SrO-modified Pd/Al2O3 three-way catalyst with advanced activity for passive selective catalytic reduction operation

Abstract

Passive selective catalytic reduction (pSCR) is a promising technology for exhaust aftertreatment applied in lean burn gasoline engines, which requires the three-way catalyst (TWC) to provide NH₃ for the downstream SCR reaction process. Consequently, in the assessment of TWC catalytic performance for pSCR operation, not only the conversion efficiency of CO, HC, and NO should be taken into account, but the generation of NH₃ is equally crucial. In this study, the modification of Pd/Al₂O₃ catalyst was realized with the assistance of SrO, and the catalytic performance in terms of both the conversion efficiency of CO/HC/NO and the production of NH₃ was measured. Additionally, the physicochemical characteristics of the SrO-modified catalysts were evaluated in comparison to those of the unmodified Pd/Al₂O₃ through various analytic techniques. The findings indicate that incorporating SrO into the Pd/Al₂O₃ system enhances the conversion efficiency for CO, HC, and NO, and more importantly, a larger generation of NH₃ is achieved, and the most effective concentration of SrO is identified as 4 wt.%. Based on the characterization results, it is found that SrO mainly interacts with tetra-coordinated or penta-coordinated Al sites on the surface of the catalyst, which brings about weakened surface acidity. The beneficial effect of SrO is primarily linked to its capacity to enhance the thermal durability of the Al₂O₃ support, facilitate the distribution of Pd-related particles, and adjust the chemical states of Pd species. Additionally, it could modify the reduction characteristics and the desorption performance of NH₃ over the catalyst.