Mechamism Study Of Heterogeneous Reactions Between COS And Typical Atmospheric Oxides

Carbonyl sulfide (COS) is one of the most important sulfur-containing species in the atmosphere. Because of low reactivity, it can be transported into the stratosphere, and then photolyzed to form SO₂, and stratospheric sulfate eventually. It is the dominant nonvolcanic source of stratospheric sulfate. An increase in stratospheric sulfate levels has important climatic implications as well as heterogeneous chemical effects that may alter the stratospheric ozone concentration. In addition, aerosol can provide surface with reactive sites on which heterogeneous reactions could occur in the atmospheric. These processes can lead to the formation of secondary aerosol, and affect atmospheric chemical composition. It is therefore high significance to study heterogeneous reaction of COS on the surface of aerosol, which can provide data for evaluation of sulfate formation and its effect on global climate.Heterogeneous uptake of carbonyl sulfide on various typical atmospheric oxides was investigated in a static reaction chamber using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Combined with other surface analysis techniques, such as Ion Chromatogram (IC) and Raman Spectroscopy, several conclusion were drawn as follows:Firstly, Heterogeneous reactions of Carbonyl sulfide on various typical oxides were investigated. It was found that COS can be oxidized to form gaseous CO₂ and surface SO₄^2- or HCO₃^-/CO₃^2-. About 70% of adsorbed COS was oxidized by surface oxygen ions on hematite, with other active sites such as surface hydroxyl groups accounting for additional residual loss. On the basis of experiment data, uptake coefficients for different samples were calculated and a plausible reaction mechanism was proposed.Secondly, heterogeneous reactions of hemitie-NaCl and alumina-NaCl mixure were studied. It was found that the addition of NaCl inhibited the reaction activity of hematite and alumina. Surface character variety in the mixing process was studied by pre-adsorption experiments carbon dioxide with and using Raman Spectroscopy.Thirdly, effect of basic gas on heterogeneous reaction of carbonyl sulfide was investigated. It was found that the pre-adsorption of basic gases greatly enhance the reactivity of oxides. Higher basicity leads to higher catalytic activity.