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 O-2 + 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 degrees 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 SO2.