Catalytic converter

A three-way catalytic converter on a gasoline-powered 1996Dodge Ram Van

A catalytic converter is a vehicle emissions control de-vice that converts toxic pollutants in exhaust gas to lesstoxic pollutants by catalyzing a redox reaction (oxidationor reduction). Catalytic converters are used in internalcombustion engines fueled by either petrol (gasoline) ordieselincluding lean burn engines.The rst widespread introduction of catalytic converterswas in the United States automobile market. Manufactur-ers of 1975 model year equipped gasoline-powered ve-hicles with catalytic converters to comply with the U.S.Environmental Protection Agency's stricter regulation ofexhaust emissions.[1][2][3][4] These two-way converterscombined carbon monoxide (CO) with unburned hydro-carbons (HC) to produce carbon dioxide (CO2) and water(H2O). In 1981, two-way catalytic converters were ren-dered obsolete by three-way converters that also reduceoxides of nitrogen (NOx);[1] however, two-way convert-ers are still used for lean burn engines.Although catalytic converters are most commonly appliedto exhaust systems in automobiles, they are also used onelectrical generators, forklifts, mining equipment, trucks,buses, locomotives, motorcycles, and airplanes. They arealso used on some wood stoves to control emissions.[5]This is usually in response to government regulation, ei-ther through direct environmental regulation or throughhealth and safety regulations.

1 HistoryThe catalytic converter was invented by Eugene Houdry,a French mechanical engineer and expert in catalytic oilrening[6] who lived in the U.S. around 1950. Whenthe results of early studies of smog in Los Angeles werepublished, Houdry became concerned about the role ofsmoke stack exhaust and automobile exhaust in air pollu-tion and founded a company, Oxy-Catalyst. Houdry rstdeveloped catalytic converters for smoke stacks calledcats for short. Then he developed catalytic convertersfor warehouse fork lifts that used low grade non-leadedgasoline.[7] Then in the mid-1950s he began research todevelop catalytic converters for gasoline engines used oncars. He was awarded United States Patent 2742437 forhis work.[8]

Widespread adoption of catalytic converters didn't occuruntil more stringent emission control regulations forcedthe removal of the anti-knock agent tetraethyllead, frommost gasoline, because lead was a 'catalyst poison' andwould deactivate the converter by forming a coating onthe catalysts surface, eectively disabling it.[9]

Catalytic converters were further developed by a series ofengineers including John J. Mooney and Carl D. Keith atthe Engelhard Corporation,[10] creating the rst produc-tion catalytic converter in 1973.[11]

Dr. William C. Pfeerle developed a catalytic combustorfor gas turbines in the early 1970s, allowing combustionwithout signicant formation of nitrogen oxides and car-bon monoxide.[12][13]

2 Construction

Cutaway of a metal-core converter

The catalytic converters construction is as follows:

1. The catalyst support or substrate. For automotive

1

2 3 TYPES

Ceramic-core converter

catalytic converters, the core is usually a ceramicmonolith with a honeycomb structure. Metallic foilmonoliths made of Kanthal (FeCrAl)[14] are usedin applications where particularly high heat resis-tance is required.[15] Either material is designed toprovide a large surface area. The cordierite ce-ramic substrate used in most catalytic converterswas invented by Rodney Bagley, Irwin Lachman andRonald Lewis at Corning Glass, for which they wereinducted into the National Inventors Hall of Fame in2002.[1]

2. The washcoat. A washcoat is a carrier for the cat-alytic materials and is used to disperse the materialsover a large surface area. Aluminum oxide, titaniumdioxide, silicon dioxide, or a mixture of silica andalumina can be used. The catalytic materials are sus-pended in the washcoat prior to applying to the core.Washcoat materials are selected to form a rough, ir-regular surface, which greatly increases the surfacearea compared to the smooth surface of the baresubstrate. This in turn maximizes the catalyticallyactive surface available to react with the engine ex-haust. The coat must retain its surface area and pre-vent sintering of the catalytic metal particles even athigh temperatures (1000 C).[16]

