A catalytic converter (colloquially, "cat" or "catcon") is an exhaust emission control device which converts toxic chemicals in the exhaust of an internal combustion engine into less noxious substances. Inside a catalytic converter, a catalyst stimulates a chemical reaction in which noxious byproducts of combustion are converted 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: an oxidising reaction converts carbon monoxide (CO) and unburned hydrocarbons (HC), and a reduction reaction converts oxides of nitrogen (NOx) to produce carbon dioxide (CO2), nitrogen (N2), and water (H2O).
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. These were "two-way" converters which combined carbon monoxide (CO) and unburned hydrocarbons (HC) to produce carbon dioxide (CO2) and water (H2O). Two-way catalytic converters of this type are now considered obsolete, having been supplanted except on lean burn engines Template:Citation needed by "three-way" converters which also reduce oxides of nitrogen (NOx).
Catalytic converters are still most commonly used on automobile exhaust systems, but are also used on generator sets, forklifts, mining equipment, trucks, buses, locomotives, airplanes and other engine fitted devices. They are also used on some wood stoves to control emissions. This is usually in response to government regulation, either through direct environmental regulation or through health and safety regulations.
The catalytic converter was invented by Eugene Houdry, a French mechanical engineer and expert in catalytic oil refining 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 pollution and founded a company, Oxy-Catalyst. Houdry first developed catalytic converts for smoke stacks called cats for short. Then started research in the mid 1950s to develop catalytic converters for gasoline engines. He was awarded United States Patent 2742437 for his work.
Widespread adoption of catalytic converters didn't occur until more stringent emission control regulations forced the removal of anti-knock agent tetraethyl lead 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.
Catalytic converters were further developed by a series of engineers including John J. Mooney and Carl D. Keith at the Engelhard Corporation, creating the first production catalytic converter in 1973.
The catalytic converter consists of several components:
- 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. Either material is designed to provide a high surface area to support the catalyst washcoat, and therefore is often called a "catalyst support".Template:Citation needed The cordierite ceramic 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.Template:Citation needed
- 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 maximizes the catalytically active surface available to react with the engine exhaust.
- 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 reactionsTemplate:Vague 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 catalysts, 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,Template:Clarify where its use is illegal because of the formation of dioxin.
A two-way (or "oxidation") catalytic converter has two simultaneous tasks:
- Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
- 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 monoxide emissions. 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.
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 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:
- Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2
- Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
- 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 the conflicting 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. 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.
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.
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.
For 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 catalyst 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 engine 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 manufactures 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 condition - 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 fractionTemplate:Citation needed, so particulates are cleaned up by a soot trap or diesel particulate filter (DPF). 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. 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 January 1, 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 vehicle. As long as the engine was manufactured before January 1, 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.
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.
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 included secondary 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 modern 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.
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 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.Template: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 sublime 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.
Template:Refimprove Emissions regulations vary considerably from jurisdiction to jurisdiction. Most automobile spark-ignition engines in North America have been fitted with catalytic converters since 1975, 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 as vanadium 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 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.
Some early converter designs greatly restricted the flow of exhaust, which negatively affected vehicle performance, driveability, and fuel economy. 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. Removing a modern catalytic converter in new condition will not increase vehicle performance without retuning, but their removal or "gutting" continues. 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. 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., 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.
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.
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.
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:
- 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. Carbon dioxide produced from fossil fuels is one of the greenhouse gases indicated by the Intergovernmental Panel on Climate Change (IPCC) to be a "most likely" cause of global warming. Additionally, the U.S. Environmental Protection Agency (EPA) has stated catalytic converters 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 50% of nitrous oxide emissions, nitrous oxide makes up 7.2% of greenhouse gases.
- An engine equipped with a three-way catalyst must run at the stoichiometric point, which means more fuel is consumed than in a lean-burn engine. This, in turn, means relatively more CO2</em> 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.
Because of the external location and the use of valuable precious metals including platinum, palladium, and rhodium, 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. 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, which can then cost well over $1,000 to replace.
