摘要
奈米鈀金屬觸媒於對-氯硝基苯氫化反應上有很好的反應活性，但對目標產物對-氯苯胺的選擇性很低。本研究將分成兩個章節來討論兩種不同系列的觸媒，首先本研究擔載鈀金屬於三種不同的二氧化矽上，接下來製備一系列的雙金屬鈀觸媒於二氧化矽上(鎳-鈀/二氧化矽、鉑-鈀/二氧化矽、銀-鈀/二氧化矽、鐵-鈀/二氧化矽)，分別找出兩種系列中對本反應有最適化之反應活性與選擇性的觸媒。本研究中所有的觸媒皆是使用含浸法製備，並且進行對-氯硝基苯氫化反應之測試。本研究以下列幾種儀器來鑑定觸媒之物理、化學特性及表面性質：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)，觸媒活性及選擇性則是利用液相選擇性對-氯硝基苯氫化反應來測試，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298 K，氫氣分壓為0.41 MPa，反應器攪拌速率為300 r.p.m.，反應物初濃度為0.2 M (2.54 g對-氯硝基苯粉末溶於80 ml甲醇)，使用0.1 g觸媒進行反應，反應過程中每10分鐘取樣，並以氣相層析儀分析。X光繞射儀分析結果顯示本研究中所使用的二氧化矽皆為非晶態，且金屬顆粒因為尺寸過小而無法偵測到；由穿透式電子顯微鏡影像中可以得知，鈀金屬二氧化矽觸媒系列之二氧化矽平均尺寸為35-75奈米，其金屬平均尺寸則落於2-4奈米之間，而雙金屬二氧化矽觸媒系列之二氧化矽平均尺寸為50-125奈米，其金屬平均尺寸為2-4奈米。高解析度穿透式電子顯微鏡影像顯示，在鈀/釤-二氧化矽及鉑-鈀/二氧化矽中皆可以觀察到鈀(111)之晶格影像。由X光光電子能譜儀分析結果得知，當加入鉑於鈀觸媒後，觸媒表面之金屬鈀的含量會降低，導致鉑-鈀/二氧化矽的反應速率較鈀/二氧化矽低。反應結果顯示鈀/二氧化矽系列中的三種觸媒皆對對-氯苯胺有很低的選擇率，其中以鈀/釤-二氧化矽的活性最高；而雙金屬鈀觸媒則都表現出很高的活性，其中只有鉑-鈀/二氧化矽觸媒有提高對對-氯苯胺的選擇率。
並列摘要
Nanosized palladium catalyst has been reported to be a good catalyst for hydrogenation reaction. In this study, all the catalysts were prepared by incipient-wetness impregnation method and were tested for p-chloronitrobenzene (p-CNB) hydrogenation reaction. These catalysts were characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, energy dispersive spectrometer and X-ray photoelectron spectroscopy. The liquid-phase p-CNB hydrogenation reaction was carried out in the following condition: 298 K, 0.41 MPa partial pressure of H2, stirring rate 300 rpm in a batch reactor. The reactant was 0.2 M p-CNB methanol solution (2.54 g of p-CNB dissolved in 80 ml methanol) and 0.1 g catalyst was used to carry out the reaction. Samples were withdrawn in each 10 min. The solution was analyzed by a gas chromatography. In XRD pattern, only amorphous SiO2 peak was observed in all the catalyst, and no palladium or other metal peaks were observed because the particle sizes were too small to be detected. The TEM images showed that the average particle sizes of silica support on Pd/SiO2 were between 35 to 75 nm, and the average particle sizes of metal on Pd/SiO2 were about 2-4 nm. On the other hand, the average particle sizes of SiO2 on M-Pd/SiO2 (M = Ni, Pt, Ag and Fe) were around 50-125 nm, and the average particle sizes of metal on M-Pd/SiO2 were about 2-4 nm. From HRTEM images, Pd (111) was observed in Pd/samarium-silica and Pt-Pd/SiO2, the sizes of metal were consistent with TEM images. The XPS analysis indicates that adding platinum into palladium catalyst would decrease the content of Pd0 which plays a role of activity site for hydrogenation reaction on the catalyst surface. It’s the reason why the reaction rate decreases with the order : 1Pd/SiO2 > 0.2Pt1Pd/SiO2. The results of catalytic tests showed that all the three samples on Pd/SiO2 had high activity but very low selectivity for p-chloroaniline. Various bimetallic catalysts, such as Pt-Pd/SiO2, Ni-Pd/SiO2, Ag-Pd/SiO2 and Fe-Pd/SiO2 were tested. The results showed that only Pt-Pd/SiO2 could increase the selectivity of p-CAN and still kept high activity.
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