Catalytic Catalytic ConverterConverter

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Uses of a Catalytic Uses of a Catalytic ConverterConverter

A catalytic converter is a device used to A catalytic converter is a device used to reduce the toxicity of emissions from an reduce the toxicity of emissions from an internal combustion engine.

Catalytic converters are most commonly used Catalytic converters are most commonly used in in motor vehicle exhaust systems.

Catalytic converters are also used on Catalytic converters are also used on generator sets, forklifts, mining equipment, trucks, buses, trains, and other engine-equipped machines.

A catalytic converter provides an environment A catalytic converter provides an environment for a for a chemical reaction wherein toxic combustion by-products are converted to less-toxic substances.

Brief History of Brief History of the Catalytic the Catalytic Converter.Converter.The catalytic converter was first invented by The 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 The catalytic converter was further developed by by John J. Mooney and Carl D. Keith at the Engelhard Corporation, creating the first production catalytic converter in 1973.

Construction of a Construction of a Catalytic Catalytic ConverterConverter

Metal-core converterMetal-core converter

Ceramic-core converter Ceramic-core converter

The core is often a The core is often a ceramic honeycomb in in modern catalytic converters, but modern catalytic converters, but stainless steel foil honeycombs are used, too.

The honey-comb surface The honey-comb surface increasesincreases the the amount of amount of surface area surface area available to support available to support the catalyst, and therefore is often called a the catalyst, and therefore is often called a ""catalyst supportcatalyst support". ".

A A washcoatwashcoat is used to make converters more is used to make converters more efficient, often as a mixture of efficient, often as a mixture of silica and alumina.

The washcoat, when added to the core, The washcoat, when added to the core, forms a forms a roughrough, irregular surface, which has a , irregular surface, which has a far far greater surface area greater surface area than the flat core than the flat core surfaces do, which then gives the converter surfaces do, which then gives the converter core a larger surface area, and therefore core a larger surface area, and therefore more places for active precious metal sites. more places for active precious metal sites.

The The catalyst is added to the washcoat catalyst is added to the washcoat (in suspension) before being applied to (in suspension) before being applied to the core.the core.

Platinum is the most active catalyst and is widely used.

Palladium and rhodium are two other precious metals used.

Platinum and rhodium are used as a Platinum and rhodium are used as a reduction catalyst reduction catalyst ..

Platinum and palladium are used as an Platinum and palladium are used as an oxidization catalystoxidization catalyst..

Cerium, iron, manganese and nickel are also used.

Types of Catalytic Types of Catalytic Converters.Converters.

Two Way Catalytic Two Way Catalytic ConverterConverter

A two-way catalytic converter has two A two-way catalytic converter has two simultaneous tasks. simultaneous tasks.

Oxidation of carbon monoxide to carbon dioxide: 2CO + O22 → 2CO → 2CO22

OxidationOxidation of of unburnt hydrocarbons unburnt hydrocarbons (unburnt and partially-burnt fuel) to (unburnt and partially-burnt fuel) to carbon dioxidecarbon dioxide and and water: CxxHH(2x+2)(2x+2) + + [(3x+1)/2] O[(3x+1)/2] O22 → xCO → xCO22 + (x+1) H + (x+1) H22O (a O (a combustion reaction)combustion reaction)

Unable to control Unable to control NOx gases. gases.

Three Way Three Way Catalytic Catalytic ConverterConverterReduction of nitrogen oxides to nitrogen

and oxygen: 2NOxx → xO → xO22 + N + N22

Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 2 → 2CO→ 2CO22

Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxxHH(2x+2)(2x+2) + [(3x+1)/2]O + [(3x+1)/2]O2 2

→ xCO→ xCO22 + (x+1)H + (x+1)H22OO

Unwanted reactions can occur in the three-Unwanted reactions can occur in the three-way catalyst, such as the formation of way catalyst, such as the formation of odiferous odiferous hydrogen sulfide and ammonia.

Damage to Damage to Catalytic Catalytic

ConvertersConvertersCatalyst poisoning occurs when the catalytic Catalyst poisoning occurs when the catalytic converter is exposed to exhaust containing converter is exposed to exhaust containing substances that coat the working surfaces, substances that coat the working surfaces, encapsulating the catalyst so that it cannot encapsulating the catalyst so that it cannot contact and treat the exhaust.contact and treat the exhaust.

The most notable contaminant is lead .The most notable contaminant is lead .

Any condition that causes abnormally high Any condition that causes abnormally high levels of unburned hydrocarbons — raw or levels of unburned hydrocarbons — raw or partially-burnt fuel — to reach the converter partially-burnt fuel — to reach the converter will tend to significantly will tend to significantly elevate its elevate its temperaturetemperature, bringing the risk of a , bringing the risk of a meltdownmeltdown of the substrate and resultant catalytic of the substrate and resultant catalytic deactivation and severe exhaust restriction . deactivation and severe exhaust restriction .

Negative Aspects Negative Aspects of Catalytic of Catalytic Converters.Converters.Some early converter designs created a Some early converter designs created a

great deal of restriction to the flow of great deal of restriction to the flow of exhaust, which negatively exhaust, which negatively affected affected vehicle performance, drivability, and vehicle performance, drivability, and fuel economy .fuel economy .

It had been stated that catalytic It had been stated that catalytic converters are known in a lot of cases converters are known in a lot of cases to have an excessively long to have an excessively long warm-up warm-up time periodtime period, in a great deal of cases , in a great deal of cases ranging up to thirty-minutes.ranging up to thirty-minutes.

The The Environmental Environmental

Impact of Impact of Catalytic Catalytic

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

Although catalytic converters are effective at Although catalytic converters are effective at removing hydrocarbons and other harmful removing hydrocarbons and other harmful emissions, most of exhaust gas leaving the emissions, most of exhaust gas leaving the engine through a catalytic converter is carbon engine through a catalytic converter is carbon dioxide (COdioxide (CO22), which is responsible for the ), which is responsible for the green green house house effect.effect.

Catalytic converter production requires Catalytic converter production requires palladium and/or platinum; part of the world palladium and/or platinum; part of the world supply of these precious metals is produced near supply of these precious metals is produced near the Russian city of Norilsk, where the industry the Russian city of Norilsk, where the industry (among others) has caused Norilsk to be added (among others) has caused Norilsk to be added to Time Magazine's list of most polluted places.to Time Magazine's list of most polluted places.