SO_2和H_2O对CeO_2/TiO_2/堇青石催化剂选择催化还原NO_x性能的影响

采用浸渍法制备了以堇青石为基底、氧化铈为活性组分的整体式脱硝催化剂CeO2/TiO2/堇青石催化剂。通过与商业钒基催化剂(V2O5-WO3/TiO2/堇青石)的对比研究发现,CeO2/TiO2/堇青石催化剂表现出了优良的抗硫抗水性能,经过30 h抗硫抗水实验,CeO2/TiO2/堇青石催化剂的氮氧化物转化率仍能保持在70%以上,仅下降了5%。BET、XRD、FT-IR和TG表征结果表明,在含硫含水气氛中反应时,CeO2/TiO2/堇青石和V2O5-WO3/TiO2/堇青石催化剂表面均有硫酸铵盐的生成,且前者的生成量明显低于后者。NH3-DRIFT分析结果表明,在含硫含水气氛中两种催化剂表面Brnsted酸性都被增强,而Lewis酸性有所减弱。进一步的XPS分析结果表明,烟气中的SO2+H2O会使催化剂表面Ce4+向Ce3+发生转化,从而导致化学吸附氧含量增加,这是CeO2/TiO2/堇青石催化剂具有优良抗硫抗水性能的重要原因。

Influence of SO2 and H2 O on the selective catalyit c reduction of NOx over CeO2/TiO2/cordierite cat alyst

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.