Every day to the roads of major cities come millions of cars, each of which is a source of air pollution. Therefore, to solve the pollution problems, each country produces laws that set the acceptable level of pollution for cars.
Catalytic converters, or simply catalysts are the devices in the exhaust system of a vehicle that are designed to reduce the emission of toxic exhaust gases through the reduction of nitrogen oxides and the use of oxygen for after burning of carbon monoxide and unburned hydrocarbons. In 1975, on the market appeared a new device called a catalytic converter, or simply catalyst. The first car equipped with the catalyst was a car brand Chrysler Avenger. In this car was used platinum-based catalyst with the addition of rhodium.
Gasoline is a mixture of many hydrocarbons. The main components of unleaded gasoline are:
- 20% of volatile hydrocarbons consisting of butane and pentane with a boiling point of about 0 C and 35 C, respectively. They provide volatility required for a cold start.
- 30% of aromatic substances, consisting of about 1% benzene and toluene
- 5% of the alkanes, and alkyl hydrocarbons.
Theoretically, an ideal combustion of gasoline in air yields a mixture consisting of about 14% carbon dioxide (CO2), 12% water vapor (H2O), and the balance nitrogen gas (N2). These emissions are basically not dangerous, although it is considered, emission of carbon dioxide (CO2) to contribute to global warming.
However, automobile exhaust gases also contain hydrocarbons HC (byproduct of combustion), H2, CO and nitrogen oxides NO. It is on the decline in their level are focus the catalytic converters:
- Carbon monoxide (CO) – a poisonous gas is colorless and odorless
- Hydrocarbons, also known as volatile organic compounds – one of the main components of smog, is formed by the incomplete combustion of fuel
- Nitrogen oxides (NO and NO2, which are often combined under the designation of NOx) – as a component of smog and acid rain impact on human mucosa.
Modern automotive exhaust system equipped with three catalytic converters, one for each of the substances whose emissions should be reduced.
Reduction catalyst – is the first stage of the catalytic converter. It uses platinum and rhodium to reduce emissions of NOx. When a molecule of NO or NO2 molecules occurs catalyst, it is separated from the nitrogen atom releasing oxygen – O2. The nitrogen atom is bound to another nitrogen atom to form N2.
The second stage of the catalytic converter – is oxidation catalyst. This significantly reduces the amount of unburnt fuel and carbon monoxide as a result of combustion (or oxidation) using such catalysts as palladium and platinum. This catalyst also helps CO react with unburned oxygen to form carbon dioxide CO2.
The third stage is a control system that control the fuel injection system.
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