Our environment has been polluted day by day. It is the truth that we all know that human beings are only responsible for this situation.
The main highlighted reasons for environmental pollution are mining, poor disposal of waste, industries, deforestation, and the use of fossil fuels.
Automobile and pollution
We all know that the majority of vehicles that we can see today are using petrol or diesel as fuel. So vehicles play an important role in the usage of fossil fuels.
Ignition of these types of fossil fuels is causing the emission of some highly toxic gases, Which leads to environmental pollution.
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The toxic gases emitted from an automobile are,
1. Hydrocarbons(HC): Hydrocarbons are produced from partially burned or unburned fuel.
2. Carbon monoxide(CO): Carbon monoxide is seen in the gases emitted from fully burned fuels.
So it is the responsibility of each vehicle manufacturer to comply with the government-mandated emission control norms.
In the case of an automotive engine, it is not really feasible to prevent the production of such gases inside the engine purely. But it is possible to reduce the intensity of these toxic gases through the use of some pollution control devices.
In modern car engines, the manufacturer tries to keep the air-fuel ratio very close to the stoichiometric point for the complete combustion of the fuel. It controls the production of hydrocarbons significantly.
The stoichiometric point denotes the exact air-fuel ratio for the complete combustion of fuel. For a petrol engine, this is calculated as 14.7:1 and for diesel engines, it is 14.5:1.
Anyway, there are limitations to controlling the production of such harmful gasses. So there is a need for some pollution control devices to minimize the intensity of these gases.
The chemical process that takes place inside the catalytic converter is a redox reaction. That is both the oxidation and reduction processes are occurring.
There are two types of catalytic converters
Out of these two types, the three-way catalytic converters are now commonly used in automobiles. It has an additional ability to reduce NOx emission if compared to the two-way catalytic converters.
The highly expensive metals used in the catalytic converter as a catalyst, they are
4HC + 5O2 = 4CO2 + 2H2O
3. Nitrogen oxides(NOx): Nitrogen oxides are forming the result of the reaction between nitrogen and oxygen at high temperatures.
The inhaling of carbon monoxide gases can cause many health problems in humans and other organisms. The chemicals like hydrocarbons and nitrogen oxides will cause environmental problems such as acid rain, smog, and global warming.
So it is the responsibility of each vehicle manufacturer to comply with the government-mandated emission control norms.
In the case of an automotive engine, it is not really feasible to prevent the production of such gases inside the engine purely. But it is possible to reduce the intensity of these toxic gases through the use of some pollution control devices.
In modern car engines, the manufacturer tries to keep the air-fuel ratio very close to the stoichiometric point for the complete combustion of the fuel. It controls the production of hydrocarbons significantly.
The stoichiometric point denotes the exact air-fuel ratio for the complete combustion of fuel. For a petrol engine, this is calculated as 14.7:1 and for diesel engines, it is 14.5:1.
Anyway, there are limitations to controlling the production of such harmful gasses. So there is a need for some pollution control devices to minimize the intensity of these gases.
Catalytic Converters and types
It is a pollution control device, placed in front of the muffler in an exhaust system. It is used to minimize the intensity of the toxic gasses emitting from the engine.
The chemical process that takes place inside the catalytic converter is a redox reaction. That is both the oxidation and reduction processes are occurring.
There are two types of catalytic converters
Two-way catalytic converter
Three-way catalytic converter
Three-way catalytic converter
Two-way catalytic converter
A two-way catalytic converter allows mainly two processes.
✓ Oxidation of carbon monoxide: It oxidizes the harmful carbon monoxide(CO) to form less harmful carbon dioxide(CO2).
✓ Oxidation of hydrocarbons: It oxidizes the hydrocarbons(HC) to form carbon dioxide(CO2) and water(H2O).
Three-way catalytic converter
A three-way catalytic converter allows mainly three processes.
✓ Oxidation of carbon monoxide: It oxidizes the harmful carbon monoxide(CO) to form less harmful carbon dioxide(CO2).
✓ Oxidation of hydrocarbons: It oxidizes the hydrocarbons(HC) to form carbon dioxide(CO2) and water(H2O).
✓ Reduction of nitrogen oxides: It allows for the formation of nitrogen(N2) and oxygen(O2) through the reduction of nitrogen oxides(NOx).
Out of these two types, the three-way catalytic converters are now commonly used in automobiles. It has an additional ability to reduce NOx emission if compared to the two-way catalytic converters.
The catalyst used in the catalytic converter
A catalyst is a substance that is used to increase the rate of a chemical reaction.The highly expensive metals used in the catalytic converter as a catalyst, they are
Platinum
Palladium
Rhodium
Palladium
Rhodium
For proper working, allow the maximum amount of exhaust gases to pass through the catalyst surface. So the catalysts are arranged in a specific structure to provide maximum surface area.
There are two types of catalyst structures in a catalytic converter.
Honeycomb structure
Ceramic beads
Ceramic beads
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Among these, the honeycomb structure is widely used in most cars today.
Working of a catalytic converter
The chemical process that takes place in a catalytic converter is a redox reaction, which means both oxidation and reduction are occurring.Oxidation of carbon monoxide and hydrocarbons
2CO + O2 = 2CO24HC + 5O2 = 4CO2 + 2H2O
Reduction of nitrogen oxides
2NO = N2 + O2
2NO2 = N2 + 2O2
2NO2 = N2 + 2O2