What are Catalytic Converters?

Essay by webcrCollege, UndergraduateA+, September 2002

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Catalytic Converters

What is a catalytic converter and how does it do what they do.

The term Catalytic Converter covers the stainless steel box mounted in the exhaust system. Inside the cover is the catalyst, a ceramic or metallic base with an active coating incorporating alumina, ceria and other oxides and combinations of the precious metals platinum, palladium and rhodium. The base can be protected from vibration and shock by a resilient ceramic or metallic 'mat'

The main by-products of combustion are:

Nitrogen gas (N2): Our atmosphere is 78 percent nitrogen gas, and most of this passes right through the car engine.

Carbon Dioxide (CO2): A harmless, odorless gas composed of carbon and oxygen. It is also a greenhouse gas that contributes to global warming.

Water vapor (H2O): Another by-product of combustion. The hydrogen in the fuel bonds with the oxygen in the air.

These three emissions are mostly harmless, although carbon dioxide emissions are believed to contribute to global warming.

However since the combustion process is never perfect, other more harmful emissions are produced in the process.

Carbon monoxide (CO): A colorless, odorless gas. It is poisonous and extremely dangerous in confined areas, building up slowly to toxic levels without warning if adequate ventilation is not available.

Hydrocarbons or volatile organic compounds (VOCs): Any chemical compound made up of hydrogen and carbon.

Oxides of nitrogen (NOx): Chemical compounds of nitrogen, they combine with hydrocarbons to produce smog.

These are the three main regulated emissions, and also the ones that catalytic converters are designed to reduce.

Catalytic converters can either be an oxidation or three-way type. Oxidation catalysts convert carbon monoxide (CO) and hydrocarbons (HC) to carbon dioxide (CO2) and water, but have little effect on nitrogen oxides (NOx) and particulate matter. Three-way catalysts operate...