The Effect of K Salts on SO₂–SO₃ Conversion and Denitration Behavior over V₂O₅–WO₃/TiO₂ Catalysts

Abstract

A series of V₂O₅–WO₃/TiO₂ catalysts treated by KCl or K₂SO₄ were prepared using the equal volume impregnation method. The effects of adding these K salts on SO₂–SO₃ conversion and on denitration behavior over the catalyst were studied, using reactor trials and various characterization methods, including NH₃-TPD, H₂-TPR, ICP, BET, XRD, SEM, FT-IR and XPS. The results of catalytic activity evaluation tests show that adding K salts decreases the denitration efficiency, while SO₂ enhances the activity of the KCl-poisoned catalyst to an extent. The presence of K salts also improves the SO₃ formation rate, such that the SO₃ formation rate for the K₂SO₄-poisoned catalyst is as high as 1.53% at 410 °C (compared with 0.60% for the fresh catalyst). The characterization data indicate that K salts aggregate on the catalyst surface, blocking the pores of the catalyst. The reduction ability of the catalyst is decreased slightly and new weakly acidic sites appear. In addition, the concentration of strongly acidic sites declines. SO₂ can increase the surface acidity of the catalyst. K salts increase the number of V⁵⁺=O bonds and weakly acidic sites, but consume oxygen atoms along with V and W species. Importantly, the strength of the V⁵⁺=O bonds, the concentration of surface chemically adsorbed oxygen and the V⁴⁺/V⁵⁺ ratio all played vital roles in improving the conversion of SO₂–SO₃ and in enhancing the NO reduction.

Graphical Abstract