Catalytic Canverter

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Catalytic converterFrom Wikipedia, the free encyclopedia

Catalytic converter on a 1996 Dodge Ram Van 

 A catalytic converter  is a vehicle emissions control device which converts toxic byproducts of  combustion in

the exhaust of an internal combustion engine to less toxic substances by way of  catalysed chemical reactions.

The specific reactions vary with the type of catalyst installed. Most present-day vehicles that run

on gasoline are fitted with a ―three way‖ converter, so named because it converts the three main pollutants in

automobile exhaust. The three main pollutants are carbon monoxide, unburned hydrocarbon and oxides of

nitrogen. The first two are converted to two new molecules. This happens through an oxidizing reaction which

converts carbon monoxide (CO) and unburned hydrocarbons (HC) to CO2 and water vapor. The last pollutant is

converted to three new molecules. This happens through a reduction reaction which converts oxides of

nitrogen (NOx) to CO2, nitrogen (N2) and water  (H2O).[1] 

The first widespread introduction of catalytic converters was in the United States market, where 1975 model

year  gasoline-powered automobiles were so equipped to comply with tightening U.S. Environmental Protection

 Agency regulations on automobile exhaust emissions.[2][3][4][5] These were ―two-way‖ converters which

combined carbon monoxide (CO) and unburned hydrocarbons (HC) to producecarbon dioxide (CO2)

and water  (H2O). Two-way catalytic converters of this type are now considered obsolete, having been

supplanted except on lean burn engines by ―three-way‖ converters which also reduce oxides of

nitrogen (NOx).[2] 

Catalytic converters are still most commonly used in exhaust systems in automobiles, but are also used

on generator  sets, forklifts, mining equipment, trucks, buses, locomotives, motorcycles, airplanes and other

engine-fitted devices. They are also used on some wood stoves to control emissions.[6] This is usually in

response to government regulation, either through direct environmental regulation or through health and safety

regulations.

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Catalytic oxidization is also used, but for the purpose of safe, flameless generation of heat rather than

destruction of pollutants, in catalytic heaters. 

Contents

[hide] 

1 History 

2 Construction 

3 Types 

o  3.1 Two-way 

o  3.2 Three-way 

  3.2.1 Unwanted reactions 

o  3.3 Diesel engines 

o  3.4 Lean burn spark-ignition engines 

4 Installation 

5 Damage 

6 Regulations 

7 Negative aspects 

o  7.1 Warm-up period 

o  7.2 Environmental impact 

8 Theft 

9 Diagnostics 

10 See also 

11 References 

12 Further reading 

13 External links 

[edit]History

 A modern catalytic converter used for Yamaha RX 100 modification

The catalytic converter was invented by Eugene Houdry, a French mechanical engineer and expert in catalytic

oil refining[7] who lived in the U.S. around 1950. When the results of early studies of  smog in Los Angeles were

published, Houdry became concerned about the role of smoke stack exhaust and automobile exhaust in air

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pollution and founded a company, Oxy-Catalyst. Houdry first developed catalytic converters for smoke stacks

called cats for short. Then he developed catalytic converters for warehouse fork lifts that used low grade non-

leaded gasoline.[8] Then in the mid 1950s he began research to develop catalytic converters for  gasoline

engines used on cars. He was awarded United States Patent 2742437 for his work.[9] 

Widespread adoption of catalytic converters didn't occur until more stringent emission control regulations

forced the removal of the anti-knock agent, tetraethyllead, from most gasoline, because lead was a 'catalyst

poison' and would inactivate the converter by forming a coating on the catalyst's surface, effectively disabling

it.[10] 

Catalytic converters were further developed by a series of engineers including John J. Mooney and Carl D.

Keith at the Engelhard Corporation,[11] creating the first production catalytic converter in 1973.[12] 

Dr. William C. Pfefferle developed a catalytic combustor for  gas turbines in the early 1970s, allowing

combustion without significant formation of nitrogen oxides and carbon monoxide.

