The second key to motor-vehicle pollution control is the catalytic converter.
A catalytic converter consists of a ceramic honeycomb substrate coated with a thin layer of a catalyst and mounted in a metal chamber that funnels all of the hot engine exhaust gases through the coated honeycomb.
A cutaway cross section of a catalytic converter is shown in Figure 9-2.
A catalyst is a material that encourages chemical reactions to occur but is not involved in the reaction and is not consumed.
The catalyst is specially designed to cause the pollutants carbon monoxide, nitrogen oxide, and unburned hydrocarbon compounds (soot) to be chemically converted to harmless water, nitrogen, and carbon dioxide.