Investigation of the Local Structure of Vanadium Silicalite Catalyst (VS-1) Using XAFS, FT-IR and Photoluminescence Spectroscopic Methods

Abstract

The in situ characterization of the vanadium silicalite catalyst (VS-1) was carried out using XAFS (XANES, EXAFS), FTIR and dynamic photoluminescence techniques. The FT-IR spectrum of the VS-1 catalyst at around 960 cm-1 showed the incorporation of vanadium atoms into the zeolite framework. Furthermore, XAFS measurements have indicated that the VS-1 catalyst consists of highly dispersed vanadium oxide species having a tetrahedral coordination. The VS-1 catalyst exhibited an absorption band at around 300 nm and an intense photoluminescence with a vibrational fine structure at around 450-550 nm which could be attributed to the charge transfer processes on the tetrahedral vanadium oxide species involving an electron transfer from O2- to V5+ and reverse radiative decay, respectively. These results have indicated that a highly dispersed vanadium oxide species is present within the zeolite framework as a tetrahedrally coordinated species and the charge transfer excited state of this oxide species can be well-localized in the shorter V=O bond.