| 摘要: | 本研究以傳統預先調整pH值的沉積沉澱法製備Au/FeOOH、Au/CeO2、Au/TiO2及Au/γ-Al2O3觸媒，另以經修飾的沉積沉澱法，在不預先調整金溶液pH值下製備Au/Mg2AlO觸媒，探討金觸媒於硝基苯及硝基苯乙烯選擇性氫化反應，並以XRD、TEM、XPS、CO2-TPD分析觸媒。 金觸媒於環己烷溶劑中能有效地將硝基苯氫化為苯胺，其中以Au/FeOOH及Au/γ-Al2O3觸媒有極佳活性，Au/Mg2AlO觸媒為最差，與Au/Mg2AlO觸媒於α,β-不飽和醛選擇性氫化反應有最佳活性迥然不同。 金觸媒之Au3+/Au0比值和金顆粒大小與硝基苯氫化活性的關係並不顯著，擔體弱鹼性基的多寡為影響觸媒活性的主要因素。γ-Al2O3擔體擁有最多的弱鹼性基數量，活性最好；Mg2AlO擔體有最少的弱鹼性基數量，但有最多的強鹼性OH基。擔體的弱鹼基可協助H2的不均化解離(Hδ+ & Hδ-)，有利於氫化反應的進行，強鹼性基則不利於氫化反應。 金觸媒於環己烷溶劑中能有效地選擇氫化硝基苯乙烯的硝基為乙烯苯胺。Au/FeOOH及Au/CeO2觸媒活性最佳，Au/Mg2AlO觸媒則最差，活性排序大小除Au/γ-Al2O3外，相似於硝基苯氫化反應。擔體的弱鹼性基亦為影響硝基苯乙烯選擇性氫化之重要因素。硝基苯乙烯的C=C鍵對γ-Al2O3有較強作用力，影響硝基於Au/γ-Al2O3之吸附與活化。 硝基苯氫化反應，Au/Mg2AlO、Au/FeOOH、Au/TiO2及Au/γ-Al2O3觸媒於非極性溶劑有較佳的活性及選擇率；於極性溶劑中觸媒活性較差，且有偶氮產物的生成。Au/CeO2不同於其他金觸媒，於極性溶劑有較佳活性。硝基苯乙烯選擇性氫化反應，非極性溶劑干擾硝基苯乙烯吸附的方向性，使金觸媒於非極性溶劑反不及極性溶劑。 This research, Au/FeOOH, Au/CeO2,Au/TiO2 and Au/Al2O3 catalysts was prepared by using conventional deposition precipitation method with pre-adjusting the pH value of the initial solution, and gold was dispersed on a solid base of Mg2AlO hydrotalcite using a modified deposition precipitation method. To confer gold catalysts in nitrobenzene hydrogenation and in nitrostyrene selective hydrogenation,and the catalysts were characterized by XRD,TEM,XPS and CO2-TPD. Gold catalysts can hydrogenate nitrobenzene to aniline in CXN solvent effectively. Among them, Au/FeOOH and Au/Al2O3 have found the best activity. Au/Mg2AlO have found the worst, the results were different from selective unsaturated aldehydes hydrogenation. The activity of nitrobenzene hydrogenation was not depend on the ratio of Au3+/Au0 and particle size, the amount of lewis base sites were the main factor to affect the catalyst activity. Al2O3 support has found the most weak lewis base sites , so the best activity it was. Mg2AlO support has found the least weak lewis base sites, but the most strong base OH group. The weak lewis base site can help hydrogen dissociation to yield (Hδ+ & Hδ-),it was good for hydrogenation, but strong base sites wasn’t. Gold catalysts can hydrogenate nitrostyrene to vinylaniline effectivitly in CXN solvent. Au/FeOOH and Au/CeO2 have found the best activity, Au/Mg2AlO also the worst, the activity rank, except for Au/Al2O3, was mostly like nitrobenzene hydrogenation. The weak lewis base sites of the support were also the main factor of affecting nitrostyrene selective hydrogenation. The C=C double bond of nitrostyrene has the interfact with Al2O3, and affect the activation and absorption of nitro group. Nitrobenzene hydrogenation, Au/Mg2AlO,Au/FeOOH,Au/TiO2 and Au/Al2O3 have found the better activity and selectivity in apolar solvent; The side product can be found in polar solvent, and the activity is lower. Au/CeO2 wasn’t like the other gold catalysts, it had the better activity in polar solvent. Nitrostyrene selective hydrogenation, the apolar solvent affected the direction of absorption, so the gold catalyst had the better activity in polar solvent. |
