Catalytic Reduction of NO_x in Oxygen-Rich Gas Streams, Deactivation of NO_x Storage-Reduction Catalysts by Sulfur

摘要

The results clearly reveal the existence of two pathways of deactivation for NO_x storage reduction catalysts. Under lean conditions (exposure to SO_2 and O_2) surface sulfates are formed on the storage component (Ba), which subsequently migrate into the bulk phase. These species are hardly reducible by C_3H_6 up to 550℃ and, thus, permanently block the Ba sites, which leads to a decrease of NO_x storage capacity during successive cyclic treatments. A second pathway of deactivation by sulfur species is proposed to occur during fuel-rich (reducing) conditions. Sulfides seem to be formed at 350 and 500℃ on platinum, which block the metal surface and, therefore, diminish the NO_x reduction function of the noble metal during the fuel rich reaction cycles.