All about Catalytic converter — Carengineered.com
Introduction
Automobiles produce power in the combustion chamber. This combustion takes place by burning the fuel in the presence of air.
This combustion process leads to the emission of various harmful gases such as Nitrogen Oxide, Carbon Monoxide, etc and also this combustion process is quite loud that also requires various components to reduce it.
The Catalytic Converters are the exhaust emissions control component/device that is used to reduce the emission of highly toxic gases after the combustion process from an internal combustion system engine by the catalyzing or redox reaction.
It converts almost 98% of the harmful and toxins produced into less harmful gases.
These Catalytic converters were initially used in the year 1975 in American production cars due to the EPA regulations on the toxic emission reduction.
A catalytic converter is nothing but a metal box, constructed like a honeycomb structure from inside assisted by layers of insulation and has 2 openings as the Inlet and the Outlet.
The function of the input pipe is to bring the hot and polluted fumes from the engine cylinder after the combustion process for the treatment by the catalyst and the outlet pipe is used to divert the treated gases to the tailpipe, also known as the exhaust.
This honeycomb structure is fabricated with thin and light wall channels with a layer of washcoat made up of Aluminium oxide, which in turn helps to increase the surface area allowing more of the reaction to take place.
There are 2 types of the catalysts
One of them treats nitrogen oxide pollution by using a chemical process known as the reduction process or removing oxygen.
This splits up the nitrogen oxides molecules into the nitrogen molecule and oxygen molecule gases that are harmless because they already exist in the air around us.
The other catalyst works by an opposite chemical process also known as oxidation ie the process of adding oxygen which turns carbon monoxide into carbon dioxide.
Another oxidation reaction turns unburned hydrocarbons in the exhaust into carbon dioxide and water.
Chemical reactions involved
Two-way types of catalytic converters
A 2-way (or “oxidation”, sometimes called an “oxi-cat”) catalytic converter has two simultaneous processes:
The Oxidation of carbon monoxide to carbon dioxide
2 CO + O2 → 2 CO2
The Oxidation of hydrocarbons to carbon dioxide and water
CxH2x+2 + [(3x+1)/2] O2 → x CO2 + (x+1) H2O — — -> A combustion reaction
This type of catalytic converter is widely used in diesel engines to reduce the amount of hydrocarbon and carbon monoxide emissions.
Three-way types of catalytic converters
Three-way catalytic converters (TWC) have an additional advantage leading to control gases like the emission of nitric oxide (NO) and nitrogen dioxide.
Reduction of nitrogen oxides into elemental nitrogen and oxygen:
NOx→Nx+Ox(1)
Oxidation of carbon monoxide to carbon dioxide:
CO+O2→CO2(2)
Oxidation of hydrocarbons into carbon dioxide and water:
CxH4x+2xO2→xCO2+2xH2O(3)
Catalytic restrictions and destruction
The catalytic converter is a sensitive mechanical component that is employed with precious metals coating the inside.
Without these metals, the redox reactions may not be possible.
There are several substances and chemicals that restrict the functioning of the catalytic converter.
Lead: Engines run with filtered fuel with no lead present.
Now, if a lead is added to the fuel and is then burned, it leaves a residue that coats the catalytic metals (Pt, Rh, Pd, and Au) and also helps prevents the contact with the exhaust fumes, that is necessary for performing the necessary redox reactions.
Manganese and silicon: Manganese is primarily found in the organometallic compound MMT (methylcyclopentadienyl manganese tricarbonyl).
This is important since higher performing engines generally have a high compression ratio, that would need a higher octane gas to complement the amount of compression in the engine, and has now been banned from commercial sale due to the EPA’s regulations.
Silicon can leak from the combustion chamber into the exhaust stream from the coolant inside the engine.
These contaminants prevent the catalytic converter from functioning properly.
Contribution to Global Warming
Although the catalytic converter has huge advantages and has helped reduce the toxic emissions from the car engines, it also has destructive environmental effects.
Due to the conversion of hydrocarbons and carbon monoxide, carbon dioxide is also produced. Carbon dioxide is one of the most common greenhouse gases and contributes significantly to global warming.
Along with carbon dioxide, the converters sometimes rearrange the nitrogen-oxygen compounds to form nitrous oxide. This is the same compound used in laughing gas and as a speed enhancer in cars.
Originally published at https://www.carengineered.com on August 11, 2020.
