添加劑對鈀/氧化鈰觸媒於甲苯完全氧化反應之影響; Effects of additives on Pd catalysts for catalytic oxidation of toluene

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题名:	添加劑對鈀/氧化鈰觸媒於甲苯完全氧化反應之影響;Effects of additives on Pd catalysts for catalytic oxidation of toluene
作者:	林賢昆;Lin,Hsien-Kun
贡献者:	化學工程與材料工程學系
关键词:	觸媒焚化;鈀;氧化鈰;氧化錳;金屬添加物;甲苯;VOCs combustion;Pd catalysts;CeO2;MnOx;metal additives;Toluene
日期:	2013-06-26
上传时间:	2013-07-10 11:51:21 (UTC+8)
出版者:	國立中央大學
摘要:	近年全球工業蓬勃發展，但隨之而來的環境汙染問題也日益嚴重，揮發性有機廢氣因其易擴散與高毒性的特性在減排問題上備受關注。現以觸媒燃燒法為去除有機廢氣最佳處理方式，其中貴金屬觸媒對揮發性有機廢氣的氧化有良好的效率，本研究的目的在於發展出低溫反應活性最佳的且符合經濟效益之有機廢氣物去除之金屬觸媒。本研究探討將奈米級的鈀承載於經過一系列以添加金屬物改質的氧化鈰擔體上，並比較不同製備法、以及改質擔體後甲苯氧化反應的優劣。以初濕含浸法及共沉澱法製備Pd/CeO2、Pd/CuO-CeO2、Pd/MnOx-CeO2系列觸媒，添加不同金屬或金屬氧化物以增加其活性，探討觸媒對於甲苯的完全氧化反應之影響。觸媒鑑定方面，主要是以X光繞射儀(XRD)，氮氣吸附-脫附儀(N2-sorption)，穿透式電子顯微鏡(TEM)，高解析度穿透式電子顯微鏡(HRTEM)，X光電子能譜儀(XPS)與程溫還原系統(TPR)，進行鑑定與分析。並使用甲苯作為本研究觸媒焚化之指標物。反應物甲苯之進料濃度為8.564g/m3(2085ppm)，空間流速為10,000h-1。XRD圖譜可以得到結晶良好的擔體波峰卻偵測不到鈀的波峰，代表鈀的顆粒小於儀器的偵測限制(4奈米)，配合TEM及HRTEM圖顯示鈀的顆粒約為2到4奈米，且均勻分布在擔體上，BET測量結果顯示在同樣的條件下因為添加金屬物改質使得的觸媒的表面積有明顯差異，也間接提升鈀金屬在觸媒間能分散的位置。由XPS分析中可以發現不同金屬物引入能提升鈀元素態的比例，同時增進反應活性。反應測試以共沉澱方法製備的擔體在反應活性表現上比初濕含浸法來得好，證明以共沉澱方式添加金屬引入物使擔體間有更佳的交互作用。本研究以連續式固定床反應器來量測鈀觸媒於甲苯氧化反應之活性。所有觸媒中以Pd/MnOx-CeO2系列觸媒有著較高的甲苯氧化活性，以引入Al及Zr之Pd/MnOx-CeO2觸媒活性最佳，分別於96℃及134℃達到50%甲苯轉化、且於190℃皆將甲苯完全氧化。證明在同樣的條件下，適度的引入金屬添加物能使得觸媒間產生協同作用，使得觸媒有更佳的表現。 VOCs exhausts have high volatile, high diffusivity and harmful for human body, therefore, how to reducing the amount of VOCs contamination is an important issue for environment protection. Catalytic oxidation is an effective way for treating the emissions of VOCs. Supported noble metal catalysts have been known as highly active catalysts for oxidation of hydrocarbons and have been preferentially used in commercial practices. The purpose of this study is to develop a low temperature reactivity and cost-effective metal catalyst for VOCs oxidation. In this study, a series of Pd/CeO2、Pd/CuO-CeO2、Pd/MnOx-CeO2 catalysts with different metal additives were prepared by incipient-wetness impregnation method and co-precipitation method. These catalysts which compare different preparation method and add different metal or metal oxide to increase its activity were tested for total oxidation of toluene. Finally, we compare the properties and performance of these Pd based catalysts. The samples were characterized by powder X-ray diffraction (XRD), N2-sorption, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy XPS and H2-TPR techniques. The catalysts were tested for total oxidation of toluene which the feed concentration was 8.564g/m3 (2085ppm) with GHSV=10,000h-1. The XRD patterns showed the good crystalline but no palladium peaks were observed, which represent that the particle size of palladium was too small to detect (smaller than 4nm). The TEM and HRTEM images indicate that the average particle size of palladium was about 2-4 nm and disperse well on the support. The BET surface area showed that the catalysts in the same condition will change the surface area obviously by adding the metal additives and let more active sites combine with palladium. XPS spectra showed that when different metal additives add to the catalysts which can get more metallic palladium species and increase the activity of the toluene oxidation. For the reaction test, the supports synthesized by co-precipitation method were much more active than incipient-wetness impregnation method, which proved that the supports had the better interaction by using co-precipitation method. A fixed bed continuous flow reactor was used to measure the activities of the toluene oxidation with Pd based catalysts. In all series catalysts, Pd/MnOx-CeO2 series showed the best activity especially added the Al and Zr which yielded 50% conversion at 96℃ and 134℃, and both completely oxidation of toluene at 190℃. In conclusion, adding appropriate additives to the Pd based catalysts could get the synergetic effect between the compositions which made the catalysts have better higher activity on toluene destruction.
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