3. The catalyst itself is most often a mix of preciousmetals. Platinum is the most active catalyst and iswidely used, but is not suitable for all applicationsbecause of unwanted additional reactions and highcost. Palladium and rhodium are two other preciousmetals used. Rhodium is used as a reduction cata-lyst, palladium is used as an oxidation catalyst, andplatinum is used both for reduction and oxidation.Cerium, iron, manganese and nickel are also used,although each has limitations. Nickel is not legalfor use in the European Union because of its reac-tion with carbonmonoxide into toxic nickel tetracar-bonyl. Copper can be used everywhere except NorthAmerica, where its use is illegal because of the for-mation of toxic dioxin .

3 Types

3.1 Two-wayA two-way (or oxidation) catalytic converter has twosimultaneous tasks:

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

2. Oxidation of hydrocarbons (unburnt and partiallyburnt fuel) to carbon dioxide and water: CH +[(3x+1)/2] O2 xCO2 + (x+1) H2O (a combustionreaction)

This type of catalytic converter is widely used on dieselengines to reduce hydrocarbon and carbon monoxideemissions. They were also used on gasoline engines inAmerican- and Canadian-market automobiles until 1981.Because of their inability to control oxides of nitrogen,they were superseded by three-way converters.

3.2 Three-wayThree-way catalytic converters (TWC) have the addi-tional advantage of controlling the emission of nitrogenoxides (NO), in particular nitrous oxide, a greenhousegas over three hundred times more potent than carbondioxide,[17] a precursor to acid rain and currently themost ozone-depleting substance.[18] Technological im-provements including three-way catalytic converters haveled to motor vehicle nitrous oxide emissions in the USfalling to 8.2% of anthropogenic nitrous oxide emissionsin 2008, from a high of 17.77% in 1998.Since 1981, three-way (oxidation-reduction) catalyticconverters have been used in vehicle emission control sys-tems in the United States and Canada; many other coun-tries have also adopted stringent vehicle emission reg-ulations that in eect require three-way converters ongasoline-powered vehicles. The reduction and oxidationcatalysts are typically contained in a common housing,however in some instances they may be housed sepa-rately. A three-way catalytic converter has three simulta-neous tasks:

1. Reduction of nitrogen oxides to nitrogen andoxygen: 2NO xO2 + N2

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

3. Oxidation of unburnt hydrocarbons (HC) to car-bon dioxide and water: CH + [(3x+1)/2]O2 xCO2 + (x+1)H2O.

These three reactions occur most eciently when the cat-alytic converter receives exhaust from an engine running

3.3 Diesel engines 3

slightly above the stoichiometric point. This point is be-tween 14.6 and 14.8 parts air to 1 part fuel, by weight, forgasoline. The ratio for Autogas (or liqueed petroleumgas (LPG)), natural gas and ethanol fuels is each slightlydierent, requiring modied fuel system settings whenusing those fuels. In general, engines tted with 3-waycatalytic converters are equipped with a computerizedclosed-loop feedback fuel injection system using one ormore oxygen sensors, though early in the deployment ofthree-way converters, carburetors equipped for feedbackmixture control were used.Three-way catalysts are eective when the engine is op-erated within a narrow band of air-fuel ratios near stoi-chiometry, such that the exhaust gas oscillates betweenrich (excess fuel) and lean (excess oxygen) conditions.However, conversion eciency falls very rapidly whenthe engine is operated outside of that band of air-fuel ra-tios. Under lean engine operation, there is excess oxy-gen and the reduction of NO is not favored. Under richconditions, the excess fuel consumes all of the availableoxygen prior to the catalyst, thus only stored oxygen isavailable for the oxidation function. Closed-loop controlsystems are necessary because of the conicting require-ments for eective NO reduction and HC oxidation. Thecontrol system must prevent the NO reduction catalystfrom becoming fully oxidized, yet replenish the oxygenstorage material to maintain its function as an oxidationcatalyst.Three-way catalytic converters can store oxygen from theexhaust gas stream, usually when the airfuel ratio goeslean.[19] When sucient oxygen is not available from theexhaust stream, the stored oxygen is released and con-sumed (see cerium(IV) oxide). A lack of sucient oxygenoccurs either when oxygen derived fromNO reduction isunavailable or when certain maneuvers such as hard ac-celeration enrich the mixture beyond the ability of theconverter to supply oxygen.

