Which device converts exhaust pollutants into less harmful substances through chemical reactions?

• A. Oxygen sensor
• B. Catalytic converter
• C. Muffler
• D. Exhaust manifold

Answer: (B)

Converting exhaust pollutants into less harmful substances through chemical reactions is the job of the catalytic converter. It sits in the exhaust stream and uses a catalyst made of precious metals to speed up oxidation and reduction reactions. As exhaust passes through, carbon monoxide and unburned hydrocarbons react with oxygen to form carbon dioxide and water, while nitrogen oxides are reduced to nitrogen and oxygen. This process works best after the engine reaches operating temperature, when the catalyst becomes effective. The catalytic converter is different from an oxygen sensor, which only measures oxygen levels to help adjust fuel, from a muffler, which mainly reduces noise, and from an exhaust manifold, which collects exhaust from the cylinders.