Catalytic Converters of Oxides Of Nitrogen
post Monday, 24 December 2012 speech bubble 0 comment(s)

Histogram chart comparing effectiveness of two- and three-way catalytic converters at reducing emission of hydrocarbons, nitrogen oxide, and carbon monoxide.
Three different chemical reactions would be happening concurrently. After all the reactions have occurred, mostly nitrogen, oxygen, carbon dioxide, and steam(water) would be emerging from the exhaust.

How a catalytic converter works
Artwork showing the parts inside a catalytic converter
Before catalytic converters were developed, waste gases made by car engines would blow into the exhaust tailpipe and then into the atmosphere. The converter would sit between the engine and the tailpipe, however it does not act like a filter found in everyday life: it changes the chemical composition of the exhaust gases by changing the positions of the atoms:
Artwork explaining how catalytic converters strip away pollution molecules
  1. Molecules of exhaust gases are pumped from the engine and through the honeycomb structure coated with catalyst, made from platinum, palladium, or rhodium.
  2. The catalyst break the bonds between the molecules, forming single atoms.
  3. The atoms then create bonds forming molecules of substances such as carbon dioxide, nitrogen, and water, which blow out harmlessly through the exhaust.

Molecules of exhaust gases are pumped from the engine and through the honeycomb structure coated with catalyst, made from platinum and rhodium to reduce nitrous oxides. As the nitrous oxide molecules are passing through the catalyst, it would allow the free moving oxygen to form oxygen gas by removing the nitrogen atom. The nitrogen atom that is attached to the catalyst would react with other attached nitrogen atoms to form nitrogen gas.

  • Reduction Reaction 1: 2NO => N2 + O2
  • Reduction Reaction 2: 2NO2 => N2 + 2O2
Next, an oxidative catalyst of platinum and palladium decreases emissions of carbon monoxide (CO) and unburned hydrocarbons (HC).
  • Oxidation Reaction 1: 2CO + O2 => 2CO2
  • Oxidation Reaction 2: H4C2 + 3O2 => 2CO2 + 2H2O  


Chart: Effectiveness of catalytic converters. Figures show pollutants in grams per kilometer at 80,000 kilometers. Chart drawn by Explain that Stuff.com using data for light-duty gasoline fueled vehicles from US EPA (1990), quoted in table 3.2 (page 75) of Air Pollution from Motor Vehicles: Standards and Technologies for Controlling Emissions, Faiz et al, World Bank, 1996.
http://www.explainthatstuff.com/catalyticconverters.html
http://www.explorecuriocity.org/Content.aspx?ContentID=1779
Chemistry "O"Level TextBook 
http://www.lordgrey.org.uk/~f014/usefulresources/aric/Resources/Teaching_Packs/Key_Stage_4/Acid_Rain/07.html

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