Heteroseneous oxidation of carbonyl sulfide on mineral oxides

Heterogeneous oxidation of carbonyl sulfide (OCS) on mineral oxides including SiO₂, Fe₂O₃, CaO, MgO, ZnO and TiO₂, which are the main components of atmospheric particles, were investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), ion chromatography (IC), temperature-programmed desorption (TPD), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) methods. The main products and intermediates of the heterogeneous oxidation of OCS on these oxides were identified with in situ DRIFTS and IC. The reaction mechanism and kinetics were also discussed. It is found that the reaction mechanism on these mineral oxides is the same as that on Al₂O₃ for the same final products and the intermediates at room temperature. Namely, OCS can be catalytically oxidized to produce surface SO ₄ ²⁻ species and gaseous CO₂ through the surface hydrogen thiocarbonate (HSCO ₂ ⁻ ) and HSO ₃ ⁻ species. The activity series for heterogeneous oxidation of OCS follows: Al₂O₃ ≈ CaO > MgO > TiO₂ ≈ ZnO > Fe₂O₃ > SiO₂. The specific area, basic hydroxyl and surface basicity of these oxides have effect on the reactivity. This study suggests that heterogeneous reactions of OCS on mineral dust may be an unneglectable sink of OCS. Supported by the Ministry of Science and Technology of China (Grant No. 2007CB 407301) and the National Natural Science Foundation of China (Grant No. 20637001)