Influence of Co or Ce addition on the NOx storage and sulfur-resistance performance of the lean-burn NOx trap catalyst Pt/K/TiO₂-ZrO₂

The Pt/K/TiO₂-ZrO₂ catalysts promoted by Co or Ce were prepared by successive impregnation or mechanically mixing method. The influence of Co or Ce addition on the NOx storage and sulfur-resistance performance of the catalyst was investigated carefully. The techniques of XRD, FT-IR, in-situ DRIFTS, H₂-TPR and XPS were employed for catalyst characterization. The Co or Ce addition can greatly improve the NOx storage capacity of Pt/K/TiO₂-ZrO₂ due to the enhanced oxidation ability and the release of more K sites. Ce addition induces higher K/Ti atomic ratio and larger NOx storage capacity as compared with Co addition. After sulfation and regeneration, the promoted catalysts shows more or less decreased NSC than Pt/K/TiO₂-ZrO₂ due to the formation of more sulfates, especially for the Co-promoted catalysts, which possess better oxidation ability and facilitate the formation of large sulfates. The effect of Ce addition on Pt/K/TiO₂-ZrO₂ largely depends on the addition mode. The high oxidation ability and the high K/Ti ratio of the mechanically prepared Ce-promoted catalyst make it still possess considerable NOx storage capacity (NSC) of 142 μmol/g after sulfation and regeneration. With the decrease of sulfur content in fuels, the Co- and Ce-promoted catalysts possessing large NOx storage capacity, will be applicable to the purification of lean-burn NOx.