Simultaneous removal of NO sub(x) and soot on Pt-Ba/Al sub(2)O sub(3) NSR catalysts

The potentiality of a typical Pt-Ba/Al sub(2)O sub(3) NSR catalyst in the simultaneous removal of particulate matter (soot) and NO sub(x) is investigated in this work, and compared with that of a Pt/Al sub(2)O sub(3) sample. The behaviour of the catalyst in the soot combustion and NO sub(x) removal has been separately analyzed by means of temperature programmed oxidation (TPO) experiments, isothermal combustions and transient response method (TRM), respectively. The results show that in presence of only oxygen, soot oxidation occurs slowly even at a temperature as high as 400 degree C. On the other hand, the presence of NO greatly increases the rate of soot conversion, which becomes significant at 350 degree C. The capability of the Pt-Ba/Al sub(2)O sub(3) and Pt/Al sub(2)O sub(3) catalysts to accomplish the removal of NO sub(x) in the absence and in the presence of soot was investigated under cycling conditions, i.e. alternating lean-rich phases according to the typical NSR strategy. It has been found that the Pt-Ba/Al sub(2)O sub(3) sample is able to simultaneously remove both soot and NO sub(x), as opposite to the Pt/Al sub(2)O sub(3) catalyst which effectively performs the soot oxidation but is not able to remove gas phase NO sub(x) to a significant extent. The presence of soot does not significantly affect the activity in the NO sub(x)reduction of the Pt-Ba/Al sub(2)O sub(3) catalyst. The comparable level of activity in the soot combustion which is observed between the Pt/Al sub(2)O sub(3) and the Pt-Ba/Al sub(2)O sub(3) sample in spite of the fact that the ternary sample accomplishes the removal of NO sub(x) in the gas phase has been tentatively ascribed to specific oxidizing properties of the stored nitrate species.