Photocatalytic Ethylene Polymerization over Chromium Containing Mesoporous Molecular Sieves

摘要

The photocatalytic reactivities for ethylene polymerization on chromium-containing mesoporous molecular sieves (Cr-HMS) have been investigated. The characterizations with several spectroscopic measurements, such as XAFS, ESR, UV-VIS, and photoluminescence have indicated that Cr-HMS involves tetrahedral chromium oxide (Cr-oxide) moieties which are highly dispersed and incorporated in the framework of molecular sieve with two terminal Cr=O. In the presence of ethylene, Cr-HMS exhibited photocatalytic reactivity for the ethylene polymerization not only under UV light irradiation but also visible light irradiation. The photocatalytic reactivity of the Cr-HMS mesoporous molecular sieves was found to be much higher than those of the Cr-silicalite microporous zeolite and imp-Cr/HMS prepared by the impregnation method. The efficient dynamic quenching of the photoluminescence of the Cr-oxide moieties in the excited state in the Cr-HMS by the addition of ethylene molecules was found to indicate that the charge transfer excited state of a tetrahedral Cr-oxide moieties and large pore size plays a significant role in the photocatalytic reactions.