碱金属沉积对Mn-Ce/TiO_2低温SCR催化剂性能影响

采用溶胶凝胶法制备了Mn-Ce/TiO_2低温SCR催化剂,考察了碱金属浓度与种类对催化剂活性的影响,探究了不同反应条件下钠盐沉积对活性保留分率的影响,利用SEM、BET、XRD和FT-IR对催化剂碱金属中毒原因进行了分析。结果表明,碱金属毒化后催化剂脱硝活性下降,钾中毒催化剂失活程度高于钠中毒的催化剂,2%钾中毒催化剂在160℃时NO去除率为62.0%,较新鲜催化剂下降29.2%。这主要因为碱金属毒化造成催化剂比表面积明显减小,且催化剂载体锐钛矿型TiO_2部分转化为金红石型,BET和SEM表征均说明碱金属沉积堵塞了催化剂表面的微孔。碱金属对Mn-Ce/TiO_2催化剂活性保留分率的影响表明,催化剂的颗粒粒径对其活性保留分率影响不大,碱金属含量减小、温度升高,Mn-Ce/TiO_2催化剂的活性保留分率增加,Na_2SO_4和NaCl对Mn-Ce/TiO_2催化剂的脱硝活性抑制作用大于KNO_3。

Effect of alkali metal deposition on Mn-Ce/TiO2 catalyst for NO reduction by NH3 at low temperature

A manganese and cerium oxide catalyst was prepared through sol-gel method. Effects of the concentration and type of alkali metals on performance of the Mn-Ce/TiO₂ catalysts were investigated in selective catalytic reduction of NO with NH₃. The cause of the alkali metal poisoning of the catalyst was studied and the influence of sodium salt deposition on the activity retention fraction under different reaction conditions was further studied. The catalysts were characterized by scanning electron microscope (SEM), BET surface area, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), respectively. The results show that alkali metals exhibited an inhibiting effect on the selective catalytic reduction (SCR), and the deactivation rate of Mn-Ce/TiO₂ catalyst caused by potassium poisoning was higher than that by sodium poisoning. The NO conversion was decreased from 91.2% to 62.0% at a temperature of 160℃, when the potassium content was 2%. This is mainly because the presence of the alkali metal resulted in a reduction of the specific surface area of the catalyst, and the specific surface area of the potassium poisoning of the catalyst was reduced by 34.2%. The alkali metal poisoning could cause blockage of the micropores on the surface and the transfer from anatase to rutile phase of the catalyst. The effect of alkali metal on the retention fraction of the Mn-Ce/TiO₂ catalyst indicates that the particle size of the catalyst had slight effect on its activity retention fraction. The selective catalytic reduction (SCR) activity of the Mn-Ce/TiO₂ catalyst increased along with the temperature. While the content of alkali metal decreased, the retention rate of active metal increased. The inhibitory effect of Na₂SO₄ and NaCl on the denitrification activity of Mn-Ce/TiO₂ catalyst was more significant than that of NaNO₃.