铁铈复合选择性催化还原脱硝催化剂的碱金属(钾)中毒机理

doi:10.16085/j.issn.1000-6613.2017-0264

摘要/Abstract

摘要： 采用湿法浸渍法将碱金属（钾和钠）负载到柠檬酸法制备的铁铈复合催化剂（FeCeO_x）表面模拟中毒，考察碱金属对此催化剂低温选择性催化还原（SCR）脱硝活性的影响；通过N₂吸附、程序升温脱附（NH₃-TPD、NO-TPD）、H₂程序升温还原（H₂-TPR）及原位漫反射红外傅里叶变换光谱（in situ DRIFTS）等表征技术分析了催化剂的失活原因和机理。结果表明，碱金属钾比钠对铁铈复合催化剂的脱硝活性影响更大；碱金属钾中毒后，催化剂的比表面积和氧化还原性能下降；钾降低了催化剂的低温NO_x吸附能力，尤其是减少了活性硝酸盐物种而生成更多的惰性硝酸盐物种；催化剂表面酸性的显著下降是此催化剂失活的主要因素，且Brønsted酸位和Lewis酸位两种酸性位均受到钾的影响，抑制着NH₃在催化剂表面的吸附。

关键词: 低温选择性催化还原, 碱金属中毒, 铁铈复合催化剂, 失活, 表征

Abstract: Alkali metals(potassium & sodium)were loaded on the iron-cerium composite catalysts (FeCeO_x) using wet impregnation method to simulate the poisoning phenomenon,while the FeCeO_x catalysts were synthesized by citric acid method. The effect of the alkali metals on the catalytic performance of CeFeO_x for the low temperature selective catalytic reduction (SCR) of NO_x with NH₃ was investigated. To analyze the deactivation reasons and mechanism,the catalysts were characterized by N₂ adsorption,temperature programmed desorption(NH₃-TPD,NO-TPD),H₂ temperature programmed reduction(H₂-TPR)and in situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTS)techniques. It is found that the poisoning effect of K is stronger than that of Na on this kind of catalyst. The addition of potassium reduces the specific surface area as well as the redox properties of the catalyst. NO_x adsorption of the catalyst is further influenced at low temperature. Particularly, active nitrate species decrease with the increase of inactive nitrate species. The main factor of deactivation may be the significant decline in surface acidity, including both Brønsted acid and Lewis acid, which hinders NH₃ adsorption over CeFeO_x.

Key words: low temperature SCR, alkali metal poisoning, FeCeO_x catalysts, deactivation, characterization

中图分类号:

X511

王丽霞, 仲兆平, 朱林, 杨瀚. 铁铈复合选择性催化还原脱硝催化剂的碱金属(钾)中毒机理[J]. 化工进展, 2017, 36(11): 4064-4071.

WANG Lixia, ZHONG Zhaoping, ZHU Lin, YANG Han. Alkali metal(potassium)poisoning mechanism of CeFeO_x catalysts for selective catalytic reduction of No_x[J]. Chemical Industry and Engineering Progress, 2017, 36(11): 4064-4071.

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