Heterogeneous Uptake of Carbonyl Sulfide on Hematite and Hematite−NaCl Mixtures

Abstract

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.

Comparative study of the effect of water on the heterogeneous reactions of carbonyl sulfide on the surface of α-Al<sub>2</sub>O<sub>3</sub> and MgO

“…These oxidized species were observed in this study ( Fig. 2) and in previous works (Chen et al, 2007;He et al, 2005;Liu et al, 2006;Wu et al, 2004Wu et al, , 2005. Therefore, gaseous CO 2 is more easily observed than gaseous H 2 S or surface −SH when using FTIR.…”

“…hydrogen thiocarbonate, HSCO − 2 ) was observed, the pathways of heterogeneous reactions of OCS still require further study. For example, some researchers have proposed a heterogeneous oxidation mechanism (Chen et al, 2007;He et al, 2005;Liu et al, 2006;Wu et al, 2004Wu et al, , 2005, while recently we found that heterogeneous hydrolysis of OCS can also occur on MgO (Liu et al, 2007a). Nonetheless, information on the kinetics of the heterogeneous reaction of OCS on mineral oxides is limited.…”

“…The uptake coefficients under different conditions are shown in Table 2. Chen et al (2007) measured the γ t (BET) OCS on Fe 2 O 3 to be 1.87±0.21×10 −11 by DRIFTS with the assumption that OCS accesses all of the layers of particle sample. This value should be the lowest limit and is much lower than our results due to the different samples and different methods.…”

“…(Chen et al, 2007;He et al, 2005;Liu et al, 2006;Wu et al, 2004Wu et al, , 2005, and the hydrolysis pathway has not been elucidated because previous measurements have not measured H 2 S as a reaction product. In those studies, FTIR was mainly used to investigate the reaction process; however, the sensitivity of infrared absorbance for surface −SH or gaseous H 2 S is much lower than that for CO 2 .…”

“…Liu et al: Reactions of carbonyl sulfide on the surface of α-Al 2 O 3 and MgO global source strength of ∼1000-3000 Tg year −1 (Dentener et al, 1996), is one of the most important contributors to the loading of APM. Recently, a few studies demonstrated that heterogeneous reactions of OCS can occur on APM, and on mineral oxides including Al 2 O 3 , SiO 2 , Fe 2 O 3 , CaO, MgO, MnO 2 and the mixture of Fe 2 O 3 and NaCl under ambient conditions (Chen et al, 2007;He et al, 2005;Liu et al, 2006Liu et al, , 2007aWu et al, 2004Wu et al, , 2005. Although the same intermediate (i.e.…”