[13][14]

[edit]Construction

Metal-core converter

Ceramic-core converter

The catalytic converter consists of several components:

1. The catalyst core, or  substrate. For automotive catalytic converters, the core is usually

a ceramic monolith with a honeycomb structure. Metallic foil monoliths made of FeCrAl are used in

some applications. This is partially a cost issue. Ceramic cores are inexpensive when manufactured in

large quantities. Metallic cores are less expensive to build in small production runs, and are used in

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sportscars where low back pressure and reliability under continuous high load is required. Either

material is designed to provide a high surface area to support the catalyst washcoat, and therefore is

often called a "catalyst support".[citation needed ] The cordieriteceramic substrate used in most catalytic

converters 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.[citation needed ] 

2. The washcoat. A washcoat is a carrier for the catalytic materials and is used to disperse the materials

over a high surface area. Aluminum oxide, titanium dioxide, silicon dioxide, or a mixture

of  silica and alumina can be used. The catalytic materials are suspended in the washcoat prior to

applying to the core. Washcoat materials are selected to form a rough, irregular surface, which greatly

increases the surface area compared to the smooth surface of the bare substrate. This in turn

maximizes the catalytically active surface available to react with the engine exhaust. The coat must

retain its surface area and prevent sintering of the catalytic metal particles even at high temperatures

(1000 °C).

[15]

 3. The catalyst itself is most often a precious metal. Platinum is the most active catalyst and is widely

used, but is not suitable for all applications because of unwanted additional reactions (see below) and

high cost. Palladium and rhodium are two other precious metals used. Rhodium is used as

a reduction catalyst, palladium is used as an oxidation catalyst, and platinum is used both for

reduction and oxidation. Cerium, iron, manganese and nickel are also used, although each has its

own limitations. Nickel is not legal for use in the European Union (because of its reaction with carbon

monoxide into nickel tetracarbonyl). Copper  can be used everywhere except North America,[clarification

needed ]where its use is illegal because of the formation of  dioxin. 

[edit]Types

[edit]Two-way

 A two-way (or "oxidation") catalytic converter has two simultaneous tasks:

1. Oxidation of  carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2 

2. Oxidation of  hydrocarbons (unburnt and partially burnt fuel) to carbon dioxide and water : CxH2x+2 +

[(3x+1)/2] O2 → xCO2 + (x+1) H2O (a combustion reaction)

This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon and carbon monoxideemissions. They were also used on gasoline engines in American- and Canadian-market automobiles until

1981. Because of their inability to control oxides of nitrogen, they were superseded by three-way converters.

[edit]Three-way

Since 1981, "three-way" (oxidation-reduction) catalytic converters have been used in vehicle emission control

systems in the United States and Canada; many other countries have also adopted stringent vehicle emission

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regulations that in effect require three-way converters on gasoline-powered vehicles. The reduction and

oxidation catalysts are typically contained in a common housing, however in some instances they may be

housed separately. A three-way catalytic converter has three simultaneous tasks:

1. Reduction of nitrogen oxides to nitrogen and oxygen: 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+2 + [(3x+1)/2]O2 → xCO2 +

(x+1)H2O.

These three reactions occur most efficiently when the catalytic converter receives exhaust from an engine

running slightly above the stoichiometric point. This point is between 14.6 and 14.8 parts air to 1 part fuel, by

weight, for gasoline. The ratio for   Autogas (or  liquefied petroleum gas (LPG)), natural gas and ethanol fuels is

each slightly different, requiring modified fuel system settings when using those fuels. In general, engines fitted

with 3-way catalytic converters are equipped with a computerized closed-loop feedback fuel injection system

using one or more oxygen sensors, though early in the deployment of three-way

converters, carburetors equipped for feedback mixture control were used.

Three-way catalysts are effective when the engine is operated within a narrow band of air-fuel ratios near

stoichiometry, such that the exhaust gas oscillates between rich (excess fuel) and lean (excess oxygen)

conditions. However, conversion efficiency falls very rapidly when the engine is operated outside of that band

of air-fuel ratios. Under lean engine operation, there is excess oxygen and the reduction of NOx is not favored.

Under rich conditions, the excess fuel consumes all of the available oxygen prior to the catalyst, thus only

stored oxygen is available for the oxidation function. Closed-loop control systems are necessary because of theconflicting requirements for effective NOx reduction and HC oxidation. The control system must prevent the

NOx reduction catalyst from becoming fully oxidized, yet replenish the oxygen storage material to maintain its

function as an oxidation catalyst.

Three-way catalytic converters can store oxygen from the exhaust gas stream, usually when the air-fuel

ratio goes lean.[16] When insufficient oxygen is available from the exhaust stream, the stored oxygen is released

and consumed (see cerium(IV) oxide ). A lack of sufficient oxygen occurs either when oxygen derived from

NOx reduction is unavailable or when certain maneuvers such as hard acceleration enrich the mixture beyond

the ability of the converter to supply oxygen.

