Influence of CS2 pretreatment on the NH3-SCR activity of CeO2: Synergistic promotional effect of sulfation and reduction

Abstract Due to the promotional effect on the surface acidity, SO2 had been usually used to improve the selective catalytic reduction of NOx with NH3 (NH3-SCR) over cerium oxide/cerium-based catalyst via gas phase sulfation. However, CS2 and COS, largely existing in the coke oven or/and gasification flue gas, exhibit stronger reducibility and present the unique physicochemical properties in acidity and reduction property compared to SO2. To the best of my knowledge, the reductive CS2 and COS had not been used to increase the NH3-SCR activity of cerium oxide/cerium-based catalyst. Therefore, the influence of CS2 and COS gas phase sulfation pretreatment on the NH3-SCR performance of CeO2(w/o) had been investigated with SO2 as comparison herein. The results indicate that the promotional effect of the sulfur-containing species pretreatment on the NH3-SCR performance over CeO2(w/o) decrease as following: CS2>COS>SO2, which is in accordance with the intensity of their reducibility. Compared with SO2, the pretreatment with CS2 could induce more Ce4+ to reduce to Ce3+ and generate more surface defects due to its stronger reducibility, leading to more oxygen defects and chemisorbed oxygen formed on the surface of CeO2(w/o). And the sulfation treatment could slightly decrease the crystallinity of cubic CeO2. The characterization results also confirm that the pretreatment with CS2 contributes to the formation of more sulfate species, not only enhances the abundance and strength of Bronsted acid sites on the CeO2(w/o) surface, but also helps to the generation of low-temperature Lewis acid sites compared to SO2. All these should be the crucial reasons for the best de-nitration activity over CeO2-CS2-3 in the operating temperature range. We expected that this research could provide a new strategy for designing novel CeO2-based NH3-SCR catalyst.