Catalytic converter
A catalytic converter is a vehicle emissions control device that converts
toxic pollutants in exhaust gas to less toxic pollutants, by catalyzing a redox reaction. Used
in internal combustion engines fuelled by either petrol (gasoline) or diesel, the catalytic
converter was invented by Eugene Houdry, a French mechanical engineer.
The first widespread introduction of catalytic converters was in the United States to comply with
the U.S. Environmental Protection Agency's stricter regulation of exhaust emissions. These were
“two-way” converters that were later replaced by “three-way” converters; however, two-way
converters are still used for lean burn engines.
Although catalytic converters are most commonly applied to exhaust systems in automobiles,
they are also used on electrical generators, forklifts, mining
equipment, trucks, buses, locomotives, motorcycles, airplanes. They are also used on some wood
stoves to control emissions.
Construction
The catalytic converter's construction is as follows:
1. The catalyst support or substrate. The core is usually a ceramicmonolith with a
honeycomb structure.
2. The washcoat- It’s a carrier for the catalytic materials and is used to disperse the materials
over a large surface area. Aluminum oxide, titanium dioxide, silicon dioxide, or a mixture
of silica andalumina can be used.
3. The catalyst itself, most often a mix of precious metals. Platinum is the most active
catalyst and is widely used. Palladium and rhodium are two other precious metals used.
Cerium, iron, manganese and nickel are also used.
Types
Two-way
A two-way (or "oxidation") catalytic converter has two simultaneous tasks: