A Research On The Storage-reduction Of NO_x Over Mn Modified Pd/Ba/Al Catalyst

NOx storage-reduction (NSR) technology can effectively remove NOx in the lean burn conditions, which was first proposed by the Toyota Corporation, and caused wide public attention. At present, the research on the catalysts mainly focus on the Pt-Ba-Al System. This kind of catalyst had excellent activity above 350℃, but when the temperature decreased, NO can not be effectively stored on the catalyst in the lean phase, thereby reduced the NOx removal efficiency of the catalysts.The performance of NOx storage capacity (NSC) and the activity of storage-reduction over a series of Pd/Mn/Ba/Al catalysts were investigated at different temperatures. The Pd catalysts were prepared by incipient impregnation and characterized by DRIFTS,TPD and TPSR. Some meaningful results were got as follows:1). The NOx storage capacity was studied over a series of catalysts at different temperature, it is found that the storage capacity of the catalyst is high at 30-300℃and decrease sharply at 400℃when Mn used as the storage component only; the NOx storage capacity first increased and then decreased with increasing temperature, and reached the maximum value at 400℃, when the Ba uesd as the storage component; The addition of Mn can significantly improved the storage activity of the traditional catalyst Pd/Ba/Al at low temperature, and the NOx storage capacity reached 850μmol·g-1 at 300-400℃, when the Mn and Ba used as the storage components together.2). Study of the formed species of NOx on the Pd/Ba/Al,Pd/Mn/Al and Pd/Mn/Ba/Al catalysts, it is found that the nitrite and nitrate were the main species on the catalysts.As the adsorption temperature up 300℃, the nitrate is the main NOx storage species, but the nitrate on the Mn was unstable and Mn couldn't provide the storage spaces at this temperature. However, the synergistic effect of Mn and Ba could promote the nitrate formed on the Pd/Mn/Ba/Al catalyst at the low temperature (<400℃).3). Study of the thermal stability of NOx species on the Pd/Ba/Al,Pd/Mn/Al and Pd/Mn/Ba/Al catalysts through the NOx-TPD, it is found that the thermal stability of nitrite is poor and nitrate is better. The nitrite is the main species on Mn and has poor thermal stability, the decomposition temperature of nitrate on the Ba was higher (> 500℃). The synergistic effect of Mn and Ba could promote the decompostion and decreased the decomposition temperature of nitrate on the Pd/Mn/Ba/Al catalyst. 4). Compared the NOX reduction activity of Mn/Ba/Al,Pd/Ba/Al,Pd/Mn/Al and Pd/Mn/Ba/Al catalysts, addition of Mn reduce the capacity of NOx reduction by H2-TPSR. But the reduction temperautre significantly decreased through adding Pd. This is important for reduction and regeneration of catalysts in the NOX storage-reduction (cycling).5). The temperature window of activity on the Pa/Ba/Al catalyst was narrow, the NOX conversion reached 62% at 400℃. The total NOX conversion was lower over the Pd/Mn/Al catalyst, reached 30% at 300-400℃. Compared to Pd/Ba/Al, the NOX conversion of the PMBA catalyst is three times at 300℃, from 16% to 53%.