含鈀金屬奈米觸媒在對-氯硝基苯的氫化反應上有良好的催化活性，但目標產物對-氯苯胺的選擇性較低，本研究將探討鈀金雙金屬擔載於球形二氧化矽表面形成蛋殼形觸媒之反應前後變化以及製備不同比例的鈀金觸媒進行氫化反應之應用。觸媒鑑定部分，以X光繞射儀(XRD)、穿透式顯微鏡(TEM)、高解析穿透式顯微鏡(HRTEM)、X光光電子能譜儀(XPS)來分析觸媒之物理、化學特性及表面性質，觸媒催化部分則利用液相選擇性對-氯硝基苯氫化反應測試觸媒活性與選擇性，使用的反應器為半批式反應器(Parr Reactor 4842)，反應條件如下：反應溫度為室溫，氫氣分壓為0.55 MPa，反應器攪拌速率300 rpm.，反映溶劑為甲醇，反應時間180分鐘，使用0.5 g觸媒進行反應，每10分鐘取樣一次，並使用氣相層析儀(GC)分析。 未使用之新鮮蛋殼形鈀金雙金屬觸媒金屬平均顆粒尺寸較純鈀觸媒小，於二氧化矽擔體上分布均勻，具有很多的活性金屬，而在反應初期，金屬在二氧化矽上仍能保持不錯的分散性，主要是因添加金而形成鈀金合金可避免金屬聚集效應。但經過長時間的使用還是會導致金屬聚集、顆粒變大，使活性金屬接觸面積減少進而導致觸媒失活。另外我們發現使用過後的觸媒進行氫化反應時活性大幅下降，但對-氯苯胺選擇率仍與新鮮觸媒差距不大，因此我們認為反應過後的觸媒表面之金屬顆粒組成與新鮮觸媒相似，因此選擇率並無明顯下降。此外，我們自己製備出的二氧化矽之蛋殼形觸媒金屬分散性以及催化效果可以與商業用觸媒達到一致。 ;Nano-palladium catalyst has been reported to have high activity for hydrogenation reaction but selectivity of main product, p-chloroaniline (p-CAN), was low. In this study, gold-palladium bimetals were loaded on spherical silica to form the egg-shell catalyst and used different ratio of Au/Pd metal on silica to carry out the p-CNB hydrogenation reaction. All the catalysts were characterized by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). The condition of hydrogenation reaction was room temperature as reaction temperature, 0.55MPa as H2 partial pressure and at 300 rpm stirring rate. The average particle size of Pd-Au/SiO2 fresh catalyst was smaller than that of Pd/SiO2 and the active metals were highly dispersed on SiO2 support surface. In the early stage of reaction, metals still maintained high dispersion. The main reason is adding gold as promoter can prevent metals from agglomeration and dispread Pd to single active site. However, after long time on the stream, metals agglomeration on silica surface and larger particle size were observed and resulted in decrease in active metals and lead to deactivation. Besides, the activity of catalyst was significantly decreased but selectivity of p-CAN was not obvious change in p-CNB hydrogenation reaction. Therefore, metals composition was not serious change after the reaction.
