Three-way catalysts

Three-way catalysts (TWC) are designed to simultaneously convert three pollutants to harmless emissions:

• Carbon Monoxide (CO) → Carbon Dioxide (CO₂)
• Hydrocarbons (HC) → Water (H₂O)
• Oxides of Nitrogen (NOx) → Nitrogen (N₂)

A three-way catalyst can cut CO, HC and NO_x by over 99% if the air to fuel ratio is accurately controlled. Three-way catalysts will only give full conversion of each of these three pollutants in a gas stream containing a stoichiometric ratio of CO and NO_x.