Au/MgxAlO-hydrotalcite觸媒於α,β-不飽和醛選擇性氫化反應之研究; Selective hydrogenation of α,β-unsaturated aldehydes on Au/MgxAlO-hydrotalcite catalysts

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题名:	Au/MgxAlO-hydrotalcite觸媒於α,β-不飽和醛選擇性氫化反應之研究;Selective hydrogenation of α,β-unsaturated aldehydes on Au/MgxAlO-hydrotalcite catalysts
作者:	游焜竣;Kun-Jyun You
贡献者:	化學工程與材料工程研究所
关键词:	菱水鎂鋁石;不飽和醛;選擇性氫化;金觸媒;hydrotalcite;unsaturated aldehyde;selective hydrogenation;gold catalyst
日期:	2008-06-12
上传时间:	2009-09-21 12:29:55 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本研究採用沉積沉澱法，以MgxAlO-hydrotalcite為擔體，不預先調整金溶液pH值，將擔體緩慢置入金溶液中，利用擔體本身鹼性特質，提升溶液pH值，製備具高活性的金觸媒，用於α,β-不飽和醛選擇性氫化反應研究。以肉桂醛選擇性氫化反應，探討擔體Mg/Al莫耳比、擔體煅燒溫度、及觸媒煅燒溫度等製備變因。在Mg/Al = 2、擔體與觸媒煅燒溫度100°C下，可製得活性與不飽和醇選擇率最佳的2%Au/Mg2AlO觸媒。由TEM、ICP、XPS鑑定分析得知，MgxAlO擔體具有穩定金顆粒之功能，除了金沉積量外，觸媒活性主要決定於Au3+/Au0比值，Au3+/Au0比值越高，觸媒活性與不飽和醇選擇率越好。催化反應中，2%Au/Mg2AlO觸媒對不飽和醛共軛C=C/C=O鍵中C=O鍵有良好的選擇性氫化效果，以2-己烯醛為反應物，2-己烯醇產率為76%；以肉桂醛為反應物，肉桂醇產率達到84%；以檸檬醛為反應物，橙花醇與香葉醇產率高達98%。以肉桂醛、檸檬醛、2-己烯醛、巴豆醛等反應物探討反應物分子大小與結構對2%Au/Mg2AlO觸媒催化活性與選擇率之影響。催化活性方面，不同於一般金屬觸媒催化，2%Au/Mg2AlO觸媒對大分子不飽和醛催化活性較小分子好，活性依序為肉桂醛 > 檸檬醛 > 2-己烯醛 > 巴豆醛。選擇率方面，也不同於一般立體障礙效應，C=C鍵旁有較大立體障礙的肉桂醛，其不飽和醇選擇率反不及檸檬醛；較小立體障礙之巴豆醛反應中，不飽和醇依然為主要產物。以最佳製備條件之2%Au/Mg2AlO觸媒於肉桂醛氫化反應中探討促進劑之添加、反應溫度、反應總壓、反應溶劑之影響。添加鐵及鋅於2%Au/Mg2AlO觸媒，皆能促進觸媒催化活性與不飽和醇選擇率。反應溫度越高，不但反應速率越快，不飽和醇選擇率也提升。反應總壓越高，反應速率越快，但不影響不飽和醇選擇率。溶劑效應中，不同於一般金屬催化，2%Au/Mg2AlO觸媒於非極性溶劑有利於肉桂醛氫化反應活性，但不利於肉桂醇選擇率，活性大小依序為環已烷 ≈ 正己烷 > 乙醇；肉桂醇選擇率依序為乙醇 > 環己烷 ≈ 正己烷。直鏈醇類的碳數增加，有利於反應活性，大小依序為正戊醇 > 正丁醇 > 正丙醇 > 乙醇 > 甲醇，肉桂醇選擇率則相當。 Gold was dispersed on a solid base of MgxAlO (x = Mg/Al molar ratio) hydrotalcite using a modified deposition precipitation method to obtain a good catalyst for selective hydrogenation of α,β-unsturated aldehydes. In the modified deposition precipitation method, MgxAlO suspended in water was added to the gold solution without adjusting the pH value of the initial solution. The effect of various parameters that are involved in the preparation of catalysts were examined by the hydrogenation of cinnamaldehyde, including the Mg/Al molar ratio and the calcination temperature of the MgxAlO support as well as the calcination temperature of 2%Au/MgxAlO catalyst. The catalysts were characterized by X-ray diffraction (XRD), inductively coupled plasma (ICP), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses. The optimal catalyst, 2%Au/Mg2AlO(100), was obtained using the following preparation parameters: Mg2AlO (Mg/Al = 2) calcined at 100°C as a support and 2%Au/Mg2AlO catalyst calcined at 100°C. This investigation confirms that not only gold loading of the catalyst is important, the ratio of gold states (Au3+/Au0) is also critical in determining the activity of the catalyst and the selectivity of cinnammyl alcohol. The 2%Au/Mg2AlO catalyst display a high chemoselectivity in the hydrogenation α,β-unsaturated aldehydes to unsaturated alcohols. A good yield of cinnammyl alcohol of about 84% from the hydrogenation of cinnamaldehyde and a high yield of nerol/geraniol of about 98% from the hydrogenateon of citral were obtained over the 2%Au/Mg2AlO catalyst. Many catalytic behaviors of 2%Au/Mg2AlO catalyst of selective hydrogenation of α,β-unsturated aldehydes are different from conventional hydrogenation catalysts (Pt, Ru, Ni, etc.)
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