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

摘要

In the present work the influence of the type of nobe metals present in barium oxide based NO_x storage catalysts was ivnestigated regarding the NO_x 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 mesuremetns.The flow-reactor experiments imulated NO_x storage and reduction cycles at 400 deg C in synthetic gas mixtures with oxygen,poropene and itric oxide.For the sulphur deactivation and regenerability investigations 25 ppm (v/v) SO_2 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 NO_x storatge and reduction performance.TheNO_x storage capacity was,however,found higher for catalysts containing only platinum compred to catalysts including rhodium.When exposed to SO_2 the NO_x 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 SO_2 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 SO_2.Finally,the results implied that to provide good sulphur regeneration ability of the NO_x storage catalyst,a combination of platinum and rhodium is necessary.