A DFT study on the SO2-resistant mechanism of Hg0 oxidation over Fe-doped OMS-2

Sulfur dioxide poisoning remains a critical challenge for mercury oxidation over manganese-based catalysts in coal-fired flue gas. Fe-doped OMS-2 catalysts exhibit excellent Hg 0 oxidation activity under high concentration SO 2 conditions in our previous experiment. However, the underlying mechanism responsible for their mercury removal and sulfur resistance remains unclear. In this study, focusing on the Fe-OMS-2(110) surface, both the mercury removal and sulfur resistance mechanisms of mercury oxidation over Fe-OMS-2 were systematically investigated through density functional theory calculations. The results indicate that Fe doping generates spatially differentiated Fe and Mn functional centers on the Fe-OMS-2(110) surface. The Fe sites can preferentially capture SO 2 with an adsorption energy of −1.818 eV, while Mn sites exhibit stronger O 2 activation and Hg 0 oxidation capabilities. Specifically, the rate-limiting step for O 2 dissociation at the distal Mn2 site is O–O bond cleavage, with an energy barrier of 1.07 eV. Under sulfur-containing conditions, SO 2 and its oxidation product SO 3 participate in the conversion of Hg 0 into HgSO 4 at the Mn2 site. which lowers the product-release barrier relative to the HgO pathway. Overall, the superior mercury removal and sulfur resistance performance of Fe-OMS-2 arises from the spatially differentiated functions of Fe and Mn centers, with Fe sites preferentially capturing SO 2 and Mn sites facilitating Hg 0 oxidation.