Effect of H2O and SO2 on the Selective Catalytic Reduction of NO with NH3 Over Ce/TiO2 Catalyst: Mechanism and Kinetic Study

Ce-based catalysts now were regarded as a promising alternative to substitute V2O5/WO3-TiO2 catalyst for the abatement of NOx in the flue gas. However, H2O and SO2 showed a notable effect on NO reduction over Ce based catalysts and the mechanism was not very clear. In this work, the mechanism of H2O and SO2 effect on NO reduction over Ce/TiO2 was studied using the steady state kinetic study and the reaction kinetic parameters were compared. Although H2O and SO2 both showed a promotion on NO reduction over Ce/TiO2 at higher temperatures, their mechanisms were quite different. The effect of SO2 on NO reduction over Ce/TiO2 was mainly attributed to the sulfation. The selective catalytic reduction (SCR) reaction over Ce/TiO2 at higher temperatures was promoted after the sulfation due to the promotion of NH3 adsorption. Meanwhile, the catalytic oxidation of NH3 to NO (i.e., the C-O reaction) over Ce/TiO2 at higher temperatures was suppressed after the sulfation. Therefore, the promotion of NO reduction over Ce/TiO2 at higher temperatures due to the introduction of SO2 was related to not only the inhibition of the C-O reaction but also the promotion of the SCR reaction. However, the SCR reaction over Ce/TiO2 at higher temperatures was restrained in the presence of H2O due to the inhibition of NH3 adsorption and the decrease of oxidation ability. Therefore, the promotion of NO reduction over Ce/TiO2 at higher temperatures due to the presence of H2O was mainly attributed to the inhibition of the C-O reaction.