Heterogeneous oxidation mechanism of SO2 on γ-Al2O3 (110) catalyst by H2O2: A first-principle study

Abstract

Here, we present a simulation research of the heterogeneous oxidation mechanism of SO2 on Al2O3 (mineral oxides) surface by H2O2, density functional theory (DFT) calculations was used to investigate the adsorption mechanism of SO2 and H2O2 on the perfect and Odefect γ-Al2O3 (110) surfaces. The results show that SO2 molecularly adsorbed on the prefect and Odefect surfaces, while H2O2 was adsorbed in the molecule form on the perfect surface. In particular, H2O2 dissociation only occurred on the Odefect γ-Al2O3 (110) surface. The oxygen defects not only enhanced the adsorption intensities of H2O2 and SO2, but also promoted the H2O2 decomposition (H2O2→OH + OH). Analysis of partial density of states, differential charge density and Mulliken population indicated that H2O2 decomposition followed the Haber-Weiss mechanism (formation of surface OH), and SO2 was oxidized by the OH radicals to form HOSO2 molecule when SO2 and H2O2 co-adsorbed on Odefect γ-Al2O3 (110) surface. Moreover, the lower energy barrier of H2O2 decomposition (32.69 kJ/mol) and SO2 oxidation (78.21 kJ/mol) demonstrated that SO2 to be oxidized easily by the H2O2 on the Odefect γ-Al2O3 (110) surfaces. These results can well explain the formation mechanism of OH radicals and the oxidation mechanism of SO2 by H2O2 on the mineral dust at the molecular level, which is of great significance for understanding the role of H2O2 in the heterogeneous oxidation of SO2 on the mineral dust and the formation mechanism of sulfate aerosols in the atmosphere.