1. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
2. Oxidation of hydrocarbons (unburnt and partially burnt fuel) to carbon dioxide and water:
CxH 2x+2 + [(3x+1)/2] O2 → xCO2 + (x+1) H2O (a combustion reaction)
Its widely used on diesel engines to reduce hydrocarbon and carbon monoxide emissions.
Three-way
Three-way catalytic converters (TWC) have the additional advantage of controlling the emission
of nitrogen oxides (NOx), in particular nitrous oxid. This converter has three simultaneous tasks:
1. Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N 2
2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH 2x+2 +
[(3x+1)/2]O2 → xCO2 + (x+1)H2O.
Unwanted reactions can occur in the three-way catalyst, such as the formation of
odoriferous hydrogen sulfide and ammonia.
Damage
Catalyst poisoning occurs when the catalytic converter is exposed to exhaust containing
substances that coat the working surfaces. The most-notable contaminant is lead, so vehicles
equipped with catalytic converters can be run only on unleaded fuels. Other common catalyst
poisons include fuel sulfur, manganese and silicone, which can enter the exhaust stream if the
engine has a leak that allows coolant into the combustion chamber. Phosphorus is another
catalyst contaminant
Environmental impact
Catalytic converters have reduced noxious tailpipe emissions. However, they also have some
shortcomings and adverse environmental impacts in production:
·
An engine equipped with a three-way catalyst must run at the stoichiometric point, which
means more fuel is consumed than in a lean-burn engine, approximately 10% more
CO 2 emissions from the vehicle.
·
Catalytic converter production requires palladium or platinum; part of the world supply of
these precious metals is produced near Norilsk, Russia, where the industry has caused
Norilsk to be added to Time magazine's list of most-polluted places.
-Ananya Kanodia, S3E