3.2.1 Unwanted reactions

Unwanted reactions can occur in the three-way catalyst,such as the formation of odoriferous hydrogen sulde andammonia. Formation of each can be limited by modica-tions to the washcoat and precious metals used. It is dif-cult to eliminate these byproducts entirely. Sulfur-freeor low-sulfur fuels eliminate or reduce hydrogen sulde.For example, when control of hydrogen-sulde emissionsis desired, nickel or manganese is added to the washcoat.Both substances act to block the absorption of sulfur bythe washcoat. Hydrogen sulde is formed when the wash-coat has absorbed sulfur during a low-temperature partof the operating cycle, which is then released during thehigh-temperature part of the cycle and the sulfur com-bines with HC.

3.3 Diesel engines

For compression-ignition (i.e., diesel engines), the mostcommonly used catalytic converter is the Diesel Ox-idation Catalyst (DOC). DOCs contain palladium /platinum with Aluminium oxide which serve as catalyststo oxidise the hydrocarbons and carbon monoxide withoxygen to form carbon dioxide and water.2CO + O2 2CO2CxHx + [(3x+1)/2] O2 x CO2 + (x+1) H2OThese converters often operate at 90 percent eciency,virtually eliminating diesel odor and helping to reducevisible particulates (soot). These catalysts are not activefor NO reduction because any reductant present wouldreact rst with the high concentration of O2 in diesel ex-haust gas.Reduction in NO emissions from compression-ignitionengines has previously been addressed by the addition ofexhaust gas to incoming air charge, known as exhaust gasrecirculation (EGR). In 2010, most light-duty diesel man-ufacturers in the U.S. added catalytic systems to their ve-hicles to meet new federal emissions requirements. Thereare two techniques that have been developed for the cat-alytic reduction of NO emissions under lean exhaustconditions - selective catalytic reduction (SCR) and thelean NO trap or NOx adsorber. Instead of preciousmetal-containing NOx adsorbers, most manufacturers se-lected base-metal SCR systems that use a reagent such asammonia to reduce the NO into nitrogen. Ammonia issupplied to the catalyst system by the injection of ureainto the exhaust, which then undergoes thermal decom-position and hydrolysis into ammonia. One trademarkproduct of urea solution, also referred to as Diesel Ex-haust Fluid (DEF), is AdBlue.Diesel exhaust contains relatively high levels of partic-ulate matter (soot), consisting in large part of elemen-tal carbon. Catalytic converters cannot clean up elemen-tal carbon, though they do remove up to 90 percent ofthe soluble organic fraction, so particulates are cleanedup by a soot trap or diesel particulate lter (DPF). His-torically, a DPF consists of a Cordierite or Silicon Car-bide substrate with a geometry that forces the exhaustow through the substrate walls, leaving behind trappedsoot particles. Contemporary DPFs can be manufacturedfrom a variety of rare metals that provide superior perfor-mance (at a greater expense).[20] As the amount of soottrapped on the DPF increases, so does the back pressurein the exhaust system. Periodic regenerations (high tem-perature excursions) are required to initiate combustionof the trapped soot and thereby reducing the exhaust backpressure. The amount of soot loaded on the DPF priorto regeneration may also be limited to prevent extremeexotherms from damaging the trap during regeneration.In the U.S., all on-road light, medium and heavy-duty ve-hicles powered by diesel and built after 1 January 2007,must meet diesel particulate emission limits that means

