| 摘要 |
PROBLEM TO BE SOLVED: To remove nitrate and sulfate adsorbed to a nitrogen oxide storage reduction catalyst by returning an excess air rate to an original rate after operated at a certain time, setting the excess air rate to a specific value. SOLUTION: When an excess air rate is in a lean burn state, an oxygen ion Oz- or Oz- and NOx are reacted to generate a nitrate ion NO3-, the nitrate ion NO3- is adsorbed to a surface of a catalyst 1 thereby forming a nitrate. The nitrate on the catalyst 1 is in a saturated state, the excess air rate is made slightly smaller than λ=1.0, and an internal combustion engine is operated in a rich state for five to six minutes whereby the nitrate is reacted with an unburned HC and CO contained in an exhaust gas. Accordingly, the nitrate on the catalyst 1 is decomposed into an N2, CO2 and H2O and reduced thereby to be removed. After conduction of rich spike, the excess air ratio is set again to be in the lean state (λ=1.5). Accordingly, NOx in the exhaust gas is reduced by the nitrogen oxide storage reduction catalyst to reduce the amount of NOx discharged to the atmosphere. |
