Three Way Catalytic (TWC) Converter
WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2010 Mercury Milan, 2010 Mercury Mariner, 2010 Mercury Grand Marquis, 2010 Lincoln Town Car, and 2010 Lincoln Navigator L. However, it is still accessible from the selected car via links, so may be relevant.
The TWC contains either platinum (Pt) and rhodium (Rh) or palladium (Pd) and rhodium (Rh). The TWC catalyzes the oxidation reactions of unburned HCs and CO and the reduction reaction of NOx . The 3-way conversion can be best accomplished by always operating the engine air fuel/ratio at or close to stoichiometry.