SAPO-34之微波合成與CoAPO?CuO/CeO2?La1-xSrxCo1-yMnyO3之X光吸收光譜分析; Synthesis of SAPO-34 By Microwave Heating and X-ray Absorption Spectroscopic Study of CoAPO?CuO/CeO2 and La1-xSrxCo1-yMnyO3

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題名:	SAPO-34之微波合成與CoAPO?CuO/CeO2?La1-xSrxCo1-yMnyO3之X光吸收光譜分析;Synthesis of SAPO-34 By Microwave Heating and X-ray Absorption Spectroscopic Study of CoAPO?CuO/CeO2 and La1-xSrxCo1-yMnyO3
作者:	張志強;Chih-Chiang Chang
貢獻者:	化學工程與材料工程研究所
關鍵詞:	SAPO-34;微波加熱;CoAPO;X光吸收光譜;氧化銅;Perovskite;SAPO-34;Microwave;CoAPO;XANES;EXAFS;XAS;CuO;Perovskite
日期:	2000-07-05
上傳時間:	2009-09-21 12:18:16 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本論文主要分成兩部份，第一部份是利用微波加熱來幫助合成SAPO-34，第二部份則利用X光吸收光譜術來分析CoAPO?CuO/CeO2與La1-xSrxCo1-yMnyO3中，Cu?Co?Mn的周圍環境。 SAPO-34應用於由甲醇合成小分子烯類製程，具有良好的選擇性，但以傳統的水熱法合成，需要200℃以及長達55小時的合成時間。本研究利用微波消化提供液體高動能?迅速加熱?增加分子碰撞?促使膠體溶解並混合完全等優點﹐縮短SAPO-34合成時間。經由多方的嘗試，目前已能將合成時間由水熱55小時縮短至水熱30小時加上微波2小時，而能得到不錯的SAPO-34結晶。但整體結晶度仍較完全水熱法低。將Co崁入AlPO4中形成CoAPO，可以增加沸石酸性與離子交換能力，同時改變孔道大小，使其對許多碳氫化合物的異構化製程具有良好活性與選擇性。研究Co在AlPO4中所處環境，有助於了解CoAPO的催化反應機構，而能進一步探討Co在反應中所扮演的角色。利用X光吸收光譜術可研究CoAPO中Co的局部環境，結果顯示大部分的Co以+2價存在於結構中，而經過鍛燒的樣品其Co-O距離則會增加。 CuO/CeO2對CO具有良好的氧化效果﹐可取代貴重金屬應用於觸媒轉化器。而La1-xSrxCo1-yMnyO3這種Perovskite型混合氧化物﹐具有高熱穩定性﹐對CO?碳氫化合物具有良好氧化力﹐對NO亦具有還原力﹐加上價格較低廉﹐遂有取代原本貴重金屬支撐在氧化鋁上的研究價值。本篇論文另一部份即利用X光吸收光譜術﹐針對Cu之K-吸收邊緣分析其XANES圖譜與EXAFS結果﹐來探討Cu的氧化態與周圍環境。針對La1-xSrxCo1-yMnyO3系列觸媒﹐分別以Co與Mn之K-吸收邊緣之吸收光譜﹐來分析取代元素對氧化態的影響與其鄰近氧原子之空缺狀態。由CuO/CeO2之XANES圖譜顯示Cu處於+2價，從其傅立葉轉換後之k3x(k)圖形亦可觀察出，隨著CuO的擔載量減少，Cu與Cu隔氧相鄰（Cu-O-Cu）的機會減少，而Cu之配位數有從未支撐之氧化銅的6配位下降至4.7左右的趨勢，與崁入模型之理論配位數5吻合。至於La1-xSrxCo1-yMnyO3的結果則顯示，Co的氧化態隨Mn的取代量增加而降低，Mn大量取代Co時會造成Co的配位數下降；Mn的氧化態隨Co的取代量增加而增加﹐Co大量取代Mn時則造成Mn的配位數增加；以Sr部分取代La對Co跟Mn的氧化態沒有影響﹐但會降低Co跟Mn周圍的氧原子配位數。此外，其所處的氣體環境與溫度對於各中Co與Mn的氧化態亦有所影響。 Recently much effort has been invested in the examination of the potential of microwave power for facilitating chemical reaction. The microwave-assisted synthesis of zeolites is a rather new field of research. In this study, we report the synthesis of SAPO-34 by combination of hydrothermal and microwave heating, to reduce the time of synthesis from 55 hours by hydrothermal heating to 30 hours by hydrothermal heating plus additional 2 hours by microwave heating. Metal-substituted aluminophosphate molecular sieves have recently received extensive attention for researchers working in molecular sieve science and shape-selective catalysis. The incoporation of metals into the framework can generate Brønsted acidity and ion-exchange capacity on the neutral aluminophosphate molecular sieves and modify the activity and product selectivity on hydrocarbon reactions. In this study, the local environments about the cobalt atoms in as-synthesized, calcined and hydrogen-reduced CoAPO-5 and CoAPO-11 have been studied by X-ray absorption spectroscopy. Results indicate a considerable fraction of Co2+ was oxidized to Co3+ in the calcined samples. On reduction with hydrogen, Co3+ was reduced to Co2+. Cerium oxide is widely used as a support for Pt and Rh based automobile catalysts. Ceria exhibits special features that make it a promising material for use as a support for such a redox catalyst. However, due to the ever increasing demand upon expensive PGMs, viable non-noble metal catalysts are alternative. CuO supported on ceria is an alternative. The CuO/CeO2 catalysts exhibit high catalytic activity in CO oxidation. The marked enhancement of catalytic activities is due to the combined effect of CuO and CeO2. CuO/CeO2 catalysts show a different behavior with respect to unsupported CuO. In this study, the local environment of copper is examined by means of X-ray absorption spectroscopic at the copper K-edge of CuO/CeO2 with various loading amount. From the results, it’s suggested that, in addition to the well dispersed Cu2+ species at low CuO loading, a small fraction of CuO clusters are formed above CuO loading of 0.8mmole/100m2_CeO2. The higher emission standard for automobile and motorcycle requires the catalytic converter with high thermal stability and low light off temperature. The high thermal stability of Perovskite makes them good candidates as high thermal stable catalyst in catalytic converter. X-ray absorption spectra of LaCoO3 and LaMnO3 with La partially substituted by Sr and Mn, Co partially substituted by each other were studied in order to understand the local environment around Co and Mn. The oxidation state of Co decreases when Mn substitute a large amount of Co. The oxidation state of Mn increases when Co substitute a large amount of Mn. The coordination numbers of the first oxygen shell decrease upon substitution for LaCoO3 while increase upon substitution for LaMnO3.
顯示於類別:	[化學工程與材料工程研究所] 博碩士論文

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