The DOC operates based on the principles of catalysis. The exhaust gases pass through a honeycomb-structured substrate coated with a catalyst, typically comprising precious metals like platinum, palladium, and rhodium. These catalysts facilitate the oxidation reactions that convert CO and HCs into carbon dioxide (CO₂) and water (H₂O). Additionally, the DOC can also oxidize a portion of the soluble organic fraction (SOF) of PM.