Three Way Catalytic (TWC) Converter
WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2009 Mercury Mountaineer, 2009 Mercury Milan, 2009 Mercury Mariner, 2009 Mercury Grand Marquis, and 2009 Lincoln Town Car. 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.