Structural effect and reaction mechanism of MnO_2 catalysts in the catalytic oxidation of chlorinated aromatics  

MnO_2催化剂用于催化氧化含氯芳香烃的形貌效应与反应机制研究（英文）

作　　者：Xiaole Weng Yu Long Wanglong Wang Min Shao Zhongbiao Wu 翁小乐;龙宇;王望龙;邵敏;吴忠标(浙江大学环境与资源科学学院,教育部环境修复与生态健康重点实验室,浙江杭州310058;浙江省工业锅炉炉窑烟气污染控制工程技术研究中心,浙江杭州310058;北京大学环境科学与工程学院,国家环境模拟与污染控制联合重点实验室,北京100871;暨南大学环境与气候研究所,广东广州511443)

机构地区：[1]Key Laboratory of Environment Remediation and Ecological Health,Ministry of Education,College of Environmental and Resource Sciences,ZhejiangUniversity,Hangzhou 310058,Zhejiang,China [2]Zhejiang Provincial Engineering Research Center of Industrial Boiler & Furnace Flue Gas Pollution Control,Hangzhou 310058,Zhejiang,China [3]State Joint Key Laboratory of Environmental Simulation and Pollution Control,College of Environmental Sciences and Engineering,Peking University,Beijing 100871,China [4]Environmental and climate Research institute,Jinan University,Guangzhou 511443,Guangdong,China

出　　处：《Chinese Journal of Catalysis》2019年第5期638-646,共9页催化学报（英文）

基　　金：supported by the Outstanding Youth Project of Zhejiang Natural Science Foundation(LR19E080004);the National Natural Science Foundation of China(51478418)~~

摘　　要：Various MnO2 structures have been extensively applied in catalysis. In this study,γ-MnO2,α-MnO2, and δ-MnO2 with corresponding rod, tube, and hierarchical architecture morphologies were prepared and applied for the catalytic oxidation of chlorobenzene (CB). The redox ability, H2O activation behavior, and acidity of MnO2 were analyzed using a range of techniques, including TPR, H2O-TPD, XPS, and pyridine-IR. The catalytic activities in CB oxidation were assessed;this revealed that γ-MnO2 exhibited the highest activity and best stability, owing to its enriched surface oxygen vacancies that functioned to activate O2 and H2O, and capture labile chlorine, which reacted with dissociated H2O to form HCl. All the MnO2 phases generated toxic polychlorinated by-products, including CHCl3, CCl4, C2HCl3, and C2Cl4, indicating the occurrence of electrophilic chlorination during CB oxidation. In particular, the dichlorobenzene detected in the effluents of α-MnO2 might generate unintended dioxins via a nucleophilic substitution reaction.含氯挥发性有机物(Chlorinated VOCs)被广泛应用于工业、农业、医药、有机合成等领域,在使用过程中会通过挥发、泄漏、废气排放等途径进入大气环境中,造成臭氧层破坏与光化学烟雾,且很难被生物降解,对人体具有很强的"三致"效应.在众多治理方法中,催化燃烧因高效低能耗的特点而被认为是具有应用前景的含氯VOCs处理方式,然而催化剂中毒以及毒副产物生成极大限制了该技术的工业应用.锰基催化剂由于价格低廉、来源广泛以及价态多变等特点被广泛应用于环境催化领域,包括甲醛、甲苯、CO催化氧化以及选择性催化还原脱硝等.MnO_2的晶体形貌与其催化性能息息相关,二者的构效关系已有广泛研究,但在含氯VOCs催化氧化中,MnO_2的形貌特征与催化活性、反应稳定性、副产物等的关系尚不明晰.因此,本文通过水热法制备了纳米棒状γ-MnO_2,纳米管状α-MnO_2以及具有层状结构的δ-MnO_2,系统研究了这三种形貌结构在氯苯催化氧化中的反应特征,利用XRD,XPS,TPR,TPD,吡啶-IR等手段对催化剂的形貌、表面元素价态、氧化还原性能以及表面酸性等进行了表征,获得了MnO_2在含氯VOCs催化氧化应用中的构效关系.XRD以及SEM分析结果表明,三种形貌的MnO_2样品均由水热法成功制得.H_2-TPR和O_2-TPD测试分析显示,MnO_2催化剂的氧化还原性能按如下顺序递减δ-MnO_2≥γ-MnO_2>α-MnO_2,与这些催化剂活性测试中的氯苯转化率结果一致,但与其CO_2选择性的结果不一致.氧化还原能力最佳的δ-MnO_2上CO_2选择性表现最差,即使提高温度仍无法提升.XPS结果表明,三种催化剂的Mn元素平均价态高低顺序为δ-MnO_2(3.80)>α-MnO_2(3.75)≥γ-MnO_2(3.74).δ-MnO_2催化剂表面因具有最丰富的Mn^(4+),反应过程中易生成强的Mn-Cl键,从而抑制了Cl与解离水反应生成HCl,导致催化剂富集氯失活,CO_2选择性差.对反应尾气及催化剂表面产

关 键 词：MnO2 CHLOROBENZENE Catalytic oxidation Polychlorinated byproducts Environmental risk 

分 类 号：O621.251[理学—有机化学]