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Catalytic Converter

Catalytic Converter


The catalytic converter in an automobile is an expanded section of exhaust pipe occurring upstream of the muffler in which pollutants generated in the engine are converted to normal atmospheric gases. It is an essential element in the emissions control system of modern automobiles. This technology was introduced in the United States in the late 1970s and became legally required by the early 1980s because of more stringent exhaust emission control standards. Early catalyst systems, as applied to vehicles with carburetors, attempted to oxidize carbon monoxide (CO) and unburned hydrocarbons (HC) to carbon dioxide (CO2) and water vapor, using air added by means of an air pump or rapidly actuating valve system. Although constructed from a high-surface-area alumina substrate with a noble metal (usually platinum) on the surface, their effectiveness was limited by extreme conditions of service. These problems include high temperatures (greater than 1,000°C) exacerbated by a large and variable "engine-out" pollutant load and constant vibration from roadway and engine sources.

The replacement of carburetors with computer-controlled, port fuel injection and precise air/fuel ratio control based on exhaust oxygen sensing has allowed catalytic converters to operate with close to 100 percent efficiency and better longevity, often exceeding 100,000 miles. The addition of a ceria wash coat in the form of a thin layer of porous cerium oxide and rhodium metal in conjunction with the platinum now allow for both good longevity and "three-way" operation. Not only are the small amounts of residual CO and HC oxidized, but the nitric oxide pollution emissions are simultaneously reduced to nitrogen (and some nitrous oxide, a potent atmospheric greenhouse gas, but otherwise nonpoisonous). The tetraethyl lead present in gasoline as an octane booster in the 1970s was removed not because of its effects on human health, but because it rapidly poisoned catalysts. Its removal, although coincidental, has had enormous benefits for human and environmental health. Current pressure to reduce the sulfur content of fuel arises, in part, from evidence that sulfur has a similar, but much smaller effect on catalyst longevity and effectiveness.

see also Greenhouse Gases; Lead; Ozone; Vehicular Pollution.

Internet Resource

Kovark, William, and Hermes, Matthew E. "The Role of the Catalytic Converter in Smog Reduction." Available from http://chemcases.com/converter.

Donald Stedman

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"Catalytic Converter." Pollution A to Z. . Encyclopedia.com. 27 Jul. 2017 <http://www.encyclopedia.com>.

"Catalytic Converter." Pollution A to Z. . Encyclopedia.com. (July 27, 2017). http://www.encyclopedia.com/environment/educational-magazines/catalytic-converter

"Catalytic Converter." Pollution A to Z. . Retrieved July 27, 2017 from Encyclopedia.com: http://www.encyclopedia.com/environment/educational-magazines/catalytic-converter

catalytic converter

catalytic converter Anti-pollution device used in internal combustion engines. It consists of a bed of catalytic agents through which flow the gaseous exhaust of fuel combustion. Converters located in mufflers reduce harmful unburned hydrocarbons and carbon monoxide. These converters are adversely affected by tetraethyl lead found in some gasolines.

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"catalytic converter." World Encyclopedia. . Encyclopedia.com. 27 Jul. 2017 <http://www.encyclopedia.com>.

"catalytic converter." World Encyclopedia. . Encyclopedia.com. (July 27, 2017). http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/catalytic-converter-0

"catalytic converter." World Encyclopedia. . Retrieved July 27, 2017 from Encyclopedia.com: http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/catalytic-converter-0

catalytic converter

cat·a·lyt·ic con·vert·er • n. a device incorporated in the exhaust system of a motor vehicle, containing a catalyst for converting pollutant gases into less harmful ones.

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"catalytic converter." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 27 Jul. 2017 <http://www.encyclopedia.com>.

"catalytic converter." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (July 27, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/catalytic-converter

"catalytic converter." The Oxford Pocket Dictionary of Current English. . Retrieved July 27, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/catalytic-converter

catalytic converter

catalytic converter: see internal-combustion engine.

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"catalytic converter." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 27 Jul. 2017 <http://www.encyclopedia.com>.

"catalytic converter." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (July 27, 2017). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/catalytic-converter

"catalytic converter." The Columbia Encyclopedia, 6th ed.. . Retrieved July 27, 2017 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/catalytic-converter