铁源对Fe/ZSM-5催化剂氨选择性催化还原NO的影响
Effects of Fe sources on catalytic performance of Fe/ZSM-5 for the selective catalytic reduction of NO with NH3
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摘要: 采用浸渍法,在相同的铁含量条件下,以硝酸铁、氯化亚铁、硫酸亚铁为前驱体制备了3种不同铁源Fe/ZSM-5分子筛催化剂.研究了铁源对Fe/ZSM-5催化剂NH3-SCR活性的影响,并采用X射线衍射(XRD)、比表面积和孔结构(BET)、X射线光电子能谱(XPS)、氢气程序升温还原(H2-TPR)及氨程序升温脱附(NH3-TPD)等表征手段对催化剂的结构和理化性质进行测定.结果表明,不同的铁源对Fe/ZSM-5催化剂低温段(低于350℃)的NH3-SCR催化性能影响较大,其低温活性顺序为:Fe(Cl)/ZSM-5 > Fe(S)/ZSM-5 > Fe(N)/ZSM-5.以氯化亚铁为铁源的Fe(Cl)/ZSM-5催化剂取得最佳的NH3-SCR催化活性,在233℃时NO转化率达到90%.表征结果表明,样品Fe(Cl)/ZSM-5中形成了最多的孤立Fe3+物种及中酸位数量.孤立Fe3+物种有利于增强Fe/ZSM-5催化剂的低温还原性能,改性过程中形成的中等强度酸性位有利于提高催化剂低温NH3-SCR催化性能.Abstract: With the same iron content, three types of Fe/ZSM-5 molecular sieve catalysts with different iron sources (ferrous nitrate, ferrous chloride and ferrous sulfate) were prepared by impregnation method. The effects of iron sources on the NH3-SCR performance of Fe/ZSM-5 catalysts were investigated and the physicochemical properties of the samples were characterized by XRD, BET, XPS, H2-TPR and NH3-TPD techniques. The results indicated that iron source had a great influence on the low-temperature (3-SCR performance of Fe/ZSM-5 catalysts. The order of activity of those catalysts at low temperatures was as follows:Fe(Cl)/ZSM-5 > Fe(S)/ZSM-5 > Fe(N)/ZSM-5. The sample with ferrous chloride as precursor obtained the best NH3-SCR activity, and the NO conversion of Fe(Cl)/ZSM-5 reached 90% at 233℃. Characterization result showed that the Fe(Cl)/ZSM-5 sample possessed the largest amount of isolated Fe3+ species and moderately acidic sites. Isolated Fe3+ species is beneficial to enhance the low temperature reduction performance of the Fe/ZSM-5 catalyst, and moderately acidic sites are favorable for the low-temperature catalytic performance.
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Key words:
- iron sources /
- Fe/ZSM-5 /
- NH3-SCR /
- NOx removal
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