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 °C (1,650 °F). Template: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. For every 1% of CO in the exhaust gas stream, the exhaust gas temperature will rise by 100 °C.Template:Citation needed
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 on-board computer makes comparisons between the readings of the two sensors. If both sensors show the same output, the computer recognizes that the catalytic converter either is not functioning or has been removed, and will operate a "check engine" light and retard 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. 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.
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.
- ↑ Catalytic Converters. International Platinum Group Metals Association. Retrieved January 10, 2011.
- ↑ 2.0 2.1 2.2 Palucka, Tim (Winter 2004). "Doing the Impossible". Invention & Technology 19 (3). Archived from the original on 2008-12-03. http://web.archive.org/web/20081203124718/http://www.americanheritage.com/articles/magazine/it/2004/3/2004_3_22.shtml. Retrieved 2011-12-14.
- ↑ 3.0 3.1 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(…)"
- ↑ 4.0 4.1 "General Motors Believes it has an Answer to the Automotive Air Pollution Problem". The Blade: Toledo, Ohio. 1974-09-12. http://news.google.com/newspapers?id=9tBOAAAAIBAJ&sjid=IAIEAAAAIBAJ&dq=catalytic-converter&pg=6404%2C6576523. Retrieved 2011-12-14.
- ↑ 5.0 5.1 "Catalytic Converter Heads Auto Fuel Economy Efforts". The Milwaukee Sentinel. 1974-11-11. http://news.google.com/newspapers?id=FXVQAAAAIBAJ&sjid=vBEEAAAAIBAJ&dq=catalytic-converter&pg=6134%2C2245045. Retrieved 2011-12-14.
- ↑ "Consumers - Choosing Appliances - Choosing the Right Wood Stove". Burn Wise. US EPA. http://www.epa.gov/burnwise/woodstoves.html. Retrieved 2 January 2012.
- ↑ Csere, Csaba (January 1988). "10 Best Engineering Breakthroughs". Car and Driver 33 (7): 63.
- ↑ "His Smoke Eating Cats Now Attack Traffic Smog." Popular Science, June 1955, pp. 83-85/244.
- ↑ Staff writer (undated). "Eugene Houdry". Chemical Heritage Foundation. Retrieved January 7, 2011.
- ↑ Template:Registration required "Carl D. Keith, a Father of the Catalytic Converter, Dies at 88". The New York Times. November 15, 2008.
- ↑ Template:Fix Staff writer (undated). "Engelhard Corporation". referenceforbusiness.com. Retrieved January 7, 2011.
- ↑ Brandt, Erich; Wang, Yanying; Grizzle, Jessy (2000). "Dynamic Modeling of a Three Way Catalyst for SI Engine Exhaust Emission Control". IEEE Transactions on Control Systems Technology 8 (5): 767–776. doi:10.1109/87.865850. ftp://www.eecs.umich.edu/people/grizzle/papers/TWC98.pdf.
- ↑ PDF (123 KB)
- ↑ 14.0 14.1 Crutsinger, Martin (September 29, 1982). "Kits to Foil Auto Pollution Control Are Selling Well". The Gainesville Sun.
- ↑ Ullman, Owen (June 14, 1976). "Catalytic Converter Still Controversial after Two Years of Use". The BulletinTemplate:Clarify.
- ↑ 16.0 16.1 Catalytic Converter Removal – Beat the Law – Import Tuner Magazine. Importtuner.com (2007-02-26). Retrieved on 2011-01-09.
- ↑ "Some of Us Can Only Afford a Clunker". The Palm Beach Post. February 23, 1996.
- ↑ Sale and Use of Aftermarket Catalytic Converters, US Environmental Protection Agency, US Federal Register Volume 51
- ↑ Tanner, Keith. Mazda MX-5 Miata. p. 120.
