SO_2对Mn-Ce/TiO_2低温SCR催化剂的毒化作用研究

考察了SO_2对Mn-Ce/TiO_2低温脱硝催化剂活性的影响,利用XRD、BET、SEM和XPS对其毒化作用的原因进行分析。结果表明,SO_2对催化剂活性有明显的抑制作用,使NO_x去除率由84%降至42%左右。主要是SO_2的加入造成催化剂比表面积减小,孔径为5-10 nm的孔数量减少,且催化剂晶相由锐钛矿型转化成金红石型结构,活性组分MnO_x发生晶化现象,破坏了Mn-Ti间的强相互作用。催化剂理化性质的变化造成吸附态氧转化为晶格氧的路径受阻、MnO_2含量减少和CeO_x储氧功能减弱,并且产生氧阻效应而使NO吸附和解吸受阻,造成催化剂活性降低。同时生成的硫酸铵盐在催化剂表面沉积,覆盖了催化剂表面的Lewis酸性位,使其对NH_3吸附能力减弱。

Poisoning effect of SO2 on Mn-Ce/TiO2 catalysts for NO reduction by NH3 at low temperature

Effects of SO₂ on performance of Mn-Ce/TiO₂ catalysts were investigated in the selective catalytic reduction of NO with NH₃.The catalysts were characterized by BET surface area,X-ray diffraction(XRD),scanning electron microscope(SEM),X-ray photoelectron spectroscopy(XPS),respectively.The results show that SO₂ has inhibitory effect on the selective catalytic reduction(SCR),and NO_x conversion decreases from 84% to 42% at 140℃.This is mainly because the presence of SO₂ results in the decrease of the specific surface area of the catalysis and the pore size distribution of 5-10 nm.SO₂ can cause TiO₂ transformation from anatase to rutile phase,the crystallization phenomenon of active components MnO_x,and the decrease of the strong interaction between Mn and Ti.The variations of physical and chemical properties of poisoned Mn-Ce/TiO₂ catalyst block the O₂^-→O^-→O^2- conversion path,which reduces the proportion of higher catalytic activity component MnO₂ in MnO_x,weakens oxygen storage ability of CeO_x,and accumulates absorbed oxygen on the catalyst surface decreasing the adsorption and desorption of NO on active sites.Ammonium sulfate formed on the catalyst surface covers the Lewis acid sites and decreases the adsorption amount of NH₃.