Mechanistic aspects of the reduction of stored NOx over Pt–Ba/Al2O3 lean NOx trap systems

In this paper the mechanisms that rule the reduction by hydrogen of NOx species adsorbed at different temperatures were investigated over a model LNT Pt–Ba/Al2O3 catalyst and over the corresponding Ba/Al2O3 system to address the role of the noble metal component in such mechanisms. It was found that the reduction proceeds according to a dual-step mechanism in which hydrogen reacts fast and at low temperature with nitrates producing ammonia, which however is not a terminal product as it can further react with other nitrate species leading selectively to N2. The results collected in the analysis of each of the dual-step reactions showed that they both occur through a Pt-catalyzed pathway active at very low temperatures, which does not involve the thermal decomposition of the adsorbed NOx species as a preliminary step.