Three-Way Catalytic (TWC) Converter
WARNING: This page does not describe the selected car, but rather 31 other vehicles, including the 2008 Mercury Sable, 2008 Mercury Mountaineer, 2008 Mercury Milan, 2008 Mercury Mariner, and 2008 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.
The TWC converter contains either platinum (Pt) and Rhodium (Rh) or palladium (Pd) and Rhodium (Rh). The TWC converter 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 stoichiometric.