在Perovskite氧化物上進行CO-NO反應之研究; The study of the CO-NO reaction over Perovskite Oxides

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题名:	在Perovskite氧化物上進行CO-NO反應之研究;The study of the CO-NO reaction over Perovskite Oxides
作者:	陳恩祈;En-Chi Chen
贡献者:	化學工程與材料工程研究所
关键词:	溶膠凝膠法;CO-NO反應;XANES;EXAFS;Perovskite oxides;sol-gel method;CO-NO reaction;O2-TPD;ESCA
日期:	2002-06-24
上传时间:	2009-09-21 12:20:51 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本論文主要使用sol-gel方法合成Perovskite觸媒，進行CO-NO反應的研究。因為Perovskite (ABO3)型氧化物，以及由Perovskite與AO鹽分層交錯構成的K2NiF4-type結構的Perovskite-related型氧化物，具有高度的熱穩定性，對機動車輛主要污染物CO、碳氫化合物具有良好氧化力，對NO的還原也有相當的活性。而且它們的組成可以經由金屬離子價數的控制，以部分取代的方式達到改質、調整樣品組成的目的，加上價格較低廉，所以有取代貴重金屬觸媒的研究價值。本篇論文發現以微量Sr ( x = 0.05 ~ 0.2 )取代A位置元素La的La1-xSrxMO3（ M = Mn、Fe、Co）及La2-xSrxCuO4，可以提升CO-NO反應活性；以微量Pd ( x = 0.025 ~ 0.1 )取代B位置元素Mn、Fe、Co與Cu，形成LaM1-xPdxO3 ( M = Mn、Fe、Co ) 及La2Cu1-xPdxO4，也有大幅提升CO-NO反應活性的效果。另外，負載1wt.%Pd的擔體觸媒系列中，Pd/LaMO3 (M = Co、Mn、Fe) 有很好的催化特性，優於Pd/Al2O3，其中Pd/LaCoO3和Pd/LaFeO3甚至比商業化觸媒Pt-Rh/CeO2-Al2O3活性還好；以Perovskite-related型氧化物La2CuO4作為擔體的Pd/La2CuO4活性也較原La2CuO4觸媒有所提升，但不及Pd/LaMO3 (M = Co、Mn、Fe)的改進效果。氧氣程溫脫附結果顯示，隨著Sr取代Perovskite氧化物中La的量增加，在300oC到600oC之間的脫附氧氣(α´波峰)的量也有所增加。X光吸收光譜分析可以解釋A位置元素部份取代的Perovskite觸媒所產生的氧空缺對CO-NO反應活性的影響，當Sr取代La時，B位置元素的配位數減少，而且氧空缺也隨之增多。因此CO-NO反應的活性增加可以歸因於Sr取代所造成的氧空缺增加。從ESCA分析，可以有助於了解觸媒樣品表面的Pd氧化態，從實驗結果得知其氧化價數為+2 ~ +4之間。 In this study, Perovskite oxides synthesized by sol-gel method are used as the catalyst for the CO-NO reaction. Perovskites ABO3 and related oxides have recently received much attention as catalysts for various reactions. The diversity of physicochemical properties and catalytic activities of perovskite and related oxides are derived from the fact that they exhibit a wide range of oxygen non-stoichiometry, and that their composition can be varied extensively in the form of AA’BB’O3 compounds, allowing control of the valence state of metal ions by an appropriate choice of subsistent. They are also lower-cost than noble metals and the high thermal stability of perovskite oxides makes them good candidates as high thermal stable catalysts in catalytic converter. Results indicate that not only partial substitution of La by Sr in Perovskite oxides but also partial substitution of Co、Mn、Fe and Cu by Pd in Perovskite oxides can improve the activity of the CO-NO reaction. Different supported Pd catalysts in this study show good activity in the CO-NO reaction. The catalytic activity in the CO-NO reaction over 1wt.% Pd/LaCoO3 and Pd/LaFeO3 is even better than that over the commercial catalyst Pt-Rh/CeO2-Al2O3. The results of O2-TPD show that the amounts of desorbed oxygen between 300 to 600℃(α´peak) increases with the increasing amount of Sr substitution for La in Perovskite oxides. X-ray absorption spectroscopy results show decrease of coordination numbers when Sr substitutes La. Oxygen vacancies are generated by partial substitution of La by Sr. The increase of activity for the CO-NO reaction can be attributed to the increase of oxygen vancancies upon substitution. The results of ESCA help us to understand that the palladium in the Pd-containing catalysts remains in an oxidized form.
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