| dc.description.abstract | Au觸媒近年來被發現可應用於α,β-不飽和醛選擇性氫化反應，優先氫化共軛C=C/C=O鍵中的C=O鍵成不飽和醇。本實驗室過去將Au負載在Mg2AlO–hydrotalcite鹼性擔體上，製得高活性Au/Mg2AlO觸媒，進行α,β-不飽和醛選擇性氫化反應研究，發現Au3+/Au0比值越高觸媒活性與不飽和醇選擇率越好、不飽和醛分子越大反應活性越好、且非極性溶劑有利於反應，不同於一般Pt、Ni氫化反應金屬觸媒於小分子與極性溶劑有較好活性。因此主張反應物分子於金觸媒表面吸附作用力為類似物理作用力的偶極作用力與瞬間偶極作用力而非一般金屬之共價作用力。
本研究為了解此觀點是否適用於其他擔體金觸媒，選用有關α,β-不飽和醛選擇性氫化反應文獻所採用的擔體FeOOH、TiO2及γ-Al2O3，製備不同擔體金觸媒，於相同反應條件下進行α,β-不飽和醛選擇性氫化反應。發現Au3+/Au0比值與活性的關係並不像Au/Mg2AlO觸媒一般顯著，甚至Au/TiO2呈現相反趨勢；Au/FeOOH與Au/γ-Al2O3觸媒則看不到Au3+/Au0比值與活性的關係，反應活性與金顆粒大小有關。顯示Au/Mg2AlO觸媒主張Au3+/Au0比值越高，反應活性越好的觀點不能普遍適用於其它擔體金觸媒，活性的趨勢仍由金顆粒大小所主導。
以乙醇與環己烷探討溶劑效應，Au/Mg2AlO觸媒於非極性溶劑有利於α,β-不飽和醛選擇性氫化反應，其它擔體金觸媒與溶劑的關係大致與Au/Mg2AlO一致，但也有例外。
以檸檬醛、肉桂醛、葉醛與巴豆醛等反應物探討反應物分子大小與結
構對金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，金觸媒對大分子不飽和醛催化活性較佳，活性依序為檸檬醛(C10) > 肉桂醛(C9) > 葉醛(C6) > 巴豆醛(C4)。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。顯示反應物分子於金觸媒表面吸附作用力確實與一般金屬不同。
擔體效應的探討，證實金觸媒的敏感性，擔體本身的性質會直接或間接影響到金觸媒於α,β-不飽和醛選擇性氫化反應的活性與選擇率。不同擔體金觸媒之間，金顆粒大小不代表絕對的活性指標，除了Au3+/Au0比值高，有利於反應活性，擔體的鹼性也扮演重要的有利角色。Mg2AlO-hydrotalcite鹼性擔體用於α,β-不飽和醛選擇性氫化反應具有優異的表現，顯現出鹼性擔體於α,β-不飽和醛選擇性氫化反應的優勢，可製備出具有高活性的金觸媒。
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| dc.description.abstract | In recent year, Au catalyst was found that can be applied to liquid-phase selective hydrogenation of α,β-unsaturated aldehyde and was more advantage for hydrogenation C=O band of conjugation C=C/C=O band to become unsaturated alcohol (UOL). Our research in the past, Gold was dispersed on a solid base of Mg2AlO hydrotalcite using a modified deposition precipitation method to obtain a good catalyst for selective hydrogenation of α,β-unsturated aldehydes. The investigation confirms the activity of Au/Mg2AlO catalyst and selectivity of unsaturated alcohols are proportion of the Au3+/Au0 ratio. Many catalytic behaviors of Au/Mg2AlO catalyst of selective hydrogenation of α,β-unsturated aldehydes are different from conventional hydrogenation catalysts such as Pt and CoB catalyst which had good activity in polar solvent and smaller molecular weight α,β-unsaturated aldehydes. Inversely, Au/Mg2AlO catalyst had higher active in nonpolar solvent and bigger molecular weight α,β-unsaturated aldehydes. Besides, cinnamaldehyde have the most larger steric hindrance of the phenyl group around the conjugated C=C bond, but the selectivity of cinnamyl alcohol from cinnamaldehyde reduction is smaller than that of nerol/geraniol from citral. It is also difference from general catalyst. Hence, we advocate the surface adsorption between gold catalyst and reactant was similar of the dipole-dipole interaction and dispersion force which was such as physical interaction not as the covalent interaction of gerenal metal catalyst.
This research, in order to understand the hydrogenation characteristics of Au/Mg2AlO catalyst in α,β-unsaturated aldehydes whether generally be suitable for the other support gold catalyst, selected support FeOOH、TiO2 and γ-Al2O3 which were used and adopted in relevant literature to prepare gold catalyst for selective hydrogenation of α,β-unsaturated aldehyde in the same conditions. The result discover the relationship of Au3+/Au0 ratio and activity is not clean as Au/Mg2AlO catalyst, even is opposite on Au/TiO2; The activity of Au/FeOOH and Au/γ-Al2O3 are related with gold particle size. So, the claim that activity is proportion of the Au3+/Au0 ratio is not generally suitable for the other support gold catalyst.
Choosing ethanol and cyclohexane as reaction solvent to investigate solvent effect. The other support gold catalysts are similar with Au/Mg2AlO catalyst is good for selective hydrogenation of α,β-unsaturated aldehyde in nonpolar solvent, but also have an exception.
In comparision to the conventional hydrogenation catalysts, gold catalyst is more activity for bigger molecular weight α,β-unsaturated aldehydes. The order is citral (C10) > cinnamaldehyde (C9) > leaf aldehyde (C6) > crotonaldehyde (C4).
Besides, the selectivity of cinnamyl alcohol from cinnamaldehyde reduction is smaller than that of nerol/geraniol from citral, it also prove the surface adsorption between gold catalyst and reactant is difference with general metal catalyst.
The discussion of support effect confirm the sensitivity of gold catalyst and the properties of support oneself will dierct or indirect to affect gold catalyst’s reactive avtivity. Between the different support gold catalyst, the gold particle size does not absolutely represent to the active target. The ratio of Au3+/Au0 is advantageous to the activity and the basic of support also play the important role.
A solid base of Mg2AlO hydrotalcite can prepare highly active gold catalysts and show the superiority of base support for selective hydrogenation of α,β-unsaturated aldehyde.
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