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High performance catalytic materials for heterogeneous oxidative organic functional group transformations
|關鍵字:||高效能催化劑;heterogeneous catalyst;氧化反應;ruthenium;molecular oxygen;alcohol;amine oxidation||出版社:||化學系所||摘要:||
Development of heterogeneous metal oxide catalytic system with selective redox transition and highly recyclic feature is of challenging research in synthetic organic chemistry. In consideration with stability and reusability, very limited attention has been given so for. Nafion® is a rigid perfluropolymer backbone containing polymer bearing ion-exchangeable sulfonic acid terminal group (-SO3-.H+), extensively used as a solid-state protonic conductor in fuel cell applications and seldom used for chemical modification and in synthetic organic chemistry. In this thesis, we are presenting nano ruthenium oxide pyrochlore (Ru2Pb2O7, Pyc) modified Nafion® membrane (designated as |NPyc|) catalyst for selective organic functional group transformations including oxidation of alcohols to aldehyde and ketone, amine to nitriles under ambient conditions. We are covering preparation, characterization by XRD, SEM, SECM, AFM, TGA, XAS and catalytic organic synthesis in triphasic medium with cooxidants such as H2O2, NaOCl and O2. Under optimal working condition, the membrane catalyst showed very good selectivity and good turnover for wide range of organic compounds. The |NPyc| catalyst can be recycled over >100 times without any catalytic degradation. As to the mechanism, a high valent-oxo ruthenium redox species, perruthenate/ruthenate redox couple (Pyc-RuO4-/Pyc-RuO42-) exists in the |NPyc| believed to participate in the oxidation reaction with the co-oxidants.
In continuation to the above studies, a novel ruthenium functionalized nickel hydroxide (designated as Ru/Ni(OH)2) catalyst containing specific Ru-Ru and Ru-OHhydroxo bondings was prepared by simple solution phase procedures and characterized by XRD, IR, TGA, SEM, XPS and XAS (EXAFS and XANES). By using this as a new catalyst, series of alcohols were cleanly oxidized to corresponding aldehydes and ketones with higher turnover factors (~132 h-1) than that of the literature reports, which were based on the monomeric Ru and Ru-Ru bonded catalysts. The Ru/Ni(OH)2 can be recycled and reused without any leaching of metals. As to the mechanism, a low valent-hydroxo ruthenium species (Ru-OH) exists on the surface of the Ru/Ni(OH)2 believed to participate in the aerobic alcohol oxidation reaction via a hydridometal pathway.
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