NO x storage behavior and sulfur-resisting performance of the third-generation NSR catalysts Pt/K/TiO 2–ZrO 2

Abstract

The NO x storage and reduction (NSR) catalysts Pt/K/TiO 2–ZrO 2 were prepared by an impregnation method. The techniques of XRD, NH 3-TPD, CO 2-TPD, H 2-TPR and in situ DRIFTS were employed to investigate their NO x 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 NO x 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 CO 2-TPD results indicate that the decomposition performance of K 2CO 3 is largely determined by the surface property of the TiO 2–ZrO 2 support. The interaction between the surface hydroxyl of the support and K 2CO 3 promotes the decomposition of K 2CO 3 to form –OK groups bound to the support, leading to low NO x storage capacity but high sulfur-resisting ability, while the interaction between the highly dispersed K 2CO 3 species and Lewis acid sites gives rise to high NO x storage capacity but decreased sulfur-resisting ability. The optimal calcination temperature of TiO 2–ZrO 2 support is 650 °C.