摘要
奈米鈀觸媒在對-氯硝基苯的氫化反應上有很好的催化活性且相較於其他貴金屬觸媒有較低的材料成本，唯獨對目標產物對-氯苯胺的選擇性較低。本研究中，首先探討奈米鈀觸媒與不同的金屬形成雙金屬觸媒後，用於對-氯硝基苯的氫化化反應上造成反應選擇率的差異。再來製備不同比例之鈀銅雙金屬觸媒擔載於二氧化鈦上，找出對本反應有最適化之反應活性與選擇性的鈀銅金屬觸媒。所使用的雙金屬觸媒，皆使用含浸法來製備，在進行反應前使用硼氫化鈉還原之。觸媒鑑定部分，以X光繞射儀(XRD)、穿透式電子顯微鏡(TEM)、高解析度穿透式電子顯微鏡(HRTEM)、X光光電子能譜儀(XPS)等來鑑定觸媒之物理、化學特性和表面性質；觸媒催化反應部分，利用液相選擇性對-氯硝基苯氫化反應來測試觸媒的活性與選擇性，使用之反應器為半批式反應器(Parr Reactor 4842)，反應條件設定：反應溫度303K；氫氣分壓為0.55 MPa；反應器攪拌速率300 rpm.，反應物起始濃度為0.2M (2.54 g對-氯硝基苯粉末溶於80 ml甲醇)；使用0.5 g觸媒進行反應，直到反應完全。 反應結果顯示鈀與銅形成奈米鈀銅雙金屬觸媒擔載在二氧化鈦擔體上之反應催化效果最佳，此觸媒可降低反應條件，達到在低壓與常溫下發生反應，且加入少量的銅可以大幅提升奈米鈀觸媒對此氫化反應之目標產物對-氯苯胺的選擇率、保有奈米鈀觸媒本身對氫化反應有相當高的反應活性之特性。加入銅金屬之後可降低奈米鈀觸媒的氧化態、增加反應活性點且銅的氧化物可保護鈀顆粒避免氧化。利用鈀觸媒的良好反應活性與銅觸媒對反應的高選擇性可使觸媒應用更廣泛。
並列摘要
Nano-palladium catalyst has been reported to have high activity for hydrogenation reaction due to its excellent absorb ability of hydrogen. Comparing with other noble metals (Pt, Ru, Au etc.), Pd has relativity low cost. In this study, palladium-containing bimetals were loaded on titanium dioxide. Bimetallic Pd catalysts have been prepared and tested for p-chlornitrobenzene (p-CNB) hydrogenation reaction. All of the catalysts were prepared by incipient-wetness impregnation method using NaBH4 to reduce the metal cations. These catalysts were characterized by X–ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM), energy dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS). The activity test of liquid-phase p-CNB hydrogenation reaction was carried out with following reaction condition: 303K, 0.55MPa H2¬ partial pressure, stirring rate under 300 rpm in a batch reactor. 0.2M p-CNB methanol solution (2.54g p-CNB dissolved in 80 ml MeOH) as the reactant and 0.5g palladium-containing catalyst were used to catalyze this reaction. During the run, the samples were withdrawn periodically and analyzed by a gas chromatography. The results revealed that adding copper as an additive into the catalyst would enhance the dispersion of Pd.. The selectivity of main product, p-chloroaniline (p-CAN), was more than 90%. Palladium catalyst could operate in mild the reaction conditions, i.e, hydrogenation reaction could be carried out at room temperature and low hydrogen pressure. Adding Cu into Pd catalyst slightly caused the activity to decrease but provided significantly increase in selectivity of p-CNB to p-CAN.
參考文獻
延伸閱讀
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