【作者】 薛晓敏；

【导师】 周仁贤；

【作者基本信息】 浙江大学 ， 化学， 2011， 硕士

【摘要】 含卤VOCs是VOCs中对大气环境的危害尤为显著的一类污染物,卤代烃类尤其是氯代烃类(CVOCs)不仅可以破坏大气的臭氧层(1个Cl自由基最多可消耗106个臭氧分子),而且对人类的身体健康和生态造成持久的、积累性的影响。CVOCs由于具有良好的溶解性能和反应惰性而作为一种重要的化工原料和有机溶剂被广泛地应用。国内外关于含氯有机化合物的消除方法,主要包括热消除、生物学处理、光催化降解、加氢脱氯等,其中催化氧化净化以转化温度低、选择性高而成为最经济、最可靠的方法,在消除CVOCs方面的应用也愈来愈受到人们的关注。氯代烃类与非氯代烃类的催化氧化区别在于C-Cl的断裂取代了C-H的断裂,虽然从热力学上分析C-C1的断裂应该更有利,但所生成的C1可强吸附在催化剂的表面上,一方面更容易导致催化剂的失活,另一方面生成的C12可与烃类反应生成多氯烃类,造成二次污染。本论文中,我们选择HZSM-5分子筛为载体,比较系统地研究了硅铝比对HZSM-5及其负载Ce02催化剂上DCE催化氧化性能的影响。在此基础上,研究了掺杂过渡金属MOx(M=Cr、Mn、Fe、Co、Ni和Cu)对CeO2/HZSM-5催化剂上DCE氧化性能的影响和规律,探讨了CrOx-CeO2/HZSM-5催化剂上DCE、DCM和TCE催化降解机理。同时利用XRD、N2吸脱附、H2-TPR、NH3-TPD、DCE-TPSR等手段对负载型催化剂的织构-结构、氧化还原性质和表面酸性等进行了表征分析,得到了如下结果：1.对比研究了不同硅铝比的HZSM-5分子筛及其负载Ce02催化剂上DCE的催化氧化性能。结果表明,低硅铝比(SiO2/Al2O3=22)的HZSM-5(22)分子筛及其负载Ce02催化剂对DCE的催化降解活性最高。Ce02与HZSM-5之间的相互作用明显提高了氧物种的流动性,同时也增加了催化剂中弱酸与强酸的密度比例,从而提高了DCE脱氯生成C2H3C1的能力及其中间产物的深度氧化。2.对比研究了9%M/HZSM-5(22)和9%M-12%CeO2/HZSM-5(22)催化剂上DCE的催化降解性能。结果表明,与其单组分的9%M/HZSM-5(22)催化剂的催化降解活性比较,掺杂Ce02对9%Ni/HZSM-5(22)和9%Cu/HZSM-5(22)上DCE的降解活性有所下降,而对9%Cr/HZSM-5(22)催化剂的活性却有明显提高。9%M-12%CeO2/HZSM-5(22)催化剂对DCE的催化降解活性顺序为：9%Ni-12%CeO2/HZSM-5(22)> 9%Co-12%CeO2/HZSM-5(22)、9%Mn-12%CeO2/ HZSM-5(22)> 9%Cu-12%CeO2/HZSM-5(22)、9%Cr-12%CeO2/HZSM-5(22)> 9%Fe-12%CeO2/HZSM-5(22)> 12%CeO2/HZSM-5(22)。弱酸和中强酸位密度的增加对DCE脱氯生成C2H3C1有明显的促进作用。但掺杂Cu、Co和Mn的催化剂上生成了较多的C2HCl3和C2C14等多氯副产物,而掺杂Ni的催化剂上生成了较多的CH3Cl副产物,这可能与其金属阳离子的强酸性位有关。过渡金属与Ce02的共同掺杂,提供了活性氧物种及提高了其流动性,有利于提高DCE的深度氧化性能,尤其Cr的添加显著提高了中间产物C2H3C1进一步脱氯降解的能力,避免了多氯副产物和CH3Cl副产物的产生。3.比较研究了9%Cr-12%CeO2/HZSM-5(22)、9%Cr/HZSM-5(22)、12%CeO2/ HZSM-5(22)和HZSM-5(22)催化剂上各活性组分之间的协同作用对催化降解性能的影响及催化剂的稳定性。结果表明,由于CrOx-CeO2的相互作用,有助于活性组分的稳定,并促进了活性氧物种的流动性,从而有效地避免了积炭的形成和活性组分的流失,显著提高了CrOx-12%CeO2/HZSM-5(22)催化剂的活性和稳定性。不同反应物在9%Cr-12%CeO2/HZSM-5(22)催化剂上的反应活性顺序为：DCE>TCE>DCM。更多还原

