محول حفزي

محول حفزي ثلاثي الاتجاهات على شاحنة دودج رام 1996 تدور بالجاسولين.

محاكاة للسريان داخل محول حفزي

المحول الحفزي catalytic converter هوجهاز للتحكم في الانبعاثات يحوّل الغازات السامة والملوثات في غاز العادم إلى ملوثات أقل سمية بحفز تفاعل أكسدة-اختزال. المحولات الحفزية المستخدمة مع محركات الاحتراق الداخلي التي تعمل بالبترول (جاسولين) أوبالديزل — بما في ذلك محركات الحرق اللين وكذلك سخانات الكيروسين والمواقد.

أول استخدام على نطاق واسع للمحولات الحفزية كان في سوق سيارات الولايات المتحدة. للالتزام بالتنظيمات المشددة للوكالة الأمريكية لحماية البيئة حول انبعاثات العادم، فللسيارات التي تعمل بالجاسولين بدءاً من سنة موديل 1975 أصبح لزاماً عليها حتى تُزوَّد بمحول حفزي. تلك المحولات "ثنائية الاتحاه" جمعت الأكسجين مع أول أكسيد الكربون (CO) والهيدروكربونات غير المحترقة (HC) لانتاج ثاني أكسيد الكربون (CO₂) وماء (H₂O). وفي 1981، أصبحت المحولات الحفزية ثنائية الاتجاه لاغية بظهور المحولات "ثلاثية الاتجاه" التي أيضاً تختزل أكاسيد النيتروجين (NOx); إلا حتى المحولات ثنائية الاتجاه مازالت تستخدم لمحركات الحرق اللين. وذلك لأن المحولات ثلاثية الاتجاه تتطلب إما احتراقي غني أوحسابي لتختزل بنجاح أكاسيد النيتروجين.

Although catalytic converters are most commonly applied to exhaust systems in automobiles, they are also used on electrical generators, forklifts, mining equipment, trucks, buses, locomotives and motorcycles. 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. A catalytic converter has to be changed every 100 000 / 120 000 km in order to be efficient. It is important to recycle this part of the car.

التاريخ

The catalytic converter was invented by Eugene Houdry, a French mechanical engineer and expert in catalytic oil refining, who moved to the United States in 1930. 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 called Oxy-Catalyst. Houdry first developed catalytic converters for smoke stacks called "cats" for short, and later developed catalytic converters for warehouse forklifts that used low grade, unleaded gasoline. In the mid-1950s, he began research to develop catalytic converters for gasoline engines used on cars. He was awarded United States Patent 2,742,437 for his work.

Widespread adoption of catalytic converters did not occur until more stringent emission control regulations forced the removal of the anti-knock agent tetraethyl lead from most types of gasoline. Lead is a "catalyst poison" and would effectively disable a catalytic converter by forming a coating on the catalyst's surface.

Catalytic converters were further developed by a series of engineers including John J. Mooney, Carl D. Keith, Antonio Eleazar at the Engelhard Corporation, creating the first production catalytic converter in 1973.

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.

التصنيع

Cutaway of a metal-core converter

Ceramic-core converter

The catalytic converter's construction is as follows:

The catalyst support or substrate. For automotive catalytic converters, the core is usually a ceramic monolith with a honeycomb structure. Metallic foil monoliths made of Kanthal (FeCrAl) are used in applications where particularly high heat resistance is required. Either material is designed to provide a large surface area. 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.
The washcoat. A washcoat is a carrier for the catalytic materials and is used to disperse the materials over a large 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).
Ceria or ceria-zirconia. These oxides are mainly added as oxygen storage promoters.
The catalyst itself is most often a mix of precious metal. Platinum is the most active catalyst and is widely used, but is not suitable for all applications because of unwanted additional reactions 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 limitations. Nickel is not legal for use in the European Union because of its reaction with carbon monoxide into toxic nickel tetracarbonyl.^[]Copper can be used everywhere except Japan.^[]

انظر أيضاً

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

الهامش

^ Palucka, Tim (Winter 2004). "Doing the Impossible". Invention & Technology. 19 (3). Archived from the original on ثلاثة December 2008. Retrieved 14 December 2011.
^ Petersen Publishing (1975). "The Catalytic Converter". In Erwin M. Rosen (eds.). The Petersen Automotive Troubleshooting & Repair Manual. New York, NY: Grosset & Dunlap. p. 493. ISBN . For years, the exhaust system (...) remained virtually unchanged until 1975 when a strange new component was added. It's called a catalytic converter(...)CS1 maint: uses editors parameter (link)
^ "General Motors Believes it has an Answer to the Automotive Air Pollution Problem". The Blade: Toledo, Ohio. 12 September 1974. Retrieved 14 December 2011.
^ "Catalytic Converter Heads Auto Fuel Economy Efforts". The Milwaukee Sentinel. 11 November 1974. Retrieved 14 December 2011.
^ "Choosing the Right Wood Stove". Burn Wise. US EPA. Retrieved 2 January 2012.
^ https://www.catalyticconverterrecycling.com
^ Csere, Csaba (January 1988). "10 Best Engineering Breakthroughs". Car and Driver. 33 (7): 63.
^ "Exhaust Gas Made Safe" Popular Mechanics, September 1951, p. 134, bottom of page
^ "His Smoke Eating Cats Now Attack Traffic Smog". Popular Science, June 1955, pp. 83-85/244.
^ "Eugene Houdry". Chemical Heritage Foundation. Retrieved 27 October 2016.
^ نطقب:Registration required "Carl D. Keith, a Father of the Catalytic Converter, Dies at 88". The New York Times. 15 November 2008.
^ Staff writer (undated). "Engelhard Corporation". referenceforbusiness.com. Retrievedسبعة January 2011.
^ 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
^ Worthy, Sharon. "Connecticut chemist receives award for cleaner air technology". Bio-Medicine. 23 June 2003. Retrieved 11 December 2012.
^ Pischinger, Univ.-Prof. Dr.-Ing. Stephan (2011). Verbrennungsmotoren Band 2 (24 ed.). Aachen, Germany: Lehrstuhl Für Verbrennungskraftmachinen. p. 335.
^ Martin Votsmeier, Thomas Kreuzer, Jürgen Gieshoff, Gerhard Lepperhoff. Automobile exhaust Control, in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH 2002. DOI: 10.1002/14356007.a03_189.pub2
^ Kašpar, J.; Fornasiero, P.; Graziani, M. (1999). "Use of CeO2-based oxides in the three-way catalysis". Catalysis Today. 50 (2): 285–298. doi:10.1016/S0920-5861(98)00510-0. ISSN 0920-5861.

للاستزادة

Keith, C. D., et al. U.S. Patent 3٬441٬381 : "Apparatus for purifying exhaust gases of an internal combustion engine". 29 April 1969
Lachman, I. M. et al. U.S. Patent 3٬885٬977 : "Anisotropic Cordierite Monolith" (Ceramic substrate).خمسة November 1973
Charles H. Bailey. U.S. Patent 4٬094٬645 : "Combination muffler and catalytic converter having low backpressure". 13 June 1978
Charles H. Bailey. U.S. Patent 4٬250٬146 : '"Caseless monolithic catalytic converter".عشرة February 1981
Srinivasan Gopalakrishnan. GB patent 2397782: "Process And Synthesizer For Molecular Engineering of Materials". 13 March 2002.