不同阳离子(NH4+,Na+,K+,Ca2+)溴化物对商用SCR催化剂化学中毒影响机制研究

引用本文: 常化振, 史传宁, 李明冠, 张涛, 王驰中, 江莉龙, 王秀云. 不同阳离子(NH₄⁺,Na⁺,K⁺,Ca²⁺)溴化物对商用SCR催化剂化学中毒影响机制研究[J]. 催化学报, 2018, 39(4): 710-717. doi: 10.1016/S1872-2067(18)63011-6 shu

Citation: Huazhen Chang, Chuanning Shi, Mingguan Li, Tao Zhang, Chizhong Wang, Lilong Jiang, Xiuyun Wang. The effect of cations (NH₄⁺, Na⁺, K⁺, and Ca²⁺) on chemical deactivation of commercial SCR catalyst by bromides[J]. Chinese Journal of Catalysis, 2018, 39(4): 710-717. doi: 10.1016/S1872-2067(18)63011-6 shu

不同阳离子(NH₄⁺,Na⁺,K⁺,Ca²⁺)溴化物对商用SCR催化剂化学中毒影响机制研究

常化振 ^a, ,
史传宁 ^a, ,
李明冠 ^a, ,
张涛 ^a, ,
王驰中 ^b, ,
江莉龙 ^c, ,
王秀云 ^c,

a 中国人民大学环境学院, 北京 100872;
b 清华大学环境学院环境模拟与污染控制国家重点联合实验室, 北京 100084;
c 福州大学化肥催化剂国家工程研究中心, 福建福州 350002
基金项目:
国家重点研发计划（2016YFC0203900，2016YFC0203901）；国家自然科学基金（51778619，21577173）.

摘要: 燃煤飞灰中的碱金属和碱土金属对NH₃-SCR催化剂的活性有显著的影响.近年来，研究者针对碱金属/碱土金属氧化物对SCR催化剂中毒作用开展了大量研究.另一方面，研究普遍认为，含溴化合物对提高SCR催化剂汞氧化性能具有明显促进作用.目前为止，针对碱金属/碱土金属溴化物对SCR催化剂影响的系统研究较少.我们课题组系统研究了不同阳离子的溴化物（NH₄Br，NaBr，KBr和CaBr₂）对商用V₂O₅-WO₃/TiO₂催化剂性能的影响.
与未中毒样品相比，KBr中毒后的催化剂（记为L-KBr）上NO_x转化率明显下降，而NaBr和CaBr₂中毒的催化剂（分别记为L-NaBr和L-CaBr）上的SCR活性也有一定程度的降低.另外L-NaBr，L-KBr和L-CaBr催化剂的N₂选择性较差.XPS结果显示，KBr中毒后化学吸附氧（O_α）比例减小；同时，KBr中毒后还原性和表面酸度降低，这些可能是导致L-KBr催化剂的活性和N₂选择性变差的主要原因.对于L-CaBr催化剂，中毒后化学吸附氧O_α比例有所增加，这与H₂-TPR结果显示可还原性增强一致.O₂-TPO结果显示，L-CaBr催化剂可氧化性降低，说明CaBr₂中毒还是影响到催化剂表面的氧化还原循环.催化剂CaBr₂中毒后表面被覆盖减少了反应活性位数量，但表面酸性的增强可能会抵消活性位点损失带来的负面影响.NH₃氧化结果显示，NH₃在L-CaBr催化剂表面发生过氧化反应，特别是高温下生成较多N₂O，降低N₂选择性，这可能是高温下L-CaBr催化剂SCR活性和N₂选择性下降的重要原因.CO₂-TPD结果表明，L-KBr和L-CaBr催化剂表面碱性强度增加，可能有助于增加NO_x物种的吸附量.基于以上活性评价和表征分析结果，我们尝试建立了不同溴化物中毒的催化剂表面酸碱性、氧化还原和催化性能之间的关系.

关键词:

English

The effect of cations (NH₄⁺, Na⁺, K⁺, and Ca²⁺) on chemical deactivation of commercial SCR catalyst by bromides

a School of Environment and Natural Resources, Renmin University of China, Beijing 100872, China;
b State Key Joint Laboratory of Environment Simulation and Pollution Control(SKLESPC), School of Environment, Tsinghua University, Beijing 100084, China;
c National Engineering Research Center of Chemical Fertilizer Catalyst, Fuzhou University, Fuzhou 350002, Fujian, China
Received Date: 20 November 2017
Revised Date: 28 December 2017
Fund Project:
This work was supported by the National Key R&D Program of China (2016YFC0203900, 2016YFC0203901) and National Natural Science Foundation of China (51778619, 21577173).

Abstract: Alkali and alkaline-earth metals from fly ash have a significant deactivation effect on catalysts used for selective catalytic reduction of NO_x by NH₃ (NH₃-SCR). Bromides are considered effective additives to improve Hg⁰ oxidation on SCR catalysts. In this work, the effects of different bromides (NH₄Br, NaBr, KBr, and CaBr₂) on a commercial V₂O₅-WO₃/TiO₂ catalyst were studied. NO_x conversion decreased significantly over the KBr-poisoned catalyst (denoted as L-KBr), while that over NaBr-and CaBr₂-poisoned catalysts (denoted as L-NaBr and L-CaBr, respectivity) decreased to a lesser extent compared with the fresh sample. Poor N₂ selectivity was observed over L-NaBr, L-KBr and L-CaBr catalysts. The decrease in the ratio of chemisorbed oxygen to total surface oxygen (O_α/(O_α + O_β + O_w)), reducibility and surface acidity might contribute to the poor activity and N₂ selectivity over L-KBr catalyst. The increased O_αratio was conducive to the enhanced reducibility of L-CaBr. Combined with enhanced surface acidity, this might offset the negative effect of the loss of active sites by CaBr₂ covering. The overoxidation of NH₃ and poor N₂ selectivity in NH₃ oxidation should retard the SCR activity at high temperatures over L-CaBr catalyst. The increased basicity might contribute to increased NO_x adsorption on L-KBr and L-CaBr catalysts. A correlation between the acid-basic and redox properties of bromide-poisoned catalysts and their catalytic properties is established.

Key words:

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沈阳化工大学材料科学与工程学院沈阳 110142

不同阳离子(NH₄⁺,Na⁺,K⁺,Ca²⁺)溴化物对商用SCR催化剂化学中毒影响机制研究

English

The effect of cations (NH₄⁺, Na⁺, K⁺, and Ca²⁺) on chemical deactivation of commercial SCR catalyst by bromides

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