7/29/2019 Catalytic Converter Neerav Gadhvi 09001023

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Catalytic converters are devices which convert toxic byproducts of combustion in the exhaust of

an internal combustion engine to less toxic substances by way of catalyzed chemical reactions.

Exhaust emissions from internal combustion engines contain pollutants mainly, hydrocarbons (CmHn),

carbon monoxide (CO), and nitrogen oxides (NO, NO2). By using special catalysts and a suitable air-to-fuelratio in spark-ignited internal combustion engines, the three classes of pollutants can be removed together in asingle catalytic converter.

Nowadays, most new cars are equipped with what is called a three-way catalytic converter.

A three-way catalytic converter has three simultaneous tasks:1.Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx xO2 + N22.Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 2CO23.Oxidation of unburnt hydrocarbons to carbon dioxide & water: CxH2x+2 + [(3x+1)/2]O2 xCO2 + (x+1)H2O

There are two main parts to the catalytic converter:

Reduction CatalystThe reduction catalyst is the first step that the exhaust goes through in the catalytic converter. The catalysts used

in this part are platinum and rhodium to break now NO and NO2 molecules in to N2 and O2 gases which are

non-polluting. This process occurs using either of the following two chemical equations:

For NO:2NO N2 + O2

For NO2:2NO2 N2 + 2O2

Oxidation Catalyst

The oxidation catalyst is the second stage of the catalytic converter that oxidizes hydrocarbons and carbonmonoxide with palladium and platinum as catalysts in a combustion reaction. The chemical formula for this part

is:

2CO + O2 2CO2

Cerium is also used as it promotes oxygen storage to improve oxidation efficiency.

Besides NO, CO, & hydrocarbons, diesel engines emit particulate matter & removal of it is a physical

separation process. The exhaust gas is forced to flow through a filter material with pores smaller than or similar

in size to the particles. The filter must be regenerated by burning the trapped particulate matter with the oxygen

present exhaust which requires high temperatures (550C). Since such temperatures are rarely reached in the

exhaust of diesel vehicles other methods like catalytically lowering the ignition temperature of the soot areimplemented. Also there are systems called continuously regenerating trap (CRT), here naturally occurring NO

is oxidized by a strong oxidation catalyst to NO2, which continuously oxidizes the deposited particulate matter.

Conclusion

A major remaining challenge for the automotive industry is the lowering of fuel consumption and CO 2emissions. This is also a challenge for catalyst development, since the most fuel-efficient engines operate with

excess air, & the conventional three-way catalyst does not allow NOxreduction under these conditions. New

technologies are being developed that allow fuel-efficient lean operation of the engine and at the same timeretain the high emission standards of conventional three-way catalysts.

http://en.wikipedia.org/wiki/Redoxhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Redoxhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Redoxhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Redox