- ↑ Catalytic converters, nsls.bnl.gov
- ↑ Edgar, Julian (5 October, 1999). "Goodbye 12 volts... hello 42 volts!". Autospeed. http://autospeed.com/cms/title_Goodbye-12-volts-hello-42-volts/A_0319/article.html. Retrieved 2 January 2012. "The current model BMW 750iL has a maximum electrical load of a staggering 428 amps (5.9kW)! In this car, over half of the maximum power load is from the short-term electrical heating of the catalytic converters, with the heating used so that they come up to operating temp quickly"
- ↑ Wright, Matthew. "What Exactly is a Catalytic Converter? The Science Behind Catlytic Converters". About.com. http://autorepair.about.com/od/glossary/ss/how-it_catalyti_3.htm. Retrieved 2009.
- ↑ Le Treut, H; Somerville, R.; Cubasch, U; Ding, Y; Mauritzen, C; Mokssit, A; Peterson, T.; and Prather, M. (2007) (PDF). Historical Overview of Climate Change Science In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Solomon, S.; Qin, D.; Manning, M.; Chen, Z.; Marquis, M.; Averyt, K.B.; Tignor, M.; and Miller, H.L., editors). Cambridge University Press. pp. 5, 10. http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter1.pdf. Retrieved January 18, 2009.
- ↑ Wald, Matthew (May 29, 1998). "Autos' Converters Cut Smog But Add to Global Warming". The New York Times. http://www.nytimes.com/1998/05/29/us/autos-converters-cut-smog-but-add-to-global-warming.html?ref=matthewlwald.
- ↑ Walsh, Bryan (undated (circa 2007)). "The World's Most Polluted Places — From Lead in the Soil to Toxins in the Water and Radioactive Fallout in the Air, The Blacksmith Institute Has Created a List of the World's Worst Ecological Disaster Areas". Time. http://www.time.com/time/specials/2007/article/0,28804,1661031_1661028_1661022,00.html. Retrieved January 7, 2011.
- ↑ Fraga, Brian (2011-11-30). "Carver police investigating catalytic converter thefts". South Coast Today. http://www.southcoasttoday.com/apps/pbcs.dll/article?AID=/20111130/NEWS/111300325/-1/NEWSMAP. Retrieved 2011-12-21.
- ↑ "Catalytic Converter Theft".
- ↑ Murr, Andrew (January 9, 2008). "An Exhausting New Crime — What Thieves Are Stealing from Today's Cars". Newsweek. Retrieved January 7, 2011.
- ↑ Johnson, Alex (February 12, 2008). "Stolen in 60 Seconds: The Treasure in Your Car — As Precious Metals Prices Soar, Catalytic Converters Are Targets for Thieves". MSNBC. Retrieved January 7, 2011.
- ↑ "Converters Taken by Car Lot Thieves". PoconoNews. July 2, 2009.
- ↑ "Settlement Involves Illegal Emission Control 'Defeat Devices' Sold for Autos". June 1, 2007. http://eponline.com/articles/2007/07/01/settlement-involves-illegal-emission-control-defeat-devices-sold-for-autos.aspx.
- ↑ "Check Engine Lights Come On for a Reason". Concord Monitor. January 12, 2003.
- Howstuffworks: "How Catalytic Converters Work"
- High Temperature Insulation Wool — Automotive Applications
- Keith, C. D., et al., – U.S. Patent 3,441,381 – "Apparatus for purifying exhaust gases of an internal combustion engine" – April 29, 1969
- Lachman, I. M. et al., – U.S. Patent 3,885,977 – "Anisotropic Cordierite Monolith" (Ceramic substrate) – November 5, 1973
- Charles H. Bailey, – U.S. Patent 4,094,645 – "Combination muffler and catalytic converter having low backpressure" – June 13, 1978
- Charles H. Bailey, – U.S. Patent 4,250,146 – '"Caseless monolithic catalytic converter" – February 10, 1981
- Srinivasan Gopalakrishnan – GB 2397782</span> – "Process And Synthesizer For Molecular Engineering Of Materials" – March 13, 2002
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