Catalytic Reduction Of SO₂ With CO Over The γ-Al₂O₃ Based Catalysts

Sulfur dioxide is one of the major components of atmospheric pollution. Currently operating desulfurization based on wet scrubbing is a costly process requiring a large space with complicated facilities and disposal of the used sorbents. Direct catalytic reduction of SO₂ to elemental sulfur can not only remove SO₂ pollution but also obtain elemental sulfur. The aim of the present paper is to study the catalysis for SO₂ reduction by CO.Firstly, various catalyst formulations have been investigated for this reaction. It has been found that the Fe₂O₃/γ-Al₂O₃ with 20% Fe content exhibited the best performance. Under the optimal conditions, 99.98% of SO₂ conversion and 98.27% of sulfur yield were obtained at 300℃when the high-surface-areaγ-Al₂O₃ (448 m²/g) was used as the support. This is one of the best catalytic performance reported so far.The presulfidation was necessary to activate the catalyst by forming the catalytically active species FeS₂. We studied in detail the presulfidation process of Fe₂O₃/γ-Al₂O₃ catalyst with reacting gas, and proposed the sulfidation mechanism. To reveal the catalysis mechanism, transient response techniques including SO₂-TPD, CO-TPSR and COS-TPSR, together with XRD, were employed. The results show that there are two kinds of FeS₂ species formed on the catalyst surface during sulfidation: active and less active FeS₂ species, which can react with CO to form COS at low and high temperatures, respectively. The active FeS₂ species were the main active sites in the reaction.It was also found that the addition of La, Ce or Zr could improve the catalyticactivity of the Fe₂O₃/γ-Al₂O₃ by increasing the number of active FeS₂ species.Finally, microwave plasma was for the first time employed in the reduction of SO₂ by CO or by carbon. By coupling the microwave plasma with the catalytic function, it was found that the reaction temperature for SO₂ reduction with CO was greatly decreased. Even without the catalyst, SO₂ could be reduced by carbon with high efficiency under microwave plasma.