Influence of platinum and rhodium composition on the NOx storage and sulphur tolerance of a barium based NOx storage catalyst

In the present work the influence of the type of noble metals present in barium oxide based NOx storage catalysts was investigated, regarding the NOx storage performance, NO oxidation, NO reduction, sulphur deactivation and sulphur regenerability. Monolith samples with combinations of platinum and rhodium, were prepared, tested in a flow-reactor, and characterised by XPS measurements. The flow-reactor experiments simulated NOx storage and reduction cycles at 400degreesC in synthetic gas mixtures with oxygen, propene and nitric oxide. For the sulphur deactivation and regenerability investigations 25 ppm (v/v) SO2 was added to the feed gas stream. From the experiments, it was concluded that a combination of platinum and rhodium is required to achieve good NOx storage and reduction performance. The NOx storage capacity was, however, found higher for catalysts containing only platinum compared to catalysts including rhodium. When exposed to SO2 the NOx storage capacity also seemed to deactivate faster for the samples containing rhodium than for samples with platinum as the sole noble metal. Additionally, it was observed that platinum gives high NO oxidation activity during the lean periods both with and without SO2 present in the gas feed. During the rich periods, rhodium showed high activity for NO reduction in sulphur free gas feed as well as in the presence of SO2. Finally, the results implied that to provide good sulphur regeneration ability of the NOx storage catalyst, a combination of platinum and rhodium is necessary. (C) 2003 Elsevier B.V. All rights reserved.