Temperature sensitive long-term stability of MnOx/TiO2 catalysts for selective catalytic reduction of NOx with NH3 at low temperature†

IF 2.5 3区 化学 Q2 CHEMISTRY, MULTIDISCIPLINARY
Ruoxuan Bai, Rongkun Jiang, Zixiao Yu, Junqi Wang, Yiqing Zeng and Shule Zhang
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Abstract

A number of efforts have been made to improve the NH3-SCR activity of MnOx based catalysts at low temperature, but few studies have focused on their long-term stability. In this study, MnOx/TiO2 (MnTi) catalysts prepared via wet impregnation were subjected to 30-h long-term stability tests under laboratory conditions to investigate their stability for the selective catalytic reduction (NH3-SCR) of NOx at low temperatures (80–200 °C), and combined with XRD, BET, XPS, H2-TPR, and in situ DRIFTS analysis to elucidate deactivation mechanisms. The results show that the reaction temperature has a great influence on the formation, decomposition, and transformation of nitrate species. Nitrate species, especially stable nitrate species, continuously accumulate on the catalyst surface at relatively low temperatures (≤160 °C in this work), which might block the active sites and hinder the conversion of Mn3+ to Mn4+, thereby leading to deactivation of the MnTi catalyst. In contrast, nitrate species on the catalyst surface can react or decompose rapidly at a high enough temperature (≥200 °C in this work), which facilitates the exposure of active sites and dynamic equilibrium of the Mn4+/Mn3+ redox cycle, resulting in the high long-term stability. We expect that this work will arouse researchers’ attention toward the long-term stability of NH3-SCR catalysts in the study of improving their catalytic activity at low temperature.

Abstract Image

低温下NH3选择性催化还原NOx的MnOx/TiO2催化剂的温敏长期稳定性
为了提高MnOx基催化剂在低温下的NH3-SCR活性,人们做了很多努力,但对其长期稳定性的研究却很少。本研究通过湿浸渍法制备MnOx/TiO2 (MnTi)催化剂,在实验室条件下进行了30 h的长期稳定性测试,考察其在低温(80-200℃)下选择性催化还原(NH3-SCR) NOx的稳定性,并结合XRD、BET、XPS、H2-TPR和原位DRIFTS分析来阐明失活机理。结果表明,反应温度对硝酸盐的生成、分解和转化有很大的影响。在较低温度下(本研究≤160℃),硝酸盐,尤其是稳定的硝酸盐在催化剂表面不断积累,可能会阻断活性位点,阻碍Mn3+向Mn4+的转化,从而导致MnTi催化剂失活。相反,催化剂表面的硝酸盐在足够高的温度下(本研究≥200℃)可以快速反应或分解,有利于活性位点的暴露和Mn4+/Mn3+氧化还原循环的动态平衡,从而具有较高的长期稳定性。希望本工作能引起研究者在提高NH3-SCR催化剂低温催化活性的研究中对其长期稳定性的关注。
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来源期刊
New Journal of Chemistry
New Journal of Chemistry 化学-化学综合
CiteScore
5.30
自引率
6.10%
发文量
1832
审稿时长
2 months
期刊介绍: A journal for new directions in chemistry
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