Sulfation effect of Ce/TiO2 catalyst for the selective catalytic reduction of NOx with NH3: mechanism and kinetic studies

Abstract

Ceria-based catalysts are competitive substitutes for the commercial SCR catalysts due to their high SCR activity and excellent redox performance. For a better understanding of the SO₂ poisoning mechanism over ceria-based catalysts, the sulfation effect of the Ce/TiO₂ catalyst on the SCR activity over a wide reaction temperature range was systematically studied via comprehensive characterizations, in situ DRIFT studies and kinetic studies. The results demonstrated that the NO conversion at 150 °C is significantly inhibited by the formation of cerium sulfites/sulfates due to the inhibited redox properties and excessive adsorption of NH₃, which restrict the dissociation of NH₃ to NH₂, resulting in a much lower reaction rate of E–R reaction over the sulfated Ce/TiO₂ catalyst. With the increase in the reaction temperature, the reaction rate of the E–R reaction significantly increased due to the improved redox properties and weakened adsorption of NH₃. Moreover, the rate of the C–O reaction over the sulfated Ce/TiO₂ catalysts is obviously lower than that of the fresh Ce/TiO₂ catalyst. The promotion of NO conversion over the sulfated catalyst at 330 °C is attributed to both the increase in the reaction rate of E–R reaction and the inhibition of the C–O reaction.