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

To investigate the heterogeneous oxidation mechanisms of SO2 by HONO on the α-Fe2O3 surfaces, the individual and combined adsorption characteristics of SO2 and HONO on the perfect and Odefect α-Fe2O3 (001) surfaces were calculated the density functional theory. Results revealed that SO2 was molecularly adsorbed while HONO was dissociated on prefect and Odefect surfaces. Oxygen defect significantly augmented the adsorption intensities of SO2 and HONO and accelerated decomposition (HONO →·OH + NO) of HONO. Analysis of electronic structures demonstrated demonstrated that the decomposition of HONO followed the Haber-Weiss mechanism. HOSO2 was generated (SO2 + ·OH → HOSO2) on the prefect and Odefect 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; Odefect: 50.20 kJ/mol) and SO2 oxidation (prefect: 46.90 kJ/mol; Odefect: 31.09 kJ/mol) suggested that SO2 was easily oxidized by HONO on the α-Fe2O3 (001) surface.