[edit]Unwanted reactions

Unwanted reactions can occur in the three-way catalyst, such as the formation of odoriferous hydrogen

sulfide and ammonia. Formation of each can be limited by modifications to the washcoat and precious metals

used. It is difficult to eliminate these byproducts entirely. Sulfur-free or low-sulfur fuels eliminate or reduce

hydrogen sulfide.

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For example, when control of hydrogen-sulfide emissions is desired, nickel or  manganese is added to the

washcoat. Both substances act to block the absorption of  sulfur  by the washcoat. Hydrogen sulfide is formed

when the washcoat has absorbed sulfur during a low-temperature part of the operating cycle, which is then

released during the high-temperature part of the cycle and the sulfur combines with HC.

[edit]Diesel engines

For compression-ignition (i.e., diesel engines), the most commonly used catalytic converter is the Diesel

Oxidation Catalyst (DOC). This catalyst uses O2 (oxygen) in the exhaust gas stream to convert CO (carbon

monoxide) to CO2 (carbon dioxide) and HC (hydrocarbons) to H2O (water) and CO2. These converters often

operate at 90 percent efficiency, virtually eliminating diesel odor and helping to reduce

visible particulates (soot). These catalysts are not active for NOx reduction because any reductant present

would react first with the high concentration of O2 in diesel exhaust gas.

Reduction in NOx emissions from compression-ignition engines has previously been addressed by the addition

of exhaust gas to incoming air charge, known as exhaust gas recirculation (EGR). In 2010, most light-duty

diesel manufacturers in the U.S. added catalytic systems to their vehicles to meet new federal emissions

requirements. There are two techniques that have been developed for the catalytic reduction of NOx emissions

under lean exhaust conditions - selective catalytic reduction (SCR) and the lean NOx trap or  NOx adsorber . 

Instead of precious metal-containing NOx adsorbers, most manufacturers selected base-metal SCR systems

that use a reagent such as ammonia to reduce the NOx into nitrogen. Ammonia is supplied to the catalyst

system by the injection of  urea into the exhaust, which then undergoes thermal decomposition and hydrolysis

into ammonia. One trademark product of urea solution, also referred to as Diesel Emission Fluid (DEF),

is  AdBlue. 

Diesel exhaust contains relatively high levels of particulate matter (soot), consisting in large part of

elemental carbon. Catalytic converters cannot clean up elemental carbon, though they do remove up to 90

percent of the soluble organic fraction [citation needed ], so particulates are cleaned up by a soot trap or  diesel

particulate filter  (DPF). Historically, a DPF consists of a Cordierite or Silicon Carbide substrate with a geometry

that forces the exhaust flow through the substrate walls, leaving behind trapped soot particles. Contemporary

DPFs can be manufactured from a variety of rare metals that provide superior performance (at a greater

expense).[17]  As the amount of soot trapped on the DPF increases, so does the back pressure in the exhaust

system. Periodic regenerations (high temperature excursions) are required to initiate combustion of the trapped

soot and thereby reducing the exhaust back pressure. The amount of soot loaded on the DPF prior to

regeneration may also be limited to prevent extreme exotherms from damaging the trap during regeneration. In

the U.S., all on-road light, medium and heavy-duty vehicles powered by diesel and built after 1 January 2007,

must meet diesel particulate emission limits that means they effectively have to be equipped with a 2-Way

catalytic converter and a diesel particulate filter. Note that this applies only to the diesel engine used in the

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vehicle. As long as the engine was manufactured before 1 January 2007, the vehicle is not required to have the

DPF system. This led to an inventory runup by engine manufacturers in late 2006 so they could continue selling

pre-DPF vehicles well into 2007.[18] 

[edit]Lean burn spark-ignition engines

For  lean burn spark-ignition engines, an oxidation catalyst is used in the same manner as in a diesel engine.

Emissions from Lean Burn Spark Ignition Engines are very similar to emissions from a Diesel Compression

Ignition engine.

[edit]Installation

Many vehicles have a close-coupled catalysts located near the engine's exhaust manifold. This unit heats up

quickly due to its proximity to the engine, and reduces cold-engine emissions by burning off hydrocarbons from

the extra-rich mixture used to start a cold engine. When catalytic converters were first introduced, most

vehicles used carburetors that provided a relatively rich air-fuel ratio. Oxygen (O2) levels in the exhaust stream

were generally insufficient for the catalytic reaction to occur efficiently, so most installations includedsecondary

air injection which injected air into the exhaust stream to increase the available oxygen and allow the catalyst to

function. Some three-way catalytic converter systems have air injection systems with the air injected between

the first (NOx reduction) and second (HC and CO oxidation) stages of the converter. As in the two-way

converters, this injected air provides oxygen for the oxidation reactions. An upstream air injection point, ahead

of the catalytic converter, is also sometimes present to provide oxygen during engine warmup, which causes

unburned fuel to ignite in the exhaust tract before reaching the catalytic converter. This reduces the engine

runtime needed for the catalytic converter to reach its "light-off" or operating temperature.

