Fe/Mn-MOFs with monocarboxylic acid-induced defects enhances the catalytic oxidation of calcium sulfite in desulfurization ash

[Display omitted] •Fe/Mn-BMOFs are constructed through a defect engineering strategy.•The 3 h oxidation rate of CaSO3 reached 96.09 % with more than 34 times of improvement.•In situ ESR shows that the catalytic oxidation process produces O2–.•DFT calculations reveals that the formation of SO42− from SO5− is the controlling step. The application of catalysis is an effective way to enhance calcium sulfite oxidation reactions, which is essential to the calcium-based wet flue gas desulfurization and the handle and/or utilization of the solid by-product from semi-dry desulfurization process, i.e., desulfurization ash. In this report, we present a method for constructing Fe/Mn(BDC)(DMF,OA) bimetallic catalysts with defect engineering by using monocarboxylic acids with varying chain lengths as regulators. After removing the monocarboxylic acid, the unsaturated coordinated iron and manganese active sites in Fe/Mn(BDC)(DMF,OA) become more abundant. This makes it easier to adsorb O2 and activate it into reactive oxygen species (O2–), which in turn activates the radical chain reaction and promotes the production of sulfur-oxygen free radicals(SO5−). Density functional theory (DFT) calculations show that the synergistic effect of Fe-Mn bimetallic catalysts reduces the energy barrier for SO42− formation, thereby accelerating the oxidation of sulfite. Upon addition of Fe/Mn(BDC)(DMF,OA), the oxidation rate of calcium sulfite within 3 h increased from 2.76 % to 96.09 %, compared to non-catalytic oxidation. After five cycles, the 3 h oxidation rate of calcium sulfite decreased by 10.42 % compared to the first cycle, and the higher leaching rate of Mn element was the main reason for the decrease in catalytic performance. The catalyst is non-toxic and economical, showing significant potential for resource utilization of CaSO3-containing desulfurization ash.