Study of DPNR catalysts for combined soot oxidation and NOx reduction

The behavior of a model PtBa/Al2O3 model NSR catalyst in both the NOx storage/reduction and soot oxidation is investigated in this work. It is found that the presence of soot negatively influences the NOx storage capacity of the catalyst, evaluated at 623 K in presence of water and CO2 in the feed stream: in fact the amounts of NOx 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 NOx 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 N2 the major reaction product along with minor amounts of ammonia. During the storage of NOx, soot oxidation takes place. Notably, the stored NOx participate in the soot oxidation upon release of NO2 and O2 which actively oxidize soot. However a direct participation of the adsorbed NOx species in the oxidation of soot cannot be excluded.