What is the function of a catalytic converter?

• A. Increase engine horsepower by burning extra fuel
• B. Filter exhaust particulates in the exhaust stream
• C. Cool the exhaust gas before it reaches the tailpipe
• D. Reduce pollutants by converting CO, hydrocarbons, and NOx into CO2, H2O, and N2 through catalytic reactions

Answer: (D)

The function of a catalytic converter is to reduce harmful exhaust pollutants by speeding up chemical reactions that convert toxic gases into less harmful ones. Inside, precious metals act as catalysts to promote oxidation and reduction: carbon monoxide and unburned hydrocarbons react with oxygen to form carbon dioxide and water, while nitrogen oxides are reduced to nitrogen and oxygen. This works best when the engine is running at the right air–fuel balance and the exhaust is hot enough for the catalyst to be effective. It’s not primarily a filter or a cooler, and it doesn’t directly increase engine power.