The effect of metal oxide additives (WO3, MoO3, V2O5, Ga2O3)on the oxidation of NO and SO2 over Pt/Al2O3 and Pt/BaO/Al2O3 catalysts

For NOx storage, the oxidation of NO to NO2 is an important step in the storage mechanism. In the firstpart of this work, model WO3/Pt/Al2O3, MoO3/Pt/Al2O3, V2O5/Pt/Al2O3, Ga2O3/Pt/Al2O3 and Pt/Al2O3 catalysts were prepared and used in flow reactor experiments. Heating ramp oxidation and steady state oxidation experiments were performed in order to investigate the catalytic activity for NO oxidation both in the presence and absence of SO2 in the reaction gas mixture. In the absence of SO2, the WO3 and MoO3 containing catalysts showed a significantly higher NO oxidation activity than the other catalysts. When SO2 was included in the reaction gas mixture, the NO oxidation activity decreased for all catalysts, but the MoO3 containing catalyst was less affected by the presence of SO2 and also showed the lowest SO2 oxidation activity. In the second part of this work, model Pt/BaO/Al2O3 and Pt/BaO/MoO3/Al2O3 catalysts were prepared and used in heating ramp oxidation and transient flow reactor experiments in order to investigate the effects of NO oxidation activity enhancement and suppression of the activity for SO2 oxidation on NOx storage capacity. Both catalysts showed equal NOx storage capacity in the sulphur free cycles. When SO2 was included in the reaction gas mixture, the NOx storage capacity declined faster for the Pt/BaO/MoO3/Al2O3 catalyst than for the Pt/BaO/Al2O3 catalyst, due to sulphur poisoning which resulted in a faster decrease in the regeneration capacity during rich periods. (C) 2003 Elsevier B.V. All rights reserved.