Many newer [vague] vehicles do not have air injection systems. Instead, they provide a constantly varying air-fuel

mixture that quickly and continually cycles between lean and rich exhaust. Oxygen sensors are used to monitor

the exhaust oxygen content before and after the catalytic converter and this information is used by

the Electronic control unit to adjust the fuel injection so as to prevent the first (NOx reduction) catalyst from

becoming oxygen-loaded while ensuring the second (HC and CO oxidization) catalyst is sufficiently oxygen-

saturated.

[edit]Damage

Catalyst poisoning occurs when the catalytic converter is exposed to exhaust containing substances that coat

the working surfaces, encapsulating the catalyst so that it cannot contact and treat the exhaust. The most-

notable contaminant is lead, so vehicles equipped with catalytic converters can be run only on unleaded fuels.

Other common catalyst poisons include fuel sulfur , manganese (originating primarily from the gasoline

additive MMT), and silicone, which can enter the exhaust stream if the engine has a leak that

allows coolant into the combustion chamber. Phosphorus is another catalyst contaminant. Although

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phosphorus is no longer used in gasoline, it (and zinc, another low-level catalyst contaminant) was until

recently widely used in engine oil antiwear additives such as zinc dithiophosphate (ZDDP). Beginning in 2006,

a rapid phaseout of ZDDP in engine oils began.[citation needed ] 

Depending on the contaminant, catalyst poisoning can sometimes be reversed by running the engine under a

very heavy load for an extended period of time. The increased exhaust temperature can sometimes liquefy or

sublimate the contaminant, removing it from the catalytic surface. However, removal of lead deposits in this

manner is usually not possible because of lead's high boiling point.

 Any condition that causes abnormally high levels of unburned hydrocarbons—raw or partially burnt fuel—to

reach the converter will tend to significantly elevate its temperature, bringing the risk of a meltdown of the

substrate and resultant catalytic deactivation and severe exhaust restriction. Vehicles equipped with OBD-

II diagnostic systems are designed to alert the driver to a misfire condition by means of flashing  the "check

engine" light on the dashboard.

[edit]Regulations

This section needs additional citations for verification. Please help improve this article  by adding citations to

reliable sources. Unsourced material may be challenged and removed. (January 2012) 

Emissions regulations vary considerably from jurisdiction to jurisdiction. Most automobile spark-ignition engines

in North America have been fitted with catalytic converters since 1975,[2][3][4][5] and the technology used in non-

automotive applications is generally based on automotive technology.

Regulations for diesel engines are similarly varied, with some jurisdictions focusing on NOx (nitric oxide and

nitrogen dioxide) emissions and others focusing on particulate (soot) emissions. This regulatory diversity is

challenging for manufacturers of engines, as it may not be economical to design an engine to meet two sets of

regulations.

Regulations of fuel quality vary across jurisdictions. In North America, Europe, Japan and Hong Kong, gasoline

and diesel fuel are highly regulated, and compressed natural gas and LPG (Autogas) are being reviewed for

regulation. In most of Asia and Africa, the regulations are often lax: in some places sulfur  content of the fuel

can reach 20,000 parts per million (2%). Any sulfur in the fuel can be oxidized to SO2 (sulfur dioxide) or even

SO3 (sulfur trioxide) in the combustion chamber . If sulfur passes over a catalyst, it may be further oxidized in

the catalyst, i.e., SO2 may be further oxidized to SO3. Sulfur oxides are precursors to sulfuric acid, a major

component of  acid rain. While it is possible to add substances such asvanadium to the catalyst washcoat to

combat sulfur-oxide formation, such addition will reduce the effectiveness of the catalyst. The most effective

solution is to further refine fuel at the refinery to produce ultra-low sulfur diesel. Regulations in Japan, Europe

and North America tightly restrict the amount of sulfur permitted in motor fuels. However, the expense of

producing such clean fuel may make it impractical for use in developing countries. As a result, cities in these

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countries with high levels of vehicular traffic suffer from acid rain, which damages stone and woodwork of

buildings, poisons humans and other animals, and damages local ecosystems. 

