https://scholars.lib.ntu.edu.tw/handle/123456789/177233
標題: | 負載於中孔洞氧化鋯之觸媒其表面酸性鑑定與催化行為研究 Study in Surface Acidity and Catalytic Behavior of Mesoporous Zirconia-supported Catalysts |
作者: | 黃志超 Hwang, Chi-Chau 牟中原指導 |
關鍵字: | 中孔洞氧化鋯;異構化反應;溴化反應;Mesoporous zirconia;Isomerization reaction;Bromination reaction | 公開日期: | 2006 | 摘要: | 一、固體酸的合成、鑑定、及應用於直鏈烷類異構化反應: 直鏈烷類的異構化反應在石油工業上扮演著相當重要的角色,而經由異構化所得到的產物其辛烷值得以大幅度的提升。本研究主要是將Tungstate及Sulfate分別負載於具有中孔結構的氧化鋯載體上,並且以鋁作為此觸媒的活化劑。研究中發現:經由鋁活化的中孔洞硫酸鋯觸媒能在低溫、常壓條件下,進行直鏈丁烷的異構化反應,並且得到轉化率高且穩定性佳的催化表現。 我們也透過一系列的觸媒結構鑑定、表面的酸性鑑定、和觸媒本身的氧化還原特性,配合理論計算來對反應機制進行詳細的探討。 二、仿生物酵素(V-HPO)的合成、鑑定及應用於Phenol Red的溴化 反應: 鹵化反應常被應用在工業及藥物合成上。海洋中也有大量的鹵素化合物,其中的均具有抗菌、抗病毒、抗炎等生物活性。本世紀初,許多海洋生化學家認為天然鹵素化合物的生成與鹵素過氧化酶有關,其中又以釩鹵過氧化物酶(V-HPO)最為重要。 研究中的第二部分,我們利用鎢金屬負載於氧化鋯載體上,經過特定的鍛燒溫度及前處理,使其具有與V-HPO相似的化學官能基,並選用可由UV-vis 偵測的Phenol Red Bromination作為測試反應,溴的來源則來自於NH4Br取代過去的Br2。研究結果發現:以鎢為基礎的仿生酵素在水溶液及近乎中性的反應條件下,所得到的催化效率幾乎和V-HPO在酸性、有機相反應時相當。同時我們也使用了另一種前過渡金屬 “Re” 來取代原先的鎢金屬作為仿生觸媒。利用Re2O7本身獨特的物性及化性,經適溫鍛燒後,使其在大表面積的中孔洞氧化鋯載體上具有高度的分散性,藉此創造出更多的活性位置。此類觸媒的催化效率比V-HPO高出十倍之多,且穩定性高,能經再生後重複使用,是目前芳香族化合物在非均相溴化反應上最佳的觸媒。 Mesoporous zirconia, synthesized from surfactant templating, was employed to disperse alumina and tungstate (AW/m-ZrO2) and then used as a catalyst for the isomerization of n-butane. After calcination at 700 oC, tetragonal phase of zirconia was formed with high surface area. Furthermore, the catalyst AW/m-700 performed exceptionally well, and gave maximum rate and stability at reaction temperature of 250 oC, compared to other tungstated zirconia-based catalyst reported so far. Moderate calcination temperature leads to the presence of more Brönsted acid sites with higher acid strength. In comparison with the normal dense phase zirconia catalyst, AW/m-ZrO2 showed higher activity than the corresponding AW/d-ZrO2. The difference in catalytic activities was examined by various surface characterization techniques, and was attributed to different degree of dispersion of tungstate on the surface of m-ZrO2. In the second part, we focused on the alumina sulfate supported on mesoporous zirconia (AS/m-ZrO2). Our primary goal was to understand the origin of the catalytic active sites and the roles of these sites in the various stages of reaction. Three kinds of acid sites were determined by pyridine adsorption with XPS (N 1s core-level). The remarkable performance of the Al-promoted catalysts is due to an optimum balance of these acid sites, and the catalytic activity seems to correlate directly with the amount of weak Brönsted acid sites. 27Al MAS-NMR and in-situ DRIFT results elucidate the origin and the role of these acid sites in the various stages of isomerization reaction. EPR experiments explore the existence of O2-; the active species eliminates hydrogen atoms to form n-butene and starts the overall reaction in our experiment. The promotion effect of Ga on sulfated zirconia catalyst was studied in n-butane isomerization reaction and compared with Al-promoted catalyst. Our NH3-TPD and DRIFT studies reveal that the enhanced acid sites are due to the addition of Al and Ga promoters to mesoporous zirconia. AS/m-ZrO2 promoted by Al seems to bring greater contribution to the acidity of catalyst than that by Ga. Therefore, the improved activity of AS/ZrO2 over S/ZrO2 catalyst is related to the increased acidity created by the Al promoter, while the Ga promotion effect is then through a redox mechanism in the acid catalyzed initiation mechanism. Finally, highly dispersed biomimetic catalysts tungstated zirconia (WZ) and mesoporous ziconia-supported rhenium oxide (Re/m-ZrO2) were prepared by a simple impregnation method and excellent catalytic performances were obtained in liquid phase bromination of phenol red using hydrogen peroxide and ammonium bromide under neutral condition. It was shown that the activity of phenol red bromination reaction depends directly on the dispersion of WOx or ReOx species over support surfaces. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/51642 | 其他識別: | en-US |
顯示於: | 化學系 |
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ntu-95-R93223030-1.pdf | 23.31 kB | Adobe PDF | 檢視/開啟 |
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