tell If You’re a Victim of Catalytic Converter Theft

Types of Catalysts

how catalytic converter works

Let’s look at the two main types of catalysts and the metals they’re made from in gasoline-powered vehicles:

Oxidation Catalyst

Oxidation catalysts are comprised of platinum metals and palladium metals. Whenever carbon monoxide and unburned fuel flow to the oxidation catalysts, these elements are converted into water and carbon dioxide.

Reduction Catalyst

Reduction catalysts are comprised of rhodium metals and palladium metals. When the nitrogen oxide of the fumes hit the reduction catalysts, these elements are converted into oxygen and nitrogen. This is very important for reducing smog because nitrogen oxide is one of the main elements of smog.

In the old days, there used to be only two-way oxidation in a catalytic converter. This meant there were only oxidation catalysts and no reduction catalysts.

However, governments in both Canada and the United States became concerned about nitrogen oxide and the oxidation catalysts’ inability to convert them. As a result, the regulations surrounding catalyst converters changed so that 3-way oxidation/reduction was now required.

See Also: How to Clear a Clogged Catalytic Converter (DIY)

Diesel Oxidation Catalyst

As for diesel vehicles, they have their own separate catalyst called a diesel oxidation catalyst. This catalyst can take hydrocarbons and carbon monoxide and convert them into carbon dioxide and water.

Oxygen is used by the catalyst in the exhaust fuel stream to make this happen. The efficiency rate of the diesel oxidation catalyst is 90%. Most of the visible particles and emission odor are reduced or removed.


Previously, catalyst converters had cheaper metals like nickel, iron, cerium, and manganese. But these did not do a thorough enough job in converting the toxic emission gases into less harmful ones.

Due to the changing regulations surrounding carbon emission standards, car manufacturers had no choice but to use more expensive metals in their catalyst converters. It just so happens that platinum, rhodium, and palladium are the best metals for hydrocarbon reduction and nitrogen oxide reduction.

If you ever need to replace your catalyst converter, it will likely cost you between $1,000 and $3,000. Again, you’re paying for the precious metals and their value. Don’t take the cheap way out and avoid changing the catalyst converter. Otherwise, you may face legal problems in your location if you get caught.


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