Abstract
This study investigates the soot oxidation activity and mechanism of an Al2O3-supported Ag2SO4 catalyst with novel active species. The Ag2SO4/Al2O3 catalyst exhibits higher soot oxidation activity under loose contact conditions compared to Ag/Al2O3 and Ag/CeO2 catalysts. Moreover, it is hardly affected by sulfur poisoning and maintains its high activity after sulfur poisoning treatment. High-temperature X-ray diffraction measurements suggest that a part of Ag2SO4 on the Al2O3 support melts and creates contact between the Ag2SO4 and soot at temperatures over 400 °C, resulting in higher soot oxidation activity even under loose contact conditions. The soot oxidation mechanism over the Ag2SO4/Al2O3 catalyst is probed by oxygen isotope exchange analysis and operando X-ray absorption fine structure measurements, which reveal that the oxygen chemically bound in Ag2SO4 is utilized for soot oxidation. In particular, the above oxidation features a reversible redox cycle comprising partial reduction of Ag2SO4 to metallic Ag that is further re-oxidized to Ag2SO4 by the gas-phase oxygen.
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