Sulfur Dioxide Capture by Heterogeneous Oxidation on Hydroxylated Manganese Dioxide

Here we demonstrate that sulfur dioxide (SO2) is efficiently captured via heterogeneous oxidation into sulfate on the surface of hydroxylated manganese dioxide (MnO2). Lab-scale activity tests in a fluidized bed reactor showed that the removal efficiency for a simulated flue gas containing 5000 mg.Nm(-3) SO2 could reach nearly 100% with a GHSV (gas hourly space velocity) of 10000 h(-1). The mechanism was investigated using a combination of experimental characterizations and theoretical calculations. It was found that formation of surface bound sulfate proceeds via association of SO2 with terminal hydroxyls. Both H2O and O-2 are essential for the generation of reactive terminal hydroxyls, and the indirect role of O-2 in heterogeneous SO2 oxidation at low temperature was also revealed. We propose that the high reactivity of terminal hydroxyls is attributed to the proper surface configuration of MnO2 to adsorb water with degenerate energies for associative and dissociative states, and maintain rapid proton dynamics. Viability analyses suggest that the desulfurization method that is based on such a direct oxidation reaction at the gas/solid interface represents a promising approach for SO2 capture.