How Does a Catalytic Converter Reduce Emissions?

A catalytic converter contains a honeycomb ceramic or metallic substrate coated with platinum, palladium, and rhodium. As hot exhaust gases flow through, these metals catalyse three main reactions: oxidation of carbon monoxide to carbon dioxide, oxidation of unburned hydrocarbons to CO₂ and water, and reduction of nitrogen oxides (NOₓ) to nitrogen and oxygen. This "three-way" converter works best at operating temperatures above 400°C and requires a precisely controlled air-fuel mixture. Modern converters reduce harmful emissions by over 90%. The precious metals are so valuable that catalytic converter theft has become a significant problem worldwide.