Catalytic Converter

BY THOMAS CHERIAN C HERIAN A11MAE17 A11MAE17 DINESH TEJ A11MAE18 A11MAE18 VITU - ARAI

CONTENTS 

Introduction & History of Catcon

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Construction of Catcon & Location

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Types Of Catcon

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Damage to Catcons

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Negative aspects of Catcon

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Conclusion

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References

WHAT IS A CATALYTIC CONVERTER (CATCON) 

 A catalytic converter is a vehicle emissions control device which converts toxic by products of combustion in the exhaust of  an internal combustion engine to less toxic substances by way of  catalysed chemical reactions.

BRIEF HISTORY OF THE CATALYTIC CONVERTER 

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Catalytic converter was first invented by Eugene Houdry in the 1950’s. Tetra ethyl lead present in gasoline poisoned the converter by forming a coating on the catalyst’s surface, effectively disabling it. The catalytic converter was further  developed bu John J. Mooney and Carl D. Keith at the Engelhard Corporation, creating the first production of catalytic converter in 1973.

LOCATION OF CATCON

USES OF A CATCON 

Used to reduce toxicity of emissions from an IC engine.

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Mostly used in motor vehicle exhaust system.

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Catcons are also used in gensets, forklift, mining equipments, trucks, buses, trains and other engineequipped machines.

COMPONENTS OF CATCON 4 Components 

Mat

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Ceramic substrate

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Can

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Catalyst

CONSTRUCTION OF CATCON

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Metal core converter & Ceramic core converter. The core is often a ceramic honeycomb(codierite 2 MgO • 2AI2O3 • 5SiO2) in modern catalytic converters, but stainless steel foil honeycombs are also used. Metallic cores are less expensive to build in small production runs, and are used in sportscars where low back pressure and reliability under continuous high load is required. The honeycomb surface increases the amount of surface area available to support the catalyst, and is called a “catalyst support”.

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 A washcoat( Aluminum oxide, titanium dioxide, silicon dioxide, or a mixture of silica and alumina can be used) is used to make the converter more efficient, often as a mixture of silica & alumina. The washcoat when added to the core, forms a rough, irregular surface, which has a far greater surface area than the flat core surfaces do, which then gives the converter  core a larger surface area, and therefore more places for active precious metal sites.

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The catalyst is added to the washcoat before being applied to the core.

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Pt is the most active catalyst and is most widely used.

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Pt & Rh are used as reduction catalysts.

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Pt & Pd are used as oxidaton catalysts.

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Cerium, Fe, Mn & Ni are also used.

CATCON LIGHT OFF TEMPERATURE 

Light off temperature of a catalytic converter is the temperature at which the catalytic converter become 50% effective.

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Typical light off temperature is 250 -300 degree celsius.

TYPES OF CATCON 

2 way catcon

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3 way catcon

2 WAY CATALYTIC CONVERTER 

Used in diesel engines

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Has two simultaneous tasks

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Oxidation of CO to CO2

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Oxidation of unburned hydrocarbons to C02 & water.

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Unable to control Nox emissions.

3 WAY CATALYTIC CONVERTER 

Used in SI engines.

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There is control of Nox, CO & HC emissions.

1.

Reduction of nitrogen oxides to nitrogen and oxygen.

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Oxidation of CO to CO2.

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Oxidation of unburned hydrocarbons to C02 & water 

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These three reactions occur most efficiently when the catalytic converter  receives exhaust from an engine running slightly above the stoichiometric point. This is between 14.6 and 14.8 parts air to 1 part fuel, by weight, for gasoline.

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When lean, the system is in oxidizing condition. In that case, the converter's two oxidizing reactions are favoured, at the expense of the reducing reaction.

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During rich condition reduction of NOx is favoured, at the expense of CO and HC oxidation. Three-way catalytic converters can store oxygen from the exhaust gas stream ( using Cerium), usually when the air fuel ratio goes lean. When insufficient oxygen is available from the exhaust stream the stored oxygen is released and consumed. This happens either when oxygen derived from Nox reduction is unavailable or certain maneuvers such as hard acceleration enrich the mixture beyond the ability of the converter to compensate.

EQUATIONS FOR REACTIONS IN A CATCON 

CO + NO

CO2 + N2

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C8H18 + NO

CO2 + N2 + H2O

DAMAGE TO CATCONS 

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Catalytic poisoning occurs when the catalytic converter is exposed to exhaust containing substances that coat the working surfaces, thus encapsulating the catalyst so that it cannot contact and treat the exhaust. The most notable contaminant is lead. Other common catalyst poisons include fuel sulphur, manganese, silicone, and phosphorous.

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 Any condition that causes abnormally high levels of unburned hydrocarbons (raw or partially burned fuels) 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

NEGATIVE ASPECTS OF CATCON 

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Some early converter designs created a great deal of restriction to the flow of  exhaust, which negatively affected vehicle performance, drivability and fuel economy. Has a long warm-up time period. The catalyst light off temperature is 250  – 300 degree celsius. 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.

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Reduces fuel economy of cars resulting in a greater use of fossil fuels.

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 Although catcon reduces the hydrocarbons & other harmful emissions, most of the exhaust gases leaving the engine through the catcon is CO2, which is responsible for  greenhouse effect.

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Pt, Pd & Rh are precious metals and hence are expensive.

CONCLUSION 

Catalytic converter is a very effective device to reduce the emissions from IC engines.

REFERENCES [1]Heck, R. M., Farrauto, R. J. and Gulati, S. T., Catalytic Air  Pollution Control: Commercial Technology, 2nd Ed. John Wiley & Sons, New York; 2002 [2] Gulati, S. T., Ceramic Catalyst Supports for Gasoline Fuel, Chap.2 in Structured Catalysts and Reactors, 2nd Ed. Taylor & Francis Group, Boca Raton, FL; 2006

[3] Catalytic Converters. International Platinum Group Metals  Association. Retrieved January 10, 2011. [4] http://en.wikipedia.org/wiki/Catalytic_converter  [5]