What Is a Catalytic Converter?
A catalytic converter, often called a “cat,” is an emissions-control device installed in a vehicle’s exhaust system. Its job is to reduce harmful pollutants created during combustion before exhaust gases leave the tailpipe.
Most modern gasoline-powered vehicles use one or more catalytic converters as part of their factory exhaust system.
What Is the Purpose of a Catalytic Converter?
The purpose of a catalytic converter is to reduce harmful exhaust emissions produced by an internal-combustion engine.
In gasoline vehicles, a catalytic converter helps reduce carbon monoxide, unburned hydrocarbons, and nitrogen oxides. These pollutants contribute to poor air quality and smog.
What Is Inside a Catalytic Converter?
Inside a catalytic converter is a honeycomb-shaped substrate with thousands of small passages for exhaust gases to flow through. The substrate is commonly made from ceramic or metal.
That honeycomb is coated with catalyst materials that may include platinum, palladium, and rhodium. These metals create a large reactive surface area that helps the exhaust gases chemically react as they pass through the converter.
How Do Catalytic Converters Work?
As hot exhaust gases flow through the honeycomb, the catalyst coating speeds up chemical reactions that make certain pollutants less harmful.
In a gasoline three-way catalytic converter:
- Carbon monoxide is converted into carbon dioxide.
- Unburned hydrocarbons are converted into carbon dioxide and water vapor.
- Nitrogen oxides are reduced into nitrogen and oxygen.
The converter does not trap or store exhaust pollutants. It changes them through chemical reactions.
For the converter to work efficiently, the engine must maintain a near-correct air-fuel ratio. Oxygen sensors send information to the engine computer, which adjusts fuel delivery to help the catalytic converter operate properly.
Do Diesel Vehicles Have Catalytic Converters?
Diesel vehicles use catalyst-based exhaust aftertreatment systems, but they are different from the three-way catalytic converters commonly used on gasoline vehicles.
A diesel exhaust system may include a diesel oxidation catalyst, diesel particulate filter, and selective catalytic reduction system. Together, these components reduce hydrocarbons, carbon monoxide, soot, and nitrogen oxide emissions.
When Did Catalytic Converters Become Common?
Early catalytic-converter development began in the 1950s. Catalytic converters became common on U.S. vehicles beginning with 1975-model cars as manufacturers worked to meet stricter federal emissions requirements.
Modern three-way catalytic converters became more effective as oxygen sensors and computer-controlled fuel injection became common in the early 1980s.
What Does CARB-Compliant Mean?
CARB stands for the California Air Resources Board. CARB has stricter emissions requirements than federal EPA standards for many aftermarket emissions-control parts.
A CARB-compliant catalytic converter is approved for specific vehicle applications and carries a CARB Executive Order number. Before buying a replacement converter, verify the vehicle’s year, engine size, emissions label, and the state where the vehicle is registered.
Why Are Catalytic Converters Stolen?
Catalytic converters can be targeted for theft because they contain small amounts of valuable precious metals, including platinum, palladium, and rhodium.
Vehicles with easily accessible exhaust systems may be more vulnerable. Common prevention options include parking in well-lit areas, using security cameras, installing a converter shield or anti-theft device, and engraving the vehicle identification number onto the converter.