4 6 REGULATIONS

they eectively have to be equipped with a 2-Way cat-alytic converter and a diesel particulate lter. Note thatthis applies only to the diesel engine used in the vehicle.As long as the engine was manufactured before 1 January2007, the vehicle is not required to have the DPF system.This led to an inventory runup by engine manufacturersin late 2006 so they could continue selling pre-DPF ve-hicles well into 2007.[21] During the re-generation cycle,most systems require the engine to consume several gal-lons of fuel in a relatively short amount of time in orderto generate the high temperatures necessary for the cycleto complete. This has been shown to adversely aect theoverall fuel economy of vehicles equipped with DPF sys-tems, especially in vehicles that are driven mostly in cityconditions where frequent acceleration requires a largeramount of fuel to be burned and therefore more soot tocollect in the exhaust system.

3.4 Lean burn spark-ignition enginesFor lean burn spark-ignition engines, an oxidation catalystis used in the same manner as in a diesel engine. Emis-sions from Lean Burn Spark Ignition Engines are verysimilar to emissions from a Diesel Compression Ignitionengine.

4 InstallationMany vehicles have a close-coupled catalytic converterlocated near the engines exhaust manifold. This unitheats up quickly due to its proximity to the engine, and re-duces cold-engine emissions by burning o hydrocarbonsfrom the extra-rich mixture used to start a cold engine.When catalytic converters were rst introduced, most ve-hicles used carburetors that provided a relatively rich air-fuel ratio. Oxygen (O2) levels in the exhaust stream weregenerally insucient for the catalytic reaction to occureciently, so most installations included secondary airinjection which injected air into the exhaust stream to in-crease the available oxygen and allow the catalyst to func-tion.Some three-way catalytic converter systems have air in-jection systems with the air injected between the rst(NO reduction) and second (HC and CO oxidation)stages of the converter. As in the two-way converters, thisinjected air provides oxygen for the oxidation reactions.An upstream air injection point, ahead of the catalyticconverter, is also sometimes present to provide oxygenduring engine warm up, which causes unburned fuel toignite in the exhaust tract before reaching the catalyticconverter. This reduces the engine runtime needed forthe catalytic converter to reach its light-o or operatingtemperature.Most newer vehicles are electronic fuel injection systems,and thus, do not have air injection systems. Instead,

they provide a constantly varying air-fuel mixture thatquickly and continually cycles between lean and rich ex-haust. Oxygen sensors are used to monitor the exhaustoxygen content before and after the catalytic converterand this information is used by the Electronic control unitto adjust the fuel injection so as to prevent the rst (NOreduction) catalyst from becoming oxygen-loaded whileensuring the second (HC and CO oxidation) catalyst issuciently oxygen-saturated.

5 DamageCatalyst poisoning occurs when the catalytic converter isexposed to exhaust containing substances that coat theworking surfaces, encapsulating the catalyst so that it can-not contact and treat the exhaust. The most-notable con-taminant is lead, so vehicles equipped with catalytic con-verters can be run only on unleaded fuels. Other com-mon catalyst poisons include fuel sulfur, manganese (orig-inating primarily from the gasoline additive MMT), andsilicone, which can enter the exhaust stream if the en-gine has a leak that allows coolant into the combustionchamber. Phosphorus is another catalyst contaminant.Although phosphorus is no longer used in gasoline, it (andzinc, another low-level catalyst contaminant) was until re-cently widely used in engine oil antiwear additives such aszinc dithiophosphate (ZDDP). Beginning in 2004, a limitof phosphorus concentration in engine oils was adoptedin the API SM and ILSAC GF-4 specications.Depending on the contaminant, catalyst poisoning cansometimes be reversed by running the engine under a veryheavy load for an extended period of time. The increasedexhaust temperature can sometimes liquefy or sublimatethe contaminant, removing it from the catalytic surface.However, removal of lead deposits in this manner is usu-ally not possible because of leads high boiling point.Any condition that causes abnormally high levels of un-burned hydrocarbonsraw or partially burnt fueltoreach the converter will tend to signicantly elevate itstemperature, bringing the risk of a meltdown of the sub-strate and resultant catalytic deactivation and severe ex-haust restriction. Vehicles equipped with OBD-II diag-nostic systems are designed to alert the driver to a misrecondition by means of ashing the check engine lighton the dashboard.

