Mechanistic insight into the synergistic effect of O2 and SO2 for improving removal of arsenic over Mn-modified Fe2O3-based sorbent

Iron-based materials are promising sorbents for controlling arsenic emissions. However, the effects of SO₂, especially the synergistic mechanism of As₂O₃ adsorption under the combined effects of O₂ and SO₂, remain inadequately explored. This study investigated for the first time the impact of the newly formed surface resulting from the adsorption and dissociation of O₂ and SO₂ on the adsorption of As₂O₃. The results showed that Mn_3f and Fe_3f sites were the active sites for the adsorption of O₂ and SO₂, which competed with As₂O₃ and hindered its adsorption. Conversely, dissociation created more reactive sites, which promoted the process. Selectivity analysis revealed that As₂O₃ preferentially adsorbed on the dissociated surface, highlighting the dominance of the promotion effect. Finally, starting from the adsorption sequence of O₂ and SO₂, the impact of arsenic adsorption and oxidation was examined on sorbents created through the sequential adsorption of O₂ and SO₂. Regardless of the adsorption sequence, active O atoms with catalytic effects were exposed, supporting the enhanced removal of arsenic under the synergistic effect of O₂ and SO₂. Building upon this analysis, a theoretical framework for efficiently removing As₂O₃ from O₂ and SO₂ flue gases using Mn-modified Fe₂O₃-based materials was developed.