[edit]Negative aspects

This article's Criticism or Controversy section may compromise the article's neutral point of view of the

subject. Pleaseintegrate the section's contents into the article as a whole, or rewrite the material. (July 2012) 

Some early converter designs greatly restricted the flow of exhaust, which negatively affected vehicle

performance, driveability, and fuel economy.[19] Because they were used with carburetors incapable of precise

fuel-air mixture control, they could overheat and set fire to flammable materials under the car .[20] While

removing a modern catalytic converter in new condition will net only a very small increase vehicle performance,

the removal of a 6 year old modern catalyst resulted in a 3.4% increase in horsepower [21] To many performance

enthusiasts, this modest increase in power for very little cost encourages the removal or "gutting" of the

catalytic converter .[19][22] In such cases, the converter may be replaced by a welded-in section of ordinary pipe

or a flanged "test pipe" ostensibly meant to check if the converter is clogged by comparing how the engine runs

with versus without the converter, which facilitates reinstallation of the converter in order to pass an emission

test.[21] In many jurisdictions, it is illegal to remove or disable a catalytic converter for any reason other than its

direct and immediate replacement. In the United States, for example, it is a violation of Section 203(a)(3)(A) of

the 1990 Clean Air Act for a vehicle repair shop to remove a converter from a vehicle, or cause a converter to

be removed from a vehicle, except in order to replace it with another converter.,[23] and Section 203(a)(3)(B)

makes it illegal for any person to sell or to install any part that would bypass, defeat, or render inoperative any

emission control system, device, or design element. Vehicles without functioning catalytic converters generally

fail emission inspections. The automotive aftermarket supplies high-flow converters for vehicles with upgraded

engines, or whose owners prefer an exhaust system with larger-than-stock capacity.[24] 

[edit]Warm-up period

Vehicles emit most of their pollution during the first five minutes of engine operation before the catalytic

converter has warmed up sufficiently to be effective.[25] 

In 1999, BMW introduced an electrically heated catalyst, which they called "E-CAT", in

their  750iL sedan. Heating coils inside the catalytic converter assemblies are electrified just after engine start,

bringing the catalyst up to operating temperature very quickly to qualify the vehicle for  low emission

vehicle (LEV) designation.[26] 

[edit]Environmental impact

Catalytic converters have proven to be reliable and effective in reducing noxious tailpipe emissions. However,

they also have some shortcomings and adverse environmental impacts in production:

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   Although catalytic converters are effective at removing hydrocarbons and other harmful emissions, they do

not reduce the emission of carbon dioxide (CO2) produced when fossil fuels are burnt.[27] 

  Carbon dioxide produced from fossil fuels is one of the greenhouse gases indicated by

the Intergovernmental Panel on Climate Change (IPCC) to be the leading cause of  global warming.[28]

  The U.S. Environmental Protection Agency (EPA) has stated automobile emissions are a significant and

growing cause of global warming, because of their release of  nitrous oxide(N2O), a greenhouse gas over

three hundred times more potent than carbon dioxide. The EPA states that motor vehicles contribute

approximately 8.2% of anthropogenic nitrous oxide emissions in 2008, from a high of 17.77% in 1998.

  Nitrous oxide makes up 7.2% of greenhouse gases.[29] 

   An engine equipped with a three-way catalyst must run at the stoichiometric point, which means more fuelis consumed than in a lean-burn engine. This, in turn, means relatively more CO2 emissions from the

vehicle. Nevertheless, catalyst-equipped engines produce cleaner exhaust than lean-burn engines.

  Catalytic converter production requires palladium or  platinum; part of the world supply of these precious

metals is produced near  Norilsk, Russia, where the industry (among others) has caused Norilsk to be

added to Time magazine's list of most-polluted places.[30] 

[edit]Theft

Because of the external location and the use of valuable precious metalsincluding platinum, palladium, rhodium, and gold, converters are a target for thieves. The problem is especially

common among late-model trucks and SUVs, because of their high ground clearance and easily removed bolt-

on catalytic converters. Welded-in converters are also at risk of theft, as they can be easily removed with a

reciprocating saw.[31][32][33] Theft removal of the converter can often inadvertently damage the car's wiring or fuel

line resulting in dangerous consequences. Rises in metal costs in the U.S. during recent years have led to a

large increase in theft incidents of the converter ,[34] which can then cost well over $1,000 to replace.[35] 

[edit]Diagnostics

Various jurisdictions now legislate on-board diagnostics to monitor the function and condition of the emissions-

control system, including the catalytic converter. On-board diagnostic systems take several forms.

