CeO2/TiO2 Monolith Catalyst for the Selective Catalytic Reduction of NOx with NH3: Influence of H2O and SO2

The influences of H2O and SO2 on CeO2/TiO2 monolith catalyst for the selective catalytic reduction(SCR) of NOx with NH3 were investigated. In the absence of SO2, H2O inhibited the SCR activity, which might be ascribed to the competitive adsorption of H2O and reactants such as NH3 and/or NOx. SO2 could promote the SCR activity of CeO2/TiO2 monolith catalyst in the absence of H2O, while in the presence of H2O it speeded the deactivation. During the SCR reaction in SO2-containing gases, Ce(III) sulfate species formed on the catalyst surface, resulting in the enhancement of Bronsted acidity. This played a significant role in the enhanced SCR activity. However, in the presence of both H2O and SO2, a large amount of ammonium-sulfate salts formed on the catalyst surface, which resulted in the blocking of catalyst pores and deactivated the catalyst. In addition, the NOx conversion was more sensitive to gas hourly space velocity in the presence of H2O than in the absence of H2O. The relatively high space velocity would result in a higher formation rate of ammonium-sulfate salts on per unit catalyst in the presence of H2O and SO2, which caused obvious deactivation of Ce/TiO2 monolith catalyst.