| 摘要: | 一般工業上所使用的觸媒大多數為球形觸媒，為了可以充分利用到所有的金屬活性，將金屬擔載於球形擔體上以形成蛋殼形觸媒，本研究主要以鈀銅雙金屬擔載於二氧化矽之蛋殼形觸媒與粉末觸媒進行氫化反應之應用。觸媒鑑定的部份，以光學顯微鏡、穿透式電子顯微鏡、高解析度穿透式電子顯微鏡及X光光電子能譜儀，著重於蛋殼形觸媒於反應前後以及加入不同比例的金之物理、化學特性及表面性質之分析，觸媒催化反應部份，利用液相選擇性對氯硝基苯之氫化反應來測試觸媒活性與對氯苯胺之選擇率，使用的反應器為半批式反應器，反應條件如下：反應溫度298 K，氫氣分壓為550 kPa，反應器攪拌速率為300 rpm。
以氫氣還原過後之新鮮蛋殼形觸媒的金屬層厚度較薄，金屬顆粒小，於擔體表面之分佈平均，活性之金屬也較多，反之，使用過後的蛋殼形觸媒金屬層變厚，原因為銅有向核遷移之現象，故二氧化矽的外圍顏色變深，此外，金屬顆粒有較大且團聚的現象，於表面之非活性金屬也變多，證明觸媒有衰退之現象。反應測試之結果顯示鈀銅擔載於二氧化矽之粉末觸媒對於此氫化反應之活性與選擇率均差，而使用鈀銅蛋殼形觸媒的效果甚佳，加入少量的金屬不僅能達到不錯的選擇率，反應速率不高的結果也能改善一般粉末觸媒使反應太快而可能造成金屬使用不完全的現象，另外，加入極少量的金於鈀銅蛋殼形觸媒中可使催化效果提升，原因為活性金屬的增加，此反應結果亦可被其顆粒大小變得比鈀銅蛋殼形觸媒更小之分析結果所驗證，因此，於對氯硝基苯之氫化反應，鈀銅擔載於二氧化矽之蛋殼形觸媒的反應效果較佳，並且最重要的是，我們能成功地製備出催化效果幾乎一樣的鈀銅蛋殼形觸媒。
;The spherical catalyst was mostly used in industries. In order to use active metal adequately, the metal was supported on the spherical carrier to form the egg-shell catalyst. In this study, egg-shell and powdered catalyst which Cu-Pd bimetals were supported on spherical SiO2 were introduced to carry out the application of p-CNB hydrogenation reaction. All the egg-shell catalysts were characterized by OM, TEM, HRTEM, and XPS. As for the activity test of liquid phase p-CNB hydrogenation reaction, the reaction condition were 298 K of reaction temperature, 0.55 MPa H2 partial pressure, and stirring rate under 300 rpm in a batch reactor.
From the results, thinner metal layer, smaller particle size, better dispersion of metals, and the larger amount of active metals were found in fresh egg-shell catalysts compare with the used ones. The thick metal layer of used egg-shell catalysts was due to the migration of Cu into the inner core. Besides, larger particle size, the agglomeration, and smaller amount of active metals were also observed in used egg-shell catalysts. In the reaction test, both activity and p-CAN selectivity of powdered catalysts were poor in comparison with egg-shell catalysts. Adding small amount of metals could not only achieve good selectivity, but the result of low reaction rate also improved the fast reaction of using powdered catalyst which might lead to the inadequate use of metals. Moreover, the addition of very small amount of Au could enhance the catalysis of Cu-Pd/SiO2 egg-shell catalyst. Therefore, Cu-Pd/SiO2 egg-shell catalyst showed better selectivity of this reaction. Most important of all, catalyst with egg-shell structure was successfully made by ourselves which had almost the same catalytic result. |