【Abstract】 Halogenated hydrocarbons, especially chlorinated volatile organic compounds (CVOCs), constitute a significant fraction of toxic air containments. They not only can destroy the ozone layer (one free radical of Cl consumes a maximum of 106 molecules of O3), but also cause long-lasting and cumulative effects on human health and the ecological system. Chlorinated hydrocarbons have been widely used as industrial chemicals and organic solvents because of their relative inertness in chemical processes and their ability to dissolve many compounds. Various disposal methods have been investigated for the abatement of CVOCs world-wide, mainly are thermal incineration, biological degradation, photocatalytic degradation, hydrodechlorination et. al. Catalytic oxidation has gained much attention as the most economic and efficient technique for CVOCs destruction due to its lower conversion temperature and higher selectivity. The difference between catalytic oxidation of chlorinated hydrocarbons and non-chlorinated hydrocarbons is the replacement of C-H bond breaking by C-Cl bond breaking. It is known that the cleavage of C-Cl bond is more easily through thermal analysis. However, the strong adsorption of Cl species on the catalyst surface not only causes the deactivation of catalyst, but also results in the production of polychlorinated hydrocarbons, which will lead to the secondary pollution.In this paper, HZSM-5 zeolite was chosen as the support, the influences of different SiO2/Al2O3 ratios and the introduction of CeO2 to HZSM-5 on the catalytic performance for DCE destruction were systematically studied. Based on the above results, further investigation of the effect of transition metal oxides MOX (M=Cr, Mn, Fe, Co, Ni and Cu) added to CeO2/HZSM-5 catalysts on the catalytic performance for DCE destruction was done. Moreover, the mechanisms of catalytic decomposition of DCE, DCM and TCE over CrOx-CeO2/HZSM-5 catalysts were also studied. The texture-structure, surface acidity distribution and redox properties of these catalysts were characterized by XRD, N2 adsorption/desorption, NH3-TPD, H2-TPR and DCE-TPSR techniques. Some specific conclusions from this work are drawn as follows:1. Catalytic performances for DCE destruction over HZSM-5 zeolites with different SiO2/Al2O3 ratios and CeO2/HZSM-5 catalysts were studied. The results show that HZSM-5(22) and CeO2/HZSM-5(22) exhibit the highest catalytic activity. The interactions between CeO2 and HZSM-5 improve the migration of oxygen species and increase the ratio of strong acid concentration to weak acid concentration, which promote the dehydrochlorination of DCE to form C2H3Cl and the deep oxidation of the intermediates.2. The catalytic performances for DCE destruction over 9%M/HZSM-5(22) and 9%M-12%CeO2/HZSM-5(22) catalysts were investigated. It is found that the addition of CeO2 to 9%Ni/HZSM-5(22) and 9%Cu/HZSM-5(22) catalysts causes a decline in catalytic activity, whereas the catalytic performance of 9%Cr-12%CeO2/HZSM-5(22) is significantly prompted compared with that of 9%Cr/HZSM-5(22). The sequence of the catalytic activity of 9%M-12%CeO2/HZSM-5(22) catalysts for DCE destruction is as follows:9%Ni-12%CeO2/HZSM-5(22)> 9%Co-12%CeO2/HZSM-5(22), 9%Mn-12%CeO2/HZSM-5(22)> 9%Cu-12%CeO2/HZSM-5(22),9%Cr-12%CeO2/ HZSM-5(22)> 9%Fe-12%CeO2/HZSM-5(22)> 12%CeO2/HZSM-5(22). With regard to the production of intermediates, the increasing concentration of weak and medium strong acid sites promotes the formation of C2H3Cl from dehydrochlorination of DCE. Due to the strong acidity of metal cations, large amount of C2HCl3 and C2Cl4 are generated over Cu, Co and Mn impregnated catalysts, and more CH3Cl is formed over Ni contained catalysts. The co-existence of transition metal oxides and CeO2 improves the mobility of active oxygen species in the catalysts, which is in favor of the deeper oxidation of DCE. The doping of Cr significantly improves the further dehydrochlorination of C2H3C1 and inhibits the formation of polychlorinated by-products.3. The influence of the synergy between active phases on the catalytic performance and the stability of 9%Cr-12%CeO2/HZSM-5(22),9%Cr/HZSM-5(22),12%CeO2/ HZSM-5(22) and HZSM-5(22) catalysts were studied. The results indicate that the interactions between CrOx and CeO2 avoid coke deposition and loss of active components, since they stabilize the active components and prompt the mobility of active oxygen species. Consequently,9%Cr-12%CeO2/HZSM-5(22) shows the best catalytic activity and stability. The catalytic activity for the oxidation of different CVOCs over 9%Cr-12%CeO2/HZSM-5(22) is displayed as follows:DCE> TCE> DCM.更多还原