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Controlling Air Pollution
The internal combustion in a modern car emits various atmospheric pollutants, these are mainly:
Oxides of nitrogen
CO is a poisonous gas emitted into the atmosphere from the incomplete combustion of hydrocarbons
and other organic compounds. Most of it comes from traffic pollution. It is very dangerous because it
can replace the oxygen in the blood and have severe problems. Catalytic converters help oxidise CO
into CO .
1) Adsorption of CO onto active sites on the catalyst
2) Reaction with NO
3) Desorption of CO from the catalyst surface.
Oxides of Nitrogen
Nitrogen oxides are produced during high temperature combustion process as some of the nitrogen
from the air is oxidised by the oxygen. Two oxides of nitrogen are produced: nitrogen monoxide NO;
and nitrogen dioxide NO . So the mixture is commonly referred to as NO . They cause smog, create
low level ozone and contribute to acid rain. Catalytic converters help reduce oxides of nitrogen into
nitrogen, N .
1) Adsorption of NO onto active sites on the catalyst surface
2) Reaction with CO
3) Desorption of N from the catalyst surface.
Not all fuel burns in the engine-some escapes unchanged. The hydrocarbons are toxic and
carcinogenic. Catalytic converts help by oxidising the hydrocarbons to carbon dioxide and water.
The Catalytic Converter
Catalytic converters help remove those 3^ pollutants by:
How a catalytic converter functions
CO and NO gas molecules diffuse over the catalytic surface of the metal. Some of the molecules are
absorbed on to the metal surface, (held by adsorption) forming temporary bonds. These bonds hold
the molecules in the correct position to react together on the metal surface. After the reaction, the
CO and N products are desorbed from the surfaces and diffuse away from the catalytic surface.