What happens to the exhaust gases in a catalytic converter?

In a catalytic converter, exhaust gases undergo a chemical reaction facilitated by catalysts that convert harmful pollutants into less harmful substances. Specifically, the catalytic converter typically reduces nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (HC) into nitrogen (N2), carbon dioxide (CO2), and water (H2O).

This process occurs through two main types of reactions: oxidation and reduction. During oxidation, carbon monoxide and unburned hydrocarbons are transformed into carbon dioxide and water. During reduction, nitrogen oxides are converted into nitrogen and oxygen. The use of catalysts (such as platinum, palladium, and rhodium) is crucial, as they lower the activation energy needed for these reactions to occur, making the conversion efficient at the temperatures typically present in the exhaust system.

The option suggesting that the gases are expelled with no change does not reflect the purpose or function of a catalytic converter, as that would go against its role in emission control. Similarly, gases being cooled and released or igniting further do not accurately represent the fundamental operation of this important engine component.