SnO₂-CeO₂/Spherial Activated Carbon Based Catalysts For Low-Temperature Selective Catalytic Reduction Of NO With NH₃

Nitrogen oxides (NOX) in flue gas are major air pollutants that must be removed before emission. Selective catalytic reduction (SCR) with NH3 is widely used to remove NOx, and due to the high SCR activity at low temperature, wide operating temperature window and non-toxic, CeO2-MnOx catalysts have gained extensive attention. But these catalysts still have poor tolerance to SO2. Based on the excellent characteristics of Spherical activated carbon (SAC), such as good sphericity, high mechanical strength, controlled pore size distribution and excellent adsorption performance properties, and the SnOx-CeO2 synergistic catalytic function, SnOx-CeO2-MnOx/SAC and SnOx-CeO2/SAC catalysts were prepared. The work further studied NO removal activities and the resistance to SO2 of SnOx-CeO2-MnOx/SAC and SnOx-CeO2/SAC catalysts, and got following results.(1) NO conversion was reduced by the addition of SnOx to CeO2-MnOx/SAC catalyst at low temperatures of 80～160℃, but it was still high at temperature of 200～280℃. The SnOx-CeO2-MnOx/SAC catalyst with a molar ratio of Sn/Mn=0.25 showed the best NO removal activity, with a NO conversion higher than 95.8% at 200～280℃. NO conversion gradually decreased at 80～280℃ with the increasing Sn/Mn molar ratio from 0.5 to 1. However, when the Sn/Mn molar ratio increased to 2, it increased at high temperature of 220～280℃.(2) CeO2-MnOx/SAC catalyst activity at lower temperatures decreased by the addition of a small amount of SnOx, because the addition could cause micropore plugging. On the contrary, the addition of SnOx could improve catalyst activity at higher temperatures. This activity increase may be contributed to the improvement of MnOx and CeO2 distribution on the surface and surface acidity on CeO2-MnOx/SAC.(3) The SnOx-CeO2/SAC catalyst with a molar ratio of Sn/Ce= 0.5 showed the best NO removal activity, with a NO conversion higher than 98% at 100～280℃. As the Sn/Mn molar ratio increasing from 0.5 to 2, NO conversion gradually decreased at low temperatures of 80～180℃.(4) The addition of SnOx to CeO2-MnOx/SAC and CeO2/SAC catalysts enhanced their resistance to SO2, and SnOx-Ce02/SAC showed better SO2 resistance than SnOx-CeO2-MnOx/SAC. In the absence of SO2, For SnOx-CeO2/SAC catalyst, NO conversion is 98.6% at 240℃. After the introduction of SO2 into the reactants, NO conversion decreased to 87.8% in 480min. The main reason for leading to deactivation was the deposition of ammonium sulfates and ammonium sulfites on the surface.