Experimental and mechanism studies on the catalytic reduction of SO₂ by CO over Fe₂O₃/γ-Al₂O₃ in the presence of H₂O

Abstract

The present research explored experimental and mechanism studies on the catalytic reduction of SO₂ by carbon monoxide (CO) over Fe₂O₃/γ-Al₂O₃ to elemental sulfur in the presence of H₂O. The varieties and concentrations of intermediates in the catalytic reduction at different temperatures were investigated. Carbonyl sulfide (COS) and H₂S were formed as intermediates below 400 °C, while only H₂S was observed at or above 400 °C. H₂S resulted from the hydrolysis of COS over Fe₂O₃/γ-Al₂O₃ in the presence of H₂O. When the temperature was below 400 °C, COS hydrolyzed partially, and reduction of SO₂ by CO followed the intermediary mechanism of COS and the Claus reaction mechanism of H₂S. However, COS hydrolyzed completely at or above 400 °C and the catalytic reaction only followed the Claus reaction mechanism of H₂S. Moreover, XRD analysis indicated that in the catalytic reduction of SO₂ by CO over Fe₂O₃/γ-Al₂O₃, Fe₂O₃ was initially reduced to Fe₃O₄ by CO, and then the oxygen of SO₂ was accepted by the oxygen vacancy of Fe₃O₄ leading to the formation of elemental sulfur; finally, the active substance FeS₂ formed, which suggests that the formation of Fe₃O₄ plays a key role in the initial reaction.