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What Is a Converter?
A catalytic converter (colloquially, "Cat" or "Catcon") is a device used to reduce the toxicity of emissions from an internal combustion engine. First widely introduced on series-production automobiles in the U.S. market for the 1975 model year to comply with tightening EPA regulations on auto exhaust, catalytic convertors are still most commonly used in motor vehicle exhaust systems. Catalytic converters are also used on generator sets, forklifts, mining equipment, trucks, buses, trains, and other engine-equipped mechines. A catalytic converter provides an environment for a chemical reaction wherein toxic combustion by-products are converted to less-toxic substances.

1) History 

The catalytic converter was invented by Eugene Houdry, a French mechanical engineer who lived in the United States. About 1950, when the results of early studies of smog in Los Angeles were published, Houdry became concerned about the role of automobile exhaust in air pollution and founded a special company,Oxy-Catalyst, to develop catalytic converter for gasoline engines - an idea ahead of its time for which he attained a patent (US2742437). But until I lead could be eliminated form gasoline (lead was introduced in 1920's to raise octane levels), it poisoned any catalystic. 
The catalytic converter was later on further developed by John J. Mooney and Carl D. Keith at the Engelhard Corporation, creating the first production catalytic converter in 1973. 

2) Construction 

The catalytic converter consists of several components: 
1. The core, or substrate. The core is often a ceramic honeycomb in modern catalytic converter, but stainless steel foil honeycombs are used, too. The honey-comb surface increases the amount of surface area available to support the catalyst, and therefore is often called a "catalyst support". the ceramic substrate was invented by Rodney Bagley, Irwin Lachman and Ronald Lewis at Corning Glass, for which they were inducted into the National Inventors Hall of Fame in 2002.
2. The washcoat. A washcoat is used to make converters more efficient, often as a mixture of silica and alumina. The washcoat, when added to the core, forms a rough, irregular surface, which has a far greater surface area than the flat core surfaces do, which then gives the converter core a larger surface area, and therefore more places for active precious metal sites. The catalyst is added to the washcoat (in susoension) before being applied to the core.
3. The catalyst itself is most often a precious metal. Platinum is the most active catalyst and is widly used. It is not suitable for all application, however, because of unwanted addition reactions and/or cost. Palladium and rhodium are two other precious metals used. Platinum and rhodium are used as a reduction catalyst, while platinum and palladium and rhodium are used as an oxidization catalyst. Cerium iron, manganese and nikel are also used, although each has its own limitations. Nickel is not legal for use in the European Union (due to reaction with carbon monoxide). While copper can be used, its use is illegal in North America due to the formation of dioxin.

3) Types

                       A two-way catalytic converter has two simultaneous Taskes:
           1. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 --> 2CO2

          2. Oxidation of unburnt hydrocarbons (Unburnt and partially -burnt fuel) to carbon dioxide and water:   CxH2x + 2+2+2xO2 -->xCO2 + 2xH2O (a combustion reaction)

The type of catalytic converter is widely used on diesel engines to reduce hydrocarbon and carbon monoxide emissions. They were also used on spark ignition (Gasoline) engines in USA market automobiles through 1981. when the two-way converter's inability to control NOx led to its supersession by three-way converters.
         Three -Way
                           Since 1981, three-way catalytic converters have been used in vehicle emission control systems in North America and many other countries on roadgoing vehicles. A three-way catalytic converter has three simultaneous tasks:
         1. Reduction of nitrogen oxides to nitrogen and oxygn: 2NOx --> xO2 + N2
         2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 --> 2CO2
         3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2xO2-->xCO2+2xH2O
These three reactions occur most efficiently when the catalytic converter receives exhaust from an engine running slightly above the stoichiometric point. This is between 14.6 and 14.8 parts air to 1 part fuel, by weight, for gasoline. The raito for LPG, naural gas and ethanol fuels is slightly different, requiring modified fuel system setting when using those fuels. Genrally, engines fitted with 3-way catalytic converter are equipped with a computerised closed-loop feedback fuel injection system employing one or more oxygen sensors, though early in the deployment of 3-way converter, carburetors equipped for feedback mixture control were used. While a 3-way catalyst can be in an open-loop system, Nox reduction efficiency is low. Within a narrow fuel/ai ratio band surrounding stoichiometry, conversion of all three pollutants is nealy complete. However, outside of that band, conversion efficiency falls off very rapidly. When there is more oxygen than required, then the system is said to be running lean, and the system is in oxidizing condition. In that case, the converter's two oxidizing reactions (oxidation of CO and hydrocarbons) are favoured, at the expense of the reducing reaction. When there is excessive fuel, then the engine is running rich. The reductionof NOx is favoured, at the expense of CO and HC Oxidation.
**Detail Came from Wikipedia - The Free Encyclopedia.**


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