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    Title: 雜多酸觸媒之製備與酸性鑑定
    Other Titles: Preparation and acidity characterization of heteropolyacids (HPAs)
    Authors: 楊芷宜;Yang, Chih-yi
    Contributors: 淡江大學化學工程與材料工程學系碩士班
    張裕祺;Chang, Yu-chi
    Keywords: 三甲基磷氧化物;磷鎢酸;固體超強酸;trimethylphosphine oxide;12-tungstophosphoric acid;superacid
    Date: 2009
    Issue Date: 2010-01-11 05:41:22 (UTC+8)
    Abstract: 利用鹼性三烷基磷氧(如三甲基磷氧化物;TMPO)為吸附探針分子,配合固態31P 魔角旋轉核磁共振(MAS NMR)光譜實驗技術來鑑定固體酸觸媒的酸性特性是一項極為有用的實驗方法。本論文即是利用此一技術與特點,針對磷鎢酸,磷鎢酸銫鹽以及中孔洞氧化矽SBA-15分子篩負載磷鎢酸等固體酸系統的酸性特性進行研究,深入探討改變銫離子交換濃度、TMPO探針分子之吸附量及吸附樣品加熱處理溫度等相關實驗變因時之效應。所得實驗結果並配合1H及31P{1H} LG-CP MAS NMR、2D HETCOR及2D 31P-31P DQ Correlation等一維及二維NMR實驗方法進一步確認各類磷鎢酸化合物固體酸系統中酸性基分佈及其與吸附TMPO探針分子之交互作用與關聯性。並利用粉末X-光繞射(PXRD)、擴散反射式紅外霍氏光譜(DRIFT)、熱重分析(TGA)、元素分析(ICP-MS)、氮氣等溫吸附/脫附測量等傳統方法鑑定其基本物化特性。
    吾人實驗結果發現,磷鎢酸確實為固體超強酸(superacid),但是吸附TMPO之磷鎢酸樣品需經過150 oC以上加熱處理,才得以確保TMPO探針分子有效均勻分散於磷鎢酸酸性位上,否則易發生兩個TMPO分子同時吸附於一個質子(H+)酸位,即(TMPO)2H+的情況。驗證實,經加熱處理後的TMPO/HPW樣品具有三種不同超強酸強度之酸位,其化學位移分別為87.4、88.9及91.7 ppm。而以磷鎢酸銫鹽而言,在較低銫含量(z < 1.0)時,其所顯示之酸強度與HPW無異,惟其酸量的相對分佈比例改變,顯然與銫離子替代質子作用相關。而當銫含量再進一步提升(z > 1.0)時,其酸量與酸強度則皆遞減。以SBA-15負載型磷鎢酸而言,結果顯示其具有四種酸位:一種來自磷鎢酸本身、兩種來自磷鎢酸與矽材間之交互作用,而另一種則可歸屬為矽材表面之弱酸。然而,磷鎢酸的分散均勻性卻隨著負載量的增加而遞減。
    本研究結果,除提供吾人對固體超強酸的了解外,透過酸性分佈與強度的定性與定量分析,未來在酸性特性鑑定工藝及觸媒設計與應用等方面亦提供可行且有利的契機。
    Solid-state 31P magic-angle-spinning nuclear magnetic resonance (MAS NMR) of adsorbed base trialkylphosphine oxide probe molecules, such as trimethylphosphine oxide (TMPO), has been recognized as a powerful technique for characterizing acid properties of solid acid catalysts. In this sudy, this unique technique was adopted for acidity characterization of solid superacid systems, such as 12-tungstophosphoric acid,cesium salts of 12-tungstophosphoric acid and HPW supported on mesoporous silica SBA-15 molecular sieve. In particular, the effects of Cs+ ion-exchange level, base probe molecule (TMPO) loading, sample baking treatment, etc. on the variations of 1H and 31P NMR parameters were thoroughly examined. The results, taken with as well as in the absence of adsorbed TMPO, were further correlated in conjunction with additional one- and two-dimensional NMR spectroscopy, for example, 1H and 31P{1H} LG-CP MAS NMR, 2D HETCOR, and 2D 31P-31P DQ Correlation, which provide additional information on acid site distribution and their interactions with the adsorbed TMPO probe molecule. In addition, the physicochemical properties of various samples were also characterized by a variety of different techniques, such as powder X-ray diffraction (PXRD), diffuse-reflectance FT-IR (DRIFT), elemental analysis (ICP-MS), thermogravimetric analysis (TGA), and N2 adsorption-desorption isotherm measurements.
    For system in the presence of adsorbed TMPO, it was found that sample baking treatment (> 150 oC) is inevitable to ensure a homogeneous adsorption of TMPO on acid sites of HPW. For TMPO/HPW system in the absence of baking treatment, the adsorption of two TMPO molecule per protonic (H+) site, that is, (TMPO)2H+, was found. Whist for thermally treated TMPO/HPW samples, three 31P resonance of TMPO with chemical shifts of 87.4, 88.9, and 91.7 ppm were observed, revealing three different superacid sites having different acid strengths. For CszH3-zPW12O40 system with low Cs+ exchanged level (z < 1.0), while three different acid strengths identical to that of HPW were also observed, their corresponding acid concentrations tend to decrease with increasing Cs content. Further increasing the Cs+ loading > 1.0, the acid strengths of the system progressively decreased. For HPW supported on SBA-15 mesoporous silica, as many as four different acid sites were identified; one arise from HPW itself, two from interactions between HPW and silica support, and the other one from weak silanol groups of the silica support.
    The qualitative and quantitative results obtained from this study not only provoke further understanding of the solid superacid systems but also lay out a fundamental ground for acidity characterization techniques and catalyst design and applications.
    Appears in Collections:[化學工程與材料工程學系暨研究所] 學位論文

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