| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程研究所 === 98 === 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.
|
|---|