6 RegulationsEmissions regulations vary considerably from jurisdictionto jurisdiction. Most automobile spark-ignition enginesin North America have been tted with catalytic convert-ers since 1975,[1][2][3][4] and the technology used in non-automotive applications is generally based on automotivetechnology.

7.1 Warm-up period 5

Regulations for diesel engines are similarly varied, withsome jurisdictions focusing on NO (nitric oxide and ni-trogen dioxide) emissions and others focusing on partic-ulate (soot) emissions. This regulatory diversity is chal-lenging for manufacturers of engines, as it may not beeconomical to design an engine to meet two sets of regu-lations.Regulations of fuel quality vary across jurisdictions. InNorth America, Europe, Japan and Hong Kong, gaso-line and diesel fuel are highly regulated, and compressednatural gas and LPG (Autogas) are being reviewed forregulation. In most of Asia and Africa, the regulationsare often lax: in some places sulfur content of the fuelcan reach 20,000 parts per million (2%). Any sulfur inthe fuel can be oxidized to SO2 (sulfur dioxide) or evenSO3 (sulfur trioxide) in the combustion chamber. If sul-fur passes over a catalyst, it may be further oxidized in thecatalyst, i.e., SO2 may be further oxidized to SO3. Sulfuroxides are precursors to sulfuric acid, a major componentof acid rain. While it is possible to add substances such asvanadium to the catalyst washcoat to combat sulfur-oxideformation, such addition will reduce the eectiveness ofthe catalyst. The most eective solution is to further re-ne fuel at the renery to produce ultra-low sulfur diesel.Regulations in Japan, Europe and North America tightlyrestrict the amount of sulfur permitted in motor fuels.However, the direct nancial expense of producing suchclean fuel may make it impractical for use in developingcountries. As a result, cities in these countries with highlevels of vehicular trac suer from acid rain, whichdamages stone and woodwork of buildings, poisons hu-mans and other animals, and damages local ecosystems,at a very high nancial cost.

7 Negative aspectsSome early converter designs greatly restricted the ow ofexhaust, which negatively aected vehicle performance,driveability, and fuel economy.[22] Because they wereused with carburetors incapable of precise fuel-air mix-ture control, they could overheat and ignite ammablematerials under the car.[23] While removing a moderncatalytic converter in new condition will net only a verysmall increase vehicle performance, the removal of a 6-year-old modern catalyst resulted in a 3.4% increase inhorsepower[24] To many performance enthusiasts, thismodest increase in power for very little cost encouragesthe removal or gutting of the catalytic converter.[22][25]In such cases, the converter may be replaced by a welded-in section of ordinary pipe or a anged test pipe osten-sibly meant to check if the converter is clogged by com-paring how the engine runs with versus without the con-verter, which facilitates reinstallation of the converter inorder to pass an emission test.[24] In many jurisdictions, itis illegal to remove or disable a catalytic converter for anyreason other than its direct and immediate replacement.

