WO3改性CeO2-TiO2催化剂的低温NH3-NO/NO2 SCR活性和机理研究

引用本文: 陈磊, 翁鼎, 汪家道, 翁端, 曹丽. WO₃改性CeO₂-TiO₂催化剂的低温NH₃-NO/NO₂ SCR活性和机理研究[J]. 催化学报, 2018, 39(11): 1804-1813. doi: 10.1016/S1872-2067(18)63129-8 shu

Citation: Lei Chen, Ding Weng, Jiadao Wang, Duan Weng, Li Cao. Low-temperature activity and mechanism of WO₃-modified CeO₂-TiO₂ catalyst under NH₃-NO/NO₂ SCR conditions[J]. Chinese Journal of Catalysis, 2018, 39(11): 1804-1813. doi: 10.1016/S1872-2067(18)63129-8 shu

WO₃改性CeO₂-TiO₂催化剂的低温NH₃-NO/NO₂ SCR活性和机理研究

陈磊 ^a, ,
翁鼎 ^a, ,
汪家道 ^a, ,
翁端 ^b, ,
曹丽 ^b,

a 清华大学机械工程学院摩擦学国家重点实验室, 北京 100084;
b 清华大学材料学院先进材料教育部重点实验室, 北京 100084
基金项目:
国家自然科学基金（51775296，51375253）.

摘要: 在铈钛基NH₃-SCR催化材料中，改性元素对催化材料的酸性位和氧化还原性能的影响较大。本文采用过量浸渍法分别制备了CeO₂-TiO₂（CeTi）和CeO₂/WO₃-TiO₂（CeWTi）催化剂，研究了CeWTi催化材料结构、酸性位及氧化还原性能对NH₃-NO/NO₂ SCR反应性能的影响.结果发现，CeTi和CeWTi样品均有较优异的NH₃-NO/NO₂ SCR催化性能，后者略高.WO₃的加入增加了催化材料的表面酸性，对其氧化还原性能影响不大.通过对反应中间物种NH₄NO₃的研究，发现NH₄NO₃的分解主要与氧化还原性能相关，而NO还原NH₄NO₃的反应需要氧化还原能力和酸性位共同作用，即在氧化还原性能差异不大的条件下，酸性对该反应起到重要作用.而该反应也是NH₃-NO/NO₂ SCR的限速步骤，这是CeWTi催化材料活性高于CeTi催化材料的原因.
同时，为了获得NH₃-NO/NO₂ SCR反应的高活性，NO₂：NO比例宜为1：1.然而现实情况中，预氧化催化材料的氧化活性、NO_x浓度、温度等变量使得准确控制NO₂的比例较难，因此，深入了解NO₂浓度对NH₃-NO/NO₂ SCR反应的影响至关重要.本文探讨NO₂：NO的比例、O₂浓度等对NH₃-NO/NO₂ SCR反应性能的影响；并研究了不同NO₂含量条件下NH₃-NO/NO₂ SCR反应网络.通过分析CeWTi材料上NH₃-NO/NO₂ SCR反应网络可知，当NO与NO₂比例为1：1时，NH₃-SCR催化活性最高，并以快速SCR形式进行；当NO与NO₂比例为1：1消耗完全之后，剩余的NO或NO₂各自独立以标准或慢速SCR进行，不影响其本来的反应活性.催化材料的标准SCR、快速SCR和慢速SCR均取决于材料表面酸度和氧化还原性能，但快速SCR和慢速SCR对材料这两方面性能的要求相对较低.同时O₂并不参与快速和慢速SCR，而NO₂可以取代O₂作为SCR反应中主要的氧化剂，氧化Ce⁴⁺为Ce³⁺，甚至比O₂和NO再氧化活性位的能力更强，保持催化材料的高催化活性.低温条件时，慢速SCR和快速SCR反应均在材料表面生成硝酸铵中间物种，但由于慢速SCR气氛中缺乏NO将硝酸铵还原，进而引发快速SCR反应，因此材料表面快速SCR的NO_x转化率要高于慢速SCR反应；高温条件下，由于硝酸铵容易热分解，导致硝酸铵的抑制效应不太明显.NH₄NO₃分解是NO₂含量升高后N₂O的形成的主要途径.

关键词:

English

Low-temperature activity and mechanism of WO₃-modified CeO₂-TiO₂ catalyst under NH₃-NO/NO₂ SCR conditions

a State Key Laboratory of Tribology, School of Mechanical Engineering, Tsinghua University, Beijing 100084, China;
b Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
Received Date: 05 May 2018
Revised Date: 22 June 2018
Fund Project:
This work was supported by the National Natural Science Foundation of China (51775296, 51375253).

Abstract: The CeO₂-TiO₂ (CeTi) and CeO₂/WO₃-TiO₂ (CeWTi) catalysts were prepared by a sol-gel precipitation method and their NH₃-NO/NO₂ selective catalytic reduction (SCR) performance was studied. N₂O formation and effect of oxygen concentration on SCR performance over CeWTi catalyst were also investigated while varying the NO₂/NO_x ratio. Results indicate that fast SCR behavior of CeWTi catalyst has the best NH₃-NO/NO₂ SCR performance due to the catalyst reoxidation rate by NO₂ higher than by O₂. Compared with CeTi catalyst, CeWTi catalyst exhibits higher de-NO_x performance under NH₃-NO/NO₂ SCR conditions. As the CeTi and CeWTi catalysts exhibit similar redox property, addition of WO₃ provides more acid sites which accelerate the reaction between NH₄NO₃ and NO to get a superior low-temperature activity. Amount of N₂O formation shows a peak at 250℃ mainly derived from NH₄NO₃ decomposition.

Key words:

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WO₃改性CeO₂-TiO₂催化剂的低温NH₃-NO/NO₂ SCR活性和机理研究

English

Low-temperature activity and mechanism of WO₃-modified CeO₂-TiO₂ catalyst under NH₃-NO/NO₂ SCR conditions

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