NOx storage behavior and sulfur-resisting performance of the third-generation NSR catalysts Pt/K/TiO2–ZrO2

The NOx storage and reduction (NSR) catalysts Pt/K/TiO2–ZrO2 were prepared by an impregnation method. The techniques of XRD, NH3-TPD, CO2-TPD, H2-TPR and in situ DRIFTS were employed to investigate their NOx storage behavior and sulfur-resisting performance. It is revealed that the storage capacity and sulfur-resisting ability of these catalysts depend strongly on the calcination temperature of the support. The catalyst with theist support calcined at 500 °C, exhibits the largest specific surface area but the lowest storage capacity. With increasing calcination temperature, the NOx storage capacity of the catalyst improves greatly, but the sulfur-resisting ability of the catalyst decreases. In situ DRIFTS results show that free nitrate species and bulk sulfates are the main storage and sulfation species, respectively, for all the catalysts studied. The CO2-TPD results indicate that the decomposition performance of K2CO3 is largely determined by the surface property of the TiO2–ZrO2 support. The interaction between the surface hydroxyl of the support and K2CO3 promotes the decomposition of K2CO3 to form –OK groups bound to the support, leading to low NOx storage capacity but high sulfur-resisting ability, while the interaction between the highly dispersed K2CO3 species and Lewis acid sites gives rise to high NOx storage capacity but decreased sulfur-resisting ability. The optimal calcination temperature of TiO2–ZrO2 support is 650 °C.