Influence of SO₂ and H₂O on the selective catalytic reduction of NO_x over CeO₂/TiO₂/cordierite catalyst

A monolithic CeO₂/TiO₂/cordierite deNO_x catalyst was prepared by an impregnation method, with cordierite as the substrate and CeO₂ as the active component. The CeO₂/TiO₂/cordierite catalyst exhibits excellent resistance against SO₂ and H₂O in the selective catalytic reduction (SCR) of NO_x with NH₃, compared with the commercial vanadium-based catalyst (V₂O₅-WO₃/TiO₂/cordierite); the CeO₂/TiO₂/cordierite catalyst gives a conversion of NO_x above 70% after 30 h resistance test against SO₂+H₂O, only declined by 5%. BET, XRD, FT-IR and TG results indicated that ammonium sulfate is formed on the surface of both CeO₂/TiO₂/cordierite and V₂O₅-WO₃/TiO₂/cordierite catalysts during the SCR reaction in the presence of SO₂ and H₂O, but on the former, the amount of ammonium sulfate deposited is much less. NH₃-DRIFT results suggested that the surface Brønsted acidity is strengthened, whereas the surface Lewis acidity is weakened during the SCR reaction in the presence of SO₂ and H₂O. XPS results further displayed that SO₂+H₂O in flue gas may induce a reduction of Ce from Ce⁴⁺ to Ce³⁺ on CeO₂/TiO₂/cordierite catalyst, resulting in an increase of the chemisorbed oxygen amount, which contributes to the excellent resistance of the CeO₂/TiO₂/cordierite catalyst against SO₂ and H₂O during the SCR reaction.