Mechanistic and thermodynamic insights into the SO2 oxidation on MnO2 catalysts: A combined theoretical and experimental study

Manganese oxide (especially manganese dioxide [MnO2]) is an excellent catalytic material for SO2 removal in flue gas desulfurization. In this study, the effect of crystalline structure of MnO2 (α-MnO2, β-MnO2, γ-MnO2 and δ-MnO2) on their activity for SO2 oxidation was studied based on density functional theory with Hubbard U corrections (DFT + U). The calculated results showed that α-MnO2 has mild energy barriers of 0.69 eV and 0.46 eV, and β-MnO2 has poor redox performance on SO2 molecules, which has the highest energy barrier of 2.17 eV and the largest oxygen formation energy of 1.74 eV, making it difficult for the oxygen atom to remove from the surface lattice to form reactive sites. Thermodynamic calculations showed that α-MnO2 is suitable for SO2 oxidation for its low energy barriers, reaction energy close to zero in the first half, and relatively high spontaneity in the whole reaction. Experimental tests showed that α-MnO2 had the best catalytic oxidation effect, with the highest sulfur capacity (304.11 mg/g), but β-MnO2 had poor catalytic oxidation performance, with a sulfur capacity of 41.59 mg/g. This work studies the catalytic performance and mechanism of SO2 removal and proposes a strategy to improve the catalytic activity by phase structure.