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

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 x S0.1 catalyst, with modest sulfur doping, outperforms its pure CeO(2 )counterpart, achieving over 90% NOx conversion and above 98% N2 selectivity within the temperature range of 230-480 degrees C. The enhanced catalytic activity is attributed to the ability of sulfur doping to inhibit the overoxidative dehydrogenation of NH3, thus improving N-2 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 Br & oslash;nsted 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.