Study of DPNR catalysts for combined soot oxidation and NO_x reduction

The behavior of a model PtBa/Al₂O₃ model NSR catalyst in both the NO_x storage/reduction and soot oxidation is investigated in this work. It is found that the presence of soot negatively influences the NO_x storage capacity of the catalyst, evaluated at 623 K in presence of water and CO₂ in the feed stream: in fact the amounts of NO _x stored in presence of soot decrease by nearly 30% in the presence of roughly 10% (w/w) of soot. The presence of soot has a destabilizing effect on the NO_x adsorbed species, which decompose to a large extent in the absence of gas phase NO and oxygen. This has also been confirmed by dedicated TPD and TPO experiments. However the presence of soot does not appreciably affect the behavior of the PtBa/Al₂O₃ catalyst in the reduction by H₂ of the stored nitrates, being in all cases N ₂ the major reaction product along with minor amounts of ammonia. During the storage of NO_x, soot oxidation takes place. Notably, the stored NO_x participate in the soot oxidation upon release of NO ₂ and O₂ which actively oxidize soot. However a direct participation of the adsorbed NO_x species in the oxidation of soot cannot be excluded.