In the United States, for example, it is a violation of Sec-tion 203(a)(3)(A) of the 1990 Clean Air Act for a vehiclerepair shop to remove a converter from a vehicle, or causea converter to be removed from a vehicle, except in or-der to replace it with another converter.,[26] and Section203(a)(3)(B) makes it illegal for any person to sell or toinstall any part that would bypass, defeat, or render inop-erative any emission control system, device, or design el-ement. Vehicles without functioning catalytic convertersgenerally fail emission inspections. The automotive af-termarket supplies high-ow converters for vehicles withupgraded engines, or whose owners prefer an exhaust sys-tem with larger-than-stock capacity.[27]

7.1 Warm-up periodVehicles emit most of their pollution during the rst veminutes of engine operation before the catalytic converterhas warmed up suciently to be eective.[28]

In 1999, BMW introduced an electrically heated cata-lyst, which they called E-CAT, in their 750iL sedan.Heating coils inside the catalytic converter assemblies areelectried just after engine start, bringing the catalyst upto operating temperature very quickly to qualify the ve-hicle for low emission vehicle (LEV) designation.[29]

7.2 Environmental impactCatalytic converters have proven to be reliable and ef-fective in reducing noxious tailpipe emissions. However,they also have some shortcomings and adverse environ-mental impacts in production:

An engine equipped with a three-way catalyst mustrun at the stoichiometric point, which means morefuel is consumed than in a lean-burn engine. Thismeans approximately 10% more CO2 emissionsfrom the vehicle.

Catalytic converter production requires palladium orplatinum; part of the world supply of these preciousmetals is produced near Norilsk, Russia, wherethe industry (among others) has caused Norilsk tobe added to Time magazines list of most-pollutedplaces.[30]

8 TheftBecause of the external location and the use of valuableprecious metals including platinum, palladium, rhodium,and gold, converters are a target for thieves. The prob-lem is especially common among late-model trucks andSUVs, because of their high ground clearance and eas-ily removed bolt-on catalytic converters. Welded-in con-verters are also at risk of theft, as they can be easily cut

6 12 REFERENCES

o.[31][32][33] Thieves techniques for fast removal of aconverter, for instance using a portable reciprocating saw,can often damage other components of the car. Damageto components like wiring, or a fuel line, can have dan-gerous consequences. Rises in metal costs in the U.S.during recent years have led to a large increase in con-verter theft.[34] A catalytic converter can cost well over$1,000 to replace.[35]

9 Diagnostics

Various jurisdictions now legislate on-board diagnosticsto 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 rstis as a warning system, typically on two-way catalytic con-verters such as are still sometimes used on LPG forklifts.The function of the sensor is to warn of catalytic con-verter temperature above the safe limit of 750 C (1,380F). More-recent catalytic-converter designs are not assusceptible to temperature damage and canwithstand sus-tained temperatures of 900 C (1,650 F). Temperaturesensors are also used to monitor catalyst functioning: usu-ally two sensors will be tted, with one before the cata-lyst and one after to monitor the temperature rise over thecatalytic-converter core.The oxygen sensor is the basis of the closed-loop controlsystem on a spark-ignited rich-burn engine; however, it isalso used for diagnostics. In vehicles with OBD II, a sec-ond oxygen sensor is tted after the catalytic converterto monitor the O2 levels. The O2 levels are monitoredto see the eciency of the burn process. The on-boardcomputermakes comparisons between the readings of thetwo sensors. The readings are taken by voltage measure-ments. If both sensors show the same output or the rearO2 is switching, the computer recognizes that the cat-alytic converter either is not functioning or has been re-moved, and will operate a malfunction indicator lamp andaect engine performance. Simple oxygen sensor sim-ulators have been developed to circumvent this problemby simulating the change across the catalytic converterwith plans and pre-assembled devices available on the In-ternet. Although these are not legal for on-road use, theyhave been used with mixed results.[36] Similar devices ap-ply an oset to the sensor signals, allowing the engine torun a more fuel-economical lean burn that may, however,damage the engine or the catalytic converter.[37]

NO sensors are extremely expensive and are in generalused only when a compression-ignition engine is ttedwith a selective catalytic-reduction (SCR) converter, ora NO absorber catalyst in a feedback system. When t-ted to an SCR system, there may be one or two sensors.When one sensor is tted it will be pre-catalyst; when twoare tted, the second one will be post-catalyst. They are

used for the same reasons and in the same manner as anoxygen sensor: the only dierence is the substance beingmonitored.

