In-situ-IR-, -NMR-, -EPR- und -UV/Vis-Spektroskopie: Wege zu neuen Erkenntnissen in der heterogenen Katalyse

Hunger, Michael; Weitkamp, Jens

doi:10.1002/1521-3757(20010817)113:16<3040::aid-ange3040>3.0.co;2-1

Cited by 39 publications

References 196 publications

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Electron-Hole Pairs Stabilized in Al-ZSM-5 Zeolites

et al. 2002

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Photoinduced electron transfer to yield charged-separated states is the most fundamental energy conversion process of the photovoltaic effect, exciton storage in semiconductors, and photosynthesis. Ionization of organic molecules on heterogeneous catalysts [1,2] is predicted to become an exciting area of research. However, practical applications are often hampered by a rapid back reaction. Inhibition of the undesirable back-transfer of electrons requires control of both electronic and spatial properties of the system. Photoinduced charge separation can be achieved by sophisticated molecular triads and higher analogues that are currently capable of producing a charge-separated state with good yield and a lifetime of less than 1 s. [3] Microporous aluminosilicate materials such as zeolites provide an appropriate microenvironment to efficiently trap electrons. [4,5] The electron trapped in zeolites can be generated in different ways: 1) radiolysis using high-energy radiations, 2) photolysis of preadsorbed molecules, and 3) mere exposure of electrondonor compounds such as alkali metal vapor or organic compounds to dehydrated zeolites. It appears that the presence of heteroatoms such as aluminum in the siliceous framework and extra-framework cations is a requirement for efficient electron trapping. [6,7] Although the characterization of occluded organic radical ions has been established, the whereabouts of electrons within the inorganic supports remains unclear and is the subject of considerable debate. [1,2,4,5,8] Surprisingly, aluminosilicate zeolites are also known to contain electron-donor sites capable of transferring electrons to strong acceptors. Herein, we characterize the unusual system of acidic Al-ZSM-5 zeolite loaded with biphenyl (BP, C 12 H 10 ) groups in which both electron-acceptor filtered, and the volatile components were removed in vacuo. The residue was isolated by means of column chromatography (SiO 2 , dichloromethane:hexane 1:1 ± 10:1) and characterized by means of 1 H and 13 C NMR spectroscopy as well as by GC/MS and HRMS.

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