Reduction of SO2 by CO and COS over La2O 2S - A mechanistic study

The mechanism of the catalytic reduction of SO₂ by CO and COS over lanthanun oxysulfide was studied using a combination of temperature-programmed reaction coupled with mass spectrometry (TPR/MS) and feed-perturbation step-analysis techniques. The results showed that COS interacts more readily with lanthanum oxysulfide than CO does. The interaction of COS with the lanthanum catalyst was different from that of CO. In addition, COS preferentially reacted with SO₂ to form CO₂ and sulfur instead of following the disproportionation (to form CO₂ and COS) and decomposition (to form CO and sulfur) reactions. The redox mechanism is not the main reaction route for the reduction of SO₂ by CO and COS over lanthanun oxysulfide. SO₂ was strongly adsorbed by the oxysulfide and was retained in the oxysulfide even when heated in an inert gas stream, while COS was very reactive and did not remain long in the oxysulfide. These results suggest that COS has access to certain specific active sites in the oxysulfide and the catalytic reduction of SO₂ by COS possibly proceeds via adsorbed COS reacting with pools of SO₂ adspecies to form CO₂ and sulfur. © 2003 Elsevier Science B.V. All rights reserved.