鈀銅奈米金屬合金在二氧化矽粒上製備之研究;Effect of Preparation Method on the Formation of Palladium-Copper Nanoalloy in the Shell of Large Silicon Dioxide Beads

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Title:	鈀銅奈米金屬合金在二氧化矽粒上製備之研究;Effect of Preparation Method on the Formation of Palladium-Copper Nanoalloy in the Shell of Large Silicon Dioxide Beads
Authors:	黃庭臻;Huang, Ting-Chen
Contributors:	化學工程與材料工程學系
Keywords:	鈀銅合金;二氧化矽粒;彈殼型觸媒;濕式含浸法;PdCu alloy;silica bead;egg-shell catalyst,;incipient-wetness impregnation
Date:	2020-06-29
Issue Date:	2020-09-02 15:00:50 (UTC+8)
Publisher:	國立中央大學
Abstract:	金屬在二氧化矽粒上的分佈及結構，在過去及現在的化學工業中扮演非常重要的腳色，了解其製備方法，有助於提高觸媒的催化效果。在此研究中，主要研究一製備方法去形成鈀銅合金奈米金屬在蛋殼型二氧化矽粒載體上，如何製備該觸媒是非常重要的，因為PdCu/SiO2 是液相合成乙酸乙脂反應的催化劑，烯烴的乙酰氧基化，隨著液相方法改進，發展出乙烯和丙烯的氣相乙酰氧基化，但由於反應介質是酸性的，鈀和銅會遷移並且燒結，導致嚴重的失活。在此研究中，分別使用5 釐米直徑的天然二氧化矽以及3 釐米的人造二氧化矽進行研究，其中天然二氧化矽粒中含有鈉離子，可能會導致孔結構損失，而合成觸媒不含鈉離子，在製備過程中相較穩定。共有8 種不同製備步驟會在此研究中討論，包含探討是否添加氯化鋁與氫氧化鉀，以及其添加量，與鍛燒溫度對鈀銅合金與薄殼厚度的影響，利用光學顯微鏡、X 射線衍射、透射電子顯微鏡與高解析度透射電子顯微鏡來對樣品進行分析。在製備過程中，含有加入氫氧化鉀的步驟之樣品，皆能成功做出蛋殼型結構觸媒，也可以在樣品分析中看見鈀銅形成黑色合金在二氧化矽粒的殼層，且以下方法製備出來的鈀銅合金觸媒，擁有最薄的蛋殼型結構：將氯化鋁加入去子水中後滴入人造觸媒後180 ℃乾燥2 小時，將氫氧化鉀加入去子水中後滴入樣品後 110 ℃乾燥4 小時，將樣品浸漬在金屬容液中後80℃乾燥6 小時，接著在250℃ 鍛燒2 小時，在冰浴中以硼氰化鈉慢慢入樣品中還原，並在冰浴靜置30 分鐘後以去離子水水洗5 次，最後以真空乾燥25℃乾燥12 小時。;The distribution of metals in the shell of large silicon dioxide beads plays a crucial role in many industry-oriented applications over the past decades and an understanding of its preparation method is much helpful for the improvement of catalytic efficiency of the catalyst. The main purpose of this study was to develop a method to prepare the formation of alloys of palladium-copper nano-metal in the shell of silicon dioxide bead which was used as the carrier. How to prepare bi-metal on bead catalyst with an eggshell structure using in production of allyl acetate is very important to chemical industry because PdCu/SiO2 is used as the catalyst for the reaction of the gas phase acetoxylation of ethylene and propylene in industry. Since the reaction medium is acidic, Pd and Cu would migrate and sinter as time went by, causing severe deactivation. It was found that Cu would migrate to the inside core of SiO2 bead, causing deaction of the reaction. By forming PdCu nano alloy, the migration of Cu may be limited. The composition of SiO2 carriers also has some effect on the catalytic properties of the catalyst. Two SiO2 beads were tested in this study, natural and synthetic spherical silicon dioxide with 5 and 3 mm size, respectively. The natural SiO2 beads contain Na cations, which may influence the deactivation rate. In preparation, Pd and Cu metal salts were added by impregnation and potassium hydroxide solution was added to push the metal cations to shell side. The preparation procedure, such as drying, calcination, concentration of KOH solution, and the order of the above steps influence the thickness of metal shell on silica beads. The reduction method is needed to ensure Pd and Cu to form alloy on the silica surface. Eight preparation methods with various steps were carried out in this study. All the samples were characterized by optical microscope, X-ray diffraction, transmission electron microscopy, and high resolution-transmission electron microscopy. iii The synthetic silica does not have sodium cation, the pore structure was very stable after preparation of catalyst. Instead, natural silica bead contains sodium cation, it was not stable in acidic condition during preparation process, and resulted in loss of pore structure. Using KOH solution before adding metal solution in preparation could form egg-shell structure. All samples under KOH solution and reduction showed dark black spots in shell side of SiO2 beads. PdCu had thinner distribution in the shell side in synthetic silica than natural silica. The catalyst prepared by the following method had the thinnest shell among all catalysts: The silica particles were synthetic silica. AlCl3 in 10 ml DI water was added into sample and then dried at 180 ℃ for 2 h. KOH in 10 ml DI water was added into the sample and dried at 110 ℃ for 4 h. The sample was impregnated with metal salts (Na2PdCl4 and CuCl2) solution and dried at 80 ℃ for 6 h. After that, the sample was calcined at 250 ℃ for 2 h and was stirred in an ice bath and reduced with a NaBH4 solution drop by drop. Next, keeping the sample in an ice bath for 30 min and washed 5 times by DI water. The sample was vacuum dried at 25 ℃ for 12 h.
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