10 As a metaphorIn his book Immigration Wars: Forging an Ameri-can Solution, governor Jeb Bush uses the device as ametaphor, comparing skilled worker immigration into theUnited States of America to a catalytic converter. Hesays,'We cannot put aside this powerful catalytic con-verter for continued progress.'

11 See also Catalytic heater Cerium(III) oxide NOx adsorber Roadway air dispersion modeling

12 References[1] Palucka, Tim (Winter 2004). Doing the Impossible. In-

vention & Technology 19 (3). Archived from the originalon 3 December 2008. Retrieved 14 December 2011.

[2] Petersen Publishing (1975). The Catalytic Converter.In Erwin M. Rosen. The Petersen Automotive Trou-bleshooting & Repair Manual. New York, NY: Grosset& Dunlap. p. 493. ISBN 0-448-11946-3. For years,the exhaust system (...) remained virtually unchanged un-til 1975 when a strange new component was added. Itscalled a catalytic converter(...)

[3] General Motors Believes it has an Answer to the Auto-motive Air Pollution Problem. The Blade: Toledo, Ohio.12 September 1974. Retrieved 14 December 2011.

[4] Catalytic Converter Heads Auto Fuel Economy Eorts.The Milwaukee Sentinel. 11 November 1974. Retrieved14 December 2011.

[5] Choosing the Right Wood Stove. Burn Wise. US EPA.Retrieved 2 January 2012.

[6] Csere, Csaba (January 1988). 10 Best EngineeringBreakthroughs. Car and Driver 33 (7): 63.

[7] Exhaust GasMade Safe. PopularMechanics, September1951, p. 134, bottom of page

[8] His Smoke Eating Cats Now Attack Trac Smog. Pop-ular Science, June 1955, pp. 83-85/244.

[9] Sta writer (undated). Eugene Houdry. Chemical Her-itage Foundation. Retrieved 7 January 2011.

7[10] (registration required) Carl D. Keith, a Father of the Cat-alytic Converter, Dies at 88. The New York Times. 15November 2008.

[11] Sta writer (undated). Engelhard Corporation. refer-enceforbusiness.com. Retrieved 7 January 2011.

[12] Robert N. Carter, Lance L. Smith, Hasan Karim, MarcoCastaldi, Shah Etemad, George Muench, R. SamuelBoorse, Paul Menacherry and William C. Pfeerle(1998). Catalytic Combustion Technology Developmentfor Gas Turbine Engine Applications. MRS Proceedings,549, 93 doi:10.1557/PROC-549-93

[13] Worthy, Sharon. Bio-Medicine: Connecticut chemist re-ceives award for cleaner air technology. 23 June 2003.Retrieved 11 December 2012.

[14] Pischinger, Univ.-Prof. Dr.-Ing. Stephan (2011). Ver-brennungsmotoren Band 2 (24 ed.). Aachen, Germany:Lehrstuhl Fr Verbrennungskraftmachinen. p. 335.

[15] Pischinger, Univ.-Prof. Dr.-Ing. Stephan (2011). Ver-brennungsmotoren Band 2 (24 ed.). Aachen, Germany:Lehrstuhl Fr Verbrennungskraftmachinen. p. 335.

[16] Martin Votsmeier, Thomas Kreuzer, Jrgen Giesho,Gerhard Lepperho. Automobile Exhaust Control, in Ull-manns Encyclopedia of Industrial Chemistry, Wiley-VCH2002. DOI: 10.1002/14356007.a03_189.pub2

[17] EPA: Nitrous Oxide Emissions

[18] Ravishankara, A. R.; Daniel, J. S.; Portmann, R. W.(2009). Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century. Sci-ence 326 (5949): 1235. Bibcode:2009Sci...326..123R.doi:10.1126/science.1176985. PMID 19713491.

