Heterogeneous uptake of carbonyl sulfide on hematite and hematite-NaCl mixtures.

Heterogeneous uptake of carbonyl sulfide (COS) on hematite, NaCl, and a series of hematite-NaCl mixtures was investigated in a static reaction chamber at 298 K using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The adsorbed COS was oxidized on the surface of hematite and hematite-NaClmixtures, forming surface hydrogen thiocarbonate (HSCO2-), carbonate (CO3(2-)), and sulfate (SO4(2-)) species as well as gaseous CO2. The reactivity of hematite-NaCI mixtures was lower than that of hematite alone. No uptake of COS was observed on the pure NaCl sample. For mixtures, the 40% hematite + 60% NaCl sample exhibited the highest reactivity. Preadsorption experiments using CO2 as a probe molecule indicated that about 70% of adsorbed COS was oxidized by surface oxygen ions on hematite. In contrast, the Fe-CIO species formed during the sample preparation procedure is proposed to be the active site on the hematite-NaCI mixtures. A plausible reaction mechanism of the heterogeneous oxidation of COS is proposed, and atmospheric implications based on these results are discussed.