Uncovering the opposite behavior of SO2 on C3H8 oxidation over Pd/Pt-SiO2 catalysts under diverse oxygen conditions

SO 2 exhibits opposite effects on C 3 H 8 oxidation over Pd/SiO 2 and Pt/SiO 2 . • O 2 concentration regulates sulfur species evolution and SO 2 tolerance. • Sulfate species block Pd active sites and induce Pd particle sintering over Pd/SiO 2 . • Pt-O-O-S structures on Pt/SiO 2 promote C 3 H 8 adsorption and C-H cleavage. The oxygen concentration in industrial C 3 H 8 -containing exhausts fluctuates significantly (from 0.5 to 18 vol%). However, the intrinsic effect of SO 2 on catalytic C 3 H 8 oxidation under diverse oxygen conditions is greatly overlooked, leading to a discrepancy in the SO 2 tolerance of developed catalyst between laboratory and real-world emission conditions. Herein, the influences of oxygen contents on sulfur species distribution and subsequent sulfur tolerance of typical Pd/SiO 2 and Pt/SiO 2 catalysts during C 3 H 8 oxidation were systematically explored. Experimental results reveal that the oxygen concentration dramatically affects the types and contents of sulfur species over catalysts. For Pd/SiO 2 , SO 2 tends to be converted into sulfate (SO 4 2- ) species to cover the Pd 0 active sites and causes Pd particle sintering, thereby inhibiting the C 3 H 8 adsorption and oxidation. In sharp contrast, sulfite (SO 3 2- ) species form on Pt/SiO 2 , leading to a novel Pt-O-O-S active interface that enriches the adjacent Pt site with electrons, promoting C 3 H 8 adsorption and C-H cleavage and further enhancing catalytic activity. As oxygen concentration decreases, the impact of SO 2 on catalytic performance becomes more pronounced. Under the oxygen-lean conditions, Pd particles sintering caused by SO 2 is the most severe at 1 vol% O 2 , causing an 80 °C temperature increasing in 90% C 3 H 8 conversion; however, the contents of SO 3 2- species and Pt-O-O-S structures on Pt/SiO 2 are elevated, facilitating C 3 H 8 adsorption and activation. Our findings enrich the understanding of SO 2 behavior under different industrial conditions, providing a theoretical basis for the design of SO 2 -tolerant catalyst in diverse application scenarios. Download: Download high-res image (178KB) Download: Download full-size image