Exhaust catalyst system includes three-way catalyst removing reductants carbon monoxide and hydrocarbons, followed by two nitrogen oxide storage catalysts optimized for operation at different temperatures

摘要

A catalyst system (10) in an exhaust line includes successive nitrogen oxide (NOx) storage catalysts (18, 20). An Independent claim is also included for a method of purifying exhaust gas, using the above system. NOx from lean burn operation is absorbed in the first and/or second NOx storage catalyst(s). After exceeding an NOx desorption temperature at the first catalyst, and an NOx desorption temperature at the second catalyst, or after exceeding a storage volume for NOx at the first catalyst and/or a storage volume for NOx at the second catalyst, the engine is operated in a rich mode.