How does a catalytic converter reduce pollution from a gasoline engine?

A catalytic converter reduces pollution from a gasoline engine by facilitating chemical reactions that transform harmful exhaust gases into less toxic substances before they are released into the atmosphere.12

The device consists of an insulated chamber containing a ceramic honeycomb structure or pellets coated with catalysts—typically precious metals such as platinum, palladium, or rhodium. As hot exhaust gases pass through this structure, the catalysts trigger the following conversions:1342

• Oxidation: Unburned hydrocarbons and carbon monoxide are oxidized to form water vapour and carbon dioxide.14
• Reduction: Nitrogen oxides are chemically reduced into nitrogen and oxygen.13

These reactions are most effective once the converter reaches high operating temperatures, typically around 500 °C (900 °F). Because these systems cannot catalyze emissions effectively during the initial engine warm-up phase, some modern vehicles use preheating methods to minimize pollution during that period.23