Heterogeneous oxidation mechanism of SO2 on alpha-Fe2O3 (001) catalyst by HONO: Effect of oxygen defect

To investigate the heterogeneous oxidation mechanisms of SO2 by HONO on the alpha-Fe2O3 surfaces, the individual and combined adsorption characteristics of SO2 and HONO on the perfect and O-defect alpha-Fe2O3 (001) surfaces were calculated the density functional theory. Results revealed that SO2 was molecularly adsorbed while HONO was dissociated on prefect and O-defect surfaces. Oxygen defect significantly augmented the adsorption intensities of SO2 and HONO and accelerated decomposition (HONO ->center dot OH + NO) of HONO. Analysis of electronic structures demonstrated demonstrated that the decomposition of HONO followed the Haber-Weiss mechanism. HOSO2 was generated (SO2 + center dot OH -> HOSO2) on the prefect and O-defect surfaces through SO2 and HONO co-adsorption, thereby confirming that SO2 was oxidized. Moreover, the low energy barrier of HONO decomposition (prefect: 90.67 kJ/mol; O-defect: 50.20 kJ/mol) and SO2 oxidation (prefect: 46.90 kJ/mol; O-defect: 31.09 kJ/mol) suggested that SO2 was easily oxidized by HONO on the alpha-Fe2O3 (001) surface.