How Catalytic Converters Work

Today, there are millions of cars that travel the roadways throughout the United States alone, and each vehicle represents a single source of pollution. Catalytic converters work to reduce the amount of pollution that a vehicle emits by converting harmful pollutants into less harmful emissions before it exits a vehicle’s exhaust system.

History of Catalytic Converters

The first catalytic converter was invented by Eugene Houdry in 1950. Houdry was a French mechanical engineer an expert in catalytic oil refining in the United States. Houdry first had the idea for catalytic converters after becoming concerned over the effect of smoke stack exhaust and automobile exhaust in air pollution. 

After World War II, Houdry formed a company called Oxy-Catalyst and focused on reducing of health risks from automobile and industrial exhaust. His catalytic muffler, patented in 1962, greatly reduced the amount of carbon dioxide and unburned hydrocarbons. Today, the device is standard on all American cars.

In the 1950s, Houdry began research to develop catalytic converters for warehouse fork lifts before embarking on research to develop catalytic converters for gas engines in cars. 

It wasn’t until stricter emissions control regulations forced the removal of tatraethyllead from most gasoline (which rendered catalytic converters useless) that further developments were made by a series of other engineers in the early 1970s [source]. 

Read more about Federal EPA compliance on catalytic converters

Catalytic Converter Construction

All catalytic converters consist of four main components: 

Shell /Casing

The shell/casing is the outer metal portion of a catalytic converter. This serves as the housing for the "guts" of converters.

Catalyst Support (aka: Catalyst Substrate)

The catalyst substrate for cars consists of a ceramic monolith core with a honeycomb structure. In instances where high heat resistance is required, metallic foil monoliths comprised of Kanthal are used. Catalytic converters may also use ceramic beads in their structuring, though the honeycomb structure is what is most commonly found on vehicles today.


The washcoat is a carrier for catalytic materials. It is used to disperse catalytic materials over a large surface area. The materials used in the washcoat are purposely selected to form a rough, irregular surface – which increases the surface area. The increased surface area then maximizes the catalytic activity available to react with the engine exhaust. Aluminum oxide, titanium dioxide, silicon dioxide, or a mixture of silica and alumina may be used to make up the catalytic materials.

Precious Metals

Of the precious metals used in catalytic converters, the most common one is platinum. Palladium and rhodium are the two other types of precious metals used. Of these, rhodium is used as a reduction catalyst, palladium is used as an oxidation catalyst, and platinum is used for both reduction and oxidation. 

Types of Catalytic Converters 

Two-Way (aka: “oxidation”) Catalytic Converters

Two-way catalytic converters are most commonly associated with diesel engines and are used to reduce hydrocarbon and carbon monoxide emissions. They are not nearly as popular today as three-way catalytic converters due to their inability to control oxides of nitrogen. Specifically, two-way catalytic converters:

  1. Oxidize carbon monoxide into carbon dioxide
  2. Oxidize hydrocarbons into carbon dioxide and water 

Three-Way Catalytic Converters (TWC)

Most vehicles today are equipped with a three-way catalytic converter. Three-way catalytic converters get their name from the three regulated emissions that it helps to reduce. Specifically, the three-way catalytic converter: 

  1. Reduces nitrogen oxides to nitrogen and oxygen
  2. Oxidizes carbon monoxide into carbon dioxide
  3. Oxidizes unburned hydrocarbons into carbon dioxide and water

For additional information about aftermarket catalytic converters, or to ask a question about any of our inventory items, contact us today.