Sulfur-Mediated Promotion of NH3-SCR Activity on CeO2 Catalysts: An In-Depth Analysis

Abstract

To elucidate the promotional effect and underlying mechanisms of sulfur doping on the NH₃-SCR performance of CeO₂ catalysts, a detailed study of sulfated CeO₂ catalysts was conducted. The CeO_xS_0.1 catalyst, with modest sulfur doping, outperforms its pure CeO₂ counterpart, achieving over 90% NO_x conversion and above 98% N₂ selectivity within the temperature range of 230–480 °C. The enhanced catalytic activity is attributed to the ability of sulfur doping to inhibit the overoxidative dehydrogenation of NH₃, thus improving N₂ selectivity. Sulfation introduces dispersed amorphous sulfate species on the CeO₂ surface, which, despite minimally affecting the catalyst’s crystal structure and surface properties, significantly contribute to the surface acidity by generating S–OH and S═O radicals. These radicals enhance the catalyst’s reducibility and oxygen storage capacity, both crucial for the NH₃-SCR reaction. However, increasing sulfur doping content leads to the formation of bulk and quasi-bulk sulfates within CeO₂, reducing their chemical reactivity and negatively impacting NH₃-SCR activity. NH₃-TPD and Py-IR analyses reveal that sulfation increases the number of strong acid sites on the surface, introducing new Brønsted acid sites with reactivity comparable to that of Lewis acid sites. Consequently, sulfation is identified as an effective strategy to boost the SCR activity of CeO₂ catalysts, offering a promising approach for the development of more efficient catalysts for environmental protection technologies.