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

Abstract

Ce-based catalysts now were regarded as a promising alternative to substitute V 2 O 5 /WO 3 –TiO 2 catalyst for the abatement of NO x in the flue gas. However, H 2 O and SO 2 showed a notable effect on NO reduction over Ce based catalysts and the mechanism was not very clear. In this work, the mechanism of H 2 O and SO 2 effect on NO reduction over Ce/TiO 2 was studied using the steady state kinetic study and the reaction kinetic parameters were compared. Although H 2 O and SO 2 both showed a promotion on NO reduction over Ce/TiO 2 at higher temperatures, their mechanisms were quite different. The effect of SO 2 on NO reduction over Ce/TiO 2 was mainly attributed to the sulfation. The selective catalytic reduction (SCR) reaction over Ce/TiO 2 at higher temperatures was promoted after the sulfation due to the promotion of NH 3 adsorption. Meanwhile, the catalytic oxidation of NH 3 to NO (i.e., the C–O reaction) over Ce/TiO 2 at higher temperatures was suppressed after the sulfation. Therefore, the promotion of NO reduction over Ce/TiO 2 at higher temperatures due to the introduction of SO 2 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/TiO 2 at higher temperatures was restrained in the presence of H 2 O due to the inhibition of NH 3 adsorption and the decrease of oxidation ability. Therefore, the promotion of NO reduction over Ce/TiO 2 at higher temperatures due to the presence of H 2 O was mainly attributed to the inhibition of the C–O reaction.