EMISSION CONTROL TECHNOLOGIES

Three-Way Catalysts

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

Carbon Monoxide (CO) → Carbon Dioxide (CO₂)
Hydrocarbons (HC) → Water (H₂0)
Oxides of Nitrogen (NO_x) → Nitrogen (N₂)

3-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, as shown in the figure below.

There are many reaction pathways in a 3-way catalyst system, including those shown for the oxidation catalyst. The most important reactions for removing NO_x can be summarised as:

2CO + 2NO → 2CO₂ + N₂
[HC] + NO →N₂ + CO₂ + H₂O