[19] Brandt, Erich; Wang, Yanying; Grizzle, Jessy (2000).Dynamic Modeling of a Three Way Catalyst for SIEngine Exhaust Emission Control. IEEE Transac-tions on Control Systems Technology 8 (5): 767776.doi:10.1109/87.865850.

[20] http://www.synergycatalyst.com/catalyst-coating-technology/

[21] Heavy-Duty Engine and Vehicle Standards and HighwayDiesel Fuel Sulfur Control Requirements PDF (123 KB)

[22] Crutsinger, Martin (29 September 1982). Kits to FoilAuto Pollution Control Are SellingWell. The GainesvilleSun.

[23] Ullman, Owen (14 June 1976). Catalytic Converter StillControversial after Two Years of Use. The Bulletin.

[24] Beat the Law. Importtuner.com (2007-02-26). Retrievedon 2011-01-09.

[25] Some of Us Can Only Aord a Clunker. The PalmBeach Post. 23 February 1996.

[26] Sale and Use of Aftermarket Catalytic Converters, USEnvironmental Protection Agency, US Federal RegisterVolume 51

[27] Tanner, Keith. Mazda MX-5 Miata. Motorbooks. p. 120.

[28] Catalytic converters, nsls.bnl.gov

[29] Edgar, Julian (5 October 1999). Goodbye 12 volts...hello 42 volts!". Autospeed. Retrieved 2 January 2012.The current model BMW750iL has a maximum electricalload of a staggering 428 amps (5.9 kW)! In this car, overhalf of the maximum power load is from the short-termelectrical heating of the catalytic converters, with the heat-ing used so that they come up to operating temp quickly

[30] Walsh, Bryan (12 September 2007). Norilsk, Russia.TheWorlds Most Polluted Places (Time). Retrieved 7 Jan-uary 2011.

[31] Fraga, Brian (30 November 2011). Carver police investi-gating catalytic converter thefts. South Coast Today. Re-trieved 21 December 2011.

[32] Catalytic Converter Theft.

[33] Murr, Andrew (9 January 2008). An Exhausting NewCrimeWhat Thieves Are Stealing from Todays Cars.Newsweek. Retrieved 7 January 2011.

[34] Johnson, Alex (12 February 2008). Stolen in 60 Sec-onds: The Treasure in Your Car As Precious Met-als Prices Soar, Catalytic Converters Are Targets forThieves. MSNBC. Retrieved 7 January 2011.

[35] Converters Taken by Car Lot Thieves. PoconoNews. 2July 2009.

[36] Settlement Involves Illegal Emission Control 'Defeat De-vices Sold for Autos. 1 June 2007.

[37] Check Engine Lights Come on for a Reason. ConcordMonitor. 12 January 2003.

13 Further reading

Keith, C. D., et al. U.S. Patent 3,441,381: Appa-ratus for purifying exhaust gases of an internal com-bustion engine. 29 April 1969

Lachman, I. M. et al. U.S. Patent 3,885,977:Anisotropic Cordierite Monolith (Ceramic sub-strate). 5 November 1973

Charles H. Bailey. U.S. Patent 4,094,645: Com-bination muer and catalytic converter having lowbackpressure. 13 June 1978

Charles H. Bailey. U.S. Patent 4,250,146: '"Case-less monolithic catalytic converter. 10 February1981

Srinivasan Gopalakrishnan. GB 2397782: ProcessAnd Synthesizer For Molecular Engineering of Mate-rials. 13 March 2002

8 14 EXTERNAL LINKS

14 External links Catalytic converter at HowStuWorks Automotive applications of high temperature insu-lation wool

915 Text and image sources, contributors, and licenses15.1 Text

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History Construction Types Two-way Three-way Unwanted reactions

Diesel engines Lean burn spark-ignition engines

Installation Damage Regulations Negative aspects Warm-up period Environmental impact

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