Multiple Roles of SO₂ in Selective Catalytic Reduction of NO by NH₃ over V₂O₅/AC Catalyst

The role of SO₂ in the selective catalytic reduction (SCR) of NO by NH₃ over carbon-based catalysts has been studied by many researchers over the past decade. It has been reported to be positive by some but negative by others. This work examines the multiple roles of SO₂ during SCR over V₂O₅/AC catalyst in the presence of H₂O and identifies the effects of the AC source and reaction conditions on the role of SO₂. The multiple roles of SO₂ can include its competitive adsorption with reactants for V₂O₅ on the catalyst, its interaction with V₂O₅ to form VOSO₄, and pore blockage and surface modification through the formation of ammonia sulfates from the reaction of SO₂ and O₂ + H₂O + NH₃. It was found that competitive adsorption cannot be confirmed, but VOSO₄ was observed in the used catalyst. A tiny amount of VOSO₄ might result in a sharp decrease in NO conversion. The negative effect of SO₂ through VOSO₄ formation weakens with increasing SCR temperature and decreasing AC surface area. Pore blockage has little influence on the SCR activity at temperatures of 200 °C and higher. The surface modification is positive to the SCR for V₂O₅/AC made from anthracite-derived AC but negative for V₂O₅/AC derived from other sources. However, the positive effect of surface modification is overwhelmed by the negative effect of gaseous SO₂, which results in an overall negative effect of SO<sub>2