| 摘要: | 金屬在二氧化矽球形顆粒在許多化學工業的應用中扮演著重要的角色，對其製備方法的理解有助於提高催化劑的催化效率。本研究的主要目的是開發一種製備具有蛋殼結構的 Pd-Cu/SiO2球形顆粒催化劑用於生產乙酸烯丙酯的方法。醋酸丙酯是一種重要的有機化學品。在二氯化鈀存在下液相合成乙酸乙烯酯的情況下發現了烯烴的乙酰氧基化。隨後改進液相方法，然後開發乙烯和丙烯的氣相乙酰氧基化， PdCu/SiO2是該反應的催化劑。然而，由於反應介質是酸性的，Pd 和 Cu 會遷移並燒結，導致嚴重的失活。如何製造薄殼的 PdCu 奈米合金是至關重要的。在本研究中，分別使用直徑為 5 和 3 mm 的天然和合成球形二氧化矽作為載體，測試了五種具有不同步驟的製備方法。基本上，通過浸漬添加金屬鹽，然後使用鹼溶液將金屬陽離子推到殼側，利用比表面積和孔隙率分析儀，光學顯微鏡，X射線衍射，透射電子顯微鏡和高分辨率透射電子顯微鏡對樣品進行分析。天然二氧化矽含有鈉陽離子，製備時不穩定，導致孔結構損失。合成二氧化矽不含鈉陽離子，孔結構在製備中非常穩定。在製備中使用弱鹼性溶液不會產生蛋殼結構。 Pd 和 Cu 的浸漬水溶液的量也影響殼層的厚度。以下方法製備的催化劑在所有催化劑中具有最薄的殼層： (i) 浸漬Pd 和Cu 金屬陽離子溶液， (ii) 在 110℃ 下乾燥，(iii) 適度加入鹼性溶液以將金屬陽離子推向殼側， (iv) 在 450℃ 下煅燒。;The distribution of metals in a silica bead plays a crucial role in many industry-oriented applications and an understanding of its preparation method is helpful for the improvement of catalytic efficiency of catalyst. The main purpose of this study was to develop a method to prepare Pd-Cu/SiO2 bead catalyst with egg-shell structure for the production of allyl acetate. Propyl acetate is an important chemical in industry. The acetoxylation of olefins was discovered in the case of the liquid-phase synthesis of vinyl acetate in the presence of palladium dichloride. Subsequent modification of the liquid-phase process and then to the development of the gas-phase acetoxylation of ethylene and propylene was developed. PdCu/SiO2 was used as the catalyst for this reaction in industry. However, since the reaction medium is acidic, Pd and Cu would migrate and sinter, causing severe deactivation. How to make PdCu nano alloy in the thin shell is crucial. In this study, natural and synthetic spherical silica with 5 and 3 mm size, respectively, was used as the carrier. Five preparation methods with various steps were tested. In principle, metal salts were added by impregnation, and then using alkali solution to push metal cations to shell side. Drying, calicneation, and concentration of alkali solution influence the distribution of metal in silica beads significantly. All the samples were characterized by nitrogen sorption, optical microscope, X-ray diffraction, transmission electron microscopy, and high resolution-transmission electron microscopy. Natural silica bead contains sodium cation, it was not stable in acidic condition during preparation process, and resulted in loss of pore structure. The synthetic silica does not have sodium cation, the pore structure is very stable in preparation. Using weak basic solution in preparation did not form egg-shell structure. The amount of aqueous solutions of Pd and Cu cations also affected the particle size of metals. The catalyst prepared by the following method had the thinnest shell among all catalysts: (i) impregnation Pd and Cu metal cations solution, (ii) drying at 110 oC, (iii) adding basic solution in moderation to push metal cations to shell side, (iv) calcination at 450 oC. |
