METHOD FOR THE REACTIVATION OF THERMALLY AGED NITROGEN OXIDE STORAGE CATALYTIC CONVERTERS

摘要

Nitrogen oxide storage catalytic converters are used for eliminating the nitrogen oxides contained in the lean exhaust gas of lean-running engines. The purifying effect is obtained by the fact that the nitrogen oxides are stored in the form of nitrates by the storage material of the storage catalytic converter in a lean operating phase of the engine while said nitrates are decomposed and the released nitrogen oxides are reacted to nitrogen, carbon dioxide, and water with the reducing exhaust gas concentrations on the storage catalytic converter in a subsequent rich operating phase. Storage catalytic converters age thermally as a result of elevated temperatures as the catalytically active precious metal components of the catalytic converter sinter and the storage components bond with the carrier materials. According to the invention, the formation of bonds by the storage materials can be largely reversed by treating the storage material with a gas mixture containing nitrogen oxide and/or carbon dioxide and steam at temperatures ranging between 300 and 500 °C. The reactivation process can take place directly on the vehicle by adjusting adequate exhaust gas conditions or can be performed during routine maintenance by dismounting the catalytic converter and treating the same with a gas mixture in an appropriate apparatus.