Experimental and DFT Analysis To Anchor the Role of SO2 in the Heterogeneous NO Reduction over a Char Surface: SOx-Mediated Oxygen Rearrangement

The heterogeneous reduction of NO by char is important for NO source control during the combustion of organic solid wastes. SO2 manifests a significant impact of the char-NO reaction, yet the inherent mechanism is still vague. In the present study, fixed-bed experiments, in-situ X-ray photoelectron spectroscopy (in-situ XPS), and density functional theory (DFT) calculations were combined to offer empirical and theoretical evidence on the detailed impact mechanism of SO2 on the char-NO reaction. Herein, we propose the surface SOx-mediated oxygen rearrangement (SOx-MOR) mechanism for the first time. SO2 can directly promote char-NO reduction by intervening in the oxygen rearrangement process. In addition, SO2 and O-2 play a synergetic role in enhancing the NO reduction. SO2 can be oxidated into SO3 and adsorbed on the char edge, impeding the fast oxidation of char by O-2, and enhancing NO reduction. Meanwhile, NO can be reduced via the SO3-MOR mechanism, which possesses a thermodynamic priority lower than that of the SO2-MOR mechanism. In-situ XPS results further verified the surface chemical behaviors of SO(x)and the higher competitiveness of the SO2-MOR mechanism. The present study lays a foundation for NO source control by SO2.