Catalytic converters are placed in a car's exhaust system in order to reduce Nitrogen Oxides, CO, and unburned Hydrocarbons. They are referred to as catalytic converters because they use catalysts in order to speed up the reactions which remove pollutants from an automobile's exhaust. In most modern catalytic converters, the catalysts are rhodium, palladium, and platinum and the framework supporting the metal is ceria zirconia.
REDUCTION CATALYST
2NO→ N2 + O2
This reaction in the catalytic converter is important when there is too little
gasoline and the engine is producing nitrogen oxides. The
converter catalytically removes oxygen from a
nitrogen oxide, producing
harmless nitrogen and oxygen gases. Some of the oxygen is stored in the ceria zirconia
framework like a "sponge". This "sponge-like" ability of the ceria zirconia
oxide to "soak up" and later release oxygen is a major reason why modern
catalytic converters are so effective.
OXIDATION CATALYST
2CO + O 2 → 2CO2
This oxidation reaction is important when the engine has too much gasoline
and is producing CO. However, the converter catalytically
adds oxygen to a molecule this time. Some of the oxygen it needs can be squeezed out of
the ceria zirconia "oxygen sponge". Without the availability of this extra
oxygen this reaction would be difficult. Notice in the following animation
how a ceria crystal lattice provides the oxygen necessary to convert carbon
monoxide to carbon dioxide.