Temperature sensors are used for two purposes. The first is as a warning system, typically on two-way catalytic

converters such as are still sometimes used on LPG forklifts. The function of the sensor is to warn of catalytic

converter temperature above the safe limit of 750 °C (1,380 °F). More-recent catalytic-converter designs are

not as susceptible to temperature damage and can withstand sustained temperatures of 900

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°C (1,650 °F).[citation needed ] Temperature sensors are also used to monitor catalyst functioning: usually two

sensors will be fitted, with one before the catalyst and one after to monitor the temperature rise over the

catalytic-converter core.

The oxygen sensor  is the basis of the closed-loop control system on a spark-ignited rich-burn engine; however,

it is also used for diagnostics. In vehicles with OBD II, a second oxygen sensor is fitted after the catalytic

converter to monitor the O2 levels. The O2 levels are monitored to see the efficiency of the burn process. The

on-board computer makes comparisons between the readings of the two sensors. The readings are taken by

voltage measurements. If both sensors show the same output or the rear O2 is "switching", the computer

recognizes that the catalytic converter either is not functioning or has been removed, and will operate a

malfunction indicator lamp and affect engine performance. Simple "oxygen sensor simulators" have been

developed to circumvent this problem by simulating the change across the catalytic converter with plans and

pre-assembled devices available on the Internet. Although these are not legal for on-road use, they have been

used with mixed results.[36] Similar devices apply an offset to the sensor signals, allowing the engine to run a

more fuel-economical lean burn that may, however, damage the engine or the catalytic converter .[37] 

NOx sensors are extremely expensive and are in general used only when a compression-ignition engine is

fitted with a selective catalytic-reduction (SCR) converter, or a NOx absorber catalyst in a feedback system.

When fitted to an SCR system, there may be one or two sensors. When one sensor is fitted it will be pre-

catalyst; when two are fitted, the second one will be post-catalyst. They are used for the same reasons and in

the same manner as an oxygen sensor: the only difference is the substance being monitored.

[edit]See also

  Cerium(III) oxide 

  NOx adsorber  

  Roadway air dispersion modeling 

[edit]References

1. ^ Catalytic Converters. International Platinum Group Metals Association. Retrieved 10 January 2011.

2. ^ a  b  c  Palucka, Tim (Winter 2004). "Doing the Impossible". Invention & Technology  19 (3). Archived from the original on 2008-12-03.

Retrieved 2011-12-14.

3. ^ a  b  Petersen Publishing (1975). "The Catalytic Converter". In Erwin M. Rosen. The Petersen Automotive Troubleshooting & Repair

Manual . New York, NY: Grosset & Dunlap. pp. 493. ISBN 0-448-11946-3. "For years, the exhaust system (...) remained virtually

unchanged until 1975 when a strange new component was added. It's called a catalytic converter(...)"

4. ^ a  b  "General Motors Believes it has an Answer to the Automotive Air Pollution Problem". The Blade: Toledo, Ohio. 1974-09-12. Retrieved

2011-12-14.

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5. ^ a  b  "Catalytic Converter Heads Auto Fuel Economy Efforts". The Milwaukee Sentinel . 1974-11-11. Retrieved 2011-12-14.

6. ^ "Choosing the Right Wood Stove". Burn Wise. US EPA. Retrieved 2 January 2012.

7. ^ Csere, Csaba (January 1988). "10 Best Engineering Breakthroughs". Car and Driver  33 (7): 63.

8. ^ "Exhaust Gas Made Safe." Popular Mechanics, September 1951, p. 134, bottom of page

9. ^ "His Smoke Eating Cats Now Attack Traffic Smog."P opular Science, June 1955, pp. 83-85/244.

10. ^ Staff writer  (undated). "Eugene Houdry". Chemical Heritage Foundation. Retrieved 7 January 2011.

11. ^ (registration required) "Carl D. Keith, a Father of the Catalytic Converter, Dies at 88" . The New York Times. 15 November 2008.

12. ^ [unreliable source?] Staff writer  (undated). "Engelhard Corporation". referenceforbusiness.com. Retrieved 7 January 2011.

13. ^ Robert N. Carter, Lance L. Smith, Hasan Karim, Marco Castaldi, Shah Etemad, George Muench, R. Samuel Boorse, Paul Menacherry

and William C. Pfefferle (1998). Catalytic Combustion Technology Development for Gas Turbine Engine Applications. MRS Proceedings,

549, 93 doi:10.1557/PROC-549-